SWODY1
SPC AC 172000
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT FRI JUL 17 2009
VALID 172000Z - 181200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN GA THROUGH A PORTION
OF THE CAROLINAS...MID ATLANTIC AND NERN STATES...
...THERE IS A SLGT RISK OF SVR TSTMS OVER A PORTION OF THE CNTRL AND
SRN HIGH PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS OVER A PORTION OF SRN AZ AND
SWRN NM...
...CNTRL AND SRN HIGH PLAINS...
FORECAST APPEARS ON TRACK IN THIS REGION. STORM CLUSTER INCLUDING A
SUPERCELL OR TWO REMAIN IN VICINITY OF CONVECTIVELY ENHANCED
BAROCLINIC ZONE SPREADING INTO NWRN KS. THE ATMOSPHERE HAS BECOME
MODERATELY UNSTABLE FARTHER W OVER THE HIGH PLAINS AND NEW STORMS
DEVELOPING OVER THE HIGHER TERRAIN WILL SPREAD SEWD THROUGH THE HIGH
PLAINS THIS AFTERNOON AND EVENING. VERTICAL SHEAR AND THERMODYNAMIC
ENVIRONMENT WILL SUPPORT SUPERCELLS WITH VERY LARGE HAIL. ISOLATED
TORNADOES WILL ALSO BE POSSIBLE. SOME STORMS MAY EVENTUALLY EVOLVE
INTO CLUSTERS WITH A THREAT OF ISOLATED DAMAGING WIND.
...ERN VA THROUGH ERN NC...
FORECAST STILL APPEARS ON TRACK. PRIMARY SEVERE THREAT WILL REMAIN
WITH STORMS DEVELOPING OVER ERN NC AND SERN VA ALONG AND EAST OF
PRE-FRONTAL CONVERGENCE ZONE. SEE PREVIOUS DISCUSSION FOR FURTHER
DETAILS.
...OH VALLEY...
COLD FRONT EXTENDS FROM NERN OH SWWD THROUGH MIDDLE TN INTO THE
LOWER MS VALLEY. PARTIAL CLEARING IN WAKE OF CLOUDS AND CONVECTIVE
PRECIPITATION ASSOCIATED WITH VORT MAX MOVING THROUGH CNTRL PA HAS
RESULTED IN MODEST DESTABILIZATION OVER THE OH VALLEY WITH 500-1000
J/KG MLCAPE. STORMS HAVE RECENTLY INCREASED IN COVERAGE AND
INTENSITY ALONG AND AHEAD OF THE FRONT PRIMARILY ACROSS ERN OH WHERE
BELT OF 30-40 KT UNIDIRECTIONAL WLY BULK SHEAR EXISTS IN ASSOCIATION
WITH UPPER SPEED MAX ROTATING THROUGH BASE OF UPPER TROUGH. SOME OF
THIS ACTIVITY WILL REMAIN CAPABLE OF PRODUCING ISOLATED LARGE HAIL
AND DOWNBURSTS WINDS AS IT MOVES THROUGH INSTABILITY AXIS NEXT FEW
HOURS.
...NERN STATES...
WIDESPREAD CLOUDS AND CONVECTIVE PRECIPITATION DOWNSTREAM FROM VORT
MAX MOVING THROUGH CNTRL PA HAS LIMITED DESTABILIZATION POTENTIAL
OVER A PORTION OF THIS AREA. HOWEVER...SUFFICIENT WARMING OF THE
BOUNDARY LAYER HAS OCCURRED ON THE ERN FRINGE OF THE EXPANSIVE CLOUD
DECK FROM SERN NY THROUGH PARTS OF NEW ENGLAND WHERE AN AXIS OF
500-1000 J/KG MLCAPE HAS DEVELOPED. BULK SHEAR IN THIS REGION IS
ALREADY SUFFICIENT FOR ORGANIZED STORM STRUCTURES INCLUDING
SUPERCELLS AND BOWING SEGMENTS AND SOME FURTHER INCREASE IS LIKELY
TOWARD EVENING AS THE LOW LEVEL WINDS INCREASE IN RESPONSE TO
FORCING ASSOCIATED WITH APPROACHING SPEED MAX. ISOLATED DAMAGING
WIND AND LARGE HAIL APPEAR TO BE THE MAIN THREATS...THOUGH AN
ISOLATED TORNADO OR TWO CANNOT BE RULED OUT.
...SERN AZ AND SWRN NM...
RECENT SURFACE OBSERVATIONS SHOW DEWPOINTS IN THE LOW 50S OVER SRN
AZ AND SWRN NM...BUT MAY MIX DOWN INTO THE UPPER 40S TO AROUND 50 AS
DIABATIC HEATING CONTINUES. CONVECTION CURRENTLY DEVELOPING OVER THE
RIM WILL LIKELY SPREAD SWWD INTO THE VALLEYS UNDER THE INFLUENCE OF
NELY MID LEVEL FLOW ALONG SRN PERIPHERY OF UPPER RIDGE. INVERTED-V
BOUNDARY LAYERS WILL SUPPORT A THREAT OF ISOLATED DAMAGING WIND
THROUGH MID EVENING.
...ERN GA THROUGH SC...
WEAK CAP AND A DESTABILIZING BOUNDARY LAYER WILL CONTINUE TO PROMOTE
STORMS DEVELOPING IN PRE-FRONTAL WARM SECTOR FROM GA THROUGH THE
CAROLINAS. STORM COVERAGE COULD BE POTENTIALLY AUGMENTED AHEAD OF
SMALL MCV OVER NRN GA. BULK SHEAR IS RATHER MODEST WITH 25-35 KT WLY
DEEP LAYER FLOW SUPPORTIVE OF MULTICELLS. THE THREAT OF ISOLATED
DAMAGING WIND WILL EXIST WITH EWD ADVANCING MULTICELL CLUSTERS AND
LINE SEGMENTS THROUGH EARLY EVENING.
..DIAL.. 07/17/2009
.PREV DISCUSSION... /ISSUED 1121 AM CDT FRI JUL 17 2009/
...SRN APPALACHIANS NEWD INTO SWRN NEW ENGLAND...
A BROAD UPPER TROUGH WILL CONTINUE TO DIG SWD FROM THE GREAT LAKES
SWD INTO THE OH/MS VALLEYS...AS A MID LEVEL SPEED MAX SHIFTS FROM
THE MID MS VALLEY SEWD INTO THE LOWER OH VALLEY. THIS WILL PUSH A
COLD FRONT EWD THROUGH THE APPALACHIANS THIS AFTERNOON AND INTO THE
ATLANTIC COASTAL STATES TONIGHT. MOST SIGNIFICANT FEATURE FOR THE
SEVERE CONVECTION IS AN INTENSE SHORTWAVE TROUGH AND ACCOMPANYING
JET MAX THAT MOVING EWD THROUGH ERN OH/WV AT MID MORNING. AS THIS
SYSTEM MOVES ENEWD...FORCING ASSOCIATED WITH THIS WAVE...ALONG WITH
MODERATE INSTABILITY AND STRENGTHENING ENVIRONMENTAL WINDS/DEEP
LAYER SHEAR WILL BE FAVORABLE FOR SEVERAL CLUSTERS/BANDS OF SEVERE
STORMS WITH WIND AND HAIL...REFERENCE WW #592.
OTHER STRONG/SEVERE STORMS ARE EXPECTED FROM ERN PA NEWD INTO SWRN
CT WHERE FORCING WILL INCREASE LATER IN THE DAY WITH MLCAPES NEAR
1000 J/KG. A WEAK WAVE MOVING THROUGH AL MAY AID IN STRONGER SEVERE
STORMS FROM GA EWD INTO THE CAROLINAS THIS LATER AFTERNOON/EVENING.
...CENTRAL/SRN HIGH PLAINS...
MORNING WATER VAPOR IMAGERY SHOWS A SEWD MOVING SHORTWAVE TROUGH IN
FAR NW KS AND ANOTHER IN MT. THESE FEATURES WILL TRACK SEWD ACROSS
THE SRN/CENTRAL HIGH PLAINS AND AID IN CONVECTIVE DEVELOPMENT
THROUGHOUT THE FORECAST PERIOD. MOSTLY ELEVATED STORMS ARE LIKELY TO
CONTINUE INTO THE AFTERNOON ACROSS WRN NEB/KS IN ZONE OF LOW LEVEL
WARM ADVECTION/CONVERGENCE. STEEP LAPSE RATES AND DEEP LAYER SHEAR
AROUND 50 KT...DUE TO STRENGTHENING AND STRONGLY VEERING
WINDS...WILL SUPPORT A THREAT FOR PRIMARILY SEVERE HAIL. THIS
AFTERNOON....HEATING AND FORCING WITH UPPER WAVE SHOULD AID IN
SURFACE BASED STORMS DEVELOPING. ALSO...LOW CLOUDS IN ERN CO ARE
EXPECTED TO BURN OFF AND CONVERGENCE IN ERN CO SHOULD AID IN SSEWD
MOVING SUPERCELLS.
THE VERY STRONG SHEAR AND MODERATE INSTABILITY WILL BE FAVORABLE FOR
INTENSE SUPERCELLS. WHILE THE INITIAL STORMS ARE MOST LIKELY TO
PRODUCE SIGNIFICANT HAIL...THE STRENGTH OF THE SHEAR AND INSTABILITY
MAY SUPPORT A ISOLATED TORNADOES...ESPECIALLY IN ERN CO/WRN KS.
THEREAFTER...THE STORM OUTFLOWS ARE EXPECTED TO CONSOLIDATE INTO ONE
OR TWO LINEAR MCS/S. AT THAT TIME...THE THREAT WOULD EVOLVE TO MORE
OF A WIND THREAT AS THE COMPLEXES HEAD SSEWD ALONG N-S ORIENTED
INSTABILITY AXIS INTO THE TX /OK PANHANDLE.
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