Monday, May 9, 2011

May 9-10 Severe Weather Write-Up

CAPE- A measure of instability. Values over 2000 are considered unstable. Values over 4000 are considered dangerously unstable.
Lifted Index (LI): Another measure of instability. The lower the numbers, the more unstable.

This is a write up for tonight's potentially severe storms into tomorrow.
Let's start with what the predicted CAPE values are. These images will all come at once.
Chance of CAPE above 4000 6 hours away.

CAPE forecast 6 hours away

CAPE Forecast 6 hours away
As you can see, on many images, the CAPE forecast actually maxes out the legend of CAPE values. Right now, it would appear that Missouri would have the most unstable atmosphere. However, these images are forecast for 7pm CDT tonight. That means the atmosphere will be destabilizing, and luckily, limited severe storms, if any storms, are expected.
Next up is another instability indicator called LI, or Lifted Index.
Below are more images of Lifted Index forecasts.
This image actually maxes out the legend again. However, again, this will be forecast for 7 pm CDT. Thus, there will likely not be nearly as bad storms as would be otherwise at, say 1 pm CDT.

May 9 Risk of Severe Weather (Issued May 9)

Today's Overall Threat:
Tornado Threat:
Hail threat:
Damaging Wind Threat:

May 9-11 Severe Weather Event: 0z GEFS CAPE Values (Issued May 9)

CAPE- A measure of instability. Anything over 2000 j/kg is considered unstable, while anything over 4000 j/kg is considered dangerously unstable.
LLJ (Lower Level Jet Stream)- A smaller jet stream closer to Earth than the actual big jet stream separating the warm and cold air masses. This smaller jet stream typically increases in strength at night, increasing the chance for tornadic activity.

The GEFS has become so consistent with the alarmingly high CAPE values that it's hard to reject the situation.
Below is the potential for CAPEs above 4000 j/kg at 7 pm May 10.
With a 90+ percent chance of CAPE values over 4000 j/kg occurring, it can be expected that this area will go through at least some stronger storms.
Exactly 24 hours later, May 11 at 7 pm CDT, The GEFS has also portrayed another alarming scene. Below is the chance of 4000+ j/kg of CAPE.
Now, the threat has shifted more north into the Midwest. Again, the image above is May 11 7 pm CDT.

I realize these images may be disturbing to some people, seeing such an explosion of instability.
There are things that will be wrong in this event.
-There will be a very strong cap over the areas, prohibiting storms to develop.
-The actual jet stream will not be present to induce a big tornado threat.
-The Lower Level Jet Stream will be weak on May 10 and nonexistent on May 11 in the areas depicted above in the CAPE images.