Saturday, May 26, 2012

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 261249
SWODY1
SPC AC 261247

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0747 AM CDT SAT MAY 26 2012

VALID 261300Z - 271200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM PORTIONS OF THE NRN PLAINS
AND UPPER MIDWEST INTO SRN HIGH PLAINS...

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND EVENING
ACROSS PARTS OF ERN WY...

...SYNOPSIS...

80-90 KT MIDLEVEL JET STREAK OVER THE SWRN DESERTS WILL DEVELOP NEWD
INTO THE NRN HIGH PLAINS BY 27/12Z IN TANDEM WITH A POTENT VORTICITY
MAXIMUM. THE PROGRESSION OF THESE FEATURES WILL RESULT IN THE NET
EWD/NEWD MOVEMENT OF WRN U.S. TROUGH THIS PERIOD...AND THE GRADUAL
SUPPRESSION OF MIDLEVEL RIDGE ACROSS THE NRN/CNTRL PLAINS.
DOWNSTREAM FROM THE LARGE-SCALE TROUGH...A SERIES OF WEAK VORTICITY
MAXIMA FROM CNTRL KS INTO SWRN TX WILL TRANSLATE NNEWD WHILE
SUBTROPICAL STORM BERYL ADVANCES SWWD TOWARD THE SERN ATLANTIC
COAST.

AT THE SURFACE...LEE CYCLONE OVER ERN CO WILL DEEPEN TODAY WHILE
DEVELOPING SLOWLY NWD THROUGH THE CNTRL HIGH PLAINS. THIS FEATURE
WILL BEGIN TO ACCELERATE NNEWD TONIGHT INTO CNTRL SD IN RESPONSE TO
ABOVE-MENTIONED JET STREAK AND ASSOCIATED VORTICITY MAXIMUM. EXPECT
A WARM FRONT TO CONCURRENTLY MOVE/DEVELOP NWD THROUGH THE MID-MO
VALLEY INTO THE UPPER MS VALLEY/UPPER MIDWEST. THE ERN EXTENSION OF
THIS BOUNDARY WILL ASSUME COLD FRONTAL PROPERTIES AS IT SETTLES SWD
THROUGH CNTRL/SRN NEW ENGLAND AND THE NRN MID-ATLANTIC STATES.
ELSEWHERE...A DRYLINE WILL STRENGTH TODAY ACROSS THE CNTRL/SRN HIGH
PLAINS...PERHAPS MIXING EWD EARLY BEFORE RETREATING BY LATE
AFTERNOON INTO THIS EVENING.

...NRN PLAINS INTO UPPER MIDWEST AND SWD INTO SRN HIGH PLAINS...

A COUPLE OF ELEVATED TSTM COMPLEXES ARE ONGOING THIS MORNING...ONE
OVER SERN SD /SWRN MN...AND THE OTHER ACROSS SRN WI/NRN IL. THIS
ACTIVITY IS SITUATED WELL TO THE N OF SURFACE WARM FRONT AND LIKELY
FORCED BY WAA AT THE TERMINUS OF A BIFURCATED LLJ. MASS RESPONSE TO
WRN U.S. UPPER TROUGH WILL RESULT IN THE NWD MIGRATION OF THE WRN
LLJ BRANCH INTO THE NRN PLAINS AND UPPER MIDWEST...LIKELY
MAINTAINING EPISODIC ELEVATED TSTM DEVELOPMENT ALONG THE NRN EDGE OF
THE STRONGER CAP/EML BEING ADVECTED NWD THROUGH THE CNTRL PLAINS/MID
MS VALLEY REGION. GIVEN THE PRESENCE OF STEEP MIDLEVEL LAPSE
RATES...A MOIST LOW-LEVEL ENVIRONMENT...AND RELATIVELY STRONG CLOUD
BEARING SHEAR...THE MOST INTENSE STORMS WILL REMAIN CAPABLE OF LARGE
HAIL AND PERHAPS LOCALLY DAMAGING WIND GUSTS.

TO THE S OF THE ELEVATED TSTM REGIME...THE PRESENCE OF A STRONG CAP
/REF. 12Z LBF AND OAX SOUNDINGS/ AND NEUTRAL TO ONLY SLIGHT MIDLEVEL
HEIGHT FALLS THROUGH THE PEAK OF THE DIURNAL HEATING CYCLE CAST
CONSIDERABLE UNCERTAINTY ON SURFACE-BASED STORM DEVELOPMENT LATER
TODAY. CURRENT THINKING IS THAT THE HIGHEST PROBABILITY FOR STORM
INITIATION WILL BE ALONG THE DRYLINE FROM CNTRL NEB SWWD INTO WRN TX
WHERE THE DEVELOPMENT OF A HOT...DEEPLY-MIXED BOUNDARY LAYER MAY
ALLOW FOR THE LOCAL EROSION OF THE CAP. A DYNAMICAL CONTRIBUTION TO
STORM INITIATION MAY ALSO BE PROVIDED BY A COUPLE OF WEAK IMPULSES
EMBEDDED IN SUBTROPICAL MOIST PLUME FROM KS INTO TX...THOUGH DETAILS
REMAIN UNCLEAR.

WHILE ENVIRONMENTAL CONDITIONS WILL SUPPORT SUPERCELLS CAPABLE OF
LARGE HAIL AND DAMAGING WIND GUSTS ALONG THE LENGTH OF THE
DRYLINE...THE OVERLAP OF STRONGEST INSTABILITY /MLCAPE OF 2000-4000
J PER KG/ AND VERTICAL SHEAR --AND POTENTIALLY GREATER SEVERE
WEATHER THREAT-- WILL EXIST OVER THE NEB SANDHILLS INTO MID-MO
VALLEY INVOF WARM FRONT/DRYLINE INTERSECTION. BUT...GIVEN
UNCERTAINTIES IN STORM INITIATION...BASELINE SLIGHT RISK
PROBABILITIES WILL BE MAINTAINED.

...WY...

DEEP-LAYER FORCING FOR ASCENT WILL STRENGTHEN LATER TODAY INTO
TONIGHT AS EXIT REGION OF ABOVE-MENTIONED MIDLEVEL JET STREAK
GRADUALLY OVERSPREADS THE REGION. THIS WILL SUPPORT THE DEEPENING
SUBSEQUENT NWD DEVELOPMENT OF LEE CYCLONE AND ATTENDANT WARM FRONT.
LATEST MODEL GUIDANCE REMAINS CONSISTENT IN SUGGESTING THAT A NARROW
AXIS OF MODEST INSTABILITY /I.E. MLCAPE OF 500-1000 J PER KG/ WILL
DEVELOP INVOF SURFACE FRONT THIS AFTERNOON/EVENING...SUFFICIENT FOR
ISOLATED-WIDELY SCATTERED TSTM DEVELOPMENT. GIVEN VERTICAL WIND
PROFILES EXHIBITING PRONOUNCED VEERING WITH HEIGHT AND STRONG
DEEP-LAYER SHEAR...SETUP MAY YIELD A FEW SUPERCELLS CAPABLE OF HAIL
AND PERHAPS A TORNADO.

..MEAD/ROGERS.. 05/26/2012

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