SWODY2
SPC AC 210558
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1258 AM CDT THU MAY 21 2009
VALID 221200Z - 231200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
LITTLE FLUCTUATION OF THE LARGE SCALE PATTERN IS EXPECTED INTO
FRIDAY...WITH THE SEVERE POTENTIAL REMAINING RATHER LIMITED/ISOLATED
ACROSS MUCH OF THE LOWER 48. SCATTERED TSTM POTENTIAL WILL INCREASE
ACROSS THE GULF COAST REGION INTO THE LOWER/MIDDLE MISSISSIPPI
VALLEY AMIDST A GRADUAL MOISTURE INFLUX VIA A GULF OF MEXICO
LOW...WITH OTHER TSTMS ACROSS THE CENTRAL/SOUTHERN ROCKIES AND
ADJACENT HIGH PLAINS. OTHER MORE ISOLATED TSTMS WILL BE POSSIBLE
ALONG A COLD FRONT ACROSS THE OHIO VALLEY/NORTHEAST STATES.
...GULF COAST STATES TO ARKLATEX/MIDWEST...
AS THE MID ATLANTIC STATES UPPER RIDGE SHIFTS EASTWARD TOWARD THE
WESTERN ATLANTIC...IT SEEMS PROBABLE THAT THE LOW ACROSS THE GULF OF
MEXICO WILL MAKE A NORTHWARD SHIFT TOWARD THE CENTRAL GULF COAST
STATES ON FRIDAY...POTENTIALLY NEARING THE LA/MS/AL COAST LATE
FRIDAY/EARLY SATURDAY. ON THE NORTHERN PERIPHERY OF THIS LOW...A
CORRIDOR OF ENHANCED LOW LEVEL EASTERLY WINDS /AROUND 25-30 KT PER
00Z GFS AND EARLIER 12Z ECMWF GUIDANCE -- BUT STRONGER PER THE 00Z
NAM/ SHOULD PERSIST/POTENTIALLY INCREASE ALONG THE EAST-CENTRAL GULF
COAST. LOW-PERIPHERAL HEATING AND A GRADUALLY MOISTENING AIRMASS
COULD SUPPORT SOME STRONG/POTENTIALLY SEVERE WESTWARD MOVING
CLUSTERS...MAINLY FRIDAY AFTERNOON ACROSS THE CENTRAL GULF COAST
REGION/LOWER MISSISSIPPI VALLEY. SHOULD SUFFICIENT BUOYANCY /ALBEIT
MARGINAL/ DEVELOP...AND ESPECIALLY IF LOW LEVEL WINDS PROVE
STRONGER...A ROGUE TORNADO THREAT CANNOT BE RULED OUT ACROSS THE
CENTRAL GULF COAST FRIDAY AFTERNOON/NIGHT. UNCERTAINTY REGARDING THE
EVOLUTION OF THE LOW AND PERCEIVED MARGINAL NATURE OF THE THREAT
PRECLUDES SEVERE PROBABILITIES AT THIS TIME.
FARTHER NORTH...WITH A MOISTENING BOUNDARY LAYER BENEATH THE
PERIPHERY OF A WEAKENING UPPER RIDGE...OTHER TSTMS /PERHAPS A FEW
PULSE-TYPE STRONG-SEVERE/ SHOULD DIURNALLY DEVELOP AS FAR
NORTH-NORTHWEST AS THE ARKLATEX/MIDDLE MISSISSIPPI VALLEY.
...CENTRAL HIGH PLAINS...
AS LOW LEVEL FRONTAL ZONE DEVELOPS NORTHWARD...WEAK LOW LEVEL
UPSLOPE WILL CONTINUE ACROSS THE CENTRAL HIGH PLAINS INTO THE
EASTERN WY/NORTHEAST CO FRONT RANGE ON FRIDAY. WITHIN THIS
REGIME...DIURNAL TSTM DEVELOPMENT WILL BE POTENTIALLY AIDED BY ONE
OR MORE MINOR/CONVECTIVELY INDUCED MID LEVEL DISTURBANCES CROSSING
THE REGION AHEAD OF THE SOUTHERN ROCKIES UPPER LOW. MARGINAL
BUOYANCY AND VEERING WIND PROFILES COULD SUPPORT SOME SEVERE TSTMS
/HAIL MAIN THREAT/ MAINLY ACROSS EASTERN WY/NORTHEAST CO/WESTERN NEB
FRIDAY AFTERNOON...BUT HIGH LEVEL CLOUD COVER AHEAD OF THE SOUTHWEST
UPPER LOW...WEAK MID TROPOSPHERIC FLOW /GENERALLY 10-20 KT/...AND A
RESIDUALLY COOL AIRMASS /ALBEIT WARMING INTO FRIDAY/ SHOULD
GENERALLY LIMIT A SEVERE RISK.
...SOUTHERN ROCKIES/FOUR CORNERS TO SOUTHWEST TX...
SLOW MOVING/COOL UPPER LOW WILL GENERALLY REMAIN OVER AZ ON FRIDAY.
MODEST HEATING/OROGRAPHIC FORCING SHOULD RESULT IN AN AFTERNOON
UPSWING OF TSTMS FROM THE FOUR CORNERS TO SOUTHWEST TX. A FEW OF
THESE TSTMS COULD PRODUCE SMALL HAIL.
..GUYER.. 05/21/2009
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