SPC AC 231235
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0735 AM CDT THU APR 23 2009
VALID 231300Z - 241200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
THE DEEP MID LEVEL TROUGH OVER NEW ENGLAND WILL LIFT NEWD AND STRONG
HEIGHT RISES ARE EXPECTED IN ITS WAKE BY TONIGHT...DOWNSTREAM FROM
ANOTHER POSITIVE TILT TROUGH WHICH WILL CONTINUE TO MOVE SLOWLY SEWD
ACROSS THE PAC NW AND NRN ROCKIES. A SEPARATE SMALLER SCALE WAVE
OVER ERN KS...WITHIN AN INTERMEDIATE FLOW STREAM...WILL PROGRESS
NEWD OVER MO/IL IN THE REGIME OF RISING HEIGHTS...WHILE ANOTHER SRN
STREAM TROUGH MOVES SLOWLY EWD ACROSS NRN MEXICO TO THE TX BIG BEND.
A RELATIVELY SHALLOW SURFACE MOIST LAYER WITH DEWPOINTS IN THE 50S
AND 60S IS RETURNING NWD ACROSS THE GULF COAST STATES AND SRN
PLAINS...ALONG AND S OF A WARM FRONT WHICH WILL LIFT NWD ACROSS THE
MID MS VALLEY. HOWEVER...LOW-LEVEL MOISTURE IS RATHER LIMITED
ACROSS MOST OF THE CONUS...AND INSTABILITY FOR DEEP CONVECTION WILL
BE DRIVEN LARGELY BY A BROAD PLUME OF STEEP LOW-MID LEVEL LAPSE
RATES EMANATING FROM THE INTERMOUNTAIN WEST...AND BY STRONG DAYTIME
HEATING/MIXING. THIS WILL SUPPORT A FEW AREAS OF MAINLY HIGH-BASED
THUNDERSTORM DEVELOPMENT DOWNSTREAM FROM THE AFOREMENTIONED
SHORTWAVE TROUGHS TODAY...AND A CONTINUING THREAT FOR ELEVATED
STORMS OVERNIGHT.
...GA AREA TODAY...
STRONG SURFACE HEATING AND SOME LOW-LEVEL MOISTENING WILL RESULT IN
THE DEVELOPMENT OF MODERATE INSTABILITY /MLCAPE OF 1000-1500 J/KG/
ALONG THE SLOW-MOVING WARM FRONT TODAY ACROSS GA. THE BACKGROUND
REGIME OF RISING HEIGHTS IS NOT SUPPORTIVE OF WIDESPREAD
THUNDERSTORM DEVELOPMENT...BUT ISOLATED STORMS COULD FORM THIS
AFTERNOON IN THE ZONE OF WEAK ASCENT AND SMALL CONVECTIVE INHIBITION
ALONG THE BOUNDARY. IF STORMS DO FORM...THE INSTABILITY AND 0-6 KM
BULK SHEAR AROUND 30 KT COULD SUPPORT MULTICELL CLUSTERS AND/OR
MARGINAL SUPERCELL STRUCTURES WITH A THREAT FOR LARGE HAIL.
...SW TX THIS AFTERNOON INTO TONIGHT...
LOW-LEVEL MOISTURE WILL BEGIN TO RETURN NWWD UP THE RIO GRANDE
VALLEY IN ADVANCE OF THE SRN STREAM TROUGH MOVING EWD OVER NRN
MEXICO...THOUGH DAYTIME MIXING WILL LIKELY OFFSET MOISTURE ADVECTION
THIS AFTERNOON. STILL...STEEP MID LEVEL LAPSE RATES AND STRONG
SURFACE HEATING IN THE WAKE OF MORNING CIRRUS WILL CONTRIBUTE TO
SUFFICIENT SURFACE-BASED INSTABILITY FOR HIGH-BASED STORMS CAPABLE
OF PRODUCING ISOLATED STRONG OUTFLOW GUSTS AND MARGINALLY SEVERE
HAIL. SOME OF THIS CONVECTION MAY PERSIST OVERNIGHT IN AN ELEVATED
WAA REGIME WITH INCREASING MOISTURE...AND A CONTINUED THREAT FOR
ISOLATED HAIL.
...NRN ROCKIES THIS AFTERNOON TO THE NRN PLAINS TONIGHT...
A SURFACE COLD FRONT WILL MOVE SEWD ACROSS THE NRN PLAINS IN
ASSOCIATION WITH A MID-UPPER SPEED MAX TRAVERSING MANITOBA.
LOW-LEVEL MOISTURE WILL INITIALLY BE QUITE LIMITED ACROSS THE NRN
PLAINS IN ADVANCE OF THE FRONT...THOUGH A GRADUAL INCREASE IN
MOISTURE IS EXPECTED NWD FROM THE ERN PART OF THE PLAINS STATES.
MEANWHILE...STEEP LAPSE RATES WILL CONTINUE OVER THIS AREA
DOWNSTREAM FROM THE PAC NW TROUGH...AND A PLUME OF MID LEVEL
MOISTURE WILL SPREAD ENEWD FROM THE NRN ROCKIES. CONVECTION WILL
BEGIN THIS AFTERNOON NEAR THE FRONT ACROSS ERN ID/WY/SE MT WITH AN
ATTENDANT THREAT FOR ISOLATED DAMAGING WINDS AND SOME HAIL.
CONVECTION IS THEN EXPECTED TO DEVELOP ENEWD AS ELEVATED STORMS ON
THE IMMEDIATE COOL SIDE OF THE FRONT THROUGH TONIGHT ACROSS THE
DAKOTAS/MN...WHERE MID LEVEL INSTABILITY WILL BE SUFFICIENT FOR
ISOLATED LARGE HAIL.
..THOMPSON/GRAMS.. 04/23/2009
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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