SWODY1
SPC AC 251247
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0747 AM CDT MON MAY 25 2009
VALID 251300Z - 261200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A COMPLEX...BUT RELATIVELY WEAK...FLOW REGIME PERSISTS OVER THE
CONUS WITH THE PRIMARY POLAR JET OVER SRN CANADA...AND A WEAKER
SUBTROPICAL JET FROM NRN MEXICO ACROSS THE LOWER RIO GRANDE VALLEY
INTO THE GULF OF MEXICO. SEVERAL SLOW-MOVING PERTURBATIONS
ENCOMPASS THE CYCLONIC SHEAR/N SIDE OF THE SUBTROPICAL JET...WITH A
NEW TROUGH MOVING ESEWD OVER THE LOWER CO RIVER VALLEY...AND THE
PERSISTENT PSEUDO-WARM CORE LOW NOW DRIFTING NWD FROM AR TOWARD MO.
FARTHER N...A SEPARATE SHORTWAVE TROUGH EMANATING FROM THE
CENTRAL/NRN INTERMOUNTAIN REGION IS NOW PHASING WITH A WEAK NRN
STREAM TROUGH OVER THE DAKOTAS. AT THE SURFACE...THE PRIMARY
SYNOPTIC FEATURES OF INTEREST ARE A COLD FRONT WHICH WILL MOVE
SLOWLY SEWD ACROSS THE NRN/CENTRAL PLAINS IN ASSOCIATION WITH THE
PHASING MID LEVEL WAVES...A WEAK LEE TROUGH OVER THE SRN HIGH
PLAINS...AND THE SLOW NWD RETREAT OF A WARM FRONT ACROSS IL/INDIANA
IN CONJUNCTION WITH THE APPROACHING CYCLONE MOVING INTO MO.
...MID MS VALLEY TODAY...
THE PSEUDO-WARM CORE LOW OVER AR WILL DRIFT NWD OVER MO THROUGH THIS
EVENING...AND DEEP CONVECTION WILL CONTINUE TO BE FOCUSED IN ONE OR
MORE CONVERGENCE BANDS TO THE E/NE OF THE CYCLONE CENTER. LOW-LEVEL
SHEAR WILL ALSO BE STRONGEST ALONG THESE BANDS IN CONJUNCTION WITH A
NARROW BELT OF 30-40 KT LOW-LEVEL SLY/SELY FLOW. GIVEN THE
CO-LOCATION OF WEAK INSTABILITY...VERY MOIST PROFILES...AND 0-1 KM
SRH OF 150-200 M2/S2 WILL SUPPORT A FEW ROTATING STORMS CAPABLE OF
PRODUCING A BRIEF TORNADO OR TWO THIS AFTERNOON INTO EARLY EVENING.
...TX PANHANDLE INTO W CENTRAL TX THIS AFTERNOON/TONIGHT...
WEAK LEE TROUGHING IS EXPECTED TODAY ACROSS W TX BENEATH 20-35 KT
WLY FLOW ALOFT. LARGE SCALE FORCING FOR ASCENT WILL REMAIN RATHER
WEAK OVER W TX IN ASSOCIATION WITH SUBTLE SPEED MAXIMA PROGRESSING
THROUGH SHORTWAVE RIDGING BETWEEN THE UPSTREAM TROUGH IN THE
SUBTROPICAL JET OVER THE LOWER CO RIVER VALLEY...AND THE DOWNSTREAM
TROUGH OVER THE MS VALLEY. STILL...SURFACE HEATING/MIXING AND
LOW-LEVEL CONVERGENCE ALONG THE LEE TROUGH SHOULD ALLOW THE
DEVELOPMENT OF ISOLATED THUNDERSTORMS THIS AFTERNOON. THE STORM
ENVIRONMENT WILL BE CHARACTERIZED BY MLCAPE VALUES OF 1000-1500 J/KG
AND TEMPERATURE-DEW POINT SPREADS GENERALLY AOA 25 F.
MEANWHILE...LOW-MID LEVEL VERTICAL SHEAR WILL BE MARGINALLY
FAVORABLE FOR SUPERCELL STRUCTURES...THOUGH HIGH-LEVEL FLOW WILL BE
RELATIVELY WEAK AND LONG-LIVED SUPERCELLS ARE UNLIKELY. THE PRIMARY
SEVERE THREATS WILL BE ISOLATED LARGE HAIL/DAMAGING OUTFLOW WINDS
GIVEN THE MODEST VERTICAL SHEAR AND LOW-LEVEL MOISTURE...AND THESE
FACTORS ALONG WITH LIMITED STORM COVERAGE WILL LIMIT THE OVERALL
SEVERE THREAT DURING THE AFTERNOON. OVERNIGHT...A FEW ELEVATED
STORMS WITH A MARGINAL HAIL THREAT SHOULD DEVELOP/PERSIST ACROSS NW
TX/WRN OK IN CONJUNCTION WITH WAA WITH A DEVELOPING 30 KT LLJ.
...S TX THIS AFTERNOON/EVENING...
RICHER BOUNDARY LAYER MOISTURE /LOW-MID 70S DEW POINTS/ IS RETURNING
TO DEEP S TX THIS MORNING...AND STRONG SURFACE HEATING IS EXPECTED
TODAY GIVEN THE LACK OF CLOUD COVER OBSERVED THIS MORNING. MLCAPE
VALUES WILL INCREASE TO THE 2000-3000 J/KG RANGE WITH ONLY WEAK
CONVECTIVE INHIBITION. STILL...THUNDERSTORM COVERAGE IS IN QUESTION
SINCE THERE ARE NO OBVIOUS EMBEDDED SPEED MAXIMA IMMEDIATELY
UPSTREAM FROM S TX. STORM DEVELOPMENT MAY HAVE TO RELY ON THE SEA
BREEZE...OR MOVEMENT OF STORMS INTO S TX FROM CENTRAL TX DURING THE
EVENING. IF STORMS FORM...DEEP LAYER VERTICAL SHEAR WILL BE
SUFFICIENT FOR SUPERCELLS CAPABLE OF PRODUCING LARGE HAIL AND
DAMAGING WINDS...AND POTENTIALLY AN ISOLATED TORNADO WHERE STORM/SEA
BREEZE INTERACTIONS OCCUR.
...NRN PLAINS TODAY...
A SURFACE CYCLONE IN NW SD THIS MORNING WILL DEVELOP ENEWD TO NW MN
TONIGHT AS A TRAILING COLD FRONT PROGRESSES SEWD ACROSS SD AND THE
CENTRAL HIGH PLAINS. A NARROW CORRIDOR OF MOISTURE RETURN /BOUNDARY
LAYER DEW POINTS IN THE UPPER 50S TO LOWER 60S/ WILL ACCOMPANY THE
COLD FRONT AND SURFACE CYCLONE...BUT MID LEVEL LAPSE RATES WILL BE
MARGINAL OVER THIS AREA. THE NET RESULT WILL A SMALL WARM SECTOR
WITH AFTERNOON MLCAPE VALUES NEAR 1000 J/KG. OTHERWISE...PHASING
BETWEEN VERTICAL SHEAR AND INSTABILITY WILL BE POOR WITH THE
STRONGER WIND PROFILES LOCATED N OF THE SURFACE WARM SECTOR IN THE
ZONE OF WAA. THE COMBINATION OF INSTABILITY AND VERTICAL SHEAR ONLY
APPEARS SUPPORTIVE OF MULTICELL CLUSTERS...AND PERHAPS
MARGINAL/SHORT-LIVED SUPERCELL STRUCTURES...WITH AN ATTENDANT THREAT
FOR MARGINALLY SEVERE HAIL AND ISOLATED DAMAGING WINDS.
...FL PENINSULA THIS AFTERNOON...
12Z SOUNDINGS ACROSS FL SHOW THE POTENTIAL FOR AFTERNOON MLCAPE
VALUES OF 2000-3000 J/KG...WITH WEAK VERTICAL SHEAR AND SEASONALLY
COOL MID LEVEL TEMPERATURES /AROUND -10 C AT 500 MB/. A FEW WET
MICROBURSTS AND MARGINALLY SEVERE HAIL COULD OCCUR WITH AFTERNOON
STORMS ALONG THE SEA BREEZE BOUNDARIES AND WITH STRONGER STORMS
RESULTING FROM BOUNDARY/OUTFLOW INTERACTIONS.
..THOMPSON/SMITH.. 05/25/2009
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
To unsubscribe from WX-STORM send e-mail to LISTSERV@LISTSERV.ILLINOIS.EDU with
"unsub wx-storm" in the body of your message. For more information write cnovy@cox.net.
No comments:
Post a Comment