DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 151622
SWODY1
SPC AC 151620

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1120 AM CDT FRI MAR 15 2013

VALID 151630Z - 161200Z

...NO SVR TSTM AREAS FORECAST...

...OH VALLEY...
UPPER RIDGE HAS DIMINISHED OVER THE INTERMOUNTAIN REGION AS A LOW
AMPLITUDE SHORT WAVE TROUGH MOVES ACROSS MT THIS MORNING. THIS
SYSTEM IS EXPECTED TO MOVE ESEWD TOWARD THE UPPER MS VALLEY AND
GREAT LAKES LATER THIS AFTERNOON AND TONIGHT...RESULTING IN A WEAKLY
CYCLONIC WNWLY FLOW ALOFT ACROSS MUCH OF THE CONUS. AT THE
SURFACE...A LOW OVER ERN NEB/WRN IA IS FORECAST TO MOVE/REDEVELOP
EWD INTO THE MID MS VALLEY THIS EVENING CONTINUING EWD INTO THE OH
VALLEY TONIGHT.

THE NWLY FLOW PATTERN ALOFT COUPLED WITH PREVIOUS COLD FRONTAL
INTRUSION DEEP INTO THE GULF OF MEXICO WILL STRONGLY LIMIT THE
MAGNITUDE OF MOISTURE RETURN NEWD INTO THE MID MS AND OH VALLEYS IN
ADVANCE OF THE SURFACE LOW. 12Z RAOB AND SATELLITE DATA INDICATE PW
GENERALLY AOB 0.75 INCH WILL BE AVAILABLE FOR POTENTIAL CONVECTIVE
DEVELOPMENT WITH THIS SYSTEM...WITH MID/UPPER 40S SURFACE DEW POINTS
CURRENTLY MOVING NEWD ACROSS AR TOWARD THE OH VALLEY. HOWEVER...A
PLUME OF STEEPER MID LEVEL LAPSE RATES IS FORECAST TO SPREAD EWD
TOWARD THE MID MS AND UPPER OH VALLEY WHICH WILL CONTRIBUTE TO
INCREASING ELEVATED INSTABILITY /MUCAPE OF 500-800 J PER KG/ ABOVE
850 MB TONIGHT. SOME MODEL GUIDANCE INCLUDING 09Z SREF WRF-NMM AND
WRF-ARW MEMBERS APPEAR TO BE OVERPREDICTING A RAPID INCREASE IN LOW
LEVEL MOISTURE THIS AFTERNOON AND EVENING INTO THE LOWER OH
VALLEY...AND THIS IN TURN MAY RESULT IN SOME MODEL FORECASTS
INDICATING EXCESSIVELY LARGE CAPE VALUES.

MODEL CONSENSUS INCLUDING CONVECTION-ALLOWING MODELS AND SPC SSEO
DEVELOP ELEVATED STORMS BY THIS EVENING OVER PARTS OF CENTRAL IL
WITH ACTIVITY SPREADING EWD/ESEWD INTO THE OH VALLEY TONIGHT. THERE
MAY BE SUFFICIENT INSTABILITY COUPLED WITH STRONG EFFECTIVE BULK
SHEAR WITHIN THE CLOUD-BEARING LAYER FOR ISOLATED ELEVATED
SUPERCELLS TO DEVELOP...WITH STRONGER CELLS CAPABLE OF PRODUCING
MARGINALLY SEVERE HAIL. CURRENT OUTLOOK WILL MAINTAIN 5% NOCTURNAL
HAIL PROBABILITY GIVEN UNCERTAINTY ABOUT THE MAGNITUDE OF
INSTABILITY THAT WILL BE PRESENT TONIGHT.

..WEISS/GRAMS.. 03/15/2013

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