SWODY2
SPC AC 171721
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1221 PM CDT FRI SEP 17 2010
VALID 181200Z - 191200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MODELS REMAIN IN AGREEMENT WITH THE OVERALL LARGE-SCALE FLOW PATTERN
ACROSS THE LOWER 48 STATES DURING THE DAY 2 PERIOD. A LARGE E-W
ORIENTED RIDGE WILL PREVAIL OVER THE SRN HALF OF THE U.S...WHILE
FAST WLY MID-UPPER LEVEL WINDS EXTEND ALONG THE NRN TIER OF STATES
AS A DEEP CLOSED LOW TRACKS NEWD ACROSS HUDSON BAY. IN THE WEST...
SEVERAL WEAK IMPULSES WILL SHEAR NEWD ACROSS THE PACIFIC NW AND NRN
ROCKIES...WHILE A LONGWAVE TROUGH APPROACHES THE WEST COAST. IN THE
LOW LEVELS...A COLD FRONT ATTENDANT TO THE HUDSON BAY LOW WILL
SPREAD EWD FROM THE GREAT LAKES TO NEW ENGLAND THIS PERIOD...WITH
THE TRAILING PORTION OF THIS BOUNDARY MAKING SLOWER PROGRESS SEWD/
SWD INTO THE OH VALLEY/MIDWEST...MID MS VALLEY AND KS. THE MID MS
VALLEY TO KS PORTION MAY EVEN BECOME QUASI-STATIONARY BY SATURDAY
NIGHT.
...SRN IA/NRN MO/NRN IL AND VICINITY...
MODELS SUGGEST A LOW AMPLITUDE MIDLEVEL IMPULSE WILL TRACK FROM IA
TO IL/IND BY 19/00Z...BUT DIFFER IN THE TRACK AND AMPLITUDE OF THIS
FEATURE. THE 12Z NAM/00Z ECMWF SUGGEST A MORE NRN TRACK AND STRONG
FORCING/UVVS ACROSS NRN IL/IND...WHILE THE 12Z GFS IS MUCH WEAKER
WITH THE IMPULSE MOVING THROUGH NRN MO TO SRN IL SATURDAY AFTERNOON.
AT 12Z SATURDAY...ELEVATED TSTMS ARE EXPECTED TO BE ONGOING N OF THE
COLD FRONT WITHIN A ZONE OF WAA ACROSS NEB/IA IN THE NOSE OF A SWLY
LLJ. ALTHOUGH THE LLJ WILL WEAKEN SOME THROUGH THE DAY...
PERSISTENT WAA ALONG AND N OF THE SLOW MOVING COLD FRONT WILL
SUPPORT PRIMARILY ANAFRONTAL PRECIPITATION WITH EMBEDDED TSTMS
POSSIBLE GIVEN AN INFLOW OF MODERATE INSTABILITY. THERE IS SOME
POTENTIAL FOR SURFACE BASED TSTMS SATURDAY AFTERNOON ACROSS NRN MO
INTO PARTS OF CENTRAL IL AS THE COLD FRONT MOVES INTO A MODERATELY
UNSTABLE AIR MASS. HOWEVER...GIVEN STRONGER FORCING PER NAM/ECMWF
REMAINING N OF THIS REGION AND WEAK LOW LEVEL CONVERGENCE/ASCENT
ALONG THE FRONT...STORM COVERAGE REMAINS UNCERTAIN. STORMS THAT CAN
DEVELOP WILL HAVE A POTENTIAL TO BE STRONG TO SEVERE...GIVEN
MODERATE INSTABILITY AND EFFECTIVE BULK SHEAR 25-35 KT SUPPORTING AN
ISOLATED THREAT FOR HAIL/DAMAGING WIND GUSTS. OTHERWISE...A HAIL
THREAT WILL ALSO EXIST WITH THE STRONGER ELEVATED STORMS BOTH
SATURDAY MORNING AND AGAIN SATURDAY NIGHT AS THE LLJ RESTRENGTHENS
INTO THE LOWER MO VALLEY TO NRN IL/NRN IND.
..PETERS.. 09/17/2010
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