Tuesday, February 28, 2012

Severe Weather Prognosis (2/28/12)

As expected, the Storm Prediction Center did not issue a moderate risk for today, which in my eyes was a good move.
That does not, however, mean that the risk today will be zero. In reality, it is actually pretty substantial.
The first image is the overall outlook for severe storms in general. The second image indicates the chance for a tornado. I have come to learn that when there is a 10% chance of a tornado, a tornado can be reported in that 10% area. This time, however, that 10% area is so small that the chance of a tornado inside that 10% area seems lower than what it seems.

A severe weather event is possible today in Arkansas, Missouri and west Tennessee, among other states. Forecast models indicate shearing levels between the surface and 700mb to be pretty sufficient on the GFS, with speeds of above 50 knots. However, this big shearing is in Missouri, with slightly lower speeds in Arkansas, thereby slightly reducing the tornado threat. Good shearing is also present in the surface-500mb area, but again, the big wind speeds are to the north and west of the main tornado risk put out by the SPC.

Precipitation should start this afternoon and congeal into something better than disorganized cells later in the afternoon/evening. An atmospheric cap will be over the area where storms break out, but it will be a very weak one, so these storms should easily break it.

An atmospheric cap is what's called CINH in the meteorology world. CINH is detected when a layer of warm air is present over the cooler atmospheric air up in the skies (warm air in the storms rises through the cool air over the atmosphere to make storm clouds and then storms.). If this CINH is too strong, the storms will be forced to stop at the 'cap' of warm air, as the air is too warm so the storms cannot continue rising through the atmosphere. This thereby 'caps' the storm and keeps it from getting stronger.

The tornado threat in Arkansas will be an overnight one, with maximum EHI (instability and spinning motion combined) values coming into the state at 3:00 AM CST. This is a very dangerous situation, as many will be asleep and not be able to hear a tornado coming. Additionally, tornadoes are much harder to be seen at night.

I will provide another update this afternoon. Stay safe everyone.


Aran said...

The NWS is not coming through to any of the computers I have tried.

ERN WX said...

Looks mostly like a wind and hail event. But I thinnk there will be tornadoes. Andrew, I am glad that you are taking this situation very seriously. Night time tornadoes are the most dangerous. They are very hard to see. One indication can be very large hail. Folks in the areas that are expected to see strong t-storms, I suggest you stay tuned to any weather outlet available. The threat moves eastward for Wednesday. Stay safe!!!!! Andrew, thanks for alerting people to this potetial dangerous situation.