SWODY2
SPC AC 200633
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1233 AM CST SAT FEB 20 2010
VALID 211200Z - 221200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MODELS DIFFER SOME IN THE AMPLITUDE OF A SRN STREAM SHORTWAVE
TROUGH...BUT ARE IN GENERAL AGREEMENT WITH THE TIMING OF THIS
FEATURE AS IT TRACKS FROM W/NW TX AT 12Z SUNDAY TO THE MID MS/LOWER
OH VALLEYS BY 12Z MONDAY. SURFACE LOW ATTENDANT TO THIS TROUGH IS
EXPECTED TO TRACK FROM NW TX /VICINITY CDS/ ENEWD ALONG A BAROCLINIC
ZONE TO NRN AR/SRN MO BY SUNDAY EVENING AND THEN TO THE LOWER OH
VALLEY BY END OF DAY 2. A TRAILING COLD FRONT WILL MOVE E/SEWD FROM
THE SRN PLAINS TOWARD THE LOWER MS VALLEY AND OFF MUCH OF THE TX
GULF COAST BY LATE IN THE FORECAST PERIOD.
IN THE WEST...TSTMS WILL BE POSSIBLE ALONG PARTS OF THE NRN/CENTRAL
CA COAST SUNDAY AFTERNOON/EVENING AS A PACIFIC SHORTWAVE TROUGH
MOVES INTO THIS REGION.
...PARTS OF ERN OK/AR AND NERN TX...
ELEVATED TSTMS ARE EXPECTED TO BE ONGOING AT 12Z SUNDAY OVER PARTS
OF OK AND N TX WITHIN REGIME OF LOW LEVEL WAA AND FORCING FOR ASCENT
SPREADING ENEWD AHEAD OF PROGRESSIVE SHORTWAVE TROUGH. WEAK
INSTABILITY/SHEAR VALUES MAY SUPPORT A FEW STORMS WITH MARGINALLY
SEVERE HAIL. TSTM ACTIVITY SHOULD SPREAD EWD INTO THE OZARKS TO
ARKLATEX REGION ALONG THE TRACK OF SURFACE LOW AND TRAILING COLD
FRONT. FORECAST SOUNDINGS SUGGEST SOME OF THIS ACTIVITY MAY BECOME
SURFACE BASED SUNDAY AFTERNOON. THE LACK OF STRONGER MOISTURE
RETURN WILL TEND TO LIMIT THE DEVELOPMENT OF STRONGER INSTABILITY...
DESPITE STEEP MID LEVEL LAPSE RATES SPREADING ACROSS THIS REGION.
HAIL WILL BE POSSIBLE GIVEN THE STEEP LAPSE RATES...WITH THIS
POTENTIAL GREATEST FROM NERN TX INTO SRN AR WHERE EFFECTIVE BULK
SHEAR WILL BE STRONGER /AROUND 40 KT/ FOR SOME STORM ORGANIZATION.
WEAK INSTABILITY WILL LIMIT THE SEVERE WEATHER THREAT/COVERAGE AND
PRECLUDE A CATEGORICAL SLIGHT RISK.
...E TX/LA/SRN MS...
FACTORS THAT WOULD SUPPORT AN ORGANIZED SEVERE WEATHER THREAT ACROSS
E TX/LA/SRN MS ARE MORE NEGATIVE IN THIS DAY 2 OUTLOOK FOR SUNDAY...
THAN WERE INDICATED IN THE MODEL DATA FOR THIS SAME REGION/TIME
PERIOD IN THE PREVIOUS DAY 3 OUTLOOK. THE RELATIVELY POOR QUALITY
OF THE WARM SECTOR AIR MASS EXPECTED ACROSS THIS REGION ON SUNDAY IS
A KEY FACTOR IN REDUCING THE SEVERE PROBABILITIES...WITH LATEST
MODELS SHOWING WEAKER MOISTURE RETURN RESULTING IN MARGINAL
INSTABILITY. THIS COMBINED WITH STRONGER FORCING FOR ASCENT
REMAINING N OF THIS REGION ALONG TRACK OF THE SHORTWAVE TROUGH NOW
SUGGESTS A LOWER PROBABILITY FOR AN OVERALL SEVERE WEATHER THREAT
DURING DAY 2. NONETHELESS...50-60 KT WSWLY MID LEVEL WINDS
SPREADING ACROSS THIS REGION SUNDAY AFTERNOON WILL RESULT IN
EFFECTIVE SHEAR OF 40-45 KT. THIS WILL BE SUFFICIENT TO SUPPORT
SOME STORM ORGANIZATION...BUT AFOREMENTIONED MARGINAL INSTABILITY
WILL LIMIT THE COVERAGE.
..PETERS.. 02/20/2010
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