SWODY1
SPC AC 050555
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1155 PM CST SUN JAN 04 2009
VALID 051200Z - 061200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A STRONG NERN PACIFIC JET STREAK WILL DIG SEWD THROUGH THE
INTERMOUNTAIN W...EFFECTIVELY CARVING OUT A FULL LATITUDE TROUGH
OVER THE CNTRL CONUS...AS A PAIR OF PROGRESSIVE SHORT WAVE TROUGHS
OVER THE CENTRAL ROCKIES AND NRN BAJA PHASE THIS FORECAST PERIOD.
AS THIS OCCURS...SIGNIFICANT HEIGHT FALLS WILL SPREAD EWD ACROSS THE
CNTRL/SRN PLAINS TOWARD THE LOWER MO VALLEY AND AR TO E TX BY 12Z
TUESDAY.
IN THE LOW LEVELS...A SURFACE COLD FRONT ATTENDANT TO A NRN STREAM
TROUGH WILL MOVE EWD THROUGH NEW ENGLAND AND SETTLE SLOWLY SWD
THROUGH VA INTO NC. THE SRN EXTENT OF THIS BOUNDARY EXTENDING FROM
NRN GA SWWD THROUGH CENTRAL AL...SRN MS...TO SOUTH CENTRAL LA AND
THE NWRN GULF IS EXPECTED TO REMAIN STATIONARY.
...E TX/LOWER MS VALLEY...
TSTM DEVELOPMENT IS EXPECTED INTO THE AFTERNOON FROM SRN LA INTO SRN
MS AND SRN/CENTRAL AL ALONG AND S OF THE STATIONARY BOUNDARY WHERE
THE BOUNDARY LAYER WILL BE RELATIVELY MOIST /SURFACE DEWPOINTS IN
THE MID 60S/ AND WEAKLY UNSTABLE. MODELS INDICATE WEAK SUB-TROPICAL
IMPULSES EMANATING FROM THE ERN PACIFIC /S OF BAJA/ TRAVERSING THE
LOWER MS VALLEY TODAY SHOULD AID IN ASCENT FOR THIS EXPECTED TSTM
DEVELOPMENT. A SSWLY LLJ IS FORECAST TO STRENGTHEN TO 30-40 KT THIS
AFTERNOON FROM THE TX COAST INTO THE LOWER MS VALLEY...BENEATH
INCREASING SWLY MID LEVEL WINDS. EFFECTIVE BULK SHEAR OF 50 KT THIS
AFTERNOON OVER SRN LA INTO SRN MS COMBINED WITH MUCAPE 250-500 J/KG
MAY SUPPORT A FEW STRONG TO SEVERE STORMS...WITH A SUPERCELL
POSSIBLE.
THE LLJ IS EXPECTED TO STRENGTHEN /45-55 KT/ THIS EVENING THROUGH
THE OVERNIGHT PERIOD FROM THE TX COAST THROUGH THE LOWER MS VALLEY
TO THE SRN APPALACHIANS IN RESPONSE TO 60-90 METER HEIGHT FALLS...
WITH THE UPPER TROUGH...SPREADING TOWARD THE ARKLATEX REGION.
INCREASING LOW LEVEL MOISTURE/WARM AIR ADVECTION ALONG THE LLJ
COMBINED WITH STEEPER MID LEVEL LAPSE RATES SPREADING NEWD ACROSS E
TX TO NRN MS ARE EXPECTED TO SUPPORT ADDITIONAL TSTM DEVELOPMENT
AFTER 00Z ALONG AND N OF THE STALLED SURFACE BOUNDARY. MODELS
SUGGEST AN INCREASE IN NEAR-SURFACE TO SURFACE BASED CAPE BY 09-12Z
OVER SRN LA WITH VALUES RANGING FROM 500-1000 J/KG...WHILE LOW LEVEL
AND DEEP LAYER SHEAR ACROSS THIS AREA WILL BE SUPPORTIVE OF AN
INCREASING POTENTIAL FOR ORGANIZED SEVERE STORMS. GIVEN THIS THREAT
IS EXPECTED TOWARD THE END OF THE DAY 1 FORECAST PERIOD...AND SOME
UNCERTAINTY EXISTS IN THE MODELS WITH RESPECT TO COVERAGE OF SURFACE
BASED TSTM DEVELOPMENT...THIS OUTLOOK WILL HAVE LOW SEVERE
PROBABILITIES FOR WIND AND TORNADO.
MEANWHILE...A LOW PROBABILITY FOR HAIL APPROACHING AND/OR LOCALLY
EXCEEDING SEVERE VALUES HAS BEEN INTRODUCED FOR THIS EVENING INTO
THE OVERNIGHT PERIOD FROM E TX THROUGH NRN LA/SERN AR TO WRN MS.
STEEPER MID LEVEL LAPSE RATES SPREADING ACROSS THIS REGION...MAINLY
AFTER 00Z...WILL SUPPORT A HAIL THREAT WITH THE ELEVATED CONVECTION
N OF THE STALLED BOUNDARY.
..PETERS.. 01/05/2009
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