SPC AC 242054
DAY 1 CONVECTIVE OUTLOOK CORR 1
NWS STORM PREDICTION CENTER NORMAN OK
0354 PM CDT FRI JUL 24 2009
VALID 242000Z - 251200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS UPPER
MIDWEST...MID-UPPER MS VALLEY REGION...
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS COASTAL CAROLINAS...
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS MID-ATLANTIC AND LOWER
GREAT LAKES REGIONS...
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS WRN MT...
CORRECTED FOR LABEL ON WIND AREA
--- UPDATES ---
...UPPER MIDWEST...MID-UPPER MS VALLEY REGION...
SVR PROBABILITIES ADJUSTED IN ACCORDANCE WITH CONVECTIVE AND CLOUD
TRENDS...AND RELATED STABILIZATION OF AIR MASS N AND NE OF
SUPERCELL-ANCHORED MCS NOW MOVING SEWD OVER PORTIONS NERN IA...SERN
MN AND SWRN WI. WHILE ADDITIONAL TSTMS MAY FORM OVER CENTRAL/NRN WI
INVOF SFC FRONT...MORE ORGANIZED SVR THREAT THEREWITH NOW APPEARS TO
BE OVER SRN MN AND IA...ALONG AND W OF INSTABILITY GRADIENT
ASSOCIATED WITH OUTFLOW BOUNDARY FROM ONGOING COMPLEX. REF SPC WWS
616-617 AND RELATED MESOSCALE DISCUSSIONS FOR NEAR-TERM DETAILS.
...ERN KS TO NRN OZARKS REGION...LATE TONIGHT...
LOW LEVEL WAA REGIME AND ISENTROPIC LIFT TO LFC ARE EXPECTED TO
CONTRIBUTE TO TSTM DEVELOPMENT BEHIND SFC COLD FRONT AFTER
APPROXIMATELY 09Z OVER PORTIONS NERN/E-CENTRAL KS AND SWRN
MO...WITH ISOLATED SVR HAIL POSSIBLE. ANY SUCH ACTIVITY WILL BE
ROOTED IN 650-800 MB LAYER...WITH ENOUGH MOISTURE IN INFLOW REGION
TO SUPPORT ELEVATED MUCAPE 500-1000 J/KG. MID-UPPER LEVEL NNW FLOW
AND LOW LEVEL SWLY-WLY WINDS ARE FCST ACROSS PORTIONS ERN KS/WRN MO
EARLY IN PERIOD...CONTRIBUTING TO FAVORABLE DEEP-LAYER SHEAR
PROFILES FOR ORGANIZED TSTMS.
...CENTRAL HIGH PLAINS...
INCREASING POTENTIAL FOR ISOLATED SVR EXISTS INVOF WRN SEGMENT OF
SFC FRONTAL ZONE...ALONG AND E OF HIGHER TERRAIN IN SERN WY AND NERN
CO. 5-PERCENT PROBABILISTIC OUTLOOK LINES HAVE BEEN MODIFIED
ACCORDINGLY. REF MESOSCALE DISCUSSION 1660 FOR ADDITIONAL DETAILS.
..EDWARDS.. 07/24/2009
.PREV DISCUSSION... /ISSUED 1127 AM CDT FRI JUL 24 2009/
...SYNOPSIS...
UPPER LOW OVER WRN ONTARIO WILL MOVE SEWD INTO LAKE SUPERIOR
TONIGHT. THIS SYSTEM WILL EJECT UPPER LOWS OVER LAKE ERIE AND IN SRN
NEW ENGLAND NEWD THROUGH THE PERIOD. UPPER RIDGE WILL REMAIN IN THE
WEST....WITH A CLOSED QUASI-STATIONARY LOW ALOFT SITUATED IN THE ERN
WA/NRN ID AREA. AT THE SFC...COLD FRONT FROM NERN MN SEWD INTO SRN
SD WILL PROGRESS STEADILY SEWD THROUGH THE PERIOD.
...UPPER/MID MS VALLEY EWD INTO THE CENTRAL GREAT LAKES...
LOW LEVEL WARM ADVECTION HAS SUPPORTED ELEVATED STORMS WITH SEVERE
HAIL THROUGH THE MORNING ACROSS SERN MN. WIND DAMAGE WILL INCREASE
LATER TODAY WITH THESE STORMS AS THE BOUNDARY LAYER WARMS AND
EVENTUALLY SURFACE BASED STORMS/MCS EVOLVES...REFERENCE WW 616.
AS SKIES CLEAR AND TEMPERATURES WARM...OTHER STORMS ARE LIKELY TO
DEVELOP ALONG THE COLD FRONT IN WI THIS AFTERNOON AS STRONG LARGE
SCALE LIFTING ASSOCIATED WITH UPPER LOW MOVES INTO THE REGION.
STRONGLY-VEERING WIND PROFILES AND STRENGTHENING MID/UPPER LEVEL
WINDS WOULD SUPPORT SUPERCELLS WITH INITIAL STORMS. COMBINATION OF
MODERATE INSTABILITY AND 40-50 KT DEEP LAYER SHEAR WILL BE MOST
FAVORABLE FOR STORMS WITH HAIL AND DAMAGING WINDS. AN ISOLATED
TORNADO OR TWO IS POSSIBLE...GIVEN THE FORECAST OF STRONG LOW LEVEL
SHEAR/CURVED HODOGRAPHS...BUT EXPECT STRONG FRONTAL CONVERGENCE WILL
RESULT IN STORMS EVOLVING INTO A LINEAR SYSTEM... WITH DAMAGING
WINDS THEN BECOMING THE PRIMARY THREAT. THOUGH INSTABILITY WILL BE
WEAKER...THE EXPECTATION OF AN ORGANIZED MCS AND STRONG FORCING MAY
BE ENOUGH FOR THE SEVERE THREAT TO EXTEND INTO WRN LOWER MI
OVERNIGHT.
...ERN NC/SC...
QUASI-STATIONARY FRONT WAS LOCATED IN ERN NC/SC. GIVEN JET STREAK IN
REGION AND UPPER LEVEL DIFFLUENCE...STORMS ARE LIKELY TO DEVELOP
ALONG AND EAST OF BOUNDARY. MOIST BOUNDARY LAYER AND COLD
TEMPERATURES ALOFT...-10C AT 500 MB...WILL SUPPORT STRONG
INSTABILITY. THE SHEAR/INSTABILITY WILL BE FAVORABLE FOR SEVERE
STORMS DURING THE AFTERNOON/EARLY EVENING HOURS.
...NRN GREAT DIVIDE...
TSTMS HAVE PERSISTED INTO THE MORNING HOURS WITHIN WARM CONVEYOR
BELT EAST OF UPPER LOW. AS MODERATE INSTABILITY DEVELOPS WITH
DIURNAL HEATING...THE POSSIBILITY OF A FEW SUSTAINED
STORMS/SUPERCELLS WILL EXIST OVER WRN MT AND NRN ID INTO THE EVENING
HOURS.
...CENTRL PLAINS...
COMBINATION OF APPROACHING COLD FRONT AND HEATING OF MOIST BOUNDARY
LAYER MAY ALLOW ISOLATED THUNDERSTORMS TO FORM THIS AFTN
...ESPECIALLY AS ELY UPSLOPE WINDS OCCUR BEHIND FRONT OVER WRN
NEB/ERN WY. HOWEVER...MODELS SUGGEST CAPPING INVERSION WILL PREVAIL
OVER THE REGION AND SINCE THE MAIN FORCING WILL BE LOCATED ACROSS
THE MID/UPPER MS VALLEY...ONLY LOW PROBS ARE FORECAST ATTM.
...NY/PA SEWD INTO DELMARVA...
AS SHORTWAVE TROUGH PIVOTS NEWD ACROSS ENE NY AND PA...500 MB
TEMPERATURES AROUND -14C AND SURFACE TEMPERATURES IN THE 70S WILL
YIELD MLCAPES FROM 1000-2000 J/KG. ALTHOUGH DEEP LAYER SHEAR IS NOT
EXPECTED TO BE PARTICULARLY STRONG...AT 20-30 KT...-14C AT 500 MB/
AND A BELT OF MODERATE MID LEVEL WINDS MAY SUPPORT STORMS WITH 3/4
TO 1 1/4 INCH HAIL DURING THE AFTERNOON HOURS.
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