SPC AC 141716
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1216 PM CDT THU JUN 14 2007
VALID 151200Z - 161200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF TX...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE NRN HIGH
PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS OVER THE SAVANNAH RIVER
VALLEY...
...SYNOPSIS...
LARGE-SCALE BLOCKING PATTERN WILL PERSIST THROUGH THE DAY TWO PERIOD
FROM THE ERN ATLANTIC SWWD INTO THE SWRN STATES WITH PRIMARY BELT OF
WESTERLIES CONFINED TO THE PACIFIC NW THROUGH UPPER MS VALLEY. IN
THE LOW-LEVELS...THE PRIMARY FEATURES FOCUSING THE MOST ORGANIZED
STORM THREAT WILL LIKELY BE: 1) SURFACE LOW INITIALLY OVER
NWRN/N-CNTRL TX WHICH WILL DRIFT SLOWLY SWD/SWWD...2) WRN EXTENSION
OF BAROCLINIC ZONE ATTENDANT TO POLAR WESTERLIES WHICH WILL BE
SITUATED ACROSS SRN MT/NRN WY INTO WRN SD...AND 3) LOW-LEVEL
CONFLUENCE ZONE FORECAST INVOF THE SAVANNAH RIVER VALLEY FRIDAY
AFTERNOON.
...TX...
PERSISTENT SLY/SELY LOW-LEVEL FLOW AHEAD OF SURFACE LOW WILL
MAINTAIN MOIST BOUNDARY LAYER CONDITIONS WITH DEWPOINTS IN THE 60S
TO LOWER 70S. THIS MOISTURE COUPLED WITH POCKET OF COOL MID-LEVEL
TEMPERATURES /AROUND -10 C AT 500 MB/ WILL RESULT IN THE DEVELOPMENT
OF MODERATE TO STRONG INSTABILITY BY AFTERNOON OVER W-CNTRL INTO
CNTRL TX WITH MLCAPES OF 1500-3000 J/KG. FORECAST SOUNDINGS SUGGEST
THAT CAP WILL NOT BE PARTICULARLY STRONG WITH TSTMS SLOWLY
INCREASING IN COVERAGE AND INTENSITY THROUGH THE AFTERNOON HOURS.
IT APPEARS THAT THE GREATEST SEVERE WEATHER THREAT WILL OCCUR OVER
W-CNTRL TX WHERE STRONGER DEEP LAYER VERTICAL SHEAR WILL BE
COLOCATED WITH THE ANTICIPATED STRONGEST INSTABILITY.
ORGANIZED...MULTICELLULAR CLUSTERS WILL LIKELY BE
PREDOMINANT...HOWEVER A COUPLE SUPERCELLS WILL BE POSSIBLE WITH THE
PRIMARY SEVERE THREATS BEING LARGE HAIL AND DAMAGING WINDS.
...PORTIONS NRN HIGH PLAINS...
LOW-LEVEL BAROCLINIC ZONE IS FORECAST TO BECOME BETTER DEFINED WITH
TIME FRIDAY ALONG THE WY/MT BORDER WITH ELY LOW-LEVEL FLOW ADVECTING
AN INCREASINGLY MOIST BOUNDARY LAYER WWD ALONG THIS BOUNDARY. THIS
PROCESS WILL OCCUR BENEATH MODESTLY STEEP MID-LEVEL LAPSE
RATES...EFFECTIVELY CONTRIBUTING TO SBCAPES OF AROUND 1000 J/KG BY
LATE AFTERNOON OR EARLY EVENING. MID-LEVEL FLOW REGIME WILL REMAIN
LARGELY QUASI-ZONAL ACROSS REGION WITH 500 MB WINDS OF 40-50 KT
FORECAST ALONG LOW-LEVEL FRONTAL ZONE.
LARGE-SCALE FORCING FOR ASCENT IS EXPECTED TO REMAIN NEGLIGIBLE AND
IT APPEARS THAT TERRAIN AND LOW-LEVEL FRONTAL FORCING WILL BE
PRIMARY MECHANISMS INITIATING ISOLATED STORM DEVELOPMENT BY LATE
AFTERNOON/EARLY EVENING. FORECAST SOUNDINGS INDICATE THAT VERTICAL
SHEAR WILL BE QUITE SUPPORTIVE OF SUPERCELLS GIVEN EFFECTIVE BULK
SHEAR OF 50-60 KT. A TORNADO OR TWO IS POSSIBLE...THOUGH LARGE HAIL
AND DAMAGING WINDS WILL BE THE MAIN THREATS WITH THE MOST INTENSE
STORMS.
...SAVANNAH RIVER VALLEY...
AS MENTIONED ABOVE...LATEST MODEL GUIDANCE SUGGESTS THAT A LOW-LEVEL
CONFLUENCE ZONE WILL BECOME ESTABLISHED FRIDAY WITH MORE MOIST AND
UNSTABLE BOUNDARY LAYER CONFINED TO ALONG AND S OF THIS FEATURE.
LAPSE RATES WILL NOT BE PARTICULARLY STEEP...HOWEVER DEWPOINTS IN
THE 60S WILL LARGELY CONTRIBUTE TO MLCAPES OF 1000-1500 J/KG. THIS
LOW-LEVEL BOUNDARY COUPLED WITH APPROACH OF MID-LEVEL SHORT WAVE
TROUGH TRANSLATING SWD THROUGH THE CNTRL APPALACHIANS WILL
CONTRIBUTE TO AN INCREASE IN STORM COVERAGE AND INTENSITY THROUGH
THE AFTERNOON HOURS. PRIMARY CONVECTIVE MODE SHOULD BE MULTICELL
CLUSTERS WITH THE MAIN THREAT BEING DAMAGING WINDS. SOME HAIL WILL
BE POSSIBLE WITH THE STRONGEST UPDRAFTS.
...UPPER MS VALLEY...
WHILE DIURNAL...PRE-FRONTAL CONVECTIVE COVERAGE IS EXPECTED TO BE
GREATER ACROSS THIS REGION THAN NRN HIGH PLAINS SLIGHT RISK
AREA...DEEP LAYER VERTICAL SHEAR IS FORECAST TO BE CONSIDERABLY
WEAKER. A MODERATELY UNSTABLE AIR MASS IS EXPECTED TO DEVELOP AHEAD
OF FRONT OVER THE UPPER MS VALLEY SWWD INTO ERN/CNTRL SD...AND
POTENTIAL WILL EXIST FOR A FEW MARGINAL SEVERE STORMS FRIDAY
AFTERNOON AND EVENING. HOWEVER...COMBINATION OF DECREASING
LARGE-SCALE FORCING FOR ASCENT WITH PASSAGE OF SHORT WAVE TROUGH
INTO CANADA...ALONG WITH THE MARGINAL VERTICAL SHEAR SHOULD PRECLUDE
A MORE SUBSTANTIAL SEVERE THREAT.
...CNTRL/SRN FL PENINSULA...
RICHER BOUNDARY LAYER MOISTURE /DEWPOINTS IN THE 60S TO LOWER 70S/
IS EXPECTED TO REMAIN CONFINED TO SRN TWO-THIRDS OF PENINSULA
FRIDAY. LAPSE RATES WILL REMAIN RELATIVELY WEAK...WITH THE
LOW-LEVEL MOISTURE LARGELY CONTRIBUTING TO MLCAPES OF AROUND 1000
J/KG. STORMS SHOULD BECOME INCREASINGLY WIDESPREAD BY
AFTERNOON...PARTICULARLY ALONG ERN PENINSULA SEA BREEZE BOUNDARY.
MODEST DEEP LAYER VERTICAL SHEAR OF AROUND 30 KT MAY SUPPORT A FEW
ORGANIZED STORMS WITH A THREAT OF LOCALLY DAMAGING DOWNBURSTS. THIS
THREAT SHOULD TEND TO DIMINISH BY MID/LATE EVENING AS BOUNDARY LAYER
COOLS AND STABILIZES.
..MEAD.. 06/14/2007
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NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0800Z
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