SPC AC 180559
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1259 AM CDT MON APR 18 2011
VALID 191200Z - 201200Z
...THERE IS A MDT RISK OF SVR TSTMS ACROSS PORTIONS OF
AR/MO/IL/INDIANA/KY AND FAR WESTERN TN...
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE SOUTHERN PLAINS TO THE
MIDWEST/OH RIVER VALLEY...
...MIDWEST/OZARKS AND OH/MIDDLE MS RIVER VALLEYS...
A VERY ACTIVE SEVERE WEATHER DAY IS EXPECTED ACROSS THE REGION ON
TUESDAY/TUESDAY NIGHT...INCLUDING THE POSSIBILITY OF SOME STRONG
TORNADOES IN ADDITION TO LARGE HAIL AND WIDESPREAD DAMAGING WINDS
TUESDAY AFTERNOON/NIGHT.
INITIALLY...EARLY DAY ELEVATED TSTMS /SOME CAPABLE OF SEVERE HAIL/
WILL BE ONGOING ACROSS THE MIDWEST/OH RIVER VALLEY...ON THE NOSE OF
A STRONG SOUTHWESTERLY LOW LEVEL JET AND ON THE EDGE OF A
NORTHEASTWARD BUILDING ELEVATED MIXED LAYER /EML/. SUCH A HAIL
THREAT COULD INCLUDE DOWNSTATE PORTIONS OF IL/INDIANA INTO
KY/SOUTHERN OH THROUGH THE MORNING.
OTHERWISE...BENEATH AN EML-DRIVEN CAP...LOW LEVEL MOISTURE WILL
CONTINUE TO AGGRESSIVELY RETURN NORTH-NORTHEASTWARD AS STRONG
SOUTHWESTERLY LOW LEVEL WINDS ARE MAINTAINED THROUGH THE DAY. WITH
RELATIVELY RICH MOISTURE /AROUND 70 F SURFACE DEWPOINTS AND
REFERENCE THE 00Z OBSERVED CORPUS CHRISTI RAOB/ ALREADY RETURNING
INLAND ACROSS SOUTHEAST TX EARLY TODAY...IT IS PLAUSIBLE THAT A
BROAD CORRIDOR OF LOWER TO MIDDLE 60S F SURFACE DEWPOINTS WILL
BECOME INCREASINGLY ESTABLISHED TO THE EAST OF A LOWER MO VALLEY
SURFACE LOW AND ALONG/SOUTH OF A NORTHWARD MOVING WARM FRONT ACROSS
THE OH RIVER VALLEY/MIDWEST. BENEATH THE STRONG EML/PLUME OF STEEP
MID LEVEL LAPSE RATES...MODERATELY TO STRONG INSTABILITY WILL LIKELY
EXIST ACROSS THE PRE-COLD FRONTAL WARM SECTOR BY AFTERNOON...WITH
UPWARDS OF 2000-4000 J/KG OF MLCAPE POSSIBLE WITHIN A CORRIDOR FROM
EASTERN OK AND AR INTO THE SOUTHEAST HALF OF MO/DOWNSTATE IL AND
ADJACENT PORTIONS OF THE MIDDLE MS VALLEY.
A SOUTH-CENTRAL ROCKIES/CENTRAL PLAINS SHORTWAVE TROUGH EARLY
TUESDAY IS EXPECTED TO GRADUALLY AMPLIFY AND ADVANCE
NORTHEASTWARD/TAKE ON A MORE NEGATIVE TILT ESPECIALLY TUESDAY NIGHT
TOWARD THE UPPER MS RIVER VALLEY/UPPER GREAT LAKES REGION. ATTENDANT
LARGE SCALE FORCING FOR ASCENT/HEIGHT FALLS AND THE ASSOCIATED COLD
FRONT SHOULD ERODE AN OTHERWISE STRONG CAP...WITH SURFACE BASED
TSTMS LIKELY TO ERUPT BY MID/LATE AFTERNOON INTO EARLY EVENING AHEAD
OF THE DEEPENING LOWER MO VALLEY/MIDDLE MS VALLEY SURFACE LOW AND
NORTHEAST-SOUTHWEST ORIENTED COLD FRONT. SUCH VIGOROUS DEEP
CONVECTIVE DEVELOPMENT CURRENTLY APPEARS MOST LIKELY TO INITIALLY
OCCUR ACROSS CENTRAL/SOUTHWEST MO AS WELL AS WESTERN IL AND
NORTHWEST AR/NORTHEAST OK.
AMPLE LOW LEVEL MOISTURE/VERY STEEP LAPSE RATES AND DEEP LAYER
SHEAR OF 40-50 KT COINCIDENT WITH THE COLD FRONT/ADJACENT WARM
SECTOR WILL BE FURTHER ACCENTUATED BY LONG/CURVING LOW LEVEL
HODOGRAPHS AIDED BY 40-55 KT WINDS WITHIN THE LOWEST 1-2 KM. WHILE
VERY LARGE HAIL AND TORNADOES /PERHAPS A FEW STRONG/ WILL BE
POSSIBLE WITH INITIAL SUPERCELLULAR DEVELOPMENT...SEVERAL FACTORS
IMPLY A QUASI-LINEAR EVOLUTION IS PROBABLE SEVERAL HOURS AFTER DEEP
CONVECTIVE INITIATION /ESPECIALLY MID EVENING AND BEYOND/ ACROSS THE
MIDWEST/OH VALLEY. THIS INCLUDES THE LIKELIHOOD/DOMINANCE OF COLD
FRONTAL-TYPE INITIATION /GIVEN A STOUT EML OTHERWISE ACROSS THE WARM
SECTOR/...AS WELL AS RELATIVELY MODEST HIGH LEVEL FLOW/SHEAR AS
COMPARED TO THE LOWER-MIDDLE TROPOSPHERE. UPSCALE GROWTH INTO AN
INCREASINGLY WELL-ORGANIZED/ACCELERATING SQUALL LINE...INCLUDING
LEWP/BOW EVOLUTIONS....IS PROBABLE TUESDAY NIGHT ACROSS THE OH
VALLEY. AS SUCH...A WIDESPREAD DAMAGING WIND AND ISOLATED TORNADO
THREAT SHOULD EVOLVE BY MID/LATE EVENING...AND CONTINUE INTO THE
OVERNIGHT. A RELATIVELY BROAD WARM/MOIST SECTOR ASIDE...THIS WILL BE
SUPPORTED ON THE LARGE SCALE BY THE ANTICIPATED DEEPENING PHASE OF
THE SURFACE CYCLONE TOWARD THE UPPER GREAT LAKES AND A
REINVIGORATION OF A NOCTURNALLY ENHANCED LOW LEVEL WIND FIELD /50-60
KT SOUTHWESTERLY WINDS AROUND 1-2 KM/.
...SOUTHERN PLAINS/ARKLATEX...
PARTIALLY ATTRIBUTABLE TO MORE MODEST LARGE SCALE FORCING FOR ASCENT
AT THESE LATITUDES...A RELATIVELY MORE ISOLATED SEVERE THREAT WILL
BE POSSIBLE IN VICINITY OF THE NORTH-SOUTH DRYLINE ACROSS EASTERN
OK/NORTHEAST TX INTO WESTERN AR/FAR NORTHWEST LA. SUPERCELLS CAPABLE
OF LARGE HAIL AND PERHAPS A TORNADO WILL BE POSSIBLE TUESDAY LATE
AFTERNOON/EVENING. THE COLD FRONT WILL GRADUALLY OVERTAKE THE
DRYLINE FROM NORTHWEST TO SOUTHEAST ACROSS EASTERN OK INTO AR AND
EVENTUALLY NORTH TX/FAR NORTHWEST LA TUESDAY NIGHT. FARTHER
WEST...OTHER MORE ISOLATED/MARGINAL SEVERE TSTMS WITH A HAIL/WIND
RISK COULD DEVELOP ALONG THE WESTWARD EXTENSION OF THE
SOUTH-SOUTHEASTWARD MOVING COLD FRONT ACROSS OK AND THE TX PANHANDLE
TUESDAY LATE AFTERNOON/EARLY EVENING.
..GUYER.. 04/18/2011
CLICK TO GET WUUS02 PTSDY2 PRODUCT
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
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