Sunday, June 30, 2013

Heat Records Quickly Falling Across Western US

A total of 31 high temperature records have been broken today, as the multi-day heat wave continues to bake much of the Western US.

Cities like Las Vegas and Reno in Nevada saw their high temperature records fall today, with the former location seeing an unconfirmed run at their all-time high temperature record at 116.1 degrees. Sacramento and Houston were among other big cities receiving broken high temperature records on this final day of June, with nearly 200 record high temperature-related records being set in the past 48 hours.

The heat wave looks to continue for at least another couple of days before the intense hot weather retreats and the weather pattern as a whole moderates. Remember to drink water often, and stay out of the sun as much as possible. This heat wave has already injured dozens, and it is possible the hospitals will be seeing more heat-related illnesses in the next few days if hydration and a relatively-normal body temperature is maintained.

Andrew

Active Weather Pattern Quieting Down

The active weather pattern we have seen in the last several weeks, where multiple significant tornadoes and severe weather outbreaks combined with the first two tropical cyclones of the Atlantic hurricane season, appears to be coming to an end in the next several days.

Projected mid level atmospheric flow turns firmly zonal by the start of the second full week of July, as strong low pressure originating from northeast Canada combines with the tendency of the atmosphere to favor ridging in the Northeast to regulate the flow over North America. When this period of zonal flow starts, no extreme hot or cold weather episodes are expected, and severe weather outbreaks are not encouraged. The lack of a wavy jet stream will permit the formation of a quiet weather pattern over North America.

Longer range forecasts favor the development of high pressure over the Rockies that may attempt to transition over into the Plains or even Ohio Valley areas. Whether that potential verifies remains to be seen. 

Andrew

Friday, June 28, 2013

Negative PDO Looking More Likely This Winter

The Negative phase of the Pacific Decadal Oscillation (PDO) appears likely as we head into this winter.

Shown above is an average of multiple globally-produced forecast models, showing sea surface temperature anomalies for November-December-January of 2013-2014. The circled area shows the trademark presence of the negative PDO- we see a body of above normal sea surface temperatures in the northeast Pacific, surrounded by below normal sea surface temperatures in the waters immediately offshore the coasts of western Canada and southern Alaska. While this covers two of the three big winter months, the PDO is called the Pacific Decadal Oscillation for a reason. We have been in the negative phase of the PDO for a while, and even without looking at this model suite, there is a decent probability that we will be in a negative PDO this winter.

In the temperature department, the negative PDO results in above normal temperatures for much of the nation. The core of the heat tends to be centered in the Southern Plains, but the Eastern Seaboard, Northeast, Midwest and Plains get in on above normal temperatures when the negative PDO arrives. It is important to note that the Pacific Decadal Oscillation is not the sole driver of weather; many other variables go into the equation of a seasonal temperature and precipitation pattern.

For precipitation, the negative PDO brings about a decidedly below normal trend in the Gulf Coast region and into the Southeast. While the severe drought observed just a year or two ago in the southern Plains has been alleviated to some point, it would only take one more winter of below normal precipitation to bring back some effects of that drought. Again, I cannot emphasize enough the fact that the PDO does not decide the entire seasonal trend- many other large and smaller-scale variables go into a seasonal weather pattern.

Andrew

Wednesday, June 26, 2013

Significant Heatwave Coming for Western US

A significant heatwave is on the way for many in the Western United States in the next week to 10 days (and beyond??)

The atmospheric pattern over the Western US will become incredibly favorable for major heat in the next 5-10 days as the mid level atmospheric flow becomes very wavy (called meridional). A very large depression in the mid level heights over the Midwest, Great Lakes and western Ohio Valley will force a very large ridge of high pressure to build over the Rockies and entire Western US. With model forecasts indicating this large depression in the atmosphere to persist over the Central US, it is very possible we could be in for a prolonged significant heat wave over the Western US.

Temperature forecasts from the GFS model have large parts of California breaching the 100 degree mark, with the maximum value just below 120 degrees. It is expected that these hot temperatures will persist throughout the mountains in California, Arizona, Nevada, Idaho, Oregon and Washington state in a multi-day hot weather event. This all begins in the next several days, and could very well persist for several days.

Remember to stay hydrated and take multiple breaks if you will be outside during this heat event.

Andrew

Energy Moving off African Coast May Spark Tropical Interest

Two major global models are now indicating a piece of energy will move off the African coast in the next week or two that may provoke a tropical concern later on in July.

The above image shows the ECMWF model and GFS model forecasting lower level winds over the Atlantic Basin for 10 days out. Looking towards the African Coast, we see elevated values off the coast of Africa on both models. While the ECMWF model is considerably weaker with this piece of energy, it is apparent that there is interest in the long range models for the tropical wave train off of Africa to get going rather soon.

While this is a rather long range forecast, I would not doubt the development of a tropical system beginning in the next 10-14 days. We are entering the prime time for hurricane development; while it will not arrive until the fall months, summer is certainly a season that needs to be watched for hurricane development.

Andrew

Monday, June 24, 2013

Severe Weather Possible Tomorrow, June 25th

First off, for those of you wondering, the blog has been quiet in the last few days as I have made significant progress on over half of the 34 winter forecasts I will be issuing this late September or early October. I will have limited time around then, so it was best to do the work now.


The Storm Prediction Center is indicating there is potential for a higher end severe weather event tomorrow. Shown above is the probability of severe weather within 25 miles of any given point. While the yellow and red areas are encompassed in the same slight risk area, the red area has a higher chance of seeing severe weather than the regions highlighted in yellow.

Model forecasts project the development of severe weather in the red area beginning tomorrow afternoon and continuing into the evening hours. While the resolution on simulated reflectivity forecasts is low, the general premise of a damaging wind/hail event is present in portions of the 30% area, while the western portion of the red area may be the spot for more isolated cells and thus a higher hail threat and maybe even a tornado potential.

Andrew

Friday, June 21, 2013

Long Range Risk Analysis - June 21, 2013

This Long Range Risk Analysis covers the timeframe from now to the next 20 days. Confidence in this analysis is Average.

Overall Synopsis
Closed low in the Pacific Northwest will be torn up and allow the pattern to become mainly zonal for a prolonged period of time. The jet stream will be displaced into Canada and not only allow for increased heat, but lower chances of significant severe weather.

Severe Weather Outlook: Medium Activity
Confidence: Average
Multiple days of severe weather are expected in the short term as the Storm Prediction Center has outlined the Northern Plains for severe weather potential. This potential will eventually die down and shift a bit further north as the zonal atmospheric flow disrupts chances at significant severe weather. To account for the short term, the activity outlook is Medium with Average confidence.

Heat Outlook: High Activity
Confidence: Above Average
Zonal flow in the medium range will permit large high pressure formation over much of the nation (save the New England area) and induce warmer temperatures for days and days on end. The core of the heat is expected in the western Plains, with hot weather still expected as far east as the Mid-Atlantic. Details on the high pressure evolution remain a bit murky, but medium-range confidence allows an Above Average confidence level of High activity.

Tropical Outlook: Medium/High Activity
Confidence: Above Average
Short term has no interest in tropical development, although from June 30th we will begin to see increased activity. Very favorable upper and mid level atmospheric pattern will allow the development of at least one tropical cyclone. Depending on the longevity of the favorable upper air pattern, multiple tropical cyclones may be observed. Confidence in development chance is high, although formation and sustainment outlook is murky. Above Average confidence on a Medium/High Activity call is favored.

Andrew

Thursday, June 20, 2013

Tropical Development Likely in Caribbean for July 4th

I believe we are likely to see tropical development in the Caribbean and/or Gulf of Mexico in the first 7 days of July. This comes as the atmosphere primes itself for a very tropically-conducive upper air pattern in these same regions.

The latest GFS model had a substantial tropical cyclone present in the Gulf of Mexico on July 1st, with landfall occurring in western Louisiana the morning of July 2nd. Pressure readings would drop below 1000 millibars in the open waters before rising as landfall occurs, as shown in the image above.

I'm really pushing for the likelihood of development in the Gulf of Mexico and/or Caribbean because the atmosphere is going to be truly primed for tropical cyclone formation to start the month of July. Global models are now agreeing on the development of a very strong Madden-Julian Oscillation event in the Eastern Pacific into the western Atlantic. This includes the Gulf of Mexico and Caribbean. This strong MJO event means enhanced chances for tropical convection in these areas. If the tropical convection from this MJO event combines with the favorable mid-level atmospheric flow being sustained by the large high pressure system over the United States (which is likely to occur), tropical development would be expected.

At this point in time, I would anticipate development to occur either in the Western Caribbean or in the Gulf of Mexico; I don't find it too likely that we would see a cyclone make its way through the entire Caribbean and Gulf of Mexico when the most conducive conditions are closer to the US Mainland. Corpus Christi TX, Houston TX, New Orleans LA, Mobile AL and Pensacola FL could all be affected by a tropical cyclone forming in the Gulf of Mexico.

Andrew

Wednesday, June 19, 2013

Short Range Risk Analysis - June 19, 2013

This Short Range Risk Analysis, made on June 19th, covers the timeframe of now to 5-7 days from today. Confidence on this analysis is Above Average.

Overall Synopsis
Large closed low over the Pacific Northwest is enabling high pressure formation over the Northern Plains, advecting instability and conditions supportive for severe weather. Ridging pattern appears to be ongoing in this timeframe from the Ohio Valley eastward, allowing for a rather quiet period for the East.

Severe Weather Outlook: Medium/High Activity
Confidence: Average
Uncertainty in previous Short Range Risk Analysis has been greatly cleared up, allowing me to see the nature of the severe weather threats in the next 5-7 days. Model guidance is confirming pieces of energy from the closed low in the Pacific Northwest will slide east and interact with ridging high pressure over the Northern Plains to create multiple severe weather opportunities in that area. Progression of the severe weather threat moves east and south by the 3 day forecast mark, with the Storm Prediction Center placing a large portion of the Midwest and Upper Plains under the gun for severe weather. Threat should continue to the end of the 7 day mark in this short range analysis, leading the outlook to a Medium/High Activity level with Average confidence.

Flooding Outlook: Medium Activity
Confidence: Above Average
Ongoing severe weather events will span multiple days across the Upper Plains, particularly from North Dakota and Minnesota to Wisconsin. Current model guidance has multiple places in these states receiving up to 6.00 inches of rain in roughly 6 days. The multiple bouts of potentially strong storms will allow for multiple days of stress on rivers. While no major flooding is currently ongoing in the areas mentioned, 6 inches of rain in 6 days is enough to put at least considerable stress on some rivers.

Heat Outlook: Medium Activity
Confidence: Very Above Average
The presence of a closed low in the Pacific Northwest has led to some high pressure development in the Northern Plains. Amplification of this high pressure to include additional areas of the Plains and Midwest is expected, with more high pressure formation occurring in the Eastern US. Coagulation into a single high pressure system is expected over time, which will push the jet stream into a zonal flow and move it north. This zonal flow will allow warmer weather to shift north into the United States, and massive high pressure will enhance that job at the 7 day mark and a little bit beyond. Confidence is Very Above Average in the Medium Activity outlook for heat, as model guidance has been consistent on large high pressure formation for days.

Tropical Outlook: Low Activity
Confidence: Average
Tropical Depression TWO continues to shift towards Mexico, dumping heavy rain across the area. Redevelopment of this depression into a tropical storm was previously expected by the National Hurricane Center, and development into a tropical storm is now expected by the agency as soon as this afternoon. I remain skeptical on the idea considering how close to land the depression is, but as the depression slows down and seemed to get its act together in the evening hours last night, I can see how strengthening can be a possibility. However, Low Activity is listed for this outlook, as no development is anticipated following TD-TWO.

Andrew

Monday, June 17, 2013

Short Range Risk Analysis - June 17, 2013

This Short Range Risk Analysis covers the time period from now until the next 3-5 days. Confidence in this full analysis is Average.

Overall Synopsis
Tropical Depression TWO has developed in the western Caribbean and is expected to make landfall in the next couple of days. Multiple severe weather chances will arise over the next few days, although their significance is in question as the active weather we have seen in the last few weeks starts to stagnate.

Severe Weather Outlook: Low/Medium Activity
Confidence: Above Normal
Today and tomorrow will feature severe weather chances in the Southern Plains, with Montana on watch the day after tomorrow. Despite these areas of concern, the next 3-5 days does not feature any areas where severe weather is expected to reach intense levels. Activity in this timeframe is thus described as Low/Medium.

Heat Outlook: Medium Activity
Confidence: Below Normal
Medium range forecast calls for the development of high pressure over the Plains as a closed low system enters the Pacific Northwest. Multiple sources indicate this ridge will arise in the next 2-3 days, extending into the full 3-5 day period of this outlook. The intensity of this ridge in its beginning days remains in question, leaving confidence in the below normal stage. The presence of this ridging pattern will allow heat to move further into the Plains during this timeframe, however, meaning the Heat outlook is at Medium activity.

Tropical Outlook: Low Activity
Confidence: Average
Tropical Depression TWO has developed in the Atlantic in the last few hours, with its origin to the east of the Yucatan Peninsula. Intensity of this depression is low, as it is only a depression. This system is expected to maintain its tropical depression status until and after landfall on the Yucatan Peninsula. After departing the Yucatan Peninsula moving west-northwest, the National Hurricane Center indicates strengthening into a tropical storm is possible before a second landfall on Mexico is observed. While I am skeptical of this storm strengthening after its first landfall, I am confident that the United States will not be affected, thus the tropical outlook has a Low activity forecast.

Andrew

Sunday, June 16, 2013

Long Range Risk Analysis - June 16, 2013

 Note: This is a new idea I had for delivering text-based messages about long range risks (varying by season) to the public. This is an example of what would be issued (while it's an example, the information is an actual forecast). Feedback is welcome.

Outlook valid for the next 15-20 days.

Overall Synopsis
Closed low coming onshore in the Pacific Northwest will allow prolonged high pressure development in the Plains, eventually extending into the Midwest. Closed low eventually is torn up and leads to zonal flow across the United States before re-emergence of prolonged high pressure development,

Severe Weather Outlook: Low/Medium Activity
Closed low entering Pacific Northwest will allow severe weather opportunities in the Southern Plains, limited only to Texas and New Mexico into Colorado at this time. Northern Plains may become involved for a short period with low expectations in a couple of days. Long range outlook becomes quiet as zonal flow takes over before the risk of severe weather goes on the upswing as we enter prolonged ridging over the Plains.

Heat Outlook: High Activity
Two periods of prolonged high pressure formation in the Plains and portions of Midwest will lead to increased flows of heat north into mainly the Plains area. Eventual zonal flow and long range Death Ridge formation potential may allow this heat to openly enter much of the nation. Long range outlook remains unusually toasty in this scenario.

Tropical Outlook: Low Activity
Lack of enhanced tropical convection over the Atlantic basin will not permit any sustained tropical cyclone formation. Current area of interest (Invest 93) is moving on land, and next chance at development appears to be over 10 days away.

Andrew

Special Weather Notice - OK/TX/KS/NE/CO/SD - June 16, 2013

A Special Weather Notice has been issued by The Weather Centre for the following areas:

-Oklahoma
-North Texas
-West Kansas
-East Colorado
-Nebraska
-South Dakota

Severe thunderstorms are beginning to form in the highlighted areas. The Storm Prediction Center has issued a severe thunderstorm watch for central and western Nebraska, and additional watches are pending for many of the highlighted regions.

Expected threats to those in the mentioned states are:

-Hail
-Damaging wind gusts
-Isolated tornado potential

Andrew

Tropical Weather Statement - June 16, 2013

This is a tropical weather statement, valid on June 16, 2013.

Invest 93 has formed in the southern Gulf of Mexico at this time. Satellite imagery indicates convection associated with this invest is robust, with intense convection on every front of this invest.

Forecast information indicates this invest will move on land in Mexico and will not pose a tropical development threat to the United States.

This will be the final statement for this invest.

Tropical Development Likely in Late June-Early July; Gulf Coast Threatened

I believe tropical development is now likely in the western Caribbean into the Gulf of Mexico in late June and early July. If development is to occur, the potential landfall zone would extend from the Florida Panhandle into Mexico. Houston, TX and New Orleans, LA would be affected.

As we move into the last week of June and early July, a massive high pressure system should overtake much of the United States in a formation referred to as the 'Death Ridge'. The term means how the high pressure system overtakes quite literally the entire nation and should extend into Canada. Unfortunately, this high pressure system brings up some intense heat from Mexico and the Southern Plains that can catch some people off-guard in northern parts of the nation and can lead to heat exhaustion and heat stroke.

The massive Death Ridge can lead to enhanced chances of tropical cyclone formation in the Caribbean and Gulf of Mexico. With tropical convection moving into a favorable area of the Gulf of Mexico (called the Madden-Julian Oscillation) in this timeframe, I find it likely that, should development occur, strengthening into a tropical storm and possibly a hurricane would occur and find its way into the red shaded areas of the Gulf Coast.

Andrew

Saturday, June 15, 2013

Preliminary 2013-2014 Winter Forecast

Hello everyone, and welcome to The Weather Centre's 2013-2014 Preliminary Winter Forecast. This forecast will deal mainly with analogs and long range models, with no official forecast being issued. I will give my educated guesses on the upcoming winter at the end of this post, however. We have a lot to discuss, so let's get on with it.

We will begin with the El Nino-Southern Oscillation (ENSO). The ENSO phenomenon involves anomalous sea surface temperatures in the waters off the coast of South America on the Equator. In the image above, you can see the colder than normal waters between 140W and 80W. These below normal waters indicate the presence of a La Nina. In the winter months, a La Nina brings about cooler weather for the northern US and a snowier winter for the Midwest and Ohio Valley. When the same areas shown in blue in the image above are orange (above normal sea surface temperatures), an El Nino is observed. This flips the effects of the La Nina, giving warmth and below-normal precipitation to the Midwest and Ohio Valley, while distributing big storms to the Northeast and Mid-Atlantic. There is also the option of not having an ENSO phase at all, where the water temperatures are neither below normal or above normal. This phase is called the 'Neutral phase', because it has neutral water temperatures. Last winter, we were in the neutral ENSO phase. Because the ENSO was too weak to have an effect on the global weather, the winter's pattern was more determined by smaller-scale indices, like the North Atlantic Oscillation (NAO), the Pacific North American index (PNA), and the Arctic Oscillation (AO), all of which will be explained later in this post. This winter, long range forecasts are going for either a neutral ENSO winter again, or a weak El Nino. While the long range model forecasts you will see below are more La Nina-ish, there is still a lot of time for long range model forecasts to change.

We will now discuss analog years. These are years that were chosen by me after seeing how close a correlation there was between three different synoptic atmospheric indices in previous springs and those same indices for this spring. Based on a rigorous examination of multiple years, the winters of 1951-1952 and 1962-1963 were seen as the best candidates for detecting what our upcoming winter could be like.

We begin with the mid-level geopotential height anomalies for these two years. For all future images unless noted, cold colors indicate low pressure/below normal, and warm colors depict high pressure/above normal anomalies. In this image, we see quite a few things. The first is multiple areas of high pressure inside or in the immediate vicinity of the Arctic Circle. These high pressure areas appear to be close enough to the North Pole that they are breaking up the polar vortex, which I had discussed in great detail last year. The synoptic effects of this high pressure presence include more accessibility for cold air to shift into lower latitudes from the Arctic Circle, as well as a weaker polar vortex in the stratosphere, which we will discuss in greater detail later on in this post. We see high pressure encompassing the area of Greenland and in the waters to the south of that landmass. The presence of high pressure in that area indicates the presence of a negative North Atlantic Oscillation (NAO) index. When the NAO is negative, the jet stream will buckle south from Canada and give many in the Central and East US a shot at cold weather. The buckled jet stream also opens the door for Nor'easters. Low pressure over North America is amplified by the presence of high pressure over the Bering Sea that appears to extend down into the West Coast. These two high pressure systems cordon off the low pressure into North America. We also see a stormy East Asia, and if you know about the 6-10 day gap between storms in East Asia and storms in the East US, you should be jumping for joy with that development. I will discuss that further later on.

Temperature anomalies for these two years show a chilly North US and a slightly mild South Plains. It looks like the negative NAO pattern we discussed above, combined with the other high pressure system in the Bering Sea and low pressure over North America will allow cold air from Canada to flood south. The coldest weather should stay in the northern tier of the United States, with the general cutoff line starting from the Mid-Atlantic into the Central Plains. The West Coast would also see warmer than normal temperatures if these analogs came to fruition.

Back to the stormy East Asian correlation, it is known that when a storm system appears in East Asia, a storm system with relatively similar strength will appear in Central and/or East Asia. My analog years in the first image showed a very stormy East Asia, and if the negative NAO is able to appear quite a bit throughout the winter (which is plausible, if above normal water temperatures in the Arctic Circle continue), Nor'easters would certainly be a very real possibility. The East Asian correlation also opens the door for potential winter storm events from the Plains to the Northeast- this correlation would benefit many in this nation who love snow.

I want to zoom in on 1962-1963, because after analyzing my three analog years (and then discounting one) up against each other for the three atmospheric teleconnections, 1962-1963 easily won in all three categories. This means that the winter of 1962-1963 could align with our upcoming winter.

 The mid-level atmospheric pattern for the winter of 1962-1963 is one only dreamed about by winter weather lovers. We have so many things going right in this picture, it's hard to know where to start. We'll begin with Greenland. Once again, we have dominant high pressure over the landmass, providing a base for a  strong negative NAO. As previously mentioned, this allows cold air and storms to hit portions of the Central and (especially) East US. High pressure observed in the first image of this post is amplified in the winter of 1962-1963, and this high pressure even extends into the Northeast Pacific and snakes into the West Coast. The placement of high pressure into the Western US allows the development of a positive Pacific-North American (PNA) pattern. In the positive PNA set-up, high pressure in the West US allows the jet stream to stay north of the ridge before plummeting south in the Central US to allow a favorable winter storm track and cold event in the Plains, Midwest and Ohio Valley. The third positive item in this image is the presence of the same two ridges of high pressure I just discussed, and their placement in the upper latitudes. These two areas of high pressure are interrupting the previously-mentioned polar vortex to allow the negative phase of the Arctic Oscillation (AO) to develop. The negative AO indicates high pressure over the Arctic, leading to a southward movement of the jet stream and subsequent outbreak of cold into much of the lower latitudes. This outbreak coud be favored towards North America if the positive PNA and negative NAO are in full bloom at the time that this happens.


Temperature anomalies across the United States for the winter of 1962-1963 were very cold, with temperature departures of 6 to 8 degrees below normal in the heart of the eastern Midwest, Great Lakes and northern Ohio Valley. A general cold trend continues for those in the Northeast, Mid-Atlantic, Southeast and Gulf Coast. The Southern Plains even get a taste of chilly weather. Considering the triple threat of the negative AO, negative NAO and positive PNA evolving (in addition to the stratosphere, which will be discussed next), these very low temperature anomalies are not surprising in the least.

This is the part i'm really excited about. Last winter, I talked a lot about the impending collapse of the polar vortex and how it could move south. It did weaken significantly and eventually collapse in on itself. Movement into Canada did occur, but the vortex did not fully enter the US (portions of North Dakota and Minnesota were clipped by it). This winter, if the winter of 1962-1963 evolves correctly, the polar vortex will be sitting right over Canada and parts of the US. The above image shows geopotential height anomalies for the 100 millibar area, defined as the lowest layer of the stratosphere and the layer most readily checked for placement of the polar vortex and areas it may affect. This image shows dominant high pressure from Greenland to Eurasia, meaning the polar vortex has to be exiled to lower latitudes; it cannot stay in the Arctic Circle with those high pressure systems. Now, if you were alive in the 1980's and still remember that decade, you may recall the month of January, 1985. If you remember it as being absolutely frigid in the last few days of that month, you remember the cold associated with the polar vortex dropping south into the US. This happened as a result of high pressure in the upper latitudes pushing the polar vortex down into the United States. A similar, weaker event of a collapsed polar vortex happened in early 2009, when many in the North US experienced very cold temperatures. If the atmospheric pattern being pictured above were to evolve, not only would we see the polar vortex angled in a position more able to push towards the United States, but prevalent high pressure over the Arctic Circle could weaken it enough to send it towards this nation in weaker (but still frigid) pieces. It's far too early to tell if this analog year will actually work out, and much, much too early to determine where the polar vortex will end up. However, if these analogs are correct, I see no reason to doubt an incoming chilly (and possibly stormy) winter.

Now that we have looked at the past, let's compare the analogs to what long range models have to say.

Shown above are two long range forecast models (GFDL and NCAR), predicting 200mb heights for the month of December 2013. Areas of blue depict general lower heights and thus low pressure areas, while reds indicate high pressure systems. The contour lines are superimposed on the images to help point out areas of differing pressure. There are four regions I want to look at here, so we'll start out with North America.

Both images show a pretty favorable set-up for cold weather as far as the 200mb level goes in North America. We have a large area of rather strong low pressure over eastern North America stretching into New England, and this is reflected by the compression of contour lines in the same region. The low pressure area over New England tells me this area would indeed be favored for at least somewhat-frequent shots of Arctic air, and the tightening of the jet stream favors this theory. The overall picture is what excites me more. If we look into the far Northern Hemisphere we see no area of low pressure- the closest persistent low pressure center is the one in North America. Now, bear with me here, the idea is pretty outland-ish. But if you were to try to place a location for the polar vortex to average out over the month of December, you would want to find the area with the lowest pressure over the general upper latitudes (including North America, northern Eurasia, and Greenland). That said, it would make sense that the polar vortex may very well have a tendency to be pushed further south towards Canada and the US.

Our second area of interest is the United States. Both models show that low pressure area trying to push into New England, but we already covered that in the above paragraph. The item I want to focus on is the West Coast into Alaska. We see a separation of the contour lines into a looser composition, as well as oranges building into those areas. This indicates the presence of high pressure, and sets up positive phase of the Pacific-North America (PNA) pattern. In the wintertime, the jet stream does exactly what is being depicted above, and this means a warm West US and cold East US. Additionally, storm systems will tend to track in a path favorable for snowfall in the Midwest, Plains and portions of the Great Lakes into the Ohio Valley. The positive PNA helps to usher in lower than normal heights across the East US, and this will deliver us into the next area of interest.

The third area of interest is the Bering Sea. Both models project strong high pressure in the vicinity of the Bering Sea region; the GFDL model (left) has high pressure square in the Bering Sea, while the NCAR model (right) has the high pressure more towards Asia but still influencing the Northern Hemisphere. In both situations, the Arctic Circle appears overcome with above normal height anomalies, indicative of high pressure in the region. High pressure in the Arctic would imply a weaker polar vortex (yes, the same vortex I discussed this previous winter), as well as tendency for cooler weather to make its way down to lower latitudes of the world. If we do have high pressure in the Bering Sea, it would be easier for instances of high pressure to overwhelm the Arctic, and this could (keyword is COULD) allow the polar vortex to be pushed further south and affect lower latitudes in significant ways.

The final area of concern is East Asia. All models I observed for December 2013 depicted a tightening of the contour lines and lowering of height anomalies in East Asia, sometimes even into the northern Pacific. I have described a few times on this blog the idea of the East Asia-East US storm correlation, where a stormy period in East Asia can mean a stormy period in the East US 6-10 days later. This would mean more chances for snow whenever East Asia got active, and if long range models are correct this active period could be quite often. If the tightened jet stream in the North Pacific and stormy East Asia evolves as predicted (combined with the possible +PNA pattern and weakened polar vortex), this winter may help those winter-loving souls damaged by the last couple of winters.



A side-by-side analysis reveals truly stunning similarities- even I did not expect to find such a strong connection. The winter of 1962-1963 and the forecast models have a whole list of similarities. Both indicate low pressure in the eastern portion of North America. The analog year sees this low pressure area as more expansive, but both the analog and forecast model center the low pressure near the Northeast US and Southeast Canada. Both models (and this is the connection that surprised me the most) also have high pressure building from the West Coast into the Bering Sea. But it gets even better than that- the location of high pressure from the West Coast on the forecast model is almost identical to where the high pressure anomalies begin in the analog winter. They both strengthen the high pressure in the Bering Sea, and continue this high pressure through Siberia and northern Eurasia. If that isn't a correlation, I don't know what is. Both items have low pressure in Eastern Asia and into the Pacific. The forecast model is definitely weaker in that aspect, but such small differences like that are to be expected. The general idea is still firm in both articles: lower pressure and a stronger jet stream in East Asia. 
It is also worth noting the differences we have here, as some of them must be addressed in this comparison. The biggest difference is the lack of high pressure over Greenland in the forecast model. I should mention that other forecast models not shown here do have prevalent high pressure over Greenland, but for all intents and purposes we will keep that difference in our back pocket to analyze in a later forecast. The other difference I see at this time is the East Asian pressure difference, and we already went over that in the above paragraph. 


Global models generally favor a cooler winter for the North Plains, Great Lakes, Ohio Valley, Upper Midwest, Northeast and generally places in the top-right quadrant of the United States (if you were to cut the nation into four pieces). Because we're a long time out from the winter, these anomalies are not that significant. As we get closer to December we will start to see these anomalies become more extreme, with the below-normal temperatures getting colder and above-normal temperatures raising their anomaly projection. In the precipitation department, a very La Nina-type set-up appears to be favored, with a stripe of above-normal precipitation from Oklahoma to the U.P. of Michigan. I'm rather skeptical of precipitation forecasts this far out and feel it's best to stick to the analogs and upper-level height anomaly charts we were looking at earlier in this post. Regardless of its accuracy, the premise of a stormy Midwest/Plains and chilly East US can raise excitement for some winter weather lovers.

SUMMARY

My analog years are matching up unusually well with long-range forecast models. While these models will change, I find it to be a good sign that there is a rather substantial amount of correlation this far out. My analogs may be revised down the road as we enter summer and early fall, and it is assured that the long range models will change. However, these are my long range estimates for this winter.

-The polar vortex may be at lower latitudes this winter.
-A wetter winter is possible for portions of the Plains and Midwest.
-Cooler weather is possible for portions of the northern US.

Thursday, June 13, 2013

Colorado Wildfires Rage; No End in Sight

The fires in Colorado continue to ravage the state, with the Black Forest fire doubling in size yesterday and becoming the most destructive in state history.

Satellite imagery above shows smoke from these fires billowing across Colorado and even into the western Plains as meteorological summer is only 13 days old. Poor winter conditions, combined with an ongoing drought through the Plains and Western states have led to the enhancement of annual wildfires.

Considering the atmospheric pattern currently in place appears to have enhanced wildfires (especially the Black Forest fire), it is unlikely we are going to see a break from these fires. The pattern coming up in the next 16 days involves little to no precipitation (under 1.00'' of rain) for areas currently experiencing these wildfires. With temperatures likely to stay high, and winds unlikely to cease in the next few days, it is highly likely that these ongoing wildfires will be enhanced.

Model projections from the HYSPLIT model suggest smoke from these wildfires will track north across Wyoming, Montana and North Dakota before shifting well into Canada. From there, any smoke still prevalent in the air mass will either circle around in Canada and shift east or dissipate in the western portion of that nation.

Regardless of where the smoke goes, it is the unfortunate probability that the next several days will see an enhancement of ongoing wildfires in the state of Colorado.

Andrew

Late June/Early July Holds Tropical Threat

Latest indications are that the next tropical threat could arise in late June into early July, and that this threat could be more formidable than when Andrea formed.

The long range forecast over the seven day period from June 20 to June 27 depicted above shows upper level divergence anomalies. Areas of green depict below normal anomalies and thus increased chances for enhanced tropical convection, while above normal anomalies signal a less favorable environment for tropical convection. The GFS Ensembles project these divergence anomalies to drop into the below-normal range and increase the risk of tropical cyclone formation. This would supposedly be associated with a Madden-Julian Oscillation (MJO) wave making its way to phases that are favorable for tropical cyclone formation. However, a comparison to other models suggests that the GFS Ensembles may be a bit too fast with the movement of this MJO wave into favorable phases, and that is why early July remains on the table for timing.

The GFS Ensembles, between June 23 and June 28, then predict a large swath of the Gulf of Mexico to be under the influence of rather substantial low mean sea level pressure (MSLP) anomalies. This would seem to indicate the willingness of the GFS Ensembles to attempt and formulate an environment favorable for tropical cyclone formation. Towards the end of this particular GFS Ensemble run, the SLP anomalies are even lower than what is shown above, leading me to believe there is a growing consensus that late June into early July is a reasonable timeframe for the Atlantic basin's second shot at tropical cyclone formation. Support by the aforementioned MJO wave would make this second shot the more formidable of the two.

Andrew

Tuesday, June 11, 2013

Derecho Likely Tomorrow; Moderate Risk Issued

The likelihood for a derecho is on the rise tomorrow, as new model data and an upgrade from the Storm Prediction Center launch Wednesday into a significant weather event status.

The Storm Prediction Center has issued a moderate risk of severe weather for much of Illinois, nearly all of Indiana and the western half of Ohio in anticipation of a potentially significant weather event tomorrow. Latest reasoning from the SPC cites abundant and high instability in the highlighted areas, as well as high moisture content in the lower levels of the atmosphere as supportive for a significant damaging wind event. Expectation is for isolated supercells to grow into a bowing line segment, with the potential for a derecho to evolve.

Model probabilities for derecho formation tomorrow afternoon into the evening hours are pretty high, with upwards of a 70 percent chance of derecho formation across nearly all of the moderate risk area. My personal expectation is for the moderate risk to be modified slightly further east to account for increasing derecho parameters late Wednesday into early Thursday, however if the moderate risk were to remain unchanged I would understand the reasoning.

Evolution of this significant weather event should commence with multiple cells in northern and western Illinois before coagulation of these cells brings about a line segment of storm cells. With time, this segment should easily bow out and develop the danger for some serious damaging winds. Derecho formation is most likely to commence in east-central Illinois, throughout Indiana and into western Ohio. High resolution models initiate convection in the early afternoon hours, roughly around 4 PM Central time. Upscale development into a sustained bowing segment should ramp up going into the evening hours of 6 or 7 PM central.

 Oddly enough, this bow segment is expected to follow an almost identical path as the June 2012 derecho that left thousands upon thousands with damaged property across a wide swath of this country.  While the environment is not conducive for an incredibly damaging derecho like the one observed last year, it is very possible we could see a weaker derecho move through Indiana and Ohio after commencing in Illinois. Damage is possible.

Andrew

Monday, June 10, 2013

Wednesday Derecho Could Hit Areas Affected By June 2012 Derecho

I have a very real concern that many of the same areas affected by the late June 2012 derecho may be affected by another potential derecho coming up this Wednesday. It should be noted that derechos cannot be accurately predicted, and this may end up just being a regular cluster of thunderstorms.


The Storm Prediction Center has issued a slight risk of severe weather from far western Illinois to central Pennsylvania, expanding from south central Michigan to the bottom 2/3rds of Ohio and Indiana, as the image shows above. This slight risk area is not angled in a position I would expect to see with a derecho potential, but then again, we are still 2 days out from the potential event. The Storm Prediction Center indicates there is room for an upgrade (possibly to a moderate risk of severe weather) for Wednesday, as their discussion shows: ...THE MIDWEST...
   AS THE POTENT SHORT-WAVE TROUGH CROSSES THE MIDWEST...EXPECT SHOWERS
   AND THUNDERSTORMS TO INCREASE THROUGH THE AFTERNOON...WITHIN AN
   AIRMASS ACQUIRING MODERATE INSTABILITY IN CONJUNCTION WITH DAYTIME
   HEATING.  THE GFS AND NAM DIFFER WITH SURFACE FRONTAL EVOLUTION/LOW
   POSITION ACROSS THIS AREA...SO DETAILS REMAIN DIFFICULT TO
   DETERMINE...BUT IN GENERAL A RELATIVELY BROAD ZONE OF AT LEAST
   ISOLATED HAIL/WIND POTENTIAL IS EVIDENT GIVEN MODERATE WLY WINDS
   WITHIN THE LOWER TO MIDDLE TROPOSPHERE ACROSS THIS REGION.  ONCE
   DETAILS BECOME A BIT MORE CLEAR...MORE SUBSTANTIAL WIND THREAT MAY
   BECOME EVIDENT ACROSS PARTS OF THIS AREA...WHICH WOULD WARRANT
   INCREASED PROBABILITIES IN LATER FORECASTS.

A certain WRF model has a thunderstorm complex entering Illinois by 8:00 AM central time. Other forecast parameters gained from the NAM model depict a very moist surface environment, with precipitable water values closing in on 2.00'' in northern Illinois and surface dewpoints beyond 70 degrees. This high moisture content, combined with instability surpassing the 3000 j/kg mark, sets up conditions deemed as appropriate for potential derecho formation by multiple publications from various sources around the National Weather Service. The shape this complex takes on as it moves into Illinois kind of gives away the idea that it will be at least a bow echo; maybe not a full-fledged derecho, but it will at least be some sort of bowing segment that will add to the damaging wind threat. Cities like Chicago IL, Gary IN and South Bend MI could all be affected by this bow segment.

By 2:00 PM Eastern time, this bow segment has progressed into Ohio, practically running over the same areas that were hit by the devastating June 29, 2012 derecho event. This WRF model projects the bowing segment to remain rather small as it moves into Ohio and beyond, although there is still a lot of time for the track and size of this potential derecho to change. Columbus OH, Caldwell OH, Kenton OH and Dayton OH could all be affected by this potential derecho.

Quick note of comparison to those concerned about this being a repeat of June 29- this bow segment event looks to be weaker than the June 2012 derecho, and should cover less ground. The area it tracks over may be very similar, but as far as any potential damage goes, it will likely be exponentially less than what was seen on June 29.

Andrew

Sunday, June 9, 2013

'Ring of Fire' Pattern Ramps Up Severe Weather Threat

The upcoming weather pattern will signal the start of summer with the Ring of Fire pattern evolving over the Plains, leading to increased chances of severe weather over parts of the nation.

Over the next 10 or more days, we should see development of high pressure over the Plains, leading to that high pressure system settling in over the region and permitting the development of the Ring of Fire. In the Ring of Fire pattern, high pressure fills much of the Plains and sits there for a prolonged period. In response, multiple mesoscale convective systems (MCS's) will form on the edge of this high pressure system (usually the north and east sides of the ridge). It is these MCS's that put the 'fire' in the Ring of Fire. Short range models already have over three MCS's hitting Iowa and Illinois in the next 84 hours, which could lead to over 2 inches of rain in some spots.

The Ring of Fire pattern is considered one of the better patterns for severe weather. It's not a convective system every few days- we're talking instances of possibly more than once MCS each day. No guarantees on if that will happen this time around, but the potential is certainly there.

Andrew

Friday, June 7, 2013

Tropics Heat Back Up in Late June, Early July

After the first named storm of the 2013 Atlantic Hurricane season was also the first system to make landfall on the US Mainland this season, questions arise as to if the rest of the season will involve more landfalls and tropical cyclone formations. While my Official Outlook can address those questions, the one we're here to answer is when the next shot at tropical cyclone formation is.

The long range GFS model has been supportive of another tropical cyclone forming in the Gulf of Mexico, proceeding to make landfall in either Texas or Mexico. This would supposedly happen in the final days of June. While the GFS has been trending with this idea, I see a much better potential coming on in the first weeks of July, as what could be a strong Madden-Julian wave makes its way eastward towards the Atlantic. Already in the Gulf of Mexico we can see some light shades of green, meaning below normal velocity potential values and thus a better chance for tropical convection to fire up in the area. If the MJO wave is able to sustain itself and shift into the Atlantic, I would not be surprised to see a solid hurricane (or multiple tropical systems) form as a result.

With a pattern still conducive to development sticking around to the end of June on the US Mainland, it is possible that the chances of tropical cyclone formation may be enhanced.

Andrew

Thursday, June 6, 2013

Tropical Storm Andrea - Bulletin #2

Satellite imagery for Tropical Storm Andrea shows that the system has indeed strengthened overnight, with her western flank now starting to build back in the immediate vicinity around the eye. Aircraft reconnaissance last night showed very strong winds in the southeast quadrant of this tropical storm, where winds maxed out at or just above 60 knots. That little eye-like feature we see would be another sign of strengthening if the system wasn't right up against Florida.

My potential landfall zone now extends further north, from Apalchicola to roughly New Port Richey, FL. My expected point for landfall is nearly due west of Gainesville, but that could change in coming hours. Landfall is expected in the afternoon, with tropical storm force winds already starting to scrape west-central Florida. With a tornado watch in effect, it can be expected that an all-day tornado threat will continue to evolve today. We have already seen a few reports of tornadoes, but nothing in an outbreak context is expected.

Andrew

Wednesday, June 5, 2013

Tropical Storm Andrea - Bulletin #1


As we hinted at on May 28th, satellite imagery and aircraft reconnaissance  confirms the formation of Tropical Storm Andrea at this hour, allowing the Atlantic tropical season to get off to a fast start. Satellite imagery depicts a strong eastern flank of Andrea but a very quiet western side to this tropical storm. Considering the conditions in the Gulf of Mexico aren't totally primed for tropical formation, the rather unusual build of this cyclone isn't that extraordinary. Satellite imagery also indicates clouds from Andrea have already overspread Florida, and it is in Florida where I expect the primary landfall to occur.

Atmospheric steering winds for this afternoon over the Atlantic basin are shown to be trying to push Andrea due north into Alabama, and the official National Hurricane Center track predicts the tropical storm to move slightly north in coming hours. However, going into the next few days, it is anticipated that these steering winds will begin to gain a more eastward component, allowing Andrea to maintain less of a northward track and more of an eastward track, combining to make for a northeast movement.

Landfall is expected to occur Thursday afternoon.
I believe the potential landfall zone will extend from the immediate vicinity of Cross City to Sarasota, Florida. This zone is where the models are converging for a landfall. The yellow star indicates where I believe the cyclone will make landfall. This landfall spot would be right around Hudson and New Port Richey. It is expected almost everyone in this potential landfall zone could experience tropical storm force winds and potentially flooding rains. Preparation plans are advised to be activated as the first named system of 2013 becomes the first landfalling system of 2013.

Andrew

Arctic Sea Ice Forecasts Very Ominous

Long range forecasts concerning Arctic sea ice are pretty ominous, with the above image showing as little as 3 million square kilometers of sea ice present just 100 days away.

The image above, from Steven Cavallo, shows the latest ensemble forecast of sea ice over the Arctic as far as 100 days out. We see a plot of the average sea ice values over the next 100 days, and the ensemble prediction superimposed on it. The ensembles take the sea ice values at below normal levels in the next month before really dropping off after the 30 day mark. From the beginning of June onwards, it is predicted that the Arctic will have sea ice levels less than half the typical values for that time of year.

In the very long range, this could impact the winter by not being able to hold as much sea ice, and thus allowing the Arctic Circle to be warmer than normal. This could then allow the polar vortex to weaken, which in turn may move to the lower latitudes at points during the winter. Bear in mind a LOT needs to happen before we can get that sequence underway, but this is a good first step for those wanting to see the polar vortex weaken into winter.

Andrew

Tuesday, June 4, 2013

Long Range Winter Prospects Very Favorable

Reminder: My Preliminary 2013-2014 Winter Forecast comes out Saturday, June 15 at 12:00 PM Central Time.

Long range weather models are predicting a very favorable winter for those snow lovers and plowers who have been in a big deficit in the past two years.

Shown above are two long range forecast models, predicting 200mb heights for the month of December 2013. Areas of blue depict general lower heights and thus low pressure areas, while reds indicate high pressure systems. The contour lines are superimposed on the images to help point out areas of differing pressure. There are four regions I want to look at here, so we'll start out with North America.

Both images show a pretty favorable set-up for cold weather as far as the 200mb level goes. We have a large area of rather strong low pressure over eastern North America stretching into New England, and this is reflected by the compression of contour lines in the same region. The low pressure area over New England tells me this area would indeed be favored for at least somewhat-frequent shots of Arctic air, and the tightening of the jet stream favors this theory. The overall picture is what excites me more. If we look into the far Northern Hemisphere we see no area of low pressure- the closest persistent low pressure center is the one in North America. Now, bear with me here, the idea is pretty outland-ish. But if you were to try to place a location for the polar vortex to average out over the month of December, you would want to find the area with the lowest pressure over the general upper latitudes (including North America, northern Eurasia, and Greenland). That said, it would make sense that the polar vortex may very well have a tendency to be pushed further south towards Canada and the US.

Our second area of interest is the United States. Both models show that low pressure area trying to push into New England, but we already covered that in the above paragraph. The item I want to focus on is the West Coast into Alaska. We see a separation of the contour lines into a looser composition, as well as oranges building into those areas. This indicates the presence of high pressure, and sets up positive phase of the Pacific-North America (PNA) pattern. In the wintertime, the jet stream does exactly what is being depicted above, and this means a warm West US and cold East US. Additionally, storm systems will tend to track in a path favorable for snowfall in the Midwest, Plains and portions of the Great Lakes into the Ohio Valley. The positive PNA helps to usher in lower than normal heights across the East US, and this will deliver us into the next area of interest.

The third area of interest is the Bering Sea. Both models project strong high pressure in the vicinity of the Bering Sea region; the GFDL model (left) has high pressure square in the Bering Sea, while the NCAR model (right) has the high pressure more towards Asia but still influencing the Northern Hemisphere. In both situations, the Arctic Circle appears overcome with above normal height anomalies, indicative of high pressure in the region. High pressure in the Arctic would imply a weaker polar vortex (yes, the same vortex I discussed this previous winter), as well as tendency for cooler weather to make its way down to lower latitudes of the world. If we do have high pressure in the Bering Sea, it would be easier for instances of high pressure to overwhelm the Arctic, and this could (keyword is COULD) allow the polar vortex to be pushed further south and affect lower latitudes in significant ways.

The final area of concern is East Asia. All models I observed for December 2013 depicted a tightening of the contour lines and lowering of height anomalies in East Asia, sometimes even into the northern Pacific. I have described a few times on this blog the idea of the East Asia-East US storm correlation, where a stormy period in East Asia can mean a stormy period in the East US 6-10 days later. This would mean more chances for snow whenever East Asia got active, and if long range models are correct this active period could be quite often. If the tightened jet stream in the North Pacific and stormy East Asia evolves as predicted (combined with the possible +PNA pattern and weakened polar vortex), this winter may help those winter-loving souls damaged by the last couple of winters.

Don't forget, as the note at the top says, my Preliminary 2013-2014 Winter Forecast will be released Saturday, June 15th at 12:00 PM central time.

Andrew

Saturday, June 1, 2013

June 1, 2013 Special Atlantic Tropical Discussion

This is a special Atlantic Tropical Discussion from The Weather Centre.

Model guidance and the synoptic flow over the next 5-10 days tells me we are likely to see development of a tropical cyclone in the Gulf of Mexico that may very well lead to a landfall in the Florida Panhandle. Model guidance then depicts this tropical cyclone to hug the Eastern Seaboard up through the Mid-Atlantic before jogging off out to sea.

The pattern across the Atlantic will be stagnant, with high pressure spread out across the waters. This will enable any potential tropical formation to stick close to the coastline and stay in the Caribbean and/or Gulf of Mexico. It looks like that set-up will enable that principle to work itself into the first 10 days of June, when we expect tropical development to occur in the Gulf of Mexico and pose a threat to land. The most common landfall area has been northern Florida, and solutions that have taken that landfall path have then taken the remnants of the tropical cyclone up the Eastern Seaboard.

Model uncertainty remains high at this point, and the tropical cyclone may not even form when it comes down to it. However, if one does form in the Gulf, these are the areas I would expect to be affected.

On another note, what would you think about me using a grid-type of graphic like the one pictured below? This is a prototype and will be changed, but what are your thoughts on it? Like or dislike?

Yellow: Threat of tropical cyclone effects
Red: Threat of tropical cyclone landfall
Andrew