Long Range Lookout: Winter Slipping Away

Preword: Recently, I have been caught up in the swing of the stratosphere and investing all of my confidence in just a few factors. Starting today, I will present the good and bad sides of the forecasted weather, even though you may not find it as exciting as my other posts.

In a disastrous recurrence of last winter, the winter of 2012-2013 has so far brought little snow and only modestly increased cold in comparison to last winter. Don't get me wrong, this winter has had many more advantages than last, but still remains dismal. The long range will be a classic, painstaking case of some factors looking good while other factors ruin the party. We start with the current 500 millibar anomalies over the Northern Hemisphere. Blues indicate low pressure areas and reds show high pressure regions. Deeper shades of each color indicate stronger modes of their respective pressure systems. We can see a deep blue positioned over the Great Lakes in the wake of a very powerful storm system that impacted much of the nation's population. This area of cold will move on out of the region later on as we head towards the weekend. I want to turn your attention to eastern Asia in the upper right-hand corner of the image. See that massive high pressure system there? That will provoke high pressure in the United States as we enter next week and into the following weekend, and we could see another bout of above normal temperatures. Snow cover that was received in the past couple of days could be eradicated. This comes at a time when high pressure finally emerges into the West Coast, a good sign for cold and snow in the Midwest and East US. But, as a result of the forecasted high pressure system, it will be Alberta clippers that bring the best chances for snow.

We now move ahead to Mid-February. There is no longer high pressure over East Asia, but persistant low pressure anomalies. These low pressure anomalies would then inspire a stormy period to round out the month of February. Could these storms hit the Northeast? I'll discuss that a bit later down this article. Something that certainly is not good is that persistant low pressure in the Bering Sea. This goes with my 'some good, some bad' forecast, as this persistant low pressure in the Bering Sea can lead to above normal temperatures in south-central Canada and much of the northern United States. Even more depressing is the lack of Greenland blocking. Greenland blocking is the phrase that is used to reference persistant high pressure over Greenland. When that set-up happens, the atmospheric pattern is more inclined to introduce more wintry weather into parts of the US. A lack of this blocking leads to a more zonal, west-to-east jet stream that allows for warm temperatures and not many storms. It is very possible some of that high latitude blocking in eastern Europe (shown in deep reds) could migrate over to Europe, but that remains to be seen. Frankly, I'm not that optimistic on the idea. This dismal explanation is verified by slight high pressure in the New England area, likely as a byproduct of the low pressure in the Bering Sea, and in response to a lack of Greenland Blocking. One bit of good news is the forecasted high pressure over the Pacific Northwest. If you get high pressure in that area, the jet stream can be persuaded to dip south and let out some cold into the Northern US. Storms tend to follow a jet stream that favors wintry weather for those same regions, the Midwest and Ohio Valley for example.

Lastly, looking ahead to the heart of February just a few days after the above image, we find that the atmosphere has changed. That high pressure that was in the Pacific Northwest has now migrated into the Gulf of Alaska. This situation can then go one of two ways. The first option is for high pressure to then spread back on land into the Pacific Northwest, or the high pressure pushes west into the Bering Sea. Both moves would support a cooler pattern in the North US, but I'm not betting on it at the moment, as the consensus is not overwhelming and we are over 2 weeks away from this forecast image. We still see persistant low pressure in East Asia, adding to my theory of a stormy end to February. Also, we then see the forecast emerging for some spotty patches of high pressure in and around Greenland. Such an action could provoke a better pattern for the Northeast (notice the high pressure in New England is gone), but it's too far out for me to think about accepting or rejecting this idea.

So we could see some storms in late February, but the big story will be warmth in mid-February, with Alberta Clippers dominating that scene. Early February will be when the effects from the sudden stratospheric warming dies off, so that will add to the troubles the cold may face in the coming month.

Andrew

February 18-19 Potential Winter Storm

I am watching the timeframe of mid to late February for some wintry weather across parts of the nation.

The reason I post about this long range potential is because of a repeating pattern called the Lezak Recurring Cycle. Every fall, this pattern sets up and repeats itself every 40-60 days. That cycle length varies from year to year. This year's length is 53 days. If we go back from February 18-19, we find ourselves at the very last days of December. Looking at the 500mb map for December 29 (top image), we see a couple bumps in the contour lines, displaying low pressure systems. This could indeed produce some wintry weather within the Midwest and Great Lakes. A day later, on December 30th (bottom image), we see that the storm has shot offshore and is now impacting the Northeast.

This storm will depend on the atmospheric pattern that is in place when the system comes through. Looking at some very long range indicators, I see that this storm would indeed favor the Midwest and Ohio Valley for wintry weather. However, a lack of high pressure over Greenland could make for a more inland track that may promote more wintry weather for the Upper Midwest rather than the lower Midwest, but that is all TBD.

Andrew

February 14-16 Potential Winter Storm

If you're not into repeating patterns, this post is not for you. If you want snow, read on.

I am watching closely for the potential of a winter storm from the 14th of February to the 16th; these dates are very fluid.

The reason I post about this long range potential is because of a repeating pattern called the Lezak Recurring Cycle. Every fall, this pattern sets up and repeats itself every 40-60 days. That cycle length varies from year to year. This year's length if 53 days. If we go back from February 14-16, we arrive around the December 25-26 timeframe. If we take a look at the 500mb chart from December 26th (pictured above), we can see a storm system impacting the southern Midwest, spreading precipitation throughout the region. The Midwest and Ohio Valley would be impacted by this storm if it follows the same track as the December 25 storm did. Looking ahead to the last days of December, this storm then progressed to the Northeast. Could we see that region impacted by this system? That's not clear right now. The reason is that February may not feature as much high latitude blocking as previously thought. If this blocking does not appear near Greenland, the atmospheric pattern would not be favorable for coastal storms, and then this storm track may take a more inland pattern.

But again, this is based off the LRC pattern and does have bust (failure) potential. I post about it because this pattern has fared well this winter, and should perform well as the winter progresses.

Andrew

February 9-12 Potential Winter Storm

There is increasing potential for a winter storm occurring between the 8th and 12th of February.

The GFS model has been continuously hinting at a storm system ejecting from the Plains around the 9th of February and moving east. As it does so, the storm rides along the freezing line, which is shown above in the southernmost dashed blue line. As the GFS model forecasts above, the storm produces abundant snow across the Plains, Midwest and Ohio Valley. Previous forecasts have shown accumulating snow to occur in these areas, although exact amounts are to be determined.

The reason I post about this long range potential is because of a repeating pattern called the Lezak Recurring Cycle. Every fall, this pattern sets up and repeats itself every 40-60 days. That cycle length varies from year to year. This year's length if 53 days. If we go back 53 to 54 days from February 11th or so, we find ourselves with a very similar piece of energy in the Plains. No doubt that the LRC is indeed behind this, and its support is a big part of why I am posting about it. I find that there could be low pressure along the West Coast, something that could push this storm more towards the Plains, once again shafting the lower Great Lakes in favor of the Upper Midwest. However, if the storm adheres to the LRC pattern, cities like snow-starved Chicago could see some snowfall out of this, but again, the specifics are TBD.

Andrew

January 29 Severe Weather Event -- Updated 4:00 PM

Moderate risk continues to be in effect for Arkansas, northern Louisiana, northern Mississippi, eastern Tennessee, eastern Kentucky, southern Illinois and southeast Missouri.

As of 4:00 PM CT... strong thunderstorms were ongoing across the Plains into the Midwest, with severe weather warnings beginning to be issued as the storms move into a more favorable environment. Special noontime sounding from southern Missouri shows differing wind speeds at different levels, consistent with observed strong wind shearing in the same areas. Analog comparisons to similar soundings reveal at least one tornado did occur in a similar situation. Surface helicity observed to be quite strong, would expect an increasing tornado threat as the night goes on. However, an already-established linear severe weather event will make it hard for stronger tornadoes to evolve, hence the extreme damaging wind concern. Current lower level wind forecast indicates strong winds of over 50 knots. I anticipate these winds to increase dramatically as the evening wears on in response to the nocturnal lower level jet stream mixing with these thunderstorms and really firing them up. By that time, the damaging wind threat will take center stage, enabling many n the moderate risk area to achieve warning-criteria wind speeds.

Today is indeed a Critical Storm Action Day. All resources are now devoted to the severe weather situation, and no posts unrelated to the severe weather situation will be published.

Next update will be at approx. 5:30 PM CT

Andrew

Special Morning Update - January 29 Severe Weather Event

Today is the big day. We are seeing the Storm Prediction Center maintain a Moderate Risk call for severe weather through much of Arkansas into extreme southern Missouri, extreme northern Louisiana and a very small portion of northwest Mississippi. A slight risk exists across the Plains, Midwest and Gulf Coast.

On a side note, I am maintaining my Storm Action Day call and will not upgrade to a Critical Storm Action Day unless the environment becomes more favorable for such a call.

A tornado watch has already been issued for much of Oklahoma and a few counties in northern Texas. This comes as a result of thunderstorms firing in Oklahoma, extending back through Texas. I anticipate these storms to continue strengthening along the nocturnal lower level jet stream, already feeding on the tight pressure gradient known as a dryline, which does go right up against these thunderstorms. By the looks of them, the tornado threat is highest right now, as the storms are not yet linear and are more individualized. The threat is lower in southeast Kansas and northern Texas, where there are no watches yet. Oklahoma City could be hit by some individual storm cells in coming hours as this not-yet-linear complex of cells moves east.

My main concern at the moment is extreme damaging winds. The above forecast shows wind speeds for 9 PM Central time, with wind speeds just a few thousand feet above the ground. My worry is that these winds will be provoked to move down towards the surface as the storms begin to take on a more linear shape and evolve into a squall line. When this does happen, the risk of tornadoes drops considerably and the threat for damaging winds skyrockets. Looking at the map, we would be seeing lower level winds above 72 knots in parts of the Moderate Risk area, something that could easily provoke extreme damaging winds.

I will provide updates as often as possible throughout the day, and will do another afternoon update later on in the day.

Heed all National Weather Service watches and warnings, and be prepared to seek shelter if you are in the path of these storms.

Andrew

Nasty Day Tomorrow as Significant Severe Weather Threatens

**I am declaring a Storm Action Day tomorrow, meaning that most resources will be devoted to analyzing and tracking the severe weather situation.**

The Storm Prediction Center has issued a Moderate Risk of severe weather for tomorrow, January 29th, in the face of a possibly significant severe weather threat across the outlined area.

The NAM model is shown above with the forecast for 500mb vorticity values. The term 'vorticity' defines a spinning motion in the air. This spinning motion is synoptic, or on a large scale, so it is not a producer of tornadoes. High areas of vorticity indicate low pressure is in the area, and this is how we find low pressure systems. Looking at the forecast above, which is valid for the late evening hours of January 29th, shows our storm system pressing down into Texas and Oklahoma, depicted by the deep bending of the contour lines. Something I want you to look at is how these vorticity areas are directed. For instance, if you look closely, you will see that the base of the storm system in Texas has the highest vorticity areas tilting a little towards the Southeast (if you cannot see it, I marked it in). This is a classic example of the infamous negatively-tilted storm system. The infamy of it is that, in a negatively-tilted storm system, cold air aloft is encouraged to flow over the storm system. You weather enthusiasts know that thunderstorms rise and strengthen faster in cold air aloft, so negatively-tilted storms have a tendency to produce stronger thunderstorms than their positively-tilted storm counterparts (highest vorticity values point towards the southwest).

An analysis of the upper air for roughly the same timeframe as the image above reveals a very strained jet stream. You are viewing the forecasted wind speeds for the jet stream, which can also help us identify areas of high and low pressure. If we look near the Front Range of Colorado, we see an empty space pushing down. That is our low pressure system. Again, we are seeing higher wind speeds pointing towards the southeast than winds pointing to the southwest at the base of this empty space, affirming my suspicions of a negatively-tilted storm system. The winds on this forecast are projected to max out above 150 knots in central Texas in this forecast, and winds between 130 and 150 knots in the Central Plains. These unusually high wind values are more typical of spring! Nonetheless, the strength of these upper level winds shows that any storms that do develop will have a strong backing, at least in the jet stream.

Now we get into the forecasted simulated reflectivity, which is a forecast of what the radar could show in the future. This short range model is valid for the late morning hours of January 29th. Already, we can see some moderate rain and thunderstorms surfacing in eastern Oklahoma, and this is where I anticipate the show to start. Strong upper level winds will support eventual strengthening of these storms. However, in these late morning hours, I do not expect any big severe weather threat other than some gusty winds and hail. It's about what happens later in the day that concerns me.

We move now to the afternoon of January 29th. We now see that our storm system has blossomed, with heavy showers and elevated convection (thunderstorms that are stronger than normal, but not yet severe) ongoing in much of the eastern Plains into the Midwest. Some severe thunderstorms are ongoing in the leading edge of this squall line formation. Going by this graphic, I would expect the strongest storms to be in Arkansas and Missouri at this point, with weaker (but still heavy) storms in the Midwest.

This image, valid for the early morning hours of January 30th, shows just how big this severe weather event could be. Should this short range model's forecast verify, we could see storms stretching from border to border- Canada to Mexico (if you count the Gulf of Mexico as a border, or if you use latitudes  from northwest Mexico)! Taking a look at this image, definite strengthening has occurred in this severe weather event, with very heavy convection now plaguing the Midwest and Great Lakes. We could even see some fairly intense convection happening over Michigan. Regardless, these storms could continue through the night, if the nocturnal lower level jet stream strengthens overnight. For those unfamiliar with the term, the lower level jet stream is just like the jet stream, except weaker and located lower in the atmosphere. It is nocturnal.

I think the maps above displayed my view on the situation well, and I see no need to make a map at this moment. I do suggest, however, that all those in the Plains and southern Midwest prepare for a rough ride tomorrow, especially in the evening/overnight hours.

For you storm chasers, here's my Chase Spot: Jonesboro, AR to Jackson, TN in the evening, Memphis, TN and east after dark.

Andrew

No-Travel Notice -- January 27, 2013

**This is NOT an official statement from the National Weather Service and was issued by The Weather Centre for pure safety purposes.**

I have decided to put out a No-Travel Notice for portions of the Midwest and Great Lakes in response to the ongoing ice storm and ice yet to come. The following areas are included in this notice:

-North Illinois
-East Iowa
-Southeast Minnesota
-South Wisconsin
-Much of Michigan
-North Indiana
-Northwest Ohio

Ice continues to fall across the Midwest, especially Illinois, as a body of precipitation associated with a storm system continues to move north and east. An incoming warm front will change precipitation to all rain as the evening goes on across the Midwest, but overnight icing is likely across the central Great Lakes and portions of the Northeast. Travel is considered dangerous and potentially life-threatening in many of the highlighted areas as a result of accumulating ice. Unless you are encountering a serious emergency, travel is not advised as the ice is making roads treacherous at this time. Until the rain arrives to melt away the ice (which could take additional time), roads will continue to be very unsafe and should not be used.

Andrew

January 29-30 Potential Significant Severe Weather Event

January 29 Severe Weather Risk

January 29 Probability of Severe Weather

January 30 Severe Weather Outline

I'm continuing to observe the potential for a multi-day severe weather outbreak across much of the nation. Below is yesterday's discussion, which remains valid today.

This is the 500mb vorticity forecast for the evening of January 29th. We can see a strong storm system is present in the Southern Rockies at this timeframe, with high vorticity values being found across the mountains and Plains. The system does not appear to be tilting its highest vorticity values in any particular direction, meaning this system has a neutral tilt. This is good news for those who do not welcome severe weather, as negatively tilted systems (highest vorticity values pointing to the southeast) tend to allow enhanced severe weather chances due to cold air flowing aloft, where storms can build and strengthen faster. If you wanted to be really specific, this can be classified as a slightly positively tilted storm system, but I'm not really seeing a difference because of just how slight that positive tilt is.

This is the lower level wind speed forecast, again valid for the evening of January 29. These winds are forecasted for the 900mb level, not very high above the ground. We can see very strong winds at this level across the Midwest and South Plains into the Gulf Coast. Lower level winds reach as high as 74 knots in east Arkansas. This enhances my theory that Arkansas will be the center of the January 29th outbreak. For those unfamiliar with the implications of lower level winds, tornado potential is enhanced in areas of stronger lower level winds, as wind shear is increased and thunderstorms are encouraged to form.

The last image I will show you is something called surface-500mb shear, also known as Deep Layer Shear (DLS). Deep layer shear is looked at during severe weather potential timeframes to evaluate if there really is a tornado potential. The first ingredient for making a tornado (other than having a thunderstorm) is shear. If you don't have shear, you cannot have a solid tornado. However, the deep layer shear forecast calls for shearing above 100 knots in western Arkansas, a significant value for winter. If storm activity maintains an individual cellular formation and blossoms in the areas with high shearing, tornadoes could be strong and widespread.

Andrew

February 8-12 Potential Winter Storm

Image courtesy Tropical Tidbits

I am watching the potential for a winter storm between the 8th and 12th of February, with those dates very fluid and not nearly set in stone at this moment.

The above image shows Hour 312 of the 0z GFS model. We can see a modest storm system ejecting from the Rockies and producing wide precipitation shields across the Plains and down towards the Gulf Coast. Most notably is an area of heavy snow occurring in the Central Plains, where several inches of snow may be trying to accumulate. I cannot determine just how much, as the source of these graphics does not provide such a luxury. Nonetheless, accumulating snow would be falling in the Plains, with rain in the Southern Plains in a situation that may even produce some elevated convection.

Image courtesy Tropical Tidbits

Fast-forwarding to Hour 336 (12 hours later), we find ourselves with even heavier snow now occurring in the Midwest and western Great Lakes, into the Ohio Valley and Mid-Atlantic. I could see a very good accumulating snow event come out of this (that is, if this forecast even reappears in the next week), but again, I am in no position to determine exact amounts. Making a quick glance over to the rainy side I see heavy rain now ongoing across the Gulf Coast and Southeast. While the low pressure system is further north and not right on the Gulf Coast, I could still see the chance for some elevated convection if the cold front brings up the rear of the precipitation with some solid cool air.

So, you're most likely wondering why I am spending my time typing this much about a storm way out in the long long range of the GFS.

The answer: Lezak's Recurring Cycle (LRC).

The LRC involves a cycling pattern that repeats, or 'cycles' every 40-60 days. Each cycle length is different each year, and the pattern is most prevalent from winter into spring. This year, the cycle length is roughly 53 days. If we were to go back 53 days from February 10th, we would find ourselves on the date of December 21st, 2012- supposedly the day of the apocalypse.

This was the atmospheric set-up on the 21st. We had a deep low pressure system in the Central Great Lakes and Ohio Valley. W also observed high pressure in the Canadian Maritimes into New England, as well as in the Plains and Rockies. Deep low pressure was observed off the coast of the Pacific Northwest.

Now that we've got a look at December 21st, let's go to the forecast day of February 10th and see if we can spot any similarities that may validate or void this potential winter storm.

A quick comparison between the two yields many similarities. Let's list them all- First, we see a deep low pressure system once again present in the Ohio Valley, which is the main potential for the storm. We see the high pressure systems in the Plains and Canadian Maritimes into the New England region. The big thing we're missing is the deep low pressure system offshore of the Pacific Northwest, but that will likely come back into the model's field of vision as the time draws closer. Also worth nothing is the forecasted high pressure centered in eastern Greenland, resulting in an east-based negative NAO. The east-based negative NAO is favorable for cold and snow to reach the Central US over the Northeast, increasing the validity of this forecast.

We have suddenly established these two dates as very similar. The atmospheric pattern over North America (while not 100% spot-on) is similar enough that my confidence in this particular forecast is increasing. Now, we will definitely see this forecasted storm come and go in future model runs, but seeing such a close match between this forecast and December 21st tells me we should be watching for this timeframe to verify.

Andrew

January 29 Life-Threatening Ice Storm (Updated 1/26)

Incoming Sunday Ice Storm Will Make Travel Treacherous...

PLEASE Share to get the word out -- this could be a life-threatening event!!

An ice storm is expected to unfold over the Midwest tomorrow, bringing with it accumulating snow as high as half an inch in some places.

Synoptic scale: A storm system will advance towards the Midwest and Great Lakes on Sunday. As it does so, warm air will advect (move) across the region, promoting warm air aloft but leaving a layer of below-freezing air just above the surface. This set-up is favored for freezing rain. It appears the icy part of the storm will strike during the late morning and afternoon hours, well into the evening hours before changing back over to rain near or after midnight on Monday.

Accumulations: Accumulations from the storm are expected to be nothing to 0.2 inches in states like Minnesota, Iowa, Wisconsin, Ohio, and Indiana. Heavier totals are anticipated in northern Illinois, eastern Iowa and southern Wisconsin. Model forecasts have dropped off considerably since yesterday's making of the accumulation graphic, but still remain within my parameters.

Preparations: If you get your power from an above-ground source and you live in the dark purple area, prepare to be without power all of Sunday, possibly into Monday, depending on how fast the ice accumulates and when crews are able to restore power. Travel is considered treacherous during the day tomorrow, and the Sunday rush hour will result in numerous accidents. Avoid travel if necessary.

Andrew

Civil Emergency Message - McKenzie County, ND

From the National Weather Service:

CIVIL EMERGENCY MESSAGE
EMERGENCY MANAGEMENT
RELAYED BY NATIONAL WEATHER SERVICE BISMARCK ND
225 PM CST SAT JAN 26 2013

THE FOLLOWING MESSAGE IS TRANSMITTED AT THE REQUEST OF MCKENZIE
COUNTY EMERGENCY MANAGEMENT AND IS AN UPDATE TO THE PREVIOUS
STATEMENT.

A WILLISTON BASIN INTERSTATE GAS LINE HAS BEEN CUT APPROXIMATELY 3
MILES EAST OF ALEXANDER. AS A RESULT...THE TOWNS OF ARNEGARD AND
WATFORD CITY WILL BE WITHOUT NATURAL GAS. MONTANA DAKOTA UTILITY
CREWS ARE WORKING TO REPAIR THE LINE WHICH WILL TAKE 6 TO 8 HOURS.
THEREAFTER...MONTANA DAKOTA UTILITY CREWS WILL GO DOOR TO DOOR TO
RE-LITE ALL GAS FURNACES IN ARNEGARD AND WATFORD CITY. SOME
RESIDENTS MAY BE WITHOUT NATURAL GAS UNTIL SUNDAY MORNING BEFORE
CREWS CAN GET TO EACH RESIDENCE.

TEMPERATURES THIS AFTERNOON IN THE ARNEGARD AND WATFORD CITY AREAS
ARE EXPECTED TO WARM INTO THE MID TO UPPER 30S...WITH LOW
TEMPERATURES TONIGHT FALLING INTO THE MID 20S.

Full Polar Vortex Collapse May Lead To Brutal February for North America, Europe

I am seeing that forecasts continue to enhance my much-anticipated suspicion that we will see a full collapse of the polar vortex, and this could be happening in the next two to three weeks.

We'll go image by image. This first image above is the Day 10 forecast of heights and temperatures. Areas of lower pressure are marked with the letter L, and are also shown with decreasing numbers closer to the center. Warmer temperatures are shown in warmer colors. We can clearly see that the polar vortex is nowhere near organization, a result of several sudden stratospheric warmings (SSW), an event that forces warm air into the stratosphere and increases chances for cold air about 2-4 weeks later. Typically, if we were to find a sturdy polar vortex, there would be a single low pressure vortice centered over the Arctic. However, in the above forecast image, we see three separate vortices of the polar vortex, none of which are close enough to the Arctic for me to determine that they are in control of said area. What I can determine is that the polar vortex is beginning its dramatic collapse that could bring a brutally cold February IF, and ONLY IF the atmospheric pattern cooperates.

If you saw the title of this post mentioning North America and Europe, you may be intrigued. However, if you look towards Greenland and then look east, you will see several arching formations. This signifies high pressure in the area, possibly leading to a negative NAO, which would then enhance cold weather over those areas.

The next image shows the same height forecast and temperature outlook, but now for the 30mb region of the stratosphere, typically defined as the middle-upper stratosphere. Again, we can see a very weak polar vortex split into multiple centers and multiple vortices across this layer of the stratosphere, enhancing the case that the stratospheric polar vortex is on its last leg. I have no doubt that, should this forecast verify, this will be an irreversible act that will prevent the polar vortex from fully recovering for the rest of the winter. We just went through a historic sudden stratospheric warming in recent days, that will take some time for the vortex to heal, if that's even possible anymore. In this case, we see the main vortice over western Greenland, which usually would be a concern for the negative NAO. However, the 30mb level does not have the same effect as the 100mb level in that the 30mb level is too high up to bring about any significant weather changes to the troposphere, unlike the 100mb layer.

Our final image is of the ECMWF's potential vorticity forecast. We see a mostly blue chart with a few colored areas. The warmer colors depict areas of higher potential vorticity, which will denote low pressure areas (in this case, the polar vortex). Blues denote higher pressures, which hamper the polar vortex's formation. In the above image, valid for Day 10, we see a very disfigured polar vortex. There are three separate vortices- one if over north Canada, another over Europe and a third in Asia. The Canadian vortice will act to try and push south into more of Canada and possibly into the United States if the atmospheric pattern allows. The second vortice over Europe will act to enhance cold prospects for the continent for February, as I attested to in yesterday's article here. The third vortice over Asia will provoke storm systems to begin making a rebound in the US after a recent dry spell over much of the nation, not helped by an ongoing drought in much of the Plains and Rockies.

I'm seeing good indications that the polar vortex is on its way down, and February should end up nice and cool to round out winter. Just how cold is TBD, but things are looking up.

Andrew

January 29-31 Potential Significant Severe Weather Event

The Storm Prediction Center has issued two separate areas of severe weather potential, with the 'D4' area outlining the potential for January 29th and the purple outline hinting at January 30 for the threat area that day.

The Storm Prediction Center did issue a smaller area for severe weather about 3 days ago for the same areas in the red outline, and was present up until yesterday. Yesterday, the SPC indicated that confidence was too low to outline a severe weather area, but as you can see today, the SPC is apparently very confident in their outlook, now issuing two separate areas of threats.

This is the 500mb vorticity forecast for the evening of January 29th. We can see a strong storm system is present in the Southern Rockies at this timeframe, with high vorticity values being found across the mountains and Plains. The system does not appear to be tilting its highest vorticity values in any particular direction, meaning this system has a neutral tilt. This is good news for those who do not welcome severe weather, as negatively tilted systems (highest vorticity values pointing to the southeast) tend to allow enhanced severe weather chances due to cold air flowing aloft, where storms can build and strengthen faster. If you wanted to be really specific, this can be classified as a slightly positively tilted storm system, but I'm not really seeing a difference because of just how slight that positive tilt is.

This is the lower level wind speed forecast, again valid for the evening of January 29. These winds are forecasted for the 900mb level, not very high above the ground. We can see very strong winds at this level across the Midwest and South Plains into the Gulf Coast. Lower level winds reach as high as 74 knots in east Arkansas. This enhances my theory that Arkansas will be the center of the January 29th outbreak. For those unfamiliar with the implications of lower level winds, tornado potential is enhanced in areas of stronger lower level winds, as wind shear is increased and thunderstorms are encouraged to form.

The last image I will show you is something called surface-500mb shear, also known as Deep Layer Shear (DLS). Deep layer shear is looked at during severe weather potential timeframes to evaluate if there really is a tornado potential. The first ingredient for making a tornado (other than having a thunderstorm) is shear. If you don't have shear, you cannot have a solid tornado. However, the deep layer shear forecast calls for shearing above 100 knots in western Arkansas, a significant value for winter. If storm activity maintains an individual cellular formation and blossoms in the areas with high shearing, tornadoes could be strong and widespread.

The first real evaluation of this threat will come tomorrow, when the Storm Prediction Center places this event in either Slight, Moderate or High risk of severe weather. Right now, I think this event will end up as a Moderate Risk event when the time comes, although that's for the SPC to define, not me.

Andrew

January 27 Severe Ice Storm

A severe ice storm appears to be attempting to set up across the Midwest, Great Lakes and Ohio Valley.

As a storm system begins to approach the region shown above, temperatures will warm to near freezing levels, a perfect scenario for an ice storm. Now, freezing rain is a very tricky precipitation type that commonly comes down to a 'nowcasting' (forecasting as it happens) event, because the environment that supports freezing rain (called ZR in the weather world) is so hard to achieve.

However, recent model forecasts have been in general agreement that an ice storm will hit come Sunday afternoon into evening for the areas in dark purple. These areas could see a severe ice storm with significant travel impacts, as shown below in the Exclusive Impact Scale. I am seeing one forecast for nearly half an inch, one forecast around a quarter of an inch, and another forecast around .15'' in the dark purple areas, so I decided to go to the medium and forecast a fifth of an inch to 4/10th's of an inch, with that plus sign added in the event that half inch forecast verifies. Considering it's an outlier, I'm not that optimistic on amounts really exceeding 0.4''.

Areas in light purple will experience lighter ice accumulations, but still with substantial travel impacts. I expect the Midwest to get the higher end of this 0'' - 0.2'' forecast, with the Ohio Valley getting around the median. But again, it will likely be a nowcasting event.

Here's the Impact Scale forecast:

Andrew

Europe May See Brutal Cold in Coming Days

It is becoming apparent that Europe may intercept a batch of brutally cold air in coming weeks as a result of the collapsing polar vortex.

Shown above is the European model's potential vorticity (PV) forecast for 10 days away at the isentropic level of 380 K. The isentropic level is a fancy name for just another layer of the atmosphere. 380 K translates to roughly 200 millibars- essentially the jet stream. In areas of heightened potential vorticity, low pressure centers are found. These charts are useful in identifying pieces of the polar vortex in the wintertime when they can split, like this situation.

The above image portrays a solid piece of the polar vortex journeying south into Europe in the 10 day forecast in time to introduce potentially harmful cold. We aren't talking about some stronger than normal low pressure system, this is a piece of the polar vortex here. If we do see it come south, temperatures could go down well below 0 (Fahrenheit) in many locations across the continent.

Now, depending on how long this vortice stays in place, which I don't believe will be a long time due to a more progressive atmospheric pattern, the intensity of the cold could grow. However, as a result of that progressive-ness and the fact that the vortex is too weak to hold any bone-shattering cold, this should not be as harmful as it comes across to be. However, the elderly and young may need to be watched during the 10-14 day period if this does come to fruition, because cold is cold, and serious cold can be harmful.

Andrew

Polar Vortex Takes Another Swing at Northern US

The latest GFS model forecast has the polar vortex taking another swing at the Northern US in the next 5-7 days, as January begins to wrap up.

As I have been fearing, the multiple sudden stratospheric warmings are taking their toll on the polar vortex here at the surface. We already had the initial impact of the split polar vortex over Martin Luther King Jr. Day, and now appear to be looking at Round 2. As the 500mb forecast above details, there could be a second, stronger blast of cold air that hits the northern part of the nation. The GFS places this piece of the vortex substantially further south than the previous brush with the vortex; that one went into South Canada.

It does not matter where this piece of the vortex goes, because the ball has already been rolling on what we could face in February. I have been seeing consistent forecasts that detail a full stratospheric polar vortex breakdown, more on that later tonight.

Andrew

Stormy, Cold February Could Vindicate Winter

It appears that the potential for a stormy and cold February could vindicate at least part of what has been lost this winter, with some snow and intense cold hitting the nation throughout the incoming month of February.

The Madden Julian Oscillation, or MJO, involves placement of enhanced convection over certain areas of the Indian Ocean, Pacific Ocean and even the far western Caribbean. These different areas are divided into 8 different regions, called phases, which each affect the national weather differently. Their effects change with each season as well. Above is the ECMWF Ensemble Prediction System's MJO forecast from January 24th to February 7th. It is predicting a decrease in intensity in coming days as we remain in Phase 7, and the weakening is exhibited by the forecast line moving closer to the circle in the middle of the image, called the 'Circle of Death', because the MJO is too weak at that point to impact the weather significantly. We see that the ECMWF predicts the MJO to move into Phases 8 and 1 as we enter February. These two phases are widely acknowledged as the best phases for cold and snow during the winter, with the cold hitting the hardest across the Central and East US, and snow hitting the same areas. It is for this reason that I support a cold and potentially stormy open to February.

Something else we must keep in mind is that we have recently had a historic sudden stratospheric warming. In the sudden stratospheric warming (SSW), warm air is suddenly forced up from lower levels of the atmosphere in an act that greatly weakens the polar vortex. The polar vortex is the machine that essentially maintains control of the cold air in the Arctic. If you recall, much of the nation experienced very cold temperatures just a couple days ago. This happened as the polar vortex skirted by Southern Canada. Imagine what it could do if it was inside the US. As we enter February, the 2-4 week lag time between SSW and cold air from the stratosphere reaching the surface (because the warm air has displaced it down to the troposphere) becomes valid, meaning we could see another cold shock, and this one could be stronger, depending on where the polar vortex goes this time around.

Finally, I have been a big advocate of the proven theory that snow cover observed in Siberia during the month of October can have a big effect on the Arctic Oscillation come the following winter. We have seen this theory verify, with warmer than normal temperatures in December and early January correlating with below normal snow cover in the first half of October. However, as we enter February, we find that there was a spike in snow cover in late October, which does count as February in this sense. If we use this snow cover theory, I do see a legitimate possibility for strong, sustained cold to last in the US, but only if the rest of the atmospheric pattern cooperates.

It's certainly looking good for cold and even snow in much of the nation to kick off February, and some indications even suggest this could persist to end the final month of winter.

Andrew

February 1-3 Potential Winter Storm

Image courtesy of Tropical Tidbits

The latest GFS forecast has an accumulating snowfall in the forecast from February 1 to February 3rd.

The above image shows the precipitation type, mean sea level pressure (black contour lines) and 1000-500mb thickness (dashed and colored contour lines) for the morning of February 2nd. This would then change the storm title to February 2-3, but the event is likely to put down precipitation beginning on the 1st. It appears a modest storm system will be pushing out of the Rockies, leading to precipitation across the North Plains and into the Midwest. I do not doubt this could be the result of two separate pieces of energy, and such a scenario would result in quite a storm further east. There is high pressure off the Mid-Atlantic, something that would result in the storm track being pushed further north and west, favoring a Great Lakes Cutter storm scenario.

Moving ahead 12 hours, the storm has intensified in the Great Lakes as I expected, and heavy snow is ongoing across the Midwest, Great Lakes and Upper Midwest while a rain event occurs in the Ohio Valley and Gulf Coast regions. Judging by the liquid equivalent snow legend on the right-hand side, it would not surprise me to see upwards of 4 inches of snow in many areas of the Midwest and Great Lakes if this forecast verifies, which isn't that likely at the moment. Strong Arctic high pressure filtering in through the Plains would provoke lake effect snow in the storm's wake.

Image courtesy of Tropical Tidbits

Another 12 hours into the future, we see the storm has further intensified, and is dropping large amounts of snow across much of the Ohio Valley and Great Lakes into southern Canada. A glance at the liquid equivalent legend for the hardest-hit areas would mean nearly 10 inches of snow could be falling within a 12 hour period if ratios remain the typical 10 inches of snow to 1 inch of rain. Any higher, and we would be talking about over a foot of solid snow on the ground in parts of the Ohio Valley. Rain is overspreading the Northeast area as a result of the warm sector impacting the region with...well, warm air.

So, this is just another fantasy model forecast that won't happen, right?

NOT SO FAST!

The Lezak Recurring Cycle (LRC) is involved here. The LRC includes a repeating pattern of weather disturbances and high pressure systems that repeat, or cycle, every 40 to 60 days. The cycle length varies year by year, and no winter's LRC pattern is the same. This winter, thanks to the dedicated folks at the AccuWeather Forums, it has been found that the cycle length is 53 days. If we rewind February 3rd back 53 days, we get December 11th. Now, look below and see the comparison between the forecasted 500mb height anomaly on February 3rd (top) and the observed 500mb height pattern from December 11, 2012 (bottom).

Image courtesy Tropical Tidbits

HPC

What a coincidence- they are almost a perfect match! You have the deep low pressure in the North Plains in both, slight high pressure in the Pacific Northwest in both, and even high pressure slightly displaced from the Southeast on Dec. 11, but still just offshore on Feb. 3. This proves that the LRC does indeed have a role to play here, and if we look at observed precipitation for that time period in mid December, we find that, should a similar precipitation pattern play out, over half a foot of snow for the Ohio Valley and parts of the Midwest.

Very exciting things happening here, so stay tuned!

Andrew