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