Thursday, April 9th Potentially Widespread Severe Weather Outlook

This is the latest outlook (as of Monday, April 6th) for Thursday's potentially widespread severe weather.

Storm Prediction Center
(click all images to enlarge)

The above image shows the Storm Prediction Center outlook for Thursday, April 6th.
The following areas have been outlooked for a 15% chance of severe weather within 25 miles of any given point:

- extreme southern Wisconsin
- extreme southwestern Michigan
- Indiana
- northern and southern Illinois
- extreme eastern Iowa
- eastern Missouri
- western Kentucky
- western Tennessee
- Arkansas
- extreme northwest Mississippi
- northeast Texas
- northern Louisiana
- southeast Oklahoma

The 15% chance of severe weather, put into words, generally suggests that there is a noticeable risk for severe weather in the areas mentioned. Residents in those areas should keep an eye on the forecast as the date approaches, and watch for inclement weather when the event arrives.

The SPC has outlined the following regions for a 30% chance of severe weather within 25 miles of any given point:

- Illinois
- eastern Missouri

The 30% chance of severe weather, put into words, indicates that there is a relatively good chance that severe weather will strike the areas mentioned above. In addition, there is a risk for more significant severe weather. Residents in those areas should continue to keep an eye on the forecast for this date, and closely monitor all watches and warnings when the event date arrives.

Weather Prediction Center

We now turn our attention to the forecasted surface map on the morning of Thursday, April 9th. At this point, we see a rather potent set-up over the nation. A strong low pressure system will be moving northeast into the Midwest, dragging the warm front northward as it does so. The trailing cold front will provide the focal point for thunderstorm formation inside the warm sector.

Twisterdata

The NAM model is expecting that we will see over 3000 joules per kilogram of CAPE form by late afternoon over Iowa, Wisconsin, and Illinois. Convective Available Potential Energy, or CAPE, is the parameter that defines the amount of instability in the atmosphere. In short, higher instability means that the air is more buoyant- it is able to rise easier, and thus create thunderstorms. It is uncommon to see CAPE values in excess of 3000 j/kg, particularly this far north in the Midwest, so it is rather noteworthy.

Twisterdata

The next thing we want to look at is the wind field in the lower levels of the atmosphere. Here, we have the NAM model's projected 700 millibar wind speeds on the evening of Thursday, April 9th. We can clearly see the storm in question over Iowa and Minnesota, but what's the most eye-catching is the jet streak rounding the base of the trough earlier on, now pushing out into the Chicagoland/Milwaukee metro areas. As this happens, it should increase the wind shear for when storms begin to enter those same areas a few hours later. Summed up, this increases the tornado threat for the Illinois/Wisconsin/Missouri areas, likely why the SPC has a 30% risk over those regions.

For the tornado threat...

The Weather Channel's Dr. Greg Forbes has put out a rather ominous forecast using his TORCON indicator, which predicts the chance of a tornado within 50 miles of any given point.

THURSDAY
Severe thunderstorms in south WI, central and south MI, northwest
OH, IN, IL, east IA, MO (except northwest corner), southeast KS,
east and south-central OK, AR, west KY, west TN, northwest MS,
northwest LA, central and northeast TX. TORCON - 4 south WI,
south MI, north IL, north IN; 3 - MO, rest of IL and IN; 2 to 3
rest of area above

A TORCON of 4 has been assigned to southern Wisconsin, southern Michigan, northern Illinois, and northern Indiana. That means that there's roughly a four in ten chance that a tornado will touch down within 50 miles of any given point; that's a pretty high number.

All of the factors that support tornado formation appear to be in place. There will be buoyancy/CAPE (though the abundance of that instability is still in question), there will not be a temperature inversion aloft to prevent storm formation, the cloud bases should be low to the ground, and there will be abundant wind shear and helicity in the atmosphere. Plugging all of this into my own research (described in more depth in a previous post), the environment appears conducive for EF2 to EF3 tornadoes in that north IL/south WI corridor, if supercells can form and produce tornadoes. This is all subject to change, but there's certainly the risk of some tornadic activity for the aforementioned areas.

To summarize:

- There is an increasing threat of widespread severe weather on Thursday, April 9th.
- The most intense severe weather looks to focus on Illinois and Missouri.
- An appreciable tornado threat may exist over southern Wisconsin into northern Illinois.
- Crunching numbers indicates that IF tornadoes do form in the aforementioned areas, they may be of EF2 to EF3 strength.
- Uncertainty still exists with this event.

Andrew

Analysis of the Potential Tornado Outbreak on Wednesday, April 8th

This is a post that will detail an analysis of the potential tornado outbreak on Wednesday, April 8th. If you've been watching my discussions over the past several weeks, you've noticed how I've used my 'tornado research' to look at severe weather situations. Today, you'll get the first in-depth look at that research, and why I believe significant tornadogenesis (EF3+) is likely on Wednesday.

First, we'll go over the Storm Prediction Center outlook and frontal positions for Wednesday.

Storm Prediction Center
(click all images to enlarge)

The Storm Prediction Center's outlook for Wednesday shows a Slight risk of severe weather over southern Iowa, extreme southeast Nebraska, west-central Illinois, much of Missouri, eastern and central Kansas, and central Oklahoma. It is expected that these areas will see the brunt of the severe weather threat, with a lesser severe weather threat present in the Marginal risk (shown as MRGL) area.
There is a portion of the Storm Prediction Center's text outlook that I'd like to share; for some of you, it may be a little complicated, so I've underlined the parts that sum up the paragraph best.

 ...THE MIDWEST/MID AND LOWER MO VALLEY/CENTRAL AND SRN PLAINS...
   A MOIST BOUNDARY LAYER WILL REMAIN IN PLACE ACROSS THE CENTRAL AND
   SRN PLAINS AND MID/LOWER MO VALLEY REGION AHEAD OF THE DRYLINE AS IT
   MIXES EWD THROUGH THE AFTERNOON.  AS HEIGHT FALLS ALOFT OCCUR AHEAD
   OF THE ADVANCING UPPER TROUGH...RESULTING ASCENT WILL SUPPORT
   WEAKENING OF CAPPING AT THE BASE OF THE EML LAYER -- PARTICULARLY
   FROM SRN OK NWD INTO KS.  EVENTUALLY...ASCENT SHOULD PROVE
   SUFFICIENT TO ALLOW LOCAL BREACHES IN CAPPING -- AND RESULTING/RAPID
   DEVELOPMENT OF ISOLATED STORMS.  GIVEN A VERY UNSTABLE AIRMASS/STEEP
   LAPSE RATES ALOFT...AND AIDED BY FAVORABLY STRENGTHENING/VEERING
   FLOW WITH HEIGHT...STORMS SHOULD RAPIDLY BECOME SUPERCELLS.  ALONG
   WITH LOCALLY DAMAGING WINDS...VERY LARGE HAIL IS EXPECTED.  IN
   ADDITION...THE AMPLY MOIST BOUNDARY LAYER AND FAVORABLE LOW-LEVEL
   SHEAR -- PARTICULARLY NWD INTO KS NEARER THE ADVANCING SURFACE LOW
   -- WILL LIKELY BE SUFFICIENT TO SUPPORT RISK FOR TORNADOES.  WHILE
   OVERALL STORM COVERAGE SHOULD REMAIN WIDELY SCATTERED TO
   ISOLATED...SIGNIFICANT SEVERE WEATHER IS EXPECTED WITH ANY STORM
   WHICH DOES DEVELOP.

I underlined how the SPC foresees the rapid development of storms with any storms that are able to develop (we'll discuss that a bit later on), and how the storms would quickly turn supercellular. Additionally, locally damaging winds and very large hail is expected. Perhaps the most ominous sentence in this discussion is the last one, where the SPC indicates that any storms which do develop are expected to have significant severe weather associated with them. That's some pretty alarming wording, especially two days in advance of the event. We'll work through why this is as we go on down the post.

Weather Prediction Center

Let's now go over the forecasted surface map for Wednesday morning, about 12 hours in advance of storm activity. We see a low pressure system in the Oklahoma panhandle, with a dry line extending south into Texas. A stationary front then extends northeastward into central Illinois, where another low pressure system sits. It is expected that this frontal boundary will drift north as the day goes on, and will aide in severe weather development.

Now that we know how this threat will set up, let's go over the forecasted severe weather parameters on Wednesday evening.

Twisterdata
(click all images to enlarge)

The most critical ingredient to look at, to ensure that we have thunderstorms to begin with, is forecasted Convective Available Potential Energy, or CAPE. The higher the CAPE value, the more buoyant the air is, meaning the air is able to rise easier, and form thunderstorms. In this forecast, off of the NAM model (which is notorious for exaggerating forecasted CAPE/instability), we see values on the order of over 3000 joules per kilogram of buoyancy extending from northern Texas, through central Oklahoma, and into central Kansas. Lesser, but still prominent instability then exists across the eastern portions of the latter two states. CAPE values of over 3000 j/kg are not exactly common, so when they come up on a forecast, one tends to take note. Overall, this is a very favorable environment for thunderstorms... right? Not exactly, but we'll visit that a little later.

Twisterdata

Next, let's see how the upper air pattern looks, for the same Wednesday evening timeframe as the CAPE graphic we checked out. We see the Pacific jet stream arcing over the ridge along the western coast of North America, contributing to that jet streak rounding the base of the trough in the Rockies. What really grabs my attention, however, is the roaring subtropical jet stream entering Mexico and Baja California. That jet stream is barreling into North America at over 100 knots, and will be a big factor for Wednesday's tornado potential. We see an arm of the jet stream nosing into Oklahoma by Wednesday evening, which also sets up an area of divergence, as noted by the low wind speeds, over southern Kansas and northern Oklahoma. It's no coincidence that the greatest threat for tornadoes lies within that area of divergence.

Twisterdata

Let's now turn our attention to the lower level jet stream, once again valid for Wednesday evening. Here, we see wind speeds in excess of 45 knots over central Oklahoma and southeastern Kansas, right where the best instability is. This lower level jet will be able to advect the warm, moist air from the Gulf, as well as the drier air from the west to create this potentially severe environment. This kind of set-up is a consistently favorable one for severe weather in the Central US.

Twisterdata

There is a caveat to this severe weather situation. Model guidance is indicating that all of the wind shear, instability, and helicity in the atmosphere will have to contend with a warm layer above the surface, located just over 5,000 feet above the ground. The Storm Prediction Center appears optimistic that storms will be able to break through this warm layer and allow for scattered storms to form. If storms are able to form, they have the potential to become quite dangerous, threatening life and property, as will be shown below. For now, I'll go with the SPC, but this temperature inversion could become an issue down the road.

Now that we've evaluated all of the basic ingredients for thunderstorm and tornado formation, let's move on to a couple less conventional forecasting methods.

CIPS

We begin with the forecasted CWASP chart from the GFS model, valid on Wednesday evening. In a nutshell, the CWASP parameter is able to diagnose tornado favorability from a number of indices, combined into one. As the image tells you, percentage values over 65% tend to see the probability of significant tornadoes rise. The forecasted CWASP chart for Wednesday evening peaks at over 85% in eastern Kansas, with significant values over 80% extending across Missouri and Oklahoma, even a bit into Texas. This is the first 'red flag', per se, that Wednesday evening could be a pretty tornadic environment for any storms that form.

CIPS

A method I like to look at, but not necessarily put full trust in, is analog forecasting. In this case, the CIPS agency analyzes the forecasted conditions for a given date, and spits out the top 15 days where the atmospheric pattern was similar to those forecasted conditions. This chart is valid for the morning of April 9th, and paints a pretty ominous picture. Here, all hail, damaging wind, and tornado reports from all top 15 analog dates are combined into one picture, to give a view of where severe weather is most favored. As the text shows at the top of the page, 102 significant (EF3+) and 122 long-track tornadoes occurred in regimes similar to the one forecasted on Wednesday into Thursday. Again, I would not put my full trust in this, since there remains considerable uncertainty with regards to the entire event, as well as my own precautions with using this analog forecasting, but you get the gist of how ominous this is.

Alright, now that we've gotten past all of the computer modeling forecasts, it's time to go over why I think significant tornadogenesis (EF3+) is likely with storms that break through on Wednesday, as the SPC suggests.

This past winter, I began toying around with tornado data over the past decade or so, as well as the conditions they formed in. Fast forward a few months, and I was able to make a method that had great success in hind-casting tornado strength, before the storm cell and tornado even formed. I began applying it to this season, and it has performed well so far. Seeing as my research has been performing well, this severe weather event could be potentially dangerous, and there's a need to get the word out early and often, I figured now is the best time to share the outlook with you.

Using the NAM model (which tends to exaggerate severe weather parameters), the environment over Oklahoma City, OK is favorable for tornadoes of EF5 strength on Wednesday evening. Once again, that's from the NAM, notorious for exaggerating severe weather. When I ran it for the more-level-headed GFS model, it predicted a tornado strength of EF3 to EF4 for the same area. Another mathematical model I developed indicated a pretty high chance of significant tornadogenesis, with a strength of EF3 or greater, if storms do form.
The big caveat is that this model cannot predict if storms will form; it says that if storms do form and tornadoes are produced, that is the strength that the tornado should be. It's all new research, but has performed well in initial real-time applications.

Thus, if storms are able to break through the temperature inversion, the environment (as of the forecasts at this typing) is favorable for tornadoes to form and be of EF3+ strength.


To summarize:

- A potentially significant severe weather event is forecasted over central Kansas and northern Oklahoma on Wednesday, April 8th.
- Any storms that manage to form in these areas have a rather high potential to produce significant severe weather, including strong tornadoes.
- The environment is supportive for tornadoes to be of EF3 strength, or higher.
- Considerable uncertainty still exists with this event, and it must be monitored in coming hours and days.
- Those in the SPC highlighted risk at the top of this page should review severe weather action plans, in the event that this severe weather potential comes to fruition.

Andrew

Wednesday, April 8th Potentially Tornadic Severe Weather Outlook

There appears to be a rising threat of tornadoes on Wednesday, April 8th, for portions of the Plains.

Storm Prediction Center
(click all images to enlarge)

Since our post on this particular day's threat yesterday, the Storm Prediction Center has elevated its wording for this day, indicating that the threat has increased. Today, we see a 15% chance of severe weather within 25 miles of any given point over central Oklahoma, a sliver of north-central Texas, much of central and eastern Kansas, the majority of Missouri, and west-central Illinois. Compared to yesterday's risk area, this 15% threat area has expanded over the Plains and a bit into the Midwest, indicating the increasing confidence in a severe weather event.

Let's take a look at what factors will be playing into this severe weather threat.

Weather Prediction Center

This chart shows the forecasted surface map on Wednesday morning. We see an elongated stationary front extending from the northern Rockies into southern Kansas, central Missouri, and all the way to the Mid-Atlantic. A low pressure system is seen in the Texas panhandle, with an associated dry line across western Texas. Another low pressure system is also moving towards the Plains, shown in Utah in this graphic. By the evening hours, it is expected that this stationary front will lift north into the areas outlooked for severe weather.

Now that we see what will ignite this severe weather threat, let's start checking out the forecasted severe weather parameters.

Twisterdata

We begin with the forecasted Convective Available Potential Energy (CAPE) values for the evening of Wednesday, April 8th. The presence of CAPE, the buoyancy of air, is critical for any thunderstorm development. CAPE values indicate the ease of which warm air at the surface can rise and create thunderstorms. Higher CAPE values, in excess of 2000 joules per kilogram, can support thunderstorms at a severe level; values over 4000 joules per kilogram are considered uncommon, and can support explosive thunderstorm development.

In this forecast, a narrow band of high buoyancy stretches from the central Oklahoma/Texas border, almost due northward to central Kansas. The highest values in this corridor appear to be around 3000 joules per kilogram, indicating potentially intense thunderstorm development. It's no coincidence that the highest instability values are forecasted within that risk area put out by the Storm Prediction Center, as well as lower, but still significant CAPE values to the east.

Twisterdata

We'll now take a look at the upper air flow for the same Wednesday evening timeframe as that CAPE image we just analyzed. We clearly see the strong upper level trough over the Rockies, with a jet streak rounding the base of that trough in Colorado, New Mexico, and Arizona. Of more importance is the merging of the two jet streams over the Plains. We see the Pacific jet stream contributing a bit, with some weaker winds pushing southward to the east of that ridge along the west coast of North America, even though the northern jet is primarily in Canada. The subtropical jet stream then takes control, as it comes in to Baja California and northward into the southern Plains. We see a jet streak (embedded area of higher wind speeds) over western Texas, with the severe weather risk area just to the east of this streak. That's not a coincidence, either; tornadoes tend to form when a jet streak is displaced just west of the given region, meaning tornadoes may be favored in the eastern half of Oklahoma and eastern Kansas, as well as other states also in this SPC outline.

CIPS

Finally, we'll take a look at the forecasted CWASP parameter for Wednesday evening. The CWASP parameter gives an estimation, in percentage form, of the likelihood of tornado formation. When the forecast exceeds 65%, significant tornadoes become possible. This forecast has values over 85% in eastern Kansas and central Missouri, indicating a very tornadic environment is present. If convection does form (as the Storm Prediction Center has appeared less enthusiastic about storm coverage on this day than on Thursday), we could see multiple tornado-producing storm cells.

CIPS

To wrap up, this chart shows how tornadic Wednesday could be. This is a composite image of the top 15 analogs with environments similar to the forecasted environment on Wednesday evening. We see an abundance of tornado reports over Oklahoma and Kansas when a similar set-up presented itself, only confirming this threat.

To summarize:

- The risk for severe weather appears to be growing on Wednesday evening, especially over Kansas and Oklahoma.
- If currently forecasted conditions come to fruition, multiple tornadic storm cells could erupt over the aforementioned regions.
- Considerable uncertainty still exists.

Andrew

April 9th, 2015 Potentially Significant Severe Weather Outlook

There is an anomalously high risk for severe weather on Thursday, April 9th.

Storm Prediction Center
(click all images to enlarge)

The above image shows the Storm Prediction Center's long range outlook chart over the Day 4 to Day 8 (3 to 7 days from today) period. This particular map is valid for Thursday, April 9th, and it shows a very ominous forecast.
The SPC has outlined the following regions for a 15% chance of severe weather within 25 miles of any given point:

- extreme southern Wisconsin
- eastern Iowa
- northern and southern Illinois
- western Indiana
- northwest and extreme southeast Missouri
- east-central and southern Arkansas
- southeast Kansas
- central Oklahoma
- northeast Texas

The 15% chance of severe weather, put into words, generally suggests that there is a noticeable risk for severe weather in the areas mentioned. Residents in those areas should keep an eye on the forecast as the date approaches, and watch for inclement weather when the event arrives.

The SPC has outlined the following regions for a 30% chance of severe weather within 25 miles of any given point:

- central and southern Illinois
- much of Missouri
- all of northwest Arkansas
- extreme southeast Kansas
- eastern Oklahoma

The 30% chance of severe weather, put into words, indicates that there is a relatively good chance that severe weather will strike the areas mentioned above. In addition, there is a risk for more significant severe weather. Residents in those areas should continue to keep an eye on the forecast for this date, and closely monitor all watches and warnings when the event date arrives.

Weather Prediction Center

Let's now identify the factors playing into this severe weather threat. Looking at a surface map for the morning of Thursday, April 9th, we see an elongated stationary front which has drifted northward, now displaced over Nebraska into southern Minnesota and southern Wisconsin, diving into central Iowa and Kentucky. We also see a broad area of low pressure centered in Kansas, with a warm front draped across Missouri, a trough along the Oklahoma/Arkansas border, and a dry line in western Oklahoma and central Texas. All of these items will play a role in the severe weather risk for this day. It is expected that the broad area of low pressure will meander its way northward as the day progresses, bringing the warm sector further north as well. Going off of this map alone, any tornado threat would likely be centered along the warm front, which could move as far north as central Illinois and central Iowa.

Now that we know what will be causing this severe weather risk, let's now look at forecasted severe weather parameters.

Twisterdata

The first item that must be looked at is Convective Available Potential Energy, or CAPE. This parameter defines the amount of instability in the atmosphere. In short, higher instability means that the air is more buoyant- it is able to rise easier, and thus create thunderstorms. On the evening of April 9th, we see a broad sector of elevated instability on the order of 2000 to 3000 joules per kilogram extending from Iowa to southern Texas. Higher instability values are found in Texas and Oklahoma, where the dry line is expected to produce more instability-based storms than those further to the north.

Twisterdata

The next chart that must be looked at is the upper air flow, shown for the same timeframe as the instability chart above. The jet stream forecast shows a merged subtropical jet stream entering along Baja California, along with the jet streak produced rounding the base of the trough in the Rockies. This will likely produce an environment favorable for severe weather just east of the combined jet stream, particularly in the 30% risk areas described above. If you look closely, you'll also see an area of divergence, where the contour lines seem to bulge away from southern Wisconsin and northern Illinois. This indicates rising air, favorable for thunderstorm formation.

To summarize:

- A severe weather threat exists across the Midwest and Southern Plains on Thursday, April 9th.
- A more enhanced zone of severe weather is present in Illinois, Missouri, Arkansas, and Oklahoma.
- This could be a large-scale severe weather event, and must be monitored in coming days.
- Appreciable uncertainty still exists with the spatial coverage and extent of this event.

Andrew 

Long Range - Monthly Outlook: April 2015

This is the long range/Monthly outlook for late March into April 2015.

We'll first begin with a diagnosis of the atmosphere. For those who find the technical jargon a little overwhelming, summaries to the post are provided at the bottom of the page.

ESRL

The above image shows relative atmospheric angular momentum anomalies on the top panel, with the global anomaly on the bottom panel. According to the latest data, we are in a globally positive-AAM (+AAM) state, mainly due to a nice surge of +AAM to the equator. This has pushed the atmosphere into an El Nino mindset, which has shown up in our atmosphere. We'll go more in-depth to that later on.

ESRL

The graphic above shows the tendency anomalies of the atmospheric angular momentum on the top panel, with the net tendency on the bottom panel. Notice how we're currently recovering from a massive +AAM tendency spike, and are now in a net negative AAM tendency. The cause of this tendency is not the thing we will analyze; right now, we are noting that we're in a +AAM state with -AAM tendencies.
This fits well into the four stage descriptions of the Global Wind Oscillation (GWO), which takes those above graphics and makes them into useful data. Here's the descriptions of all four stages of the GWO; pay careful attention to the first and last sentences of each stage.

The four primary phases of the GWO are described below, along with generally cold season (November-March) probable weather impacts for the USA. The GWO recurrence interval, or "time it takes to make a circuit", ranges from a broad 15-80 days. Two of the stages project strongly on El Nino and La Nina circulation states, which are also characterized by positive (Stage 3) and negative (Stage 1) global AAM anomalies, respectively.  Stages 2 and 4 are transitional.

Stage 1 (La-Nina like) – the global relative AAM anomaly is negative. The negative anomaly is primarily due to easterly upper level wind anomalies that extend from the Eastern Hemisphere tropics to the Western Hemisphere mid-latitudes. A retracted Pacific Ocean jet stream is a key feature in the total field.  Troughs are probable across the western USA with a ridge over the southeast.  High impact weather is favored across the Plains.

Stage 2 – the global relative AAM tendency is positive. This means that negative AAM is being removed from the atmosphere by surface friction and mountains. At the same time, westerly wind anomalies are intensifying in equatorial regions of the Western Hemisphere. Fast Rossby wave dispersion events in both hemispheres are a coherent feature of this stage and Stage 4.  A cold regime is probable across the central USA.

Stage 3 (El-Nino like) – the global relative AAM anomaly is positive. Westerly wind anomalies move into the Eastern Hemisphere, broaden in latitudinal extent and link up with deep westerly flow anomalies over the mid-latitude Western Hemisphere. An extended Pacific Ocean jet stream and southward shifted storm track is observed  favoring high impact weather events along the USA west coast.

Stage 4 – the global relative AAM tendency is negative. Positive (westerly) AAM anomalies are being removed by surface friction in the Western Hemisphere mid-latitudes and through mountain torques across the Northern Hemisphere topography. The next phase of the oscillation (if there is one) is represented by easterly wind anomalies intensifying over equatorial regions of the Western Hemisphere. This stage has enhanced subtropical jets and closed lows in the subtropics favoring rainfall events over the southwestern USA.

What did you notice in each stage description? Did you notice how each description began with details on how the net (global relative) AAM or AAM tendency was positive or negative? Let's apply that here.
We saw earlier how we are in a +AAM / -AAM tendency phase right now. Using those particular sentences in each description, it appears we're in Stage 3 or Stage 4 of the Global Wind Oscillation. Let's investigate each description closer. In Stage 3, among other details, the Pacific jet stream is extended (can stretch across the Pacific), and active weather impacts the West US. In Stage 4, the subtropical jet stream is strengthened, and closed lows in the subtropics can permit heavy rainfall over the Southwest.

Do we have any of those factors?

CPC

The answer is yes. The graphic above shows 200 hPa heights and wind speeds in ~4 day periods, with the least recent panel in the top left and the most recent panel in the bottom left. Notice how the Pacific jet stream is clearly extended into the North Pacific, fulfilling our Stage 3 ideals. If you'll look back at the stage description for Stage 3, you'll notice how it says 'El-Nino Like'. This means that conditions in this stage are most likely to provoke an El Nino-like response in the atmosphere. We're already seeing that response, namely in the extended Pacific jet and the AAM charts. I expect this to continue throughout April due to ensemble agreement.

PSU

The temperature anomaly charts in the US came back very cold for the next week or so. Each individual member is shown on those smaller boxes, while the large box contains the mean temperature departure. There is very good agreement on this cold, as well, valid on March 28th.

MJO

Lastly, let's go over the tropics. We're currently seeing a very strong tropical forcing episode over Phase 8 of the Madden-Julian Oscillation, a signal that has been created thanks to a powerful convectively coupled Kelvin Wave (CCKW). The long range ECMWF ensembles believe we see this current wave dissipate before we dip back into the circle of the unknown, and this proposal is backed up by the GFS model. This renders tropical forcing useful until just about March 28th, before the wave weakens into the Circle of Death on the MJO chart. Phase 8 and Phase 1 events in this time of year routinely create warm and cold conditions, respectively, in the Midwest, Central US, and East US. I have a good feeling that the Phase 8 activity will far outpace the Phase 1 activity, keeping us in the El Nino mindset well into April.

To summarize the forecast:

- The last days of March (24-30) may see sustained cooler than average temperatures. This may persist even longer in the Northeast.
- Early April will see continued threats to the West for heavy rainfall and moisture. A warm-up is expected for this time period.
- Mid and Late April can expect more El Nino conditions, with warm weather in the Morth and stormy/cool weather in the South.

Andrew

Warmer Weather Returns After Early April Cold Blast

It looks as if warm weather will make a comeback after a stark cold shot hits to close March and open April.

Tropical Tidbits

In the image above, we see 500mb geopotential heights over the West Pacific, where reds indicate above normal values typically associated with high pressure and calm weather. Blues indicate toughing, symptomatic of colder and stormier weather on the surface. In this chart, valid on March 27th, we can see the strong ridge over Japan and areas just off to the north, with a slight trough to the south.

Using this, we can predict what the first week or so of April will be like. The Typhoon Rule tells us we can expect weather phenomena in Japan to 'happen again' here in the US about 6-10 days later. If the image above is valid on the 27th, we should expect some warmer weather around the first couple days of April. However, it's very possible this warmth is actually delayed, due to the aforementioned cold weather hitting the country at the end of March and start of April.

To summarize:

- After cold weather hitting in late March into the first couple days of April, warmer weather should make a comeback.

Andrew 

Wintry Blast Expected to Close March, Open April

After a warmer ending to March, it is expected that a cold air mass will deliver one of the last punches of wintry weather to the country.

Tropical Tidbits

The image above shows 500mb geopotential height anomalies across the West Pacific. This forecast comes off the GFS model, valid for Wednesday, March 18th. We see a strong ridge located over Japan in this image, likely a result of the deep toughing further east in the North Pacific, as well as some more activity further west. When we apply the Typhoon Rule, stating that weather events occurring over Japan will 'come back' and 're-appear' in the US 6-10 days later, we could expect a generally warmer pattern persisting through about March 26th-ish, probably a bit longer.

Tropical Tidbits

The picture becomes much more ominous by March 23rd. By that time, the GFS model expects a rather large upper level low to drop into Japan, as shown by the deep negative anomalies over the island nation. In a nutshell, this means very cold weather is expected about 6-10 days later, likely in the very final days of March and the first week or so of April. If this happened in the middle of winter, we would likely be looking at record-breaking cold. However, due to the significant loss of snow-cover as of late, as well as climatological numbers telling us how quickly our average high and low temperatures are rising, this will likely be more of a strong cold blast, as opposed to a deep freeze.

To summarize:

- Predominantly warm weather is expected to persist through the end of March.
- The last few days of March and first week of April could see a shot of rather strong cold weather.

Andrew

Long Range Outlook for March, Early April 2015

This is the Long Range Outlook for the period of March 2015 into early April 2015.

Paul Roundy

The above image is pretty complicated, but bear with me and it won't be so bad. This chart shows a longitude-by-time forecast for tropical convection anomalies (colored shadings) between 7.5º North and 7.5º South latitude, centered on the Equator. Blue colors correspond to enhanced tropical convection (thunderstorms), while yellows are indicative of suppressed convection. There are a lot of lines here, but the only ones we need to worry about are the red lines, which show the active phase of the Madden-Julian Oscillation in solid (dashed is the suppressed 'phase'), as well as the Kelvin Wave, which is in thin pink.

We currently see an MJO wave evolving from about 75 degrees East, as the red lines in that longitudinal sector show. It is expected that this wave will strengthen in the next week or two as an Equatorial Rossby Wave moves over the region, shown as a light-green delineation. The placement of tropical convection in this part of the world is equivalent to a Phase 4 MJO event. As shown in the image below, temperatures during a Phase 4 event will tend to lean warmer than normal for much of the country, but a deep snowpack across much of the North and Central parts of the US tells me this warm-up could very well be muted around March 12th.

CPC

A Kelvin Wave then forms around that March 12th period, and this convectively-coupled Kelvin Wave traverses the Pacific in time for the final days of the month. This very progressive tropical forcing theme tells me the country is likely in for some roller coaster weather patterns for the remainder of the month, despite the MJO wave signal only shifting eastward slowly in contrast to the Kelvin Wave movement. This particular chart has us reaching Phase 5 of the Madden-Julian Oscillation by the final days of March, which would typically favor a cooler than normal pattern for the Northern US.

However, this cold outlook for the end of March is working in contrast to a projected pattern shift in the Pacific, in which ensemble guidance sees a trough positioning itself along the west coast of North America to permit warmer weather in the Central and East US. With warm signals coming from the Typhoon Rule as Japan undergoes a generally-warm pattern in the next two weeks-plus, and tropical forcing not really being effective this past month due to such dominance from the Pacific pattern, I'll opt for a warmer outlook to close March.

To summarize:

- An overall cool pattern should remain in place through about mid-March.
- Model guidance is then indicating, at the very least, the synoptic (overall) weather pattern will undergo some changes for the last half of March. I see this as being a good shot for a warmer pattern.
- This warmer pattern could continue into early April.

Andrew