SWODY1
SPC AC 231954
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0254 PM CDT FRI SEP 23 2011
VALID 232000Z - 241200Z
...NO SVR TSTM AREAS FORECAST...
A COUPLE OF CHANGES HAVE BEEN MADE TO THE OUTLOOK AT 20Z. THE FIRST
CHANGE IS TO REMOVE PARTS OF NRN AL...ECNTRL TN...ERN KY AND SCNTRL
OH FROM THE THUNDER AREA WHERE A COLD FRONT IS STABILIZING THE
AIRMASS. THE SECOND CHANGE IS TO MOVE THE 5 PERCENT WIND DAMAGE
PROBABILITY LINE SLIGHTLY FURTHER EAST INTO THE CNTRL APPALACHIAN
MTNS. OTHERWISE...THE OUTLOOK LOOKS TO BE ON TRACK.
..BROYLES.. 09/23/2011
.PREV DISCUSSION... /ISSUED 1113 AM CDT FRI SEP 23 2011/
...ERN CAROLINAS/VA TIDEWATER AREA THIS AFTERNOON...
A MIDLEVEL LOW CENTERED NEAR LAKE MI WILL MOVE LITTLE THROUGH THIS
FORECAST PERIOD. A WEAK EMBEDDED SPEED MAX WILL ROTATE NNEWD THIS
AFTERNOON/EVENING FROM THE SRN APPALACHIANS TO PA...AROUND THE SERN
PERIPHERY OF THE LOW. AT THE SURFACE...THE PRIMARY SYNOPTIC LOW
WILL DRIFT NWD INVOF LAKE ERIE...WHILE A FRONT WILL REMAIN
QUASISTATIONARY FROM ERN SC/CENTRAL NC INTO THE CHESAPEAKE BAY AREA.
THIS FRONTAL SEGMENT WILL FOCUS THE MAIN CONVECTIVE DEVELOPMENT
THROUGH THE PERIOD...IN ADVANCE OF THE EJECTING SPEED MAX OVER THE
SRN APPALACHIANS.
BOUNDARY LAYER DEWPOINTS IN THE LOW-MID 70S HAVE SPREAD INLAND
ACROSS THE ERN CAROLINAS AND THE LOWER CHESAPEAKE BAY AREA.
HOWEVER...SURFACE HEATING WILL CONTINUE TO BE LIMITED THROUGH THE
AFTERNOON BY WIDESPREAD CLOUDS...AND THE DEGREE OF INSTABILITY WILL
ALSO BE LIMITED BY POOR MIDLEVEL LAPSE RATES.
MEANWHILE...DEEP-LAYER VERTICAL SHEAR IN THE WARM SECTOR WILL BE
SUFFICIENT FOR ORGANIZED CLUSTERS/EMBEDDED SUPERCELLS IN CONJUNCTION
WITH A BELT OF 30-40 KT SSWLY MIDLEVEL FLOW...AND EFFECTIVE SRH ON
THE ORDER OF 150 M2/S2. THE COMBINATION OF RELATIVELY WEAK
INSTABILITY/POOR LAPSE RATES/MOIST PROFILES WITH MODEST VERTICAL
SHEAR APPEARS MARGINALLY SUPPORTIVE OF DAMAGING WINDS AND AN
ISOLATED/BRIEF TORNADO. WILL MAINTAIN LOW WIND/TORNADO
PROBABILITIES IN THIS UPDATE...BUT THIS AREA WILL CONTINUE TO BE
MONITORED CLOSELY THROUGH THE AFTERNOON.
...WRN NY/PA TO THE SRN APPALACHIANS THIS AFTERNOON...
THE PRIMARY EMBEDDED SPEED MAX WILL ROTATE NNEWD FROM KY TO OH THIS
AFTERNOON...ROUGHLY ALONG THE SYNOPTIC COLD FRONT NEAR THE W SLOPE
OF THE APPALACHIANS. WIDESPREAD CLOUDS AND RELATIVELY COOL SURFACE
TEMPERATURES WILL KEEP INSTABILITY WEAK THROUGH THE AFTERNOON IN
ADVANCE OF THE FRONT...THOUGH THERE WILL BE SUFFICIENT MIDLEVEL
MOMENTUM TO SUPPORT A SMALL RISK FOR ISOLATED DAMAGING GUSTS THIS
AFTERNOON.
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