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Feb 20, 2014 0600 UTC Day 1 Convective Outlook

February 20, 2014

Feb 20, 2014 0600 UTC Day 1 Convective Outlook

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DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1158 PM CST WED FEB 19 2014

VALID 201200Z – 211200Z

…THERE IS A SLGT RISK OF SVR TSTMS PORTIONS OH AND TN VALLEY REGIONS TO CENTRAL GULF COAST…

…SYNOPSIS…
PROGRESSIVE UPPER-AIR PATTERN IS FCST ACROSS CONUS THIS PERIOD…FEATURING INITIALLY DISTINCT SHORTWAVE TROUGHS NOW ANALYZED OVER WRN DAKOTAS AND SRN CO/NRN NM REGION. SRN PORTION OF MID-UPPER-LEVEL VORTICITY FIELD ASSOCIATED WITH NRN-PLAINS PERTURBATION IS EXPECTED TO LINK WITH AMPLIFYING SRN-ROCKIES SYSTEM WHILE MOVING EWD ACROSS MAINLY CENTRAL/NRN PLAINS. COMBINED TROUGH SHOULD REACH FROM OZARKS TO UPPER MS VALLEY BY 21/06Z. BY THAT TIME…ACCOMPANYING/CLOSED 500-MB LOW SHOULD FORM OVER WI. BY END OF PERIOD…500-MB LOW SHOULD DEEPEN AND MOVE NEWD TO NNEWD ACROSS CENTRAL/WRN UPPER MI…WITH TROUGH ARCHING SEWD OVER WRN LOWER MI AND INDIANA THEN SSWWD ACROSS WRN TN. 250-MB JET OF 110-120 KT WAS ANALYZED AT 21/00Z OVER CO/NM…AND THIS SPEED MAX SHOULD EXPAND/ELONGATE AHEAD OF COMBINED PERTURBATION THROUGH PERIOD…WHILE GRADUALLY BECOMING MORE MERIDIONAL.

AT SFC…CYCLONE NOW NEAR CO/KS BORDER SHOULD CONTINUE TO DEEPEN AS IT TRAVELS FROM ERN KS TO SWRN WI DURING 20/12-21/00Z TIME FRAME. AT THAT TIME…COLD FRONT SHOULD EXTEND IN ARC FROM LOW ACROSS CENTRAL-ERN IL…EXTREME WRN KY…SERN AR…AND MIDDLE-UPPER COASTAL PLAIN OF TX.

…OH AND TN VALLEY REGIONS TO CENTRAL GULF COAST…
SCATTERED-NUMEROUS TSTMS IN BANDS SHOULD POSE PRIMARY THREAT OF DAMAGING GUSTS…A FEW OF WHICH MAY REACH 65-KT/SIGNIFICANT-SVR CRITERIA. TORNADO RISK EXISTS BUT IS SECONDARY TO DAMAGING TSTM WIND IN TERMS OF COVERAGE…DURATION AND NUMBER OF EVENTS PROBABLE. ALTHOUGH LOW-LEVEL AND DEEP SHEAR EACH WILL BE FAVORABLE FOR SUPERCELLS…LIKELY DOMINANCE OF LINEAR STORM MODE INDICATES PREDOMINANT SOURCE OF TORNADO RISK WILL BE QLCS-TYPE SPINUPS AND EMBEDDED MESOCIRCULATIONS ASSOCIATED WITH LEWPS AND SMALL BOWS. TORNADOES WITH SUCH REGIMES TEND BE RELATIVELY SHORT-LIVED AND SMALL…BUT ALSO…FAST-MOVING AND RAIN-WRAPPED.

THIN BAND OF CONVECTION MAY DEVELOP DURING AFTN IN ZONE OF STRONG FORCING ALONG SFC COLD FRONT…HOWEVER PRIMARY SVR-PRODUCING SWATH IS LIKELY TO ARISE IN SW-NE ORIENTED/PREFRONTAL CONVERGENCE ZONE FROM LATE AFTN INTO EARLY OVERNIGHT HOURS. 50-60 KT EFFECTIVE SHEAR MAGNITUDES WILL BE COMMON WHEREVER SFC-BASED INFLOW EXISTS WITH MAIN SQUALL LINE. 60S SFC DEW POINTS MAY REACH TO NEAR OH RIVER IN NARROW CORRIDOR PRIOR TO TSTMS…BUT RICHEST MOISTURE SHOULD RESIDE FROM TN SWD. MLCAPE SHOULD REMAIN BELOW 1000 J/KG OVER MOST OF OUTLOOK AREA BECAUSE OF WEAK LAPSE RATES ALOFT…THOUGH POCKETS OF PRECONVECTIVE DIABATIC HEATING OVER GULF COAST STATES CAN BOOST VALUES HIGHER ON MESOBETA SCALE.

AS TSTM REGIME MOVES EWD ACROSS KY/TN/AL OVERNIGHT…IT WILL OUTPACE FAVORABLE DESTABILIZATION/WAA FROM N-S…AND MOVE INTO PROGRESSIVELY LOWER-CAPE AIR WITH EWD EXTENT. NET RESULT SHOULD BE DECREASE IN OVERALL SVR POTENTIAL FROM NW-SE AND WITH TIME. HOWEVER…BECAUSE OF GREATER MOISTURE PREVALENT CLOSER TO GULF COAST…SVR RISK MAY LAST FOR MUCH OF OVERNIGHT HOURS AS CONVECTION CROSSES TN VALLEY AND GULF-COAST STATES.

FARTHER N OVER NRN PORTIONS INDIANA/OH AND LOWER MI…SVR WIND POTENTIAL DIMINISHES DUE TO PROGRESSIVELY WEAKER BUOYANCY. ALSO…LOSS OF SFC-BASED PARCELS IS EXPECTED IN RELATION TO PROGRESSIVELY DEEPER STABLE LAYER WITH NWD EXTENT…ATOP SNOW PACK. MEANWHILE…EVEN FOR THOSE STG/NEAR-SVR GUSTS THAT CAN PENETRATE TO SFC…SUBSTANTIAL TREE DAMAGE/TOPPLING ALSO BECOMES LESS PROBABLE WITH NWD EXTENT DUE TO FROZEN GROUND AND LACK OF LEAVES.

…MO-IA-IL REGION…MORNING…
EXTENSION OF STG LOW-LEVEL WAA REGIME FROM PRIOR PERIOD WILL SUPPORT CARRY-OVER POTENTIAL FOR SCATTERED TSTMS IN CLUSTERS ACROSS THIS REGION. ACTIVITY WILL BE SUPPORTED BY ISENTROPIC LIFT TO LFC…AMIDST ELEVATED MUCAPE 500-800 J/KG AND 35-45 KT EFFECTIVE SHEAR MAGNITUDES FROM ASSORTED FCST SOUNDINGS. ISOLATED SVR HAIL MAY OCCUR WITH THIS ACTIVITY DURING FIRST FEW HOURS OF PERIOD BEFORE IT MOVES NNEWD AWAY FROM MOST FAVORABLE ELEVATED INSTABILITY.

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