SPC AC 270559
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1259 AM CDT WED MAY 27 2009
VALID 281200Z - 291200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM SERN KY SSWWD INTO SWRN
AL/SERN MS...
...SYNOPSIS...
MID-LEVEL TROUGH WILL SHIFT FROM THE CENTRAL INTO THE ERN U.S. THIS
PERIOD...AHEAD OF WHICH A COLD FRONT WILL CONTINUE TO MAKE SLOW EWD
PROGRESS. THE FRONT SHOULD PROGRESS ACROSS THE OH/TN VALLEYS
THROUGH THE DAY...AND THEN SHIFT/REDEVELOP E OF THE APPALACHIANS
THROUGH THE SECOND HALF OF THE PERIOD.
...ERN KY/ERN TN SWWD INTO AL...
SHOWERS AND STORMS ONGOING AT THE START OF THE PERIOD SHOULD
INCREASE INVOF THE SLOWLY-ADVANCING COLD FRONT DURING THE
AFTERNOON...1000 TO 1500 J/KG MIXED-LAYER CAPE DEVELOPS. THOUGH
LOW-LEVEL FLOW SHOULD REMAIN WLY FROM JUST OFF THE SURFACE THROUGH
MID LEVELS...H5 FLOW IN THE 25 TO 35 KT RANGE SHOULD ALLOW MULTICELL
ORGANIZATION OR LINEAR-TYPE STRUCTURES ON THE SMALL SCALE.
THUS...THREATS FOR WIND AND HAIL APPEAR SUFFICIENT TO INTRODUCE
SLIGHT RISK FORECAST THIS PERIOD. THREAT SHOULD SHIFT EWD WITH
TIME...BUT DIMINISH INTO THE EVENING WITH THE LOSS OF DIURNAL
HEATING.
...LOWER GREAT LAKES/UPPER OH VALLEY REGION...
NAM CONTINUES TO SHOW LITTLE DESTABILIZATION AHEAD OF THE FRONT
ACROSS THE LOWER LAKES/UPPER OH VALLEY REGION...THOUGH WIDESPREAD
ACTIVATION OF THE CONVECTIVE SCHEME APPEARS TO BE THE CULPRIT. BOTH
THE GFS AND NAMKF INDICATE AROUND 1000 J/KG CAPE DURING THE
AFTERNOON IN MOST AREAS...WHICH SEEMS REASONABLE AWAY FROM ONGOING
CONVECTION.
WHILE DEEP-LAYER WIND FIELD WILL BE ROUGHLY UNIDIRECTIONAL WITH
HEIGHT...MODERATE MAGNITUDE IN THE DEEP-LAYER FLOW SHOULD SUPPORT
SOME ORGANIZATION...AS STORMS INCREASE AHEAD OF THE FRONT THROUGH
THE AFTERNOON. GIVEN THE POTENTIAL FOR WIND -- AND POSSIBLY
MARGINAL HAIL -- WITH STRONGER STORMS...WILL INTRODUCE 5%
PROBABILITY ACROSS THIS REGION. SLIGHT RISK MAY BE REQUIRED IN
LATER FORECASTS IF CONFIDENCE INCREASES THAT SUFFICIENT INSTABILITY
WILL EVOLVE DURING THE AFTERNOON.
...FAR W TX ACROSS THE RIO GRANDE VALLEY INTO DEEP S TX...
ELY LOW-LEVEL FLOW ACROSS MUCH OF TX BENEATH WEAK TO MODERATE
MID-LEVEL WLYS IS FORECAST ACROSS SRN AND WRN TX...PROVIDING SHEAR
PROFILES SUFFICIENT FOR WEAK STORM ORGANIZATION. WEAKEST
SHEAR/INSTABILITY IS FORECAST ACROSS FAR W TX AND THE TRANSPECOS
REGION...BUT WITH WEAK UPSLOPE FLOW LIKELY TO AID IN AFTERNOON
INITIATION AND WITH VEERING WINDS WITH HEIGHT...LOW HAIL/WIND
PROBABILITY APPEARS TO EXIST.
FARTHER ESEWD ALONG THE RIO GRANDE VALLEY...GREATER DESTABILIZATION
IS EXPECTED...ALONG WITH SOMEWHAT STRONGER MID-LEVEL FLOW.
HOWEVER...WITH FLOW SWITCHING FROM ELY TO WLY WITH HEIGHT NEAR 700
MB -- OR EVEN BACKING SLIGHTLY WITH HEIGHT IN THE 800 TO 700 MB
LAYER...SHEAR SHOULD REMAIN ONLY MODESTLY-FAVORABLE FOR
ORGANIZATION. THUS -- WILL MAINTAIN ONLY 5% SEVERE PROBABILITY HERE
AS WELL.
..GOSS.. 05/27/2009
CLICK TO GET WUUS02 PTSDY2 PRODUCT
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
|
