SPC Discussion and chatter about severe weather threat Saturday:
DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1229 PM CDT FRI MAY 17 2013 VALID 181200Z - 191200Z ...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF NWRN KS/SWRN NEB... ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK FROM EXTREME NWRN TX INTO SERN ND/NWRN MN... ...PLAINS... LATEST MODEL GUIDANCE IS IN GENERAL AGREEMENT REGARDING THE EVOLUTION OF UPPER TROUGH AS IT PROGRESSES ACROSS THE WRN U.S. INTO THE HIGH PLAINS LATE IN THE PERIOD. OF PARTICULAR CONCERN IS THE EXPECTED INCREASE IN MID LEVEL FLOW INTO THE HIGH PLAINS ATOP AN INCREASINGLY MOIST/BUOYANT AIRMASS. LATEST SATELLITE IMAGERY DEPICTS EXTENSIVE LOW CLOUDS ACROSS OK WITH A DECIDEDLY ELY LOW LEVEL COMPONENT WITHIN THE BOUNDARY LAYER. THIS CLOUDINESS WILL BE STUBBORN TO ERODE DURING THE DAY1 PERIOD AND IN THE ABSENCE OF MEANINGFUL THUNDERSTORM ACTIVITY ACROSS THE SRN/CNTRL PLAINS THROUGH SATURDAY MORNING ABUNDANT LOW LEVEL MOISTURE SHOULD RAPIDLY RETURN ACROSS KS INTO NEB SATURDAY. LATEST THINKING IS WARM ADVECTION MAY DRIVE A BOUT OF EARLY MORNING CONVECTION ACROSS PARTS OF THE ERN DAKOTAS BENEATH MODEST LLJ. WHILE THIS ACTIVITY MAY PRODUCE SOME HAIL...IT SHOULD SPREAD EWD INTO THE UPPER MS VALLEY DURING THE MID DAY HOURS AS A WEAK BRANCH OF THE LLJ FOCUSES INTO THIS REGION. LATEST SHORT RANGE MODEL GUIDANCE INSISTS STRONG HEATING WILL OCCUR ACROSS SERN CO INTO NWRN TX. THIS SHOULD ALLOW DRYLINE TO MIX TO A POSITION NEAR THE OK BORDER...ARCING NWWD TO A SFC LOW OVER WRN KS BY 19/00Z. WITH SFC DEW POINTS EXPECTED TO RISE WELL INTO THE MID-UPPER 60S EAST OF THE DRYLINE...EXTREME INSTABILITY MAY DEVELOP ALONG A CORRIDOR FROM WRN OK INTO NWRN KS WHERE SBCAPE COULD EXCEED 4000 J/KG. AS TEMPERATURES WARM INTO THE LOWER 90S ACROSS THE TX PANHANDLE INTO SWRN KS INHIBITION WILL BE NEGATED AND DISCRETE SUPERCELL STRUCTURES ARE EXPECTED TO DEVELOP. HAVE INCREASED THE SEVERE PROBS ACROSS PORTIONS OF KS/NEB AS THIS PORTION OF THE CNTRL PLAINS SHOULD EXPERIENCE STRONGER DEEP LAYER SHEAR...POTENTIALLY SUPPORTIVE OF TORNADOES. LATEST 12Z NAM FORECAST SOUNDINGS STRONGLY SUPPORT SUPERCELLS ACROSS THE MDT RISK REGION WITH SBCAPE IN EXCESS OF 4000 J/KG WITH SFC-6KM SHEAR ON THE ORDER OF 40KT. ADDITIONALLY...VERY LARGE HAIL MAY ACCOMPANY ANY SUPERCELLS THAT DEVELOP SATURDAY. LATEST FORECAST HAIL ALGORITHMS SUGGEST HAIL COULD EASILY EXCEED BASEBALL SIZE WITH ORGANIZED ACTIVITY. SOMEWHAT WEAKER DEEP LAYER FLOW ACROSS THE SRN PLAINS MAY LIMIT OVERALL SEVERE THREAT AND FOR THIS REASON HAVE ONLY EXTENDED 15 PERCENT THREAT INTO PORTIONS OF NWRN TX. ...TN VALLEY/CNTRL GULF STATES... WEAKENING UPPER TROUGH WILL TRANSLATE INTO THE MIDDLE TN VALLEY/NRN GULF STATES SATURDAY. MODEST NWLY FLOW ALONG BACKSIDE OF THIS FEATURE MAY PROVIDE ENOUGH SHEAR FOR ORGANIZED MULTI-CELL UPDRAFTS CAPABLE OF PRODUCING SOME HAIL/WIND. THIS ACTIVITY SHOULD BE MODULATED BY DIURNAL HEATING AND SHOULD WEAKEN WITH AFTER SUNSET. ..DARROW.. 05/17/2013
