Saturday, September 28, 2013

Special Long Range Lookout: September 28, 2013

This special Long Range Lookout will address the expectation of a colder trend in the weather in the 20+ day forecast range, and the effects of the current weather pattern on the winter ahead.

The current weather pattern involves a highly meridional (wavy) jet stream across North America, with a deep trough stretched across the West and strong ridging spread over Canada and the Great Lakes. The deep troughing is likely due to an increased stream of storms that have been shifting across the northern Pacific. The 500 millibar anomaly chart on the left displays a strong system currently stationed over the Bering Sea and into the Gulf of Alaska, and I suspect that system will move south towards the West Coast, possibly also into the West US. This train of storm systems has changed the sea surface temperature pattern across the northern Pacific as well, as the image below shows.

There is a large body of below normal sea surface temperatures stretched from the Aleutian Islands to waters well offshore of the Pacific Northwest. This development has occurred only very recently, and it was only a few weeks ago that the entire northern Pacific was well above normal in SST anomalies. The continuing storm train over the northern Pacific, aided by a favorable Madden-Julian Oscillation (which we will discuss more in-depth later), should assist in further lowering sea surface temperatures across the waters in and southeast of the Bering Sea. A potential long term implication of this new SST anomaly could mean an Aleutian Low, which would be favorable for harsh winter prospects in the East US. Despite that potential, a decisively negative PDO pattern has been present recently, and this could discourage such cold weather in the East and Central US.

We're going to dive right into some hardcore weather with an analysis of the Relative AAM tendency. The relative AAM tendency shows what its name says; the chart helps predict the tendency of the AAM index. Right now, the AAM tendency is positive, and this fits well with the current observation of a slight positive AAM. In the medium range, this should lead to a tendency for the positive phase of the East Pacific Oscillation, which encourages the formation of above normal temperatures in much of the United States, as illustrated by blizzardof96 on the AccuWeather forums.

Long term AAM projection from Nicholas Schiraldi shows a gradually lowering AAM over the next 360 hours, to the point that we see a neutral or slightly negative AAM at the end of the forecast period. This fits in well with ensemble projections of a lowering EPO in the long range, which could lead to chillier temperatures for the United States. 2-3 week lag time between the AAM suggests not only an incoming warm trend at some point in October, but also a cooler trend towards the end of next month. Exact timing is to be determined and will depend on the strength of the AAM at its low point.

On to the more interesting concept of this special Long Range Lookout, the Madden Julian Oscillation, or MJO. The MJO involves the anomaly of tropical convection along certain regions of the Pacific and Atlantic. A certain placement of this tropical convection indicates a different phase, with the MJO having 8 phases in all. Each phase has different implications on the weather here in the United States. Model guidance projects the MJO meandering around in a weak-moderate Phase 6 for the next several days. The Canadian model guidance set prefers to retrograde the MJO back into Phase 5, but agreement between the American, European and United Kingdom guidance systems says we will most likely stay in Phase 6.

Now, the MJO at Phase 6 helps to enhance tropical cyclone activity over the West Pacific, which we certainly have seen in the last couple of weeks. This above normal tropical activity in the West Pacific has greatly helped in the negative SST anomaly trend in the north central Pacific, which we discussed earlier. Should the MJO continue to work its magic with the West Pacific, there is little reason to think that this cooling trend in the waters of the North Pacific will not continue.

A key point of interest with Phase 6 of the MJO includes the persistent blocking pattern that sets up in the 10-30 day timeframe following the MJO entering Phase 6. The circled area shows these positive height anomalies as the blocking regime that would present itself between the 90W and 30W longitude areas of the 70N and 55N latitude lines. In other words, the blocking would be present across eastern Canada and much of Greenland. The positive height anomalies present in the same region in the 15-0 days prior to the MJO entering Phase 1 have verified in the last couple of weeks, with the current weather pattern image at the top of this post confirming that suspicion and strengthening the argument for this long range idea of a blocking pattern that may resemble a negative North Atlantic Oscillation.

On another note, if you look closely, you can see a swath of positive height anomalies between the 150W and 120W markers between the numbers 10 and 20 on the left side of the image. This represents a trend of ridging across the Gulf of Alaska, which appears to eventually weaken and shift west. Depending on if this Gulf of Alaska ridging does set up, the East US may have some trouble with maintaining more seasonal temperatures.

Another composite image for the weather pattern 20 days prior to a significant upper latitude blocking event nearly guarantees this idea that we will see some long term blocking in the northeast region of North America. This graphic shows 500 millibar anomaly contour lines as well as OLR anomalies in color (OLR= tropical convection, where blue indicates enhanced tropical convection and yellow portrays below normal tropical convection). The blue anomalies stationed due south of the Bering Sea suggests the MJO is supposed to be in Phase 6 twenty days prior to the significant blocking event. Model guidance confirms that we are already seeing this play out. 500mb anomalies show steadfast high pressure across the far upper latitudes, with negative height anomalies in the northern Pacific. The September 24th 500mb height chart below shows how good of a match the two images are, further helping the argument for blocking in the next 10-30 days. The 'Slow MJO' phrase on the top of that graphic above just tells that the MJO should be moving slowly through Phase 6 in order for this situation to work out, and model guidance assures us that the MJO is in no hurry to get through Phase 6.

September 24, 2013 500mb pattern
So, what can we draw from all of this?

Well, in the short term, expect this very wavy jet stream to continue, due mainly to the continuing storm train across the northern Pacific. Inconsistent but strong bouts of ridging will occur in the Central and Eastern US in response to any storm systems that bottom out in the Southwest and enhance the meridional flow of the jet stream. In the short range, warmth looks to be the buzz word. But we are just a week or two away from what could be a sizable shift in the temperature trend. If the MJO composite works out as I explained above, we should see a tendency for a decisive cool weather trend in the Plains and portions of the western Midwest, with some iffy temperature patterns in the eastern Midwest, Ohio Valley and much of the East US. Depending on how influential the ridging in Canada and Greenland is on the United States, we could see above normal temperatures in portions of the eastern half of the US. A general stormy pattern may evolve over the Great Lakes in the next 7-14 days, but I'm a little skeptical due to low confidence from some other composites I've looked at. Probably won't see any long-term wintry weather potential in much of the Central and Eastern US outside of expanding frost zones for portions of that area. The West should keep an eye out for additional wintry weather possibilities in coming days.


Wednesday, September 25, 2013

Hints of the 2013-2014 Lezak Recurring Cycle Appearing

The new Lezak Recurring Cycle, a repetitive weather pattern that shows itself in the late fall and continues through the winter and spring, is beginning to reveal itself in bits and pieces on model forecasts.

This 500 millibar anomaly chart, valid for October 6, shows a very deep storm system pushing down through the Ohio Valley and Great Lakes into the Southeast. Current model forecasts have this storm system moving relatively close to the East Coast, and if the LRC catches on to this storm system, it's possible this would be a Nor'easter event. But that prospect is laced with 'if's' and other question marks, so I won't emphasize the the idea too much.

Just ~100 hours later, we see another very deep system across southern Canada and spreading its influence into the Midwest, Great Lakes and upper Plains. That solid red line crossing the border is the freezing line. If we see this system get caught up in the LRC too, don't be surprised to see very cold weather in the Midwest, Plains and southern Canada a few times throughout the winter. Additionally, take note of the stormy Bering Sea and lower heights along the waters west of Baja California. Both of these regions would provide potential storm systems for the United States. Model forecasts not shown on this blog post do portray storm opportunities for the Plains and Midwest due to the lower heights in and around the Bering Sea area. The Baja California energy source could help the potential for big snowstorms in the Great Lakes with the presence of a Southeast Ridge, or the chance of a Nor'easter if the ridge is not present. The last item to check out is extensive blocking high pressure across the upper latitudes. If the Lezak Recurring Cycle catches on to this blocking, don't be surprised to see colder weather for the winter. But again, all of this is educated speculation at this point.

Temperature anomalies for the October 5 through October 10 timeframe show cold conditions across the Central and East US. Again, this may come up again later in the winter if the LRC follows up on this colder than normal pattern. One thing I am concerned about is the spread of warmer than normal temperatures across Canada. Going into the fall, this could limit the cold air available to the US later in the winter season. However, it's only late September, and things could do a turn-around before we hit late fall and winter. Only time will tell.


Tuesday, September 24, 2013

Final 2013-2014 Winter Forecast Release Date

The release date for the 2013-2014 Winter Forecast has been announced!

The final winter forecast will be released on SATURDAY, OCTOBER 26 at 12:00 PM Central Time. 

This will be the only forecast released on that date- due to time constraints, the European and Canadian forecasts are unable to be made and released. I will put in bits and pieces of information for each region in this final winter forecast, but it will not be a huge forecast.

Additionally, the format of my winter forecast will change. Rather than the long discussions I typically produce, the forecast will be laid out without this discussion. The reason? Most (if not all) of the information I would put in the discussion is contained in my daily posts.


Weather Ramblings: September 24, 2013

An interesting weather pattern will be evolving in the next few weeks, as we transition from summer weather to a fall-like pattern, especially in the medium and long range.

Model guidance for the 7 day forecast period shows deep troughing across the Gulf of Alaska, which helps to provoke some minimal high pressure development across the Central and Eastern United States. This high pressure is very weak when compared to typical high pressure anomalies when such deep negative height anomalies appear in the Gulf of Alaska. Such a pattern resembles a negative phase of the Pacific Decadal Oscillation, which Eric Webb of Weather Advance illustrated. The image below shows correlations of 500mb heights to the Pacific Decadal Oscillation. The image shows positive and negative colors- positive values mean the phase of the PDO would coincide with height anomalies in that area, while negative values mean the phase of the PDO would be opposite of height anomalies in any given area.

This image shows that the negative PDO produces a positive correlation with 500mb height anomalies in the Gulf Alaska- in this case, a negative PDO would provoke negative height anomalies in the Gulf of Alaska, which we see in the forecast above. That said, deep negative values are shown in the Central and East US, meaning a negative PDO would produce positive height anomalies in the aforementioned areas into Canada. The model forecast at the top of the page somewhat resembles this negative PDO pattern in the sense of deep troughing in the Gulf of Alaska, but we see no significant ridging in the east US and east Canada. The main cause of this seems to be positive height anomalies across the Arctic Circle and troughing across Europe and Asia- those two factors go against the typical -PDO pattern illustrated in the image above.

By the 264 hour mark, model guidance projects general high pressure formation across the Pacific Northwest and southwest Canada as troughing in the Gulf of Alaska shifts west to the waters south of the Bering Sea. This high pressure formation in the west coast of North America provokes the positive phase of the Pacific North American index, which helps cooler temperatures enter the central and east US. Ridging west of Greenland provides a basis for a colder weather pattern in the East US and Central US too, and thus it is no surprise that at the 360 hour mark of model guidance, deeper negative height anomalies (and colder temperatures) arise in the land east of the Rockies.

Teleconnection guidance confirms this idea of a turnaround to a positive PNA and persistent negative NAO throughout the forecast period. The bottom two panels show the West Pacific Oscillation forecast on the left and the East Pacific Oscillation on the right. Without going too in-depth with these two indexes, the negative phase helps cold weather prospects in the US, and the positive phase enhances warm weather across North America. With both oscillations projected to fall by the end of the forecast period, we could see some actual cold weather arrive in time for the second week of October.

A convection-related index called the Madden-Julian Oscillation will be heading into Phase 6 (it has 8 total phases), so let's take a look at a 500mb composite chart for worldwide longitudes zoomed in on the 70-50 north latitude.

As you can see on this chart provided by Mike Ventrice, colors on here show anomalies for the 500mb level. In this case, cold colors indicate negative height anomalies (low pressure), while warm colors show positive height anomalies (high pressure). On the left side of the image, numbers in negative and positive values are shown. Basically, the numbers indicate how many days before (negative numbers) and after (positive numbers) the MJO enters Phase 6. Taking a look at this chart, there is a large signal of strong ridging over the 90W to 30W longitudes. When looking at the 70N-55N latitudes and 90W-30W longitudes, we find Canada and Greenland in that location. So, going by the image, it is plausible to expect strong ridging of high pressure from Central Canada (90W longitude line) to eastern Greenland (30W longitude line) approximately 15 to 30+ days after the MJO enters Phase 6. With model guidance predicting the MJO entering Phase 6 in just a few days. This means I am highlighting October 8 to October 23 (and possibly beyond) for increasing chances for cold weather in portions of the US due to this ridging over eastern Canada and Greenland.


Monday, September 23, 2013

3 Reasons Why the Arctic Oscillation Will be Negative This Winter

As we approach winter, we begin to look at how certain atmospheric patterns will turn out for the season. I have found three reasons why the Arctic Oscillation should turn out negative this winter.

1. Positive Atlantic Multidecadal Oscillation (AMO)

Weekly sea temperature anomalies and monthly AMO data indicate we are in a moderate positive AMO. The AMO is shown by positive or negative sea temperature anomalies in the upper Atlantic and Arctic oceans. Taking a glance around the waters east of Canada and around Greenland, we find widespread positive temperature anomalies. While the strength of these anomalies varies, it is apparent that we are in a positive AMO scenario. Because it is called the Atlantic Multidecadal Oscillation, it would not be unreasonable to predict we see a positive AMO this winter. With the presence of warmer than normal waters around Greenland and in the Arctic, the polar vortex is weakened, leading to a negative Arctic Oscillation.

2. Warming Arctic Temperatures

Observed Arctic temperature across this year are shown above in red, with the average Arctic temperature pictured in green. The horizontal blue line depicts the freezing temperature, to identify times when ice coverage may grow or shrink, among other uses. Taking a look at the latest Arctic temperatures, we find that temperature anomalies have trended warmer since the below-normal temperatures experienced this past summer. The latest temperatures are on the drop from already-definitive above normal temperatures. The presence of warmer than normal Arctic temperatures, should they persist into the winter, will hamper development of the polar vortex and enable a negative Arctic Oscillation. Additionally, these warm Arctic temperatures may be able to enhance the positive AMO by warming up already-warm waters in the upper latitudes.

3. Low Solar Activity

This chart above shows observed sunspot values on a monthly basis, with the average trend line shown in blue. The forecast line is in red, but since it obviously has not verified and will not verify in the future, we will disregard the forecast. Notice how low we are in terms of sunspot activity now when compared to the beginning of this century, on the far left of this graph. Did you notice that the winter of 2011-2012 was warmer than normal? Take a look at the trend line for the area right above the number '12' and you can see a bump up in sunspot activity right as it crosses that '12' line. There's no coincidence here; the spike in sunspot activity did affect the winter of 2011-2012. Did you feel colder than normal for the winter of 2009-2010? The sunspot graph agrees- we saw a cold United States in that winter, as well as a minimum in the sunspot count. Now, as we progress towards the winter of 2013-2014, sunspot numbers will begin to fall off again. Chances are elevated that we see a cooler winter than those in the last few years due to, among other things, a weakening sun. With a weaker sun comes a weaker polar vortex and jet stream, helping lead to not only a negative AO, but a cooler winter.


Sunday, September 22, 2013

October SAI to Start Off Strong

The October SAI, which enables us to see how the Arctic Oscillation and winter temperatures will end up throughout the following winter, looks to start off strong when we actually enter the month of October.

The October Snow Advance Index uses Northern Hemisphere snow cover anomalies to predict the Arctic Oscillation and United States temperatures in the following winter months. If snowfall anomalies are above normal, a negative Arctic Oscillation and cooler than normal United States is favored. In the same sense, below normal snow cover anomalies across the upper latitudes result in a positive Arctic Oscillation, which helps to prevent cold air outbreaks in the US.

The image at the top of this post shows projected snow cover changes over the next 192 hours from the September 19th 0z GFS (this post was made on September 19th). On the bottom right, the percentage change in snow cover over the 192 hour period is shown as +2.73%. This is the highest increase I have seen in the last 4 or so weeks of tracking the GFS and its snow cover change forecasts.

The reason I'm excited about this high increase forecast is because of where we already are in the northern hemisphere snow cover department. This graph shows observed snow cover values (black) compared to normal (green) on the top image, with anomalies at each point on the bottom. After going through a below-normal spring and early half of summer, we find ourselves in above normal territory. With snow cover projected to shoot through the roof in the next 192 hours, it is likely we see a substantial increase in this positive snow cover anomaly by the time we get to October, when the SAI comes into effect.


Saturday, September 21, 2013

Ramblings of a Changing Pattern

The atmospheric pattern will be undergoing a shift in coming days, and this will result in a shift in temperatures as well. Let's take a look at what will be happening.

The teleconnection (various atmospheric oscillations that occur over different areas of the globe) diagnosis over the next two or so weeks does support the idea of at least a modest shift in the pattern over the northern Hemisphere. We start with the PNA index forecast on the top left panel, which is projected to spike positive by the start of October.  A positive PNA results from high pressure formation in the Western US, and related low pressure formation over the East. That said, the upstream pattern from the East would suggest summer is quickly losing steam. That's not to say we won't see a resurgence in summer-like temperatures down the road, but for the near-term, it's looking less likely. The top right panel shows the North Atlantic Oscillation (NAO) rising from deep negative values to a weaker (but still negative) position. At the end of the forecast, we see re-strengthening of the negative NAO occurring. Considering we are bound to see elongated high pressure in North America as a result of the positive PNA, it's not out of the question that the elongated high pressure may spill north towards eastern Canada.

The bottom two panels show the West Pacific Oscillation and East Pacific Oscillation forecasts on the left and right, respectively. These two indexes are closely related, as both originate from the Pacific. We see a mainly positive WPO throughout the forecast period before weakening to a neutral phase occurs. It's probable we see a more negative WPO forecast in coming days, as high pressure takes over the western coast of the US into Canada, going against the typical +WPO regime of negative height anomalies across the upper Pacific. The EPO will see a roller-coaster of positive to neutral to positive again to neutral again over the next couple of weeks. The shifting height anomalies across the northeast Pacific will be to blame, as the PNA fights for control. Don't be surprised to see periods of a -EPO play out; the -EPO helps out with cold weather prospects for much of the eastern half of Canada and the US.

 We see the +EPO (deep negative height anomalies in the NE Pacific) tangling with a persistent +PNA (weak positive height anomalies over the West US) to produce slightly below normal height anomalies in the East US by the 10 day forecast period. A negative NAO is shown with positive height anomalies west of Greenland, further helping cooler temperatures to shift into the United States.

By Hour 360, the +EPO is defeated and a +PNA controls the situation to bring steep negative height anomalies to the Central and East US. A slight -NAO also helps out.

With Typhoon Usagi and newly-formed Pabuk swirling in the Pacific, it's evident we will see some stormy times ahead in North America. As Usagi and Pabuk go throughout their lives, in addition to the formation of multiple powerful storms in the Bering Sea (see image below), it is not unlikely we see very cold weather hitting the Central and East US behind a cold front or two, depending on where the energy hits in North America. The East Coast should be on the lookout for a strong storm system in the next 2-4 weeks as a result of this stormy Pacific pattern. A continuation of the projected -NAO may lead to a coastal storm set-up, but anything beyond that is mere speculation.


2013-2014 Updated Snowfall Map: Chicago, St. Louis, Minneapolis At Risk for Major Storms

This post contains the updated snowfall map for the winter of 2013-2014. The graphic shown reflects the areas where the strongest storms may hit. It should be noted that while it is not shown, the Ohio Valley is still in line for an above-average snowfall tally this winter.

Each winter, everyone wants to know if they'll get 'The Big One'- the winter storm that defines the season and brings enormous amounts of snow to wherever it hits. For lack of a better and more simply-defined term, we address that as a blizzard in this post. For this winter, it appears the Plains and Midwest will be at the highest risk for a significant winter storm.

Among the cities included in my forecast are Chicago, Minneapolis, and St. Louis. I placed these cities under the 'High' risk for a blizzard, due to the likelihood we will see ridging in the Southeast develop. This will help to push storm systems north, and depending on how far north they go, heavy snowfalls could very well hit those in the pink area.

In the blue, I placed Wichita, Des Moines, and Rhinelander under an 'Above Normal Threat' outlook. This is mainly due to the same reasons I described above, but I feel that a lack of confidence prohibits me from upgrading these areas. Don't get me wrong here, this is not nearly set in stone and will change, but right now, I'm just a bit more cautious with those in the blue due to their uncertainty on where storms will actually go when they are pushed north and into the Plains/Midwest.

I highlighted the East Coast on the likely event that they see coastal storms this winter, but the threat is not extraordinarily high due to the possibility Southeast ridging prohibits a lot of coastal storms from heading up into the Northeast.


Thursday, September 19, 2013

Analog-Based Forecasts Favorable for Cold, Stormy Winter

Two analog-based forecasts are favorable for a cold and stormy winter in the Central and East US.

The first forecast we look at is from the TropicalTidbits site. These images show the November (left) and December (right) Z500 height anomalies. Don't look at just the colors; look closer at the contour lines. We will look at the December forecast for now.

In the December forecast, we see a few favorable things:

I. Troughing off the Baja California Coast
On the right-side image, contour lines are shown dipping down to the east of Hawaii and west of Baja California. The depression of contour lines indicates increased storminess, and this is a feature we have seen on multiple forecast models for this winter. In this case, storminess off the coast of Baja California would most likely mean storm systems would move northeast into the Plains and southern Rockies. From there, they will most likely either shift northeast to hit the Midwest, or keep south and eventually run up the Appalachians due to the feature I will discuss next.

II. Ridging in the Southeast
In the Southeast in the December forecast, you can see an arching feature. This is commonly a signal of high pressure, and this is called the Southeast Ridge in the winter. The Southeast Ridge is able to push storms north and create the Panhandle Hook, Great Lakes Cutter and Colorado Low storms. If the ridge is weak enough, we could see storms become Nor'easters down the road, but based on this forecast, I would favor a stormier Plains, Midwest and Great Lakes.

III. Ridging in the Pacific Northwest
In another common feature we have seen in model forecasts for this winter, contour lines arch up across the Pacific Northwest and western Canada. This feature is actually a specific atmospheric index called the Pacific North American Index (PNA). This analog forecast shows a positive PNA, which is shown by ridging along the western coasts of the US and Canada. The positive PNA then enables a favorable storm track for the Midwest and Great Lakes by helping to create that Southeast Ridge, and also let cold air flow south into the Plains.

IV. Negative North Atlantic Oscillation
We see ridging along the waters close to Greenland, and that is a telltate sign of a negative North Atlantic Oscillation (NAO). The negative NAO enables the jet stream to buckle south and allow cold air to flow into the Great Lakes and Northeast, while also suppressing the Southeast Ridge. With ridging down south being suppressed, storm systems can shoot up the coast and become Nor'easters. This negative NAO is a reason why I am still eyeing the Northeast for a stormy winter, even though many signs point to the Midwest and Great Lakes getting the stormy part of winter.

The other analog-based forecast we can use is the Constructed Analog, or CA model from the Climate Prediction Center. In this forecast, we see the 500 millibar anomalies on top, with temperature anomalies on the bottom. I can't really decipher the 500mb forecast because there are no contour lines, but the temperature forecast pretty much echoes the temperature forecast from the TropicalTidbits site. We see a cold Midwest, Plains and East Coast, likely a result of ridging over Greenland (negative NAO) and maybe some slight ridging along the West Coast, but the lack of contour lines does not allow me to elaborate on that further.

These two analog-based forecasts are turning out favorable forecasts for the Central and East US in terms of a wintry winter season. Whether they actually verify is to be determined, but things are looking up.


Wednesday, September 18, 2013

Long Range Lookout: Cool End of September, October Likely

It now appears the end of September and much of October will end up cooler than normal for multiple portions of the nation.

The European ensembles develop an Omega Block across much of Canada and far northern portions of the Plains. The Omega Block involves a body of high pressure being sandwiched between two areas of negative height anomalies. If you look closely at the height contours, you may be able to see what looks like the Greek letter Omega (Ω). The Omega Block pattern typically brings hot weather to those in the positive height anomaly region, and cool temperatures to those in the negative height anomalies. The Northeast, Ohio Valley and Plains will likely receive the negative height anomalies, while Canada and Greenland are inundated by positive height anomalies. Should this pattern stay in place for a prolonged period of time, it would not be impossible that we see a cooler than normal September over portions of the country that would be affected by this Omega Block. I do believe that it will be somewhat difficult to maintain this Omega Block, but I do not find it impossible that we see at least a form of a blocking pattern bring cool weather to parts of the United States.

This cool prognosis for September and October is supported further by CFS model projections of a negative North Atlantic Oscillation (bottom image) and negative Arctic Oscillation (top image). These two indexes are closely related, so it is no surprise to see these two going negative at the same time. It is epxected that the NAO and AO remain negative until at least October 10th, when the CFS starts to bring the two indexes to more neutral territory. But even in that situation, the CFS has lowered the projection from neutral to slightly negative in past model runs, which could mean we continue to see a negative AO and NAO past October 10th. Such a development would lead to a colder United States if the rest of the atmospheric pattern cooperates (indications are it would).


Tuesday, September 17, 2013

What Are The Models Saying This Winter? - CMC1 Model

This model examination will focus on the long range CMC1 model.

The image above shows predicted 200 millibar contour lines and anomalies. We're going to focus on the contour lines for right now. We start in East Asia. Looking closely at the image, we see tightened contour lines in the area around Japan. Considering there is a 6-10 day gap between storm systems in the East Asian area and storm systems in the East US, a tightening of contour lines could suggest an increased number of storm systems. This, in turn, may suggest a stormy East US this winter. We see a large ridging pattern across the Alaska/western Canada. This ridging could then provoke a colder than normal pattern to evolve across the Midwest and East US, as cold air flows southeast along the ridge. If the ridge extends far enough into Alaska, a cross-polar flow situation could set up, which would transport Siberian air to the States. A cross-polar flow is one of the situations that brings the coldest air possible to the US- another situation would be the cold air displaced to the surface as a result of a stratospheric warming. Enhancing the probability of a stormy Midwest and East Coast is the presence of lower than normal heights offshore of the Southwest. This suggests a stormy subtropical jet stream, which could lead to some snowy events for portions of the Central and East US.

The temperature forecast for the winter from the CMC1 model shows a very warm nation. We see consistently above normal temperature anomalies stretching from the West to the East. Much warmer anomalies are found in northern Canada towards Greenland, and this could be suggestive of upper latitude blocking. However, whether than actually happens remains to be seen, as temperature anomalies can be deceiving. Negative temperature anomalies are found in western Alaska, which may or may not suggest troughing in that area. Again, temperature anomalies can be deceptive, and I'm not willing to speculate beyond that.

Precipitation anomalies suggest a very wet Midwest and Northeast for this winter, with a dry Southeast. Considering the prospect of a Southeast Ridge, storms would tend to be directed north into the Midwest and Great Lakes. I would not be too surprised to see the precipitation pattern along the eastern half of the nation verify- it is in line with my current thinking for this winter. As far as the West, I would expect to see dry precipitation anomalies further to the north due to the idea of some ridging closer to the Pacific Northwest and western Canada. But this is only one model's take, and we are still months away from winter.


Monday, September 16, 2013

Persistent Stratospheric Warming Setting Stage for Winter

Stratospheric warming currently ongoing throughout this past summer and now is beginning to set the stage for this winter.

This graph shows observed temperatures in the 70 millibar region of the stratosphere from the latitudes of 65N to 90N. The red line illustrates the actual observed temperatures, while the green line shows average temperatures for that time of year. The light gray lines depict the minimum and maximum temperatures observed to this date for any certain time of year. Looking at this past summer, where the red line begins to arch up, we see the observed temperatures were consistently above the green line, meaning the stratosphere has been above normal for a while. It then tapered off for a little while, but as the zoomed-in portion on the bottom right shows, stratospheric temperatures have been on the rise for a bit, to the point where they are above normal.

The temperatures have been above normal for good chunks of the last few months, but the question now is: What is causing these above normal stratospheric temperatures?

An examination around the solar activity reveals daily sunspot trends may be at fault. This chart shows many things at once, but we want to focus on the red line, which shows daily sunspot values. Take a look at the red line after the big spike in the middle of the chart. After that spike, sunspot values take a dive, and stay in slightly below normal territory for a while. This big drop-off happens in the month of June and into early July. Taking a second glance at the stratospheric temperatures, the 70 millibar level was constantly above normal throughout this period of low sunspot numbers. A second example can be found in the time during and right before the big spike on the sunspot graph. These above normal sunspot numbers happened between April and late May. Examination of the temperature chart shows consistently below normal values in this same time frame, meaning there may be a negative correlation between daily sunspot numbers and stratospheric temperatures.

All of that said, if we continue to see the current sunspot numbers stay at unusually low values (circled in blue), the stratosphere should continue to warm. Further warming may set the stage for a warmer than normal stratosphere this winter, which would then encourage a cooler than normal winter.


Sunday, September 15, 2013

Preliminary 2013-2014 Winter Storm Tracks

This is my preliminary 2013-2014 winter forecast. Bear in mind this is all VERY preliminary, and certainly not set in stone. There are four storm tracks we will analyze here- from the top of the image to the bottom, we will analyze the Alberta Clipper, the Colorado Low, the Panhandle Hook, and the Nor'easter.

Alberta Clipper
The Alberta clipper involves a relatively low-amount snow system that originates in the Canadian province of Alberta and swings down into the US, leaving howling winds and biting cold in its wake. The clipper system is moisture-starved, leading to its usual 2-5'' snowfalls it puts down. This winter, I anticipate the Alberta Clipper to be a little less prevalent than usual, but due to a still-unknown pattern just offshore of Canada, confidence in that outlook is low.

Colorado Low
The Colorado Low is a storm system that originates from the West US and passes in or close to Colorado, depending on its eventual track downstream. The Colorado Low then moves northeast, and can bring rather significant snows to the Plains, Midwest, Great Lakes and even the Ohio Valley. This winter, I expect we will see more Colorado Lows than usual, as ridging in the West and a stormy pattern offshore the Southwest should lead to a more active storm track.

Panhandle Hook
The Panhandle Hook is essentially the motherlode storm system for the Midwest and Plains. It comes from the West US and does a hook around Oklahoma (hence the PANHANDLE Hook) before coming north and east. The Panhandle Hook is relatively rare, but when it happens, under the right conditions, over a foot of snow can hit areas affected by this system. I anticipate an above normal number of Panhandle Hook systems, as stormy conditions are expected in the region where Panhandle Hook systems originate.

The Nor'easter is quite possibly the most intense winter storm that can hit the United States. Its cousin, the Panhandle Hook, will be rather active this winter, and it's no surprise that the Nor'easter should be either normal or slightly above normal for this winter as well. It will depend on the presence (or lack) of ridging in the Southeast, which, if it were to be present, would discourage Nor'easters. I'm not sure which way I'll lean as far as if these storms will be normal or above normal. That should become clearer by October.


Saturday, September 14, 2013

Long Range Lookout: Warmth Displaced North as Omega Block Evolves

The recent warm weather that many across the nation have experienced has ended for the next several days, as a new Omega Block pattern begins to set up over the northern part of the nation.

Shown above is the long range projection of 500 millibar height anomalies across the Northern Hemisphere from the American GFS Ensembles. This is valid around the September 26th period. On this forecast map, we see deep troughing along the western coast of Canada and into the Pacific Northwest. This provokes high pressure to develop in the Central US in a situation that would typically bring hot weather back to the nation. However, the body of high pressure will be displaced further north into Canada, which will spare much of the north central US from getting in on another hot spell. As long as the stormy pattern along the western North America coast continues, the threat of warmer weather easing into the US again is not out of the realm of possibility. I do not believe that the US will end up warmer than average in the next week or two due to this high pressure being displaced north, and those who sweated out several 90+ degree days in the last week will catch a well-deserved break.

The European ensemble set takes this idea of the heat being displaced north to another level, showing the evolution of an Omega Block across the United States and Canada. The Omega Block involves a body of high pressure being sandwiched between two areas of negative height anomalies. If you look closely at the height contours, you may be able to see what looks like the Greek letter Omega (Ω). The Omega Block pattern typically brings hot weather to those in the positive height anomaly region, and cool temperatures to those in the negative height anomalies. The Northeast, Ohio Valley and Plains will likely receive the negative height anomalies, while Canada and Greenland are inundated by positive height anomalies. Should this pattern stay in place for a prolonged period of time, it would not be impossible that we see a cooler than normal September over portions of the country that would be affected by this Omega Block.


Friday, September 13, 2013

What Are The Models Saying This Winter? (9/13/13)

This post will show the GFDL model's long range forecast for the December-January-February 2013-2014 period. Additional models will be shown on here in the future.

The image above shows predicted 200 millibar contour lines and anomalies. We're going to focus on the contour lines for right now. We start in East Asia. Looking closely at the image, we see tightened contour lines in the area around Japan. Considering there is a 6-10 day gap between storm systems in the East Asian area and storm systems in the East US, a tightening of contour lines could suggest an increased number of storm systems. This, in turn, may suggest a stormy East US this winter. We see a large ridging pattern across the Alaska/western Canada. This ridging could then provoke a colder than normal pattern to evolve across the Midwest and East US, as cold air flows southeast along the ridge. If the ridge extends far enough into Alaska, a cross-polar flow situation could set up, which would transport Siberian air to the States. A cross-polar flow is one of the situations that brings the coldest air possible to the US- another situation would be the cold air displaced to the surface as a result of a stratospheric warming.

Temperature anomalies are pretty much in line with the 200mb forecast- strong warming trends in the Alaskan/west North American regions, and significant warming in eastern Canada into Greenland. The cause of this more significant body of warming is not immediately evident on the 200mb map, other than a slight ridge signal in that region. I would like to wait for another month or so to see if the GFDL corrects this east Canadian warming in the event it is incorrect. The split between the two warm air masses is where the coldest air of the season would be focused- central Canada into the Midwest.

The precipitation forecast from the GFDL suggests a very wet Pacific Northwest and southern Midwest/Ohio Valley. I'll start off by saying I am most skeptical of precipitation forecasts in the long range because they seem to be the most vulnerable to sudden change. That said, this forecast does look good for a stormier than average Ohio Valley. The trend has been for a dry Midwest and lower Ohio Valley with my analog years, but if the eastern Pacific waters begin to warm up in coming weeks, my analog years will require change that could then see a different precipitation prediction. In any case, this forecast lines up with many that believe cold weather will enter the Midwest, Great Lakes and East US due to western North America ridging, among other things.

More of these posts will come out as we dive into fall and closer to winter.


Tuesday, September 10, 2013

Pacific Sea Surface Temperatures Warming; Is an El Nino Winter Ahead?

Sea surface temperature anomalies across all four ENSO regions in the Pacific are warming in what could be a sign of the La Nina-like SST's we saw earlier this year breaking down.

A swath of above normal temperature values roughly 50 to 200 meters underwater is beginning to push towards the surface and strengthen. The swath has been present underwater for some time now; it's possible we could see further warming in weeks ahead. The CFS v2 makes a case for this idea, showing continuous warming in the main ENSO region (3.4) for the next few months. I'm not really keen on getting in with this warming idea- the CFS has proven itself wrong before with warming SST's across the Pacific, and the rapid warming the model is showing in weeks ahead may not verify.

On the chance this rapid warming does occur, the question becomes: Will we see an El Nino for this winter?

If we see the SST's warm enough, then yes, we would see an El Nino. There are numerous caveats with the premise of an El Nino this winter, but I've already explained a few of them above. What we really care about is- would this El Nino transfer into the atmosphere? Based on current projections, I would not think so. Current model forecasts and analog years suggest a cooler than normal upper US, whereas an El Nino would bring about a warm trend throughout the Plains and Midwest.

Time will tell if we actually see an El Nino develop, but right now, I am skeptical of the idea.


Sunday, September 8, 2013

2013-2014 City-by-City Winter Forecasts: Springfield (MO), Williamsport, Detroit, Wichita, Baltimore

Springfield, Missouri

Temperature: Slightly Below Average
Precipitation: Above Average
Snowfall: Slightly Above Average
Confidence: Average

Williamsport, Pennsylvania

Temperature: Slightly Below Average
Precipitation: Average
Snowfall: Slightly Above Average
Confidence: Average

Detroit, MI

Temperature: Below Average
Precipitation: Average
Snowfall: Above Average
Confidence: Slightly Above Average

Wichita, KS

Temperature: Average
Precipitation: Slightly Above Average
Snowfall: Average
Confidence: Below Average

Baltimore, Maryland

Temperature: Below Average
Precipitation: Slightly Above Average
Snowfall: Slightly Above Average
Confidence: Slightly Below Average

Saturday, September 7, 2013

Long Range Lookout: Rex Block in West Means Warmth for East

This is the first Long Range Lookout for the 2013-2014 fall, winter and early spring season. These posts will be issued each Wednesday afternoon, and if information arises that has a substantial effect on the long range, a special edition of the Long Range Lookout may be issued on the same day.

Long range ensembles are in agreement of a Rex Block setting up over the west coast of North America. The European ensemble set, shown above, projects negative height anomalies being positioned over the Pacific Northwest and southwestern Canada regions, with a corresponding positive height anomaly arising in northwest Canada and southeast Alaska. This is a classic example of a Rex Block, where negative height anomalies (low pressure) set up south of positive height anomalies (high pressure). To the east of this Rex Block, a few things can happen. If the low pressure system is angled correctly, negative height anomalies may stretch diagonally from the northeast of the low pressure system that is in the Rex Block. Another option is a zonal flow pattern, which means the jet stream is not wavy (in turn creating few opportunities for large-scale temperature anomaly patterns, negative or positive). The option we will most likely see in this situation is where the low pressure system in the Rex Block forces high pressure to set up downstream of the blocking pattern. In this case, the high pressure system would set up across south central Canada and the Great Lakes, as the ensemble set predicts above.

I expect this ridging pattern across south Canada and the Great Lakes to end roughly 3-5 days after it starts- this should not be a long-term event. The reasoning comes from an expected rising Pacific-North American index (PNA), which would allow for the departure of low pressure from the West, possibly shifting to the East. Remember that the negative PNA involves low pressure in the West and high pressure in the East, with the opposite true in a positive PNA. I have little doubt in my mind that the negative PNA we see in the projected teleconnection chart above is due to the negative height anomalies shown on the European ensembles image at the top of this post. On the right side of this image is the projected North Atlantic Oscillation over the next couple of weeks. The positive NAO pattern will be weakening to a neutral NAO, and could go to a negative NAO by the three week timeframe from today. The negative NAO encourages cooler conditions over the Central and East US, and the positive NAO we will be seeing in the next several days is a reason of why above normal temperatures are expected. The Rex Block pattern will not help matters.


Who Could See an Early Snowfall?

Light Blue: 25-50%
Dark Blue: 50% <
I believe the Upper Midwest, Central and Eastern Great Lakes will encounter an early snowfall for the upcoming fall and winter seasons.

As the chart above shows, I have highlighted much of the Northern Plains, Midwest, Ohio Valley and Northeast for the risk of an early snowfall event. I have put these areas in a 25-50% chance for an early snowfall. The states of Minnesota, Wisconsin, Michigan, northern Ohio, northwest Pennsylvania, New York and portions of the far Northeast will have above a 50% chance for an earlier than normal snowfall event. This comes as a result of what could be a favorable pattern for colder weather to hit the nation as we head into fall. Should a storm system come along in the midst of this cold air, it is very possible that a snow event could come about.

Long range forecasts for the Arctic Oscillation show a definite negative trend for the index as we head through fall and even into early December. The graphic above shows this long range forecast by today's four CFS ensemble member's forecasts for the AO, as well as the forecasts from yesterday's four CFS ensemble members. These eight forecasts average out to a decisively negative phase throughout the fall and into winter. I have little doubt that this forecast will not verify as is shown above, but it is possible we see enhanced chances for a prolonged negative AO pattern. If such a situation were to arise, the risk of an earlier than normal snowfall would rise.


Thursday, September 5, 2013

Another Model Joins the Cold Winter Prediction

Another weather model has joined the ranks of those predicting a colder than normal winter across a rather large portion of the country in coming months.

This is the Constructed Analog, or CA model from the Climate Prediction Center. It projects positive temperature anomalies to develop across the Bering Sea and Greenland areas, which may indicate positive height anomalies (high pressure) in those regions. For all intents and purposes, let's assume high pressure anomalies do exist in these two regions of positive temperature anomalies. This then leads to colder than normal temperatures flowing southeast from western Canada, spreading across the Plains, Midwest and even towards the Gulf Coast. This is actually not that far off from other forecasts made by other models, and this strengthens the argument for a colder than normal winter.

500 millibar height forecasts for the December-January-February period basically confirm the assumptions we made earlier in this post with the temperature anomalies. We see persistent positive height anomalies across the northern Pacific and Bering Sea. This is a very good sign for the chances of stratospheric warming events, which, if the atmospheric pattern is right, can allow for frigid air to move into North America. Multiple forecasts have been indicative of this positive height anomaly presence in the North Pacific, and the CA model's projection of this factor only aids in its credibility. We also see an elongated positive height anomaly swath across eastern Canada, Greenland and into northwest Europe. This is supportive of the negative North Atlantic Oscillation phenomenon, which permits a flow of cold air and enhanced coastal storm potential mainly in the Northeast, but the cold weather can spread across a wide portion of land east of the Mississippi.

So what does all of this mean? The long range models seem to be coming together, suggesting that a cold winter may really be on the way. I've been seeing more and more evidence that such a winter may be unfolding in just a few months, and this new model projection only increases my confidence.