July 21st Severe Weather Potential...
For the most part today is going to be a rather low severe weather day with more garden variety type storms with heavy rain then severe weather.
Looking at the surface map for 2 AM (now)
http://www.hpc.ncep.noaa.gov/basicwx/91fwbgus.gif
We have one cold front across the southeast and a cold front that will be moving across the Midwest towards the great lakes region. These two fronts will act as a potential trigger for any severe weather. The more widespread area of precipitation is expected to be over the SE.
Looking at the temperatures ..the heat is returning to the central part of the USA where temperatures will be in the 90s..
http://www.twisterdata.com/data/models/nam/221/maps/2012/07/21/00/NAM_221_2012072100_F24_TMPF_2_M_ABOVE_GROUND.png
Dew points across the North will be in the upper 50s to around the upper 60s and across the southeast in the 60-70 range..
http://www.twisterdata.com/data/models/nam/221/maps/2012/07/21/00/NAM_221_2012072100_F24_DPTF_2_M_ABOVE_GROUND.png
Convective Available potential energy will be from about 500-3000 depending on where you are located..
http://www.twisterdata.com/data/models/nam/221/maps/2012/07/21/00/NAM_221_2012072100_F24_CAPE_SURFACE.png
Lift Index will be about 0 to negative 7 depending on where you are located..
http://www.twisterdata.com/data/models/nam/221/maps/2012/07/21/00/NAM_221_2012072100_F24_PLI_30_0_MB_ABOVE_GROUND.png
The greatest shear will be across the northern zone with 30-40 knots ..Down in the southeast we are really lacking the shear..
http://www.twisterdata.com/data/models/nam/221/maps/2012/07/21/00/NAM_221_2012072100_F24_SHRM_500_MB.png
The greatest Helicity is across South Dakota
http://www.twisterdata.com/data/models/nam/221/maps/2012/07/21/00/NAM_221_2012072100_F24_HLCY_3000_M_ABOVE_GROUND_0_M_ABOVE_GROUND.png
And this also coincides with the greatest Energy Helicity
http://www.twisterdata.com/data/models/nam/221/maps/2012/07/21/00/NAM_221_2012072100_F24_EHI_3000_M.png
We rather be on the safe side then the sorry side and with the Helicity and the EHI across south Dakota we are going to go with a 2% tornado chance , at the very least the potential for super cells in the area. This area also will be under the influence of a strengthening lower level jet..so this will likely enhance severe in that area but this would not be till later in the evening...
Over all though severe anticipation is on the low side..
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