Tuesday, March 20, 2012
Cold Core Set Up Tomorrow?
A cut off upper level low pressure could give parts of Texas a surprise severe weather event. High resolution models are trending towards a "Cold Core" set up where low topped mini super cells could develop tomorrow producing small hail, gusty winds, and possibly a tornado or two. Right now the Storm Prediction Center does not have this area under a risk of severe weather. These types of events usually don't materialize until all the mesoscale features come together so we really won't know what will happen until the set up begins to take shape tomorrow afternoon. Looking at the image above, the amount of surface based CAPE is nothing to get excited about. Nowhere do we find CAPE at or above 1000 J/kg.
However, the image above here shows 0-3km CAPE approaching 200 J/kg, which is large enough for rapid low level convection needed to generate storms.
When we look at a forecast sounding just south of Forth Worth we can see the majority of the CAPE is located in the lower levels of the atmosphere. In fact, the LIs are positive because all of the energy is located below the 500mb level. In addition, the wind shown on the hodograph turn drastically with height, in the levels where the CAPE is located. This is producing effective bulk shear on the order of 35 to 40 knots. So with enough forcing we could see a few storms develop and in this environment they would likely be low topped super cells. The sounding above shows the maximum parcel level to be around 28,000', not very impressive when you think of severe weather. Even though the CAPE is small, the majority is in areas below freezing thanks too the cold air aloft. So small hail would be likely.
The above image is a crude surface drawing showing you where surface features are forecast to be during peak heating in conjunction with the 500mb low. The forcing associated with this low should be enough for scattered storms to develop.
In the final image above, the high resolution WRF model is breaking out an arc of scattered cells around the forcing associated with the 500mb low. If this does occur in the environment the forecast sounding predicts, these will more than likely be low topped super cells. The tornado threat looks very low thanks to the fairly high cloud base the NAM is predicting. However, the LCL is as low as 915m on the sounding above which could lead to an isolated tornado if the surface environment sets up the way it is forecast by the NAM. Right now I look for the SPC to have a 5% chance of hail tomorrow across North Texas with no tornado threat during their first outlook. Once the surface features tomorrow afternoon are known, a 2% tornado risk may be introduced.