Thursday, April 22, 2010

Moderate Risk Tomorrow


Day Two (Friday) Probablities, from SPC


Day Two (Friday) Outlook, from SPC

DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK
1228 PM CDT THU APR 22 2010

VALID 231200Z - 241200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF AR AND NRN LA...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE LOWER MS VALLEY...SRN PLAINS...OZARKS...MID MO VALLEY AND SRN PLAINS...

...A SIGNIFICANT SEVERE WEATHER EVENT POSSIBLE LATE FRIDAY AFTERNOON INTO FRIDAY EVENING ACROSS PARTS OF AR AND NRN LA......THE START OF A TORNADO OUTBREAK POSSIBLE LATE FRIDAY NIGHT INTO SATURDAY MORNING POSSIBLE ACROSS THE ARKLATEX AND LOWER MS VALLEY...

...LOWER TO MID MS VALLEY...A WELL-DEVELOPED SYSTEM OVER THE CNTRL ROCKIES WILL MOVE INTO THE SRN PLAINS FRIDAY. AN IMPRESSIVE 80 TO 90 KT MID-LEVEL JET WILL ROUND THE BASE OF THE UPPER-LEVEL TROUGH MOVING QUICKLY NEWD INTO THE SRN PLAINS FRIDAY AFTERNOON. AS LARGE-SCALE ASCENT INCREASES ACROSS THE ARKLATEX...A LOW-LEVEL JET IS FORECAST TO STRENGTHEN AND MOVE NWD ACROSS LA INTO SRN AR. CONVECTION ASSOCIATED WITH THE LOW-LEVEL JET SHOULD INITIATE ACROSS NRN LA AND SRN AR FRIDAY AFTERNOON WITH THE STORMS EXPANDING QUICKLY IN COVERAGE ACROSS ERN AR...NRN MS AND SRN MO. FORECAST SOUNDINGS FRIDAY AFTERNOON IN NRN LA AND SRN AR SHOW MODERATE INSTABILITY...STRONG DEEP LAYER SHEAR WITH 0-1 KM SHEAR AROUND 30 KT. THIS ENVIRONMENT SHOULD BE FAVORABLE FOR SUPERCELLS WITH A POTENTIAL FOR TORNADOES ESPECIALLY IF THE DEVELOPING STORMS BECOME SFC-BASED BY LATE FRIDAY AFTERNOON. AN ISOLATED STRONG TORNADO ALONG WITH A SUBSTANTIAL WIND DAMAGE THREAT WILL BE POSSIBLE AS STORMS MOVE QUICKLY NEWD OUT OF NRN LA ACROSS ERN AR AND WRN MS FRIDAY EVENING.

DURING THE OVERNIGHT PERIOD...THE UPPER-LEVEL SYSTEM ACROSS THE GREAT PLAINS IS FORECAST TO BECOME INCREASINGLY ORGANIZED. MODEL FORECASTS DEVELOP A PRONOUNCED LOW-LEVEL JET ACROSS THE NW GULF OFMEXICO FRIDAY NIGHT...MOVING THIS FEATURE QUICKLY NNEWD ACROSS LA AROUND DAYBREAK SATURDAY. THUNDERSTORMS ARE FORECAST TO INITIATE ALONG THE WRN EDGE OF THE LOW-LEVEL JET ACROSS EAST TX AFTER MIDNIGHT WITH THIS CONVECTION SPREADING NEWD ACROSS THE ARKLATEX LATE FRIDAY NIGHT INTO SATURDAY MORNING. INCREASING LARGE-SCALE ASCENT ASSOCIATED WITH THE EXIT REGION OF AN APPROACHING MID-LEVELJET...STRONG VERTICAL SHEAR AND MODERATE INSTABILITY SHOULD MAKE CONDITIONS VERY FAVORABLE FOR SUPERCELLS ACROSS THE ARKLATEX LATE IN THE PERIOD. FORECAST SOUNDINGS ACROSS NRN LA AND SRN AR FROM 09Z TO12Z SATURDAY SUGGEST LOW-LEVEL SHEAR WILL RAPIDLY BECOME FAVORABLE FOR TORNADOES. THE SYNOPTIC SETUP ALONG WITH OUTPUT FROM VARIOUS SEVERE PARAMETERS SUGGEST THAT A TORNADO OUTBREAK MAY START LATE FRIDAY NIGHT ACROSS NRN LA...SRN AR...WRN MS AND POSSIBLY FAR NE TX. TORNADOES WILL BE POSSIBLE WITH THE MORE DOMINANT DISCRETE SUPERCELLS WITH A FEW STRONG TORNADOES POSSIBLE. IN ADDITION...LARGE HAIL AND WIND DAMAGE APPEARS LIKELY WITH SUPERCELLS THAT DEVELOP FRIDAY NIGHT.

THE MAIN UNCERTAINTY CONCERNING THE OUTBREAK POTENTIAL IS TIMING WITH THE LOW-LEVEL JET LATE IN THE PERIOD. AT THIS POINT...MODEL FORECASTS FOCUS THE LOW-LEVEL JET ACROSS THE ARKLATEX AND LOWER MS VALLEY JUST BEYOND 12Z ON SATURDAY SUGGESTING THE POTENTIAL FOR A TORNADO OUTBREAK COULD HOLD OFF UNTIL AFTER 12Z SATURDAY.

...MID-MO VALLEY...AN UPPER-LEVEL LOW IS FORECAST TO MOVE INTO THE CNTRL PLAINS FRIDAY AS A CORRIDOR OF LOW-LEVEL MOISTURE SETS UP FROM ERN KS NWWD ACROSS SRN NEB WHERE SFC DEWPOINTS SHOULD BE IN THE MID 50S TO LOWER 60S F. MODEL FORECASTS DEVELOP MODERATE INSTABILITY FROM CNTRL NEB SEWD ACROSS ERN KS AND WRN MO. THUNDERSTORMS APPEAR LIKELY TO INITIATE ALONG THE INSTABILITY AXIS LATE FRIDAY AFTERNOON WHERE FORECASTS SOUNDINGS SHOW STEEP MID-LEVEL LAPSE RATES AND MODERATE TO STRONG VERTICAL SHEAR SUGGESTING SUPERCELLS WITH LARGE HAIL WILL BE POSSIBLE. VERY LARGE HAIL MAY OCCUR WITH THE MORE DOMINANT SUPERCELLS ACROSS ERN NEB...FAR NE KS AND NW MO AS THE EXIT REGION OF A MID-LEVEL JET MOVES INTO THE REGION FROM THE SOUTH. THIS COMBINED WITH MLCAPE VALUES AROUND 2000 J/KG AND 850 TO 500 MB LAPSE RATES BETWEEN 7.0 AND 7.5 C/KM MAY BE SUFFICIENT FOR VERY LARGE HAIL. THIS THREAT FOR 2 INCH AND GREATER SIZE HAIL SHOULD BE FOCUSED WITH THE MORE DOMINANT SUPERCELLS ACROSS ERN NEB...FAR NE KS AND NW MO AS THE EXIT REGION OF A MID-LEVEL JET MOVES INTO THE REGION FROMTHE SOUTH LATE FRIDAY AFTERNOON.

..BROYLES.. 04/22/2010

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