Tuesday, May 10, 2011

Severe Weather Southern Plains 5/11/2011:

Hey Chasers,

It's been a slow start to the month of May especially after that kind of April. Historically and statistcally May is the most active tornado month during the year and it looks like tomorrow will be this month's first shot at an outbreak. SPC has already issued a Moderate Risk for tomorrow and rightfully so. I actually agree to a large part with their forecast discussion and think they have done a very nice job highlighting the synoptic setup and mesoscale setup. If you're curious to read more you should head to www.spc.noaa.gov and click two-day outlook. So lets get right down to the point brief overview covering highlights and "The Go Zone"



Strong negatively tilted upper level trough exiting the four corners region. Broad area of strong upper level diffluence (250-500mb) across TX stove pipe, OK panhandle, western KS. Interesting subtropical jet feature ahead of main shortwave trough (upper level pattern looking similar to 4/14/11 though shifted 200 miles farther west, spc touches on this). Mid level flow from SW, advecting strong EML from Mexican Rockies over southern plains. At sfc, developing lee side heat low with attendant warm front/cP cold front. Surface flow is S/SE off the gulf and large area of > 60s Tds across Central/Southern Plains and Midwest. Very well defined dryline extending North from West Texas north/northeast through central KS. Moderate upper level forcing, teamed with developing sfc low, and dry line will set the stage for tomorrows action.

The Go Zone:
SPC has its highest probabilites in a zone from west of Wichita, KS south through West Central OK to around the Red River Valley for severe storms (depicted on map with blue and red zones). While I agree with this large area focused to the East of the dryline, I will elect to put my "Go Zone" for the northern (red portion) for tomorrow. 12 model guidance is suggesting elevated convection will begin early afternoon farther to the north in Central NE and NorthCentral KS closer to the warm front. As afternoon temperatures climb signifcantly farther south in KS/OK/TX. The dryline is expected to begin mixing out with moist BL to the east. SFC convection should occur later in the afternoon along/just ahead of the dryline bulge (sfc forcing). Here backed flow ahead of the sfc low and moderate 0-6km bulk shear will be maximized. Mixed layer cape should be around 2,000 J/kg and even greater as you head south towards central OK and into the Red River Valley. Veering profiles with height and backed sfc flow (above) should yield discrete rotating supercells capable of tornadoes. Main concerns with tomorrow are large dewpoint depressions (Temperatures ahead of dryline in warm sector look to reach 80s and 90s). Very strong downdrafts and wet bulb profiles are indicative of very large hail. Also, the strength of upper level forcing and mid level shear does not look as impressive as earlier systems. Storms will be slow movers (15-30kts) and could seem some classic LP dryline monsters.

Since it looks as though there will be a lull after tomorrow and wednsday, I'm thinking about heading out and trying to verify my forecast above. It's close and should be a good show!

Fearless Fantasy Forecast: o/u 18 tornado reports (probably only 4 actual tors, :]), 50 hail reports, 50 wind reports

Happy Hunting,

Dan aka Squall Line

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