SWODY2
SPC AC 201722
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1222 PM CDT FRI MAY 20 2011
VALID 211200Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE PLAINS AND MIDWEST
ACROSS THE MID/LWR MS VLY...
...SYNOPSIS...
LARGE SCALE FLOW OVER THE U.S. WILL BECOME LESS AMPLIFIED THIS
PERIOD AS A STRONG UPPER TROUGH ACROSS THE PLAINS EJECTS NEWD TOWARD
THE UPR MS VALLEY AND WRN GREAT LAKES REGION AND OCCLUDED CYCLONE
MIGRATES SLOWLY NWD TO THE DAKOTAS. STUBBORN CLOSED LOW ACROSS THE
NORTHEAST WILL BE SHUNTED OFFSHORE AS HEIGHTS RISE FROM THE ERN
GREAT LAKES TO THE APPALACHIANS AND MID ATLANTIC. MEANWHILE...A
BROAD TROUGH IS FORECAST TO DEVELOP INLAND ACROSS THE WEST COAST
WITH WEAK HEIGHT FALLS SPREADING FROM THE PAC NW TO THE LWR COLORADO
RIVER VALLEY THROUGH THE END OF THE PERIOD.
GREATEST SEVERE WEATHER POTENTIAL ON SATURDAY WILL BE LINKED TO THE
SHORT WAVE TROUGH EJECTING NEWD ACROSS THE MO AND MS RIVER VLYS...AS
WELL AS COLDER AIR ALOFT IN THE BASE OF THE LARGER SCALE CLOSED LOW
SPREADING ACROSS A RECOVERING AIRMASS OVER THE PLAINS.
...LWR/MID MS VLY TO MIDWEST...
DESPITE WIDESPREAD ONGOING CONVECTION AND COMPLEX FORECAST EVOLUTION
ACROSS THE PLAINS AT THE CURRENT TIME...00Z STORM SCALE GUIDANCE AT
36H FORECAST IS REMARKABLY SIMILAR IN DEPICTING A DECAYING MCS/QLCS
ACROSS AR/WRN TN/NRN MS EARLY SATURDAY. DYNAMIC FORCING FOR ASCENT
WITH THE PROGRESSIVE SHORT WAVE TROUGH...AND RESULTING LOW LEVEL
MASS INFLOW...WILL LIKELY SUSTAIN CONVECTIVE POTENTIAL EAST AND
NORTHEAST ACROSS THE MS RIVER VLY AND INTO THE MIDWEST THROUGH THE
DAY. WHILE GENERALLY WEAK LAPSE RATES AND MARGINAL LOW LEVEL
MOISTURE/HEATING ARE EXPECTED TO LIMIT DOWNSTREAM AIRMASS
DESTABILIZATION ACROSS THE LWR OH VALLEY...SOME INCREASE IN SEVERE
STORM POTENTIAL MAY BE EXPECTED AS THE STRONGER FORCING AND
DEEP-LAYER WIND FIELDS SPREAD ENEWD FROM IL AND IND ACROSS WRN KY
AND TN THROUGH THE AFTERNOON. FAST MOVING LINE SEGMENTS SHOULD
RESULT IN A CHANCE FOR SCATTERED DAMAGING WINDS.
GREATER AIRMASS DESTABILIZATION WILL LIKELY OCCUR ALONG THE ERN AND
SRN FLANK OF MORNING MCS ACTIVITY....FROM SRN AR AND NRN MS SWWD
ACROSS NRN LA AND ERN TX. OUTFLOW BOUNDARIES FROM EARLIER CONVECTION
WILL SERVE AS A FOCUS FOR AFTERNOON TSTM DEVELOPMENT WHERE MODEST
MID LEVEL WLY FLOW IN THE WAKE OF THE DEPARTING SHORT WAVE TROUGH
WILL PROVIDE DEEP-LAYER SHEAR SUPPORTIVE OF ORGANIZED STORMS.
HOWEVER...WEAK LARGE SCALE HEIGHT RISES MAY ACT TO LIMIT MORE
WIDESPREAD TSTM DEVELOPMENT...ESPECIALLY ACROSS LA/TX WHERE ONLY LOW
SEVERE WEATHER PROBABILITIES WILL BE MAINTAINED WITH THIS OUTLOOK.
...SRN PLAINS/MID MO RIVER VLY LATE DAY...
LATEST GUIDANCE SUPPORTS A TRAILING SHORT WAVE TROUGH ROTATING
THROUGH THE BASE OF THE LARGER SCALE UPPER TROUGH COINCIDENT WITH
DIURNAL DESTABILIZATION AND DRYLINE MIXING FROM NRN OK ACROSS ERN KS
SATURDAY AFTERNOON. LIFT AND STEEP MID LEVEL LAPSE RATES
ACCOMPANYING THIS FEATURE ARE EXPECTED TO AID AT LEAST ISOLATED TSTM
DEVELOPMENT THAT MAY EVEN EXTEND NWD WITHIN/BENEATH THE MID/UPPER
LEVEL COLD POOL ACROSS NEB/WRN IA. CYCLONIC MID LEVEL FLOW OF 25-35
KTS ATOP GENERALLY WEAKER LOW LEVEL FLOW WILL RESULT IN SHEAR
SUPPORTIVE OF ORGANIZED STORMS...SOME OF WHICH COULD PRODUCE LARGE
HAIL AND DAMAGING WIND GUSTS. ONE OR TWO CONVECTIVE CLUSTERS MAY
EVOLVE FROM THIS INITIAL ACTIVITY AND SPREAD EAST INTO IA/MO AND AR
INTO THE EVENING.
..CARBIN.. 05/20/2011
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