Friday, October 30, 2009

Risk of Severe Weather in West Alabama

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1120 AM CDT FRI OCT 30 2009

VALID 301630Z - 311200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE MS DELTA
NWD TO WRN AL AND A SMALL PORTION OF TN...

...SYNOPSIS...
SIGNIFICANT LARGE SCALE TROUGH ACROSS THE CENTER OF THE NATION WILL
BEGIN TO DE-AMPLIFY AND SPREAD ENEWD ACROSS THE MS VALLEY AND
MIDWEST THROUGH TONIGHT. THIS SYSTEM IS CHARACTERIZED BY AN
UNUSUALLY STRONG MID LEVEL JET WITH CORE WIND SPEEDS NEARING 150KT
ON THE ERN FLANK OF THE TROUGH. AS THE TROUGH AND JET TRANSITION
ENEWD ACROSS THE MIDWEST TODAY...DEEP-LAYER CYCLONE WILL TRACK FROM
MN INTO ONTARIO...AND TRAILING COLD FRONT WILL SWEEP EWD ACROSS THE
OH VALLEY. SRN SEGMENT OF THE COLD FRONT....FROM TN TO MS DELTA
REGION ATTM...WILL MAKE SLOWER PROGRESS EWD INTO VERY MOIST AIRMASS
FROM THE NRN GULF COAST ACROSS THE TN VALLEY. THIS PORTION OF THE
FRONT WILL EVENTUALLY UNDERGO FRONTOLYSIS THROUGH EARLY SATURDAY.
HOWEVER...UNTIL THEN...LIFT ACROSS FRONTAL BOUNDARY WILL BE
MAINTAINED BY MODEST LARGE SCALE ASCENT WITHIN/BENEATH RIGHT
ENTRANCE REGION OF AFOREMENTIONED MID/UPPER JET.

...MS ACROSS THE TN VALLEY...
VISIBLE SATELLITE IMAGERY SHOWS LARGE BREAKS IN CLOUD COVER ACROSS
PRE-FRONTAL WARM SECTOR FROM SERN LA AND ERN HALF OF MS NWD TO PARTS
OF TN/KY. DESPITE MARGINAL MID LEVEL LAPSE RATES DEPICTED IN MORNING
SOUNDINGS ACROSS THESE AREAS...BOUNDARY LAYER HEATING WITHIN THETA-E
RIDGE AXIS WILL CONTRIBUTE TO A MODEST INCREASE IN CAPE/DECREASE IN
CINH AHEAD OF THE APPROACHING COLD FRONT THROUGH THE AFTERNOON. SREF
GUIDANCE SHOWS AT LEAST 70 PCT PROBABILITY OF SBCAPE VALUES REACHING
500 J/KG OVER MUCH OF ERN MS AND WRN AL BY MID TO LATE AFTERNOON. IT
SEEMS REASONABLE TO EXPECT CONVECTIVE INTENSITY TO RESPOND TO THIS
INCREASE IN DIURNAL DESTABILIZATION WITH AN INCREASING CHANCE FOR
PERSISTENT/ROBUST STORM UPDRAFTS.

WHILE STRONGER MASS INFLOW HAS ALREADY SHIFTED NORTH OF MOST
UNSTABLE WARM SECTOR...IT APPEARS THAT ANY INCREASE IN STORM VIGOR
WILL STILL OCCUR IN A MORE THAN SUFFICIENTLY SHEARED KINEMATIC
REGIME TO SUPPORT BOTH FAST-MOVING STORMS...AND UPDRAFT ROTATION.
THUS...EXPECT A GRADUAL INCREASE IN TORNADO/WIND EVENT PROBABILITIES
THROUGH AFTERNOON/EARLY EVENING. TEMPORAL AND AREAL EXTENT OF THIS
POTENTIAL SHOULD REMAIN CONFINED ENOUGH TO JUSTIFY MAINTAINING
SEVERE PROBABILITIES AS FORECAST IN EARLIER OUTLOOKS.

FARTHER NORTH...ACROSS PARTS OF TN/KY...MASS FIELDS APPEAR A BIT
MORE FAVORABLE FOR SUSTAINING CONVECTION DESPITE WEAKER
DESTABILIZATION ACROSS NARROWING WARM SECTOR. IT IS POSSIBLE THAT
HEATING/MIXING AHEAD OF NARROW COLD-FRONTAL RAINBAND MAY CONTRIBUTE
TO ISOLATED STRONGER WIND GUSTS REACHING THE SURFACE WITH PASSAGE OF
LOW-TOPPED CONVECTIVE LINE.

..CARBIN/HURLBUT.. 10/30/2009
Sent from my Verizon Wireless BlackBerry

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