South Plains Potential Severe Weather Discussion

Forewarning- the NAM model we are using is not showing a definitive position for a squall line, so we are using the images that appear to maximize the threat in order to be too safe than sorry.

The South Plains is in for another round of severe weather in the next few days. Here's the low down.

The country is currently experiencing a massive warm wave as a huge warm front pulls up air north as far the cities like Lincoln, Nebraska. This warm air is being pulled up ahead of this storm system that we are watching. As we progress into the timeframe being watched for severe weather, I am seeing the low pressure system eject eastward from the Southwest. Behind it will be an enclosed pool of below-freezing temperatures. You can see this pool of cold air just west and northwest of Texas, in that oval shape. This cold air is more than likely to be an instigator for showers and thunderstorms as this cool, dry air smashes against the warm Gulf air.

Here is a chart showing various severe weather indices. Let's start with the 'observed buoyancy'. This is basically instability, known around the weather world as CAPE. CAPE values above 1000 are typically sustainable for thunderstorms, and values over 2000 units can support severe thunderstorms. In this image, we see CAPE values exceeding 1000 j/kg across easter Texas, which is where I am watching for the storms. The blue lines are absolute helicity, basically meaning spinning in the atmosphere, not accounting for CAPE. I emphasize that because CAPE is a very crucial part of severe storms, and a lot of helicity and no CAPE does not support tornadoes. In the image, we do see a lot of helicity, but it is located to the west of the area being monitored, decreasing the tornado threat in my eyes, but not nearly putting it to 0%.

This is the Energy-Helicity Index (EHI), which accounts for helicity and CAPE, making for a much more reasonable tornado threat index than just helicity. Values over 1 are considered supportive (in the very right conditions) for tornadoes. Here, we see widespread values of EHI topping out at 1. Now, just because it is not at 1 does not mean the tornado threat is 0, but it is not a good thing for storm chasers. Running through the model shows me that this is about the most reasonable it gets.

Here is a relatively unknown index that I am deciding to use to show that there remains a slight chance for some tornadic activity. This is the Vorticity Generation Potential, or VGP index. It detects the potential for spinning in the atmosphere. I cannot tell you if it is reliable, like the helicity discussion earlier in this post, as I do not know too much about VGP. I do know, however, that VGP values over 0.2 indicate an increasing chance of some tornadic activity.
In this image, we see widespread values of 0.15 to 0.20 across east Texas and Arkansas. There is a dark green area of 0.20 to 0.25 that is the highest realistic value in this situation. I say realistic because the dark green area pretty much covers where the squall line may move. Higher values denoted in the yellow areas are generally not going to be where the strongest storms occur in this situation.

Finally, we have the infamous Significant Tornado Parameter, or STP. If you viewed The Weather Centre this past summer, you saw my continuous use of STP images, with widespread red and pink colors across the South Plains and Midwest. I have come around to say that the STP is pretty much useless in detecting the potential for tornadoes. I very much like the idea, but it's realistic use is not exactly practical. That said, these values of 1 to 3 across east Texas and Arkansas are basically saying 'There is a chance for a tornado, but don't bank on it'. That is also what I am saying at this point.

I'm leaving you with the Storm Prediction Center's Day 3 outlook that shows this potential threat.

Questions may be asked below.
Also, if you are a weather fanatic and like to discuss weather, I encourage you to also comment, because it gives everyone (including me) a different insight into this situation and others.

-Andrew

Midday Prognosis

EHI values above 1 have been seen on the 12z GFS, as shown in the image attached. There will be a full post on it at 4:00 PM CST this afternoon.

-Andrew

Weekend Severe Weather Potential Post Coming Out at 4:00 PM CST Today

A new post concerning a possible squall line feature for the South Plains into the entire east half of the US will be issued at 4:00 PM CST this afternoon.

Severe Weather Possible for South Plains this Weekend

I am looking at the potential for some possible severe weather come the Saturday-Sunday timeframe this weekend. Let's take a look at the models.

Hour 144 GFS

The 12z GFS is indicating that a squall line is to form in east Texas and east Oklahoma into western Arkansas/Louisiana/Missouri on Sunday, March 11. It looks like a storm system will eject eastward from the Southwest and make a boundary of sorts that will crash into warm, humid air brought north from the strong high pressure system in place on the East Coast.
Judging by the colors on the map,  it looks to be a pretty linear squall line which would somewhat discourage super cells in a linear format. However, this is a fairly low resolution image, which means that those green areas in the rest of Arkansas could be several separate storm cells.

Hour 144 12z NOGAPS

The 12z NOGAPS also has a linear squall line hitting the South Plains, but it looks like that the squall line may be stronger according to the additional colors in west Arkansas. Also interesting is the stretch of intense precipitation north into the High Plains. This could have some interesting effects if it were to verify. The more important piece from this image is how the storm system appears to be located in north Oklahoma, almost identical to the GFS. However, I cannot exactly locate where the center is, so that is not a definite comparison.

Hour 144 12z GEM

Canada's GEM model is also portraying a squall line, but further west than what the other two models are showing. The GEM model has the storm's minimal pressure in the eastern half of Texas, farther south than the NOGAPS/GFS are showing. The GEM has always been more of a 'funny' model than much of a serious one, so for now I am discounting it. However, every model is always worth looking at, and maybe the GEM is onto something.
Either way, there remains a consensus of possible intense precipitation in the South Plains.

Hour 144 12z JMA

Here's the laughable JMA model, from the Japanese Meteorological Agency. It is never trusted, and as you can see, here is why. It is showing a snowstorm of over 5 inches in Kansas and Nebraska, as well as an extreme squall line in Arkansas and Louisiana. The JMA may even be showing a tropical system offshore Florida, but that is a whole different situation. Don't even try to take this model into account- I never do and likely never will. This is more of a just-for-looks image. However, it still falls in line with a squall line in the South.

As for the indices that can predict severe weather, there does appear to be CAPE values of up to or over 1000 j/kg of instability in Texas, which would be sustainable for general thunderstorms. The Lifted Index (LI) for this time frame is not impressive, with the lowest values of down to -4.
The 12z GFS is showing a weak atmospheric cap present over the area at hour 144, but nothing that a squall line shown above could be stopped by.
The thing that gets pretty concerning in my eyes is how deep layer shear (DLS) may be over 70 knots, which is pretty concerning for a possible tornadic scenario. Contributing to that is a 60 knot lower level jet stream and a jet stream wind speed of over 90 knots.
Something else I want to mention is how the GFS is showing 925mb level winds over 50 knots, which is pretty significant.

I will leave you with this forecast hodograph (detects possible rotation in the atmosphere, shown as a circular shape) from the 12z GFS in west Arkansas.

-Andrew

Showers, Thunderstorms Likely Wednesday Night

The NAM is forecasting the development of a linear band of showers and thunderstorms from Oklahoma to Canada. This will be as a cold front comes through to end some warm weather in the lower Great Lakes, South Central Plains and areas to the east.

Luckily, this will not be a severe weather threat. There looks to be minimum instability, maybe even the atmosphere trying to prevent thunderstorms from forming. Either way, there will not be any instability on any level to be able to initiate stronger storms for this event.

There will be the issue of mixing precipitation in west Oklahoma and west Texas to all snow in southwest Kansas. There could be some slick conditions in those areas due to the system trying to initiate some mixing and snowfall behind it. For now, snow accumulations look to be low, with snow depths ending up at around 1-2 inches.

-Andrew