SWODY1
SPC AC 160553
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1253 AM CDT TUE SEP 16 2008
VALID 161200Z - 171200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
STRONG...LOW AMPLITUDE FLOW IS EXPECTED TO DEVELOP ALONG AND N OF
THE U.S./CANADIAN BORDER BY THE END OF THE DAY 1 FORECAST PERIOD.
THIS FLOW PATTERN WILL EVOLVE AS THE WRN STATES UPPER RIDGE BUILDS
EWD INTO THE PLAINS TOWARD THE MS RIVER VALLEY AND A DOWNSTREAM
SHORT WAVE TROUGH LIFTS NEWD FROM THE OH VALLEY/LOWER GREAT LAKES
THROUGH THE NERN STATES. MEANWHILE...A CLOSED UPPER LOW...CURRENTLY
LOCATED OFF THE CA COAST AT 38N/127W...WILL BECOME AN OPEN WAVE
MOVING INLAND ACROSS NRN CA THIS AFTERNOON IN ADVANCE OF A STRONGER
UPSTREAM PACIFIC TROUGH. FARTHER SE...WATER VAPOR IMAGERY INDICATED
A COMPRESSED TROUGH EXTENDING FROM THE ERN BAY OF CAMPECHE TO THE
WRN FL PANHANDLE.
...SERN STATES...
VORTICITY LOBE/TROUGH EXTENDING SWWD FROM THE OH VALLEY/LOWER GREAT
LAKES SHORT WAVE TROUGH WILL MOVE EWD THROUGH THE LOWER MS VALLEY TO
CENTRAL GULF COAST STATES THIS FORECAST PERIOD. MEANWHILE...WEAK
MID LEVEL IMPULSES WILL TRACK NNEWD ALONG THE ERN EXTENT OF THE GULF
OF MEXICO COMPRESSED TROUGH INTO THE SERN STATES TODAY. AT 12Z
TODAY...A SURFACE FRONT SHOULD EXTEND FROM THE NC COAST SSWWD ALONG
THE SC COAST THROUGH SRN GA TO NWRN FL. THIS BOUNDARY IS EXPECTED
TO BECOME QUASI-STATIONARY WITH THE APPROACH OF THE SRN EXTENT OF
THE OH VALLEY TROUGH. A WEAK SURFACE LOW LIKELY LOCATED OVER SRN
SC/SERN GA THIS MORNING SHOULD MAINTAIN AN ONSHORE COMPONENT OVER A
SMALL PORTION OF ERN SC AND/OR SE GA WITH SURFACE DEW POINTS AROUND
70F. ISENTROPIC LIFT ATOP THE FRONTAL INVERSION WILL SUPPORT A ZONE
OF CLOUDS/PRECIPITATION OVER THE SRN APPALACHIANS INTO THE
CAROLINAS...GENERALLY N OF THE SURFACE FRONT. ALTHOUGH SURFACE-
BASED TSTMS MAY DEVELOP ACROSS THE WARM SECTOR CLOSER TO THE COAST
DURING THE AFTERNOON...WEAK FLOW/LAPSE RATES THROUGH THE TROPOSPHERE
WILL LIMIT PROBABILITIES FOR SEVERE TSTMS...BUT GUSTY WINDS MAY
ACCOMPANY THE STRONGER CORES.
...SRN GREAT BASIN/SERN CA NWD TO THE ORE CASCADES...
DESPITE SCANT LOW LEVEL MOISTURE EXTENDING FROM THE SWRN STATES TO
THE PACIFIC NW...STEEP LAPSE RATES WILL RESULT IN AT LEAST WEAK
INSTABILITY BY LATE THIS AFTERNOON INTO THE EVENING. FORCING FOR
ASCENT AND MID LEVEL MOISTURE ASSOCIATED WITH A COUPLE OF WWD MOVING
IMPULSES FROM THE SRN ROCKIES TO SERN CA AND AHEAD OF THE OPEN WAVE
MOVING ACROSS NRN CA/WRN ORE LATER TODAY SHOULD SUPPORT HIGH BASED
TSTMS. WEAK INSTABILITY SHOULD LIMIT THE THREAT FOR SEVERE STORMS
AND PRECLUDE THE INTRODUCTION OF LOW SEVERE PROBABILITIES.
HOWEVER...A FEW STRONG WIND GUSTS CAN NOT BE RULED OUT GIVEN THAT
THE STORMS WILL BE HIGH BASED.
..PETERS/CROSBIE.. 09/16/2008
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