DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 281732
SWODY2
SPC AC 281730

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM CDT SUN APR 28 2013

VALID 291200Z - 301200Z

...THERE IS A SLGT RISK OF SVR TSTMS FOR PARTS OF ERN IA...NWRN
IL...SRN WI MON LATE AFTERNOON/EVENING...

...SYNOPSIS...
AN UPPER-LEVEL TROUGH WILL GRADUALLY AMPLIFY ACROSS THE NORTHWEST.
DOWNSTREAM...LOWER AMPLITUDE AND WEAKENING DISTURBANCES WILL
PROGRESS EWD...ONE ACROSS THE UPPER MS VALLEY/GREAT LAKES AND
ANOTHER FROM THE CNTRL/SRN APPALACHIANS ACROSS THE
MID/SOUTH-ATLANTIC COAST. AT THE SURFACE...A COLD FRONT ASSOCIATED
WITH THE LEAD IMPULSE OVER THE N-CNTRL CONUS WILL UNDERGO
FRONTOLYSIS. A STRONGER COLD FRONT ASSOCIATED WITH THE AMPLIFYING
NWRN TROUGH WILL ACCELERATE AND SWEEP ACROSS THE NRN PLAINS...LIKELY
REACHING THE UPPER MS VALLEY TO CNTRL HIGH PLAINS BY EARLY TUE.

...PARTS OF THE UPPER/MID-MS VALLEY...
AS NOTED IN THE INITIAL D2 DISCUSSION...MODEL GUIDANCE /ESPECIALLY
SREF...NAM AND GFS/ MAY BE GROSSLY OVERDONE WITH THE DEGREE OF
LOW-LEVEL MOISTURE RETURN INTO THE MIDWEST BY MON AFTERNOON.
FORECAST SOUNDINGS FROM THESE MODELS INDICATE MEAN MIXING RATIOS
REACHING 12-14 G/KG WITH MINIMAL INHIBITION PRIOR TO DEPICTED
CONVECTIVE INITIATION ALONG THE DECAYING FRONT. WITH ONLY A MODERATE
SWLY LLJ ON SUN NIGHT...AND 12Z RAOBS THIS MORNING INDICATING MEAN
MIXING RATIOS OF THAT MAGNITUDE CONFINED TO DEEP S TX AND ACROSS THE
LOWER MS VALLEY...IT APPEARS A BIT FAR-FETCHED THAT THIS AMPLITUDE
OF MOISTURE RETURN WILL BE FULLY REALIZED. IN ADDITION...THE
FRONTOLYTIC NATURE OF THE BOUNDARY ALONG WITH WAA AT 700 MB LIKELY
MAINTAINING A CAPPING INVERSION WILL PROBABLY MITIGATE DIURNAL TSTM
DEVELOPMENT TO ALONG THE LEADING EDGE OF THE CAP. THIS TYPE OF
SCENARIO APPEARS FAIRLY REPRESENTED IN 12Z CONVECTION-ALLOWING WRF
GUIDANCE. AMIDST A BELT OF ENHANCED MID-LEVEL WLYS...THIS SETUP
COULD YIELD A FEW SUPERCELLS WITH LARGE HAIL AS THE PRIMARY THREAT
DURING THE LATE AFTERNOON/EVENING IF TSTMS INDEED FORM.

...S ATLANTIC COASTAL PLAIN...
DIURNAL TSTM COVERAGE WILL LIKELY BECOME SCATTERED IN ASSOCIATION
WITH A DAMPENING MID-LEVEL IMPULSE. AMIDST THE PRESENCE OF LOWER TO
MIDDLE 60S SURFACE DEW POINTS AND A BELT OF 30-40 KT MID-LEVEL
SWLYS...A FEW MULTICELL CLUSTERS MAY ORGANIZE. HOWEVER...POOR
MID-LEVEL LAPSE RATES AND POTENTIAL FOR REMNANT MORNING CONVECTION
TO RETARD SURFACE HEATING WILL MITIGATE PROBABILITIES FOR A MARGINAL
WIND THREAT ATTM.

..GRAMS.. 04/28/2013

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