DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 251731
SWODY2
SPC AC 251730

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM CDT FRI MAY 25 2012

VALID 261200Z - 271200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVER CNTRL AND SRN MN...NRN
IA...WRN WI...FAR ERN SD...

...SYNOPSIS...
AN EXPANSIVE UPPER LOW WILL BE CENTERED OVER THE GREAT BASIN SAT
MORNING...AND WILL EJECT NEWD ACROSS THE ROCKIES THROUGH THE PERIOD.
IN ADVANCE OF THIS TROUGH...A BROAD AREA OF SWLY FLOW WILL EXIST
OVER THE PLAINS...WITH AN UPPER RIDGE CENTERED OVER THE MIDDLE AND
LOWER MS VALLEY.

AT THE SURFACE...A WARM FRONT WILL LIFT NWD OUT OF NEB AND IA INTO
SD...MN AND WI BY AFTERNOON. THE ERN PORTION OF THIS BOUNDARY WILL
BE WEAK BUT WILL EXIST OVER NRN IND...OH AND PA. DEWPOINTS IN THE
MID TO UPPER 60S F WILL EXIST FROM THE CNTRL PLAINS INTO THE OH
VALLEY...RESULTING IN AMPLE INSTABILITY FOR THUNDERSTORMS.

TO THE W AND LATER IN THE DAY...LOW PRESSURE WILL DEEPEN OVER SERN
WY AND NERN CO AHEAD OF THE ADVANCING UPPER TROUGH. STRONG FORCING
WILL DEVELOP IN THIS REGION...BUT INSTABILITY WILL BE WEAK.

...NRN PLAINS/UPPER MS VALLEY...
A FAIRLY COMPLEX SCENARIO WILL UNFOLD ON SATURDAY. MODELS INDICATE
THAT MULTIPLE EPISODES OF STORMS WILL BE POSSIBLE...BUT THERE IS
DISAGREEMENT WITH EXACTLY WHERE THESE STORMS WILL FOCUS. IN A
GENERAL SENSE...AREAS OF STORMS SHOULD EXIST NEAR THE WARM FRONT
EARLY ON SAT...AND PERSIST AS THE FRONT LIFTS N. INSTABILITY AND
SHEAR WILL STRONGLY FAVOR SUPERCELLS CAPABLE OF VERY LARGE
HAIL...AND THE DEGREE OF INSTABILITY AND LARGE LOW LEVEL HODOGRAPHS
WOULD ALSO FAVOR TORNADOES. THE MAIN QUESTION IS STORM COVERAGE IN
THE WAKE OF THE EARLY ACTIVITY. THE SYNOPTIC PATTERN ALOFT IS
RELATIVELY NEUTRAL...SO THIS EVENT WILL ALMOST ENTIRELY BE DRIVEN BY
WARM ADVECTION. MODELS DO INDICATE A PLUME OF STRONGER HEATING AND
LOW LEVEL LAPSE RATES FROM ERN NEB AND PERHAPS INTO WRN IA...WHICH
COULD HELP BREAK THE CAP. AFTERNOON SOUNDINGS S OF THE WARM FRONT
OVER IA APPEAR CAPPED...BUT CONDITIONALLY FAVORABLE FOR SIGNIFICANT
SEVERE WEATHER. THUS...WILL INTRODUCE A BROAD SLIGHT RISK
AREA...WITH LATER OUTLOOKS PROVIDING GREATER PRECISION.

...NERN WY...
FORCING FOR ASCENT WILL INCREASE MARKEDLY AS THE SURFACE LOW DEEPENS
AND SHEAR PROFILES WILL BE QUITE STRONG AND VEERING WITH HEIGHT.
HOWEVER...INDICATIONS ARE THAT MOISTURE AND INSTABILITY WILL BE
LIMITED IN GENERAL WITH ONLY A NARROW AXIS OF UPPER 40S TO PERHAPS
LOWER 50S F DEWPOINTS EXTENDING WWD ALONG THE NEB/SD BORDER INTO FAR
ERN WY. S OF THIS NARROW CORRIDOR...DEEP MIXING WILL OCCUR WITH
INVERTED-V TYPE SOUNDINGS AND STRONG SHEAR. GIVEN THE STRENGTH OF
THE FORCING AND ADVANCING COLD FRONT DURING THE EVENING...THERE WILL
BE A THREAT OF ISOLATED SEVERE WIND...AND PERHAPS MARGINAL HAIL
DEPENDING ON HOW MUCH INSTABILITY EXISTS.

...OH...NRN WV...PA...
STRONG HEATING WILL OCCUR ACROSS THIS AREA...RESULTING IN AROUND
1500 J/KG MUCAPE AS DEWPOINTS REMAIN IN THE MID 60S F. WINDS ALOFT
WILL BE WEAK...AS WILL FORCING. HOWEVER...WITH FULL HEATING...AMPLE
MOISTURE...AND AT LEAST WEAK LOW LEVEL CONVERGENCE...ISOLATED
THUNDERSTORMS WILL BE POSSIBLE. SOME OF THESE STORMS MAY PRODUCE
LOCALLY STRONG TO SEVERE DOWNBURSTS...ALONG WITH MARGINALLY SEVERE
HAIL. SOME MODELS DO INDICATE A WEAK WAVE DEVELOPING ATOP THE UPPER
RIDGE...WHICH COULD HELP FOCUS CONVECTION INTO A SMALL CLUSTER.

..JEWELL.. 05/25/2012

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