Day 1 Severe Weather Outlook
06Z 02 Mar 2008
There is a MDT risk of severe thunderstorms for SW OK and N CTRL TX.
Surrounding the MDT risk area, there is a SLGT risk of severe thunderstorms for MUCH OF OK, EXTR ERN TX PANHANDLE, and much of N CTRL TX.
SYNOPSIS: Water vapor imagery and upper air analysis indicate a lead shortwave invof NM/AZ/MX border, being kicked out by an amplifying longwave trough over the Intermountain West. The LLJ is expected to veer and strengthen tonight. Deep moisture profiles already exist in much of the risk area with a strongly capped mixed layer above the moist layer, due to a strong 700mb dry punch. Moisture will continue to advect northward as the longwave trough amplifies and moves eastward. In advance of the trough axis, lee surface cyclogenesis will occur in western TX during the day tomorrow. The combination of deep moisture and strong dynamics will set up a chance for a localized severe weather event in portions of OK and TX tomorrow.
OK & TX: In response to the deepening sfc low, a dryline will sharpen across western TX tomorrow, and then mix eastward across the day. Meanwhile, to the north, a cold front will move southward, reaching possibly a CHI-STL-FWD line by the end of the forecast period. An elevated mix layer will keep things well capped and preclude significant morning convection from clouding up the warm sector. The strongest LLJ forcing should remain well to the north and east of the slight risk area. Destabilization should occur through the day; modified forecast soundings indicate SBCAPE’s around 1000-1500 J/kg with cold 500mb temps allowing for steep mid level lapse rates. As this occurs, increased dynamic forcing from the longwave to the west, an erosion of the cap, and convergence along the dryline bulge invof the Red River, will allow for storms to form in the early evening hours. Elongated, curved hodographs will allow for the potential of tornadoes with discrete supercells. As time goes on, the surging cold front will overtake the dry line, resulting in a forced squall line by the end of the period. Forecast hodographs still indicate some tornadic potential with embedded supercells or any storms that manage to form ahead of the line.
Some uncertainties still exist. Believe the GFS has a better handle on the cap strength and the initial shortwave trough, based on obs. A stronger initial shortwave could move by in the morning and leave subsidence in its wake, and the cap could fail to break in the early evening until the squall line is forced by the surging cold front. Should this scenario occur, the tornadic risk would be drastically reduced. Any drastic reducing of insolation will strengthen the cap. Attm, a 15% nonhatched tornado risk seems to be the best way to go.
FURTHER NORTHEAST: Forecast soundings indicate some CAPE all the way up to Chicago. Convergence along the cold front could spark some strong thunderstorms. These thunderstorms should remain linear and have slow eastward progression due to the orientation of the shear vector, especially in MO and southern IL. The strongest updrafts will have the potential to produce some marginally large hail and some gusty winds.
DISCLAIMER: NOT AN OFFICIAL FCST… FOR THAT STUFF GO TO SPC.
FORECASTER: Jim