SPC AC 120454
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1154 PM CDT MON AUG 11 2008
VALID 121200Z - 131200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE LOWER MS VALLEY TO
CENTRAL GULF COAST STATES...
...SYNOPSIS...
UPPER FLOW PATTERN WILL BE DOMINATED TODAY BY AN OMEGA BLOCK
EXTENDING FROM THE NERN PACIFIC EWD ACROSS CANADA. A CLOSED LOW
WILL REMAIN TRAPPED WITHIN THE RIDGE PORTION OF THIS BLOCKING
PATTERN OVER SASKATCHEWAN. MEANWHILE...PORTION OF THE TROUGH OVER
ERN CANADA IS EXPECTED TO RETROGRADE SWWD INTO THE GREAT LAKES
REGION WITH A BROAD TROUGH EVOLVING E OF THE MS RIVER VALLEY.
IN THE LOW LEVELS...A SURFACE FRONT EXTENDING GENERALLY SWD FROM AN
ATTENDANT SURFACE LOW WITH THE SASKATCHEWAN UPPER LOW WILL MOVE
SLOWLY EWD ACROSS THE UPPER MS VALLEY AND INTO NWRN MO...WHILE THE
PORTION OF THIS BOUNDARY OVER NEB SHOULD WEAKEN. A N-S LEE TROUGH
IS EXPECTED ALONG THE CENTRAL/SRN HIGH PLAINS BENEATH NWLY FLOW
ALOFT. FARTHER S...A SURFACE LOW LOCATED OVER NERN TX WILL TRACK
EWD ALONG A FRONT EXTENDING THROUGH NRN LA TO CENTRAL GULF COAST
STATES...WITH THE LOW REACHING CENTRAL AL BY 12Z WEDNESDAY.
...LOWER MS VALLEY TO CENTRAL GULF COAST STATES...
LATE EVENING WATER VAPOR IMAGERY SHOWED A CIRCULATION CENTER
CONTINUING TO MOVE EWD OVER NERN TX...WITH MODELS SUGGESTING THIS
FEATURE MAY PHASE OVER THE LOWER MS VALLEY TODAY WITH A SHORT WAVE
TROUGH CURRENTLY TRACKING SEWD ACROSS ERN KS. THE PHASING SYSTEMS
SHOULD STRENGTHEN DEEP LAYER WIND FIELDS AS HEIGHTS FALL ACROSS THE
LOWER MS VALLEY INTO CENTRAL GULF COAST STATES THIS FORECAST
PERIOD...AND THE MID/UPPER LEVEL HEIGHT GRADIENTS TIGHTEN. ALTHOUGH
LAPSE RATES WILL REMAIN QUITE WEAK WITHIN A VERY MOIST AIR MASS /PW
VALUES EXCEEDING 2 INCHES/...SOME SURFACE HEATING FROM SRN LA INTO
SRN MS MAY BOOST MLCAPE VALUES TO AROUND 1000 J/KG. THIS COMBINED
WITH MODEST EFFECTIVE BULK SHEAR SUGGESTS A FEW ORGANIZED STORMS
WILL BE POSSIBLE. LOW LEVEL SWLY WINDS INCREASING TO 40-50 KT
ACROSS THE SLIGHT RISK AREA WILL SUPPORT A THREAT FOR DAMAGING WINDS
WITH ANY OF THE STRONGER STORMS. ENLARGED LOW LEVEL HODOGRAPHS ARE
EXPECTED IN FRONTAL ZONE WHERE SURFACE WINDS WILL BE BACKED...
ENHANCING POTENTIAL FOR A FEW TORNADOES. TSTMS SHOULD PERSIST EWD
THROUGH CENTRAL GULF COAST STATES AFTER DARK WITH RICH MOISTURE
MAINTAINING WEAK INSTABILITY AS LOW LEVEL SHEAR INCREASES.
...CENTRAL/SRN HIGH PLAINS...
WIDELY SCATTERED TSTMS IN CLUSTERS MAY DEVELOP ACROSS ERN PORTIONS
CO/NM AND PERHAPS SERN WY AND NEB PANHANDLE DURING THE AFTERNOON...
IN FAVORABLY MOIST ENVIRONMENT MADE INCREASINGLY UNSTABLE THROUGH
DIURNAL HEATING. ALTHOUGH LOW-MID LEVEL WINDS WILL BE WEAK...STRONG
DIRECTIONAL SHEAR AND UPPER FLOW WILL SUPPORT SOME STORM
ORGANIZATION...WITH ISOLATED STRONG TO SEVERE GUSTS POSSIBLE INTO
WELL-MIXED SUB-CLOUD LAYER. POTENTIAL EXISTS FOR A TSTM CLUSTER TO
PROPAGATE SSEWD FROM ERN CO TOWARD NERN NM AND THE OK/TX PANHANDLES
THIS EVENING AS A SSELY LLJ STRENGTHENS ACROSS THIS REGION. THIS
ACTIVITY WOULD BE CAPABLE OF PRODUCING ISOLATED STRONG TO SEVERE
GUSTS.
...NWRN MO TO SERN MN...
MODELS SUGGEST SURFACE HEATING IN THE WAKE OF ONGOING SHOWERS/
EMBEDDED TSTMS SPREADING EWD ACROSS THE UPPER MS VALLEY AND IA AT
12Z TODAY SHOULD RESULT IN MODERATE INSTABILITY WITHIN A MOISTURE
CORRIDOR ALONG THE SURFACE FRONT. ALTHOUGH EFFECTIVE BULK SHEAR
WILL BE SUFFICIENT FOR ORGANIZED STORMS...WEAK DEEP LAYER FORCING
ACROSS THIS REGION IS EXPECTED TO LIMIT NEW TSTM DEVELOPMENT ALONG
THE FRONT THIS AFTERNOON. A FEW TSTMS THAT DO FORM WILL BE CAPABLE
OF PRODUCING STRONGER WIND GUSTS GIVEN MODERATE INSTABILITY AND
STEEPER LOW LEVEL LAPSE RATES.
..PETERS/HURLBUT.. 08/12/2008
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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