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Friday, March 2, 2012

Significant Severe Weather Episode Today (6:45 AM CST Discussion)


Overall Storm Prediction Risk

Hail Threat

Tornado Threat

Damaging Wind Threat
The Storm Prediction Center has maintained its moderate risk area. This was expected, as this will not be a world-ending situation. It will be pretty bad, but not extremely horrible.

A big thing we will be looking for is EHI in Kentucky and Tennessee. EHI is probably the best tornado predictor around, as it combines spinning and instability in the atmosphere, both crucial to make tornadoes. Values over 1 are considered 'high' EHI values.
In this image, we see the EHI above 3 in Kentucky and Tennessee, signaling that there will be ample tornado key ingredients to potentially make for some tornadoes. After this large EHI, however, it will begin to weaken with movement eastward.

We are also watching the jet stream, which will be screaming along at over 100 knots. Notice how the jet stream seems to have two horizontal leg-like features near the East Coast. That is called a split flow. Basically, it is when the jet stream is interrupted and splits into two because the rising of air is too powerful for the jet stream to go through. Split flows are sign soy an unstable atmosphere and are generally good things to look for when storm chasing.

CAPE values are referred to as instability in the meteorological world. When this CAPE is over 1000 j/kg, that typically signals the potential for thunderstorms. In values over 2000 j/kg, which is seen above, that means that the atmosphere is w supportive of severe thunderstorms. With a 2000 - 3000 j/kg CAPE and 3+ EHI values, this could very well be a very dangerously active environment for thunderstorms and tornadoes alike.

Storm chasers and meteorologists alike also look for something called deep layer shear. Basically, the more shearing there is, the better the environment for tornadoes. Looking at the image above, we see deep layer shear (DLS) values of over 100 knots present in Missouri. Luckily, that is not the area we are looking at. We are watching the Tennessee/Kentucky area, which has about 60-80 knots of DLS. That is still a pretty high number and supportive of some tornadoes.

My Thoughts

The SPC made the right move in not issuing a High Risk. Not enough of some key components will be in place/will be strong enough. However, I do think it is possible that a High Risk could be issued short term when the storms initially fire up, if they are stronger than expected. Also, 2000 - 3000 j/kg  with 3+ EHI is nothing to mess with.

Here is my tornado outlook for today.


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