DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 250558
SWODY2
SPC AC 250557

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1257 AM CDT WED APR 25 2012

VALID 261200Z - 271200Z

...THERE IS A SLGT RISK OF SVR TSTMS THU AND THU NIGHT ACROSS PARTS
OF THE CNTRL HIGH PLAINS...

...SYNOPSIS...
MODELS CONTINUE TO INDICATE THAT A MID-LEVEL HIGH CENTER WILL BEGIN
TO EVOLVE OVER THE CENTRAL CANADIAN PROVINCES DURING THIS FORECAST
PERIOD. AS THIS OCCURS...A LARGE CLOSED LOW...NOW DIGGING ACROSS
THE NORTHEAST PACIFIC...APPEARS LIKELY TO WEAKEN...WITH AN
ELONGATING/REMNANT CIRCULATION CENTER GRADUALLY SHIFTING INTO THE
BRITISH COLUMBIA COAST...WHILE ANOTHER PORTION SPLITS OFF ACROSS THE
PACIFIC NORTHWEST COAST INTO THE NORTHERN INTERMOUNTAIN REGION. AT
THE SAME TIME...WITHIN A SEPARATE BRANCH OF FLOW TO THE
SOUTH...GUIDANCE SUGGESTS THAT ANOTHER CLOSED LOW WILL GENERALLY
MAINTAIN ITS IDENTITY AS IT ACCELERATES INLAND...ACROSS SOUTHERN
CALIFORNIA/NORTHERN BAJA BY 12Z THURSDAY...INTO THE CENTRAL HIGH
PLAINS BY 12Z FRIDAY.

MEANWHILE...TO THE EAST OF THE HIGH...ANOTHER SIGNIFICANT TROUGH IS
EXPECTED TO DIG ACROSS PARTS OF ONTARIO AND QUEBEC INTO THE
NORTHEASTERN STATES. THIS WILL CONTRIBUTE TO THE MAINTENANCE OF
CYCLONIC MID/UPPER FLOW ACROSS MUCH OF THE EAST...IN THE WAKE OF THE
AMPLIFIED UPPER TROUGH NOW BEGINNING TO DEPART THE ATLANTIC
SEABOARD.

SUBSTANTIVE BOUNDARY LAYER MODIFICATION OVER THE GULF OF MEXICO IN
THE WAKE OF THIS LATTER FEATURE WILL BE SLOW TO OCCUR...AND THE LACK
OF BETTER MOISTURE RETURN OFF THE GULF OF MEXICO SEEMS LIKELY TO
LIMIT THE CONVECTIVE POTENTIAL FOR THIS PERIOD. CONCERN STILL
EXISTS THAT MODELS...PARTICULARLY THE NAM...MAY BE TOO AGGRESSIVE
WITH MOISTENING ALONG AND SOUTH OF A DEVELOPING FRONTAL ZONE
ASSOCIATED WITH THE EVOLVING UPPER PATTERN...FROM PORTIONS OF THE
MID ATLANTIC COAST INTO THE CENTRAL PLAINS BY LATE THURSDAY
AFTERNOON. IT IS POSSIBLE THAT EVAPOTRANSPIRATION COULD AUGMENT A
WEAK MOISTURE INFLUX NOW ONGOING ACROSS THE WESTERN GULF COAST.
HOWEVER...DEW POINTS MAY NOT EXCEED 60-64F...AND EVEN THIS MAY BE
CONFINED TO BENEATH STRONGER MID-LEVEL CAPPING ADVECTING
NORTHEASTWARD ACROSS THE SOUTHERN PLAINS...WITH MID/UPPER 50S MORE
PROBABLE ACROSS THE CENTRAL HIGH PLAINS...AND NOT MUCH HIGHER ACROSS
THE OHIO/TENNESSEE VALLEYS INTO THE MID ATLANTIC STATES.

...CENTRAL HIGH PLAINS...
MOISTENING ALONG AND EAST OF THE DEEPENING LEE SURFACE TROUGH STILL
SHOULD CONTRIBUTE TO SUFFICIENT DESTABILIZATION FOR STRONG/ SEVERE
STORM DEVELOPMENT LATE THURSDAY AFTERNOON AND EVENING...IN THE
PRESENCE OF STEEP LAPSE RATES...AND FORCING/SHEAR ASSOCIATED WITH
THE APPROACHING UPPER IMPULSE. VARIABILITY LINGERS CONCERNING WHEN
THIS FEATURE WILL CROSS THE CENTRAL/SOUTHERN ROCKIES...BUT AT LEAST
ISOLATED TO WIDELY SCATTERED SUPERCELL DEVELOPMENT APPEARS
LIKELY...BEFORE UPSCALE GROWTH INTO ONE OR TWO LARGER STORM CLUSTERS
BECOMES MORE PROBABLE...FROM PARTS OF NORTHEAST COLORADO/SOUTHWEST
NEBRASKA INTO WESTERN KANSAS...BY LATE EVENING.

...OH/TN VALLEY INTO MID ATLANTIC...
MODELS ARE SUGGESTIVE THAT A MID-LEVEL IMPULSE AND ASSOCIATED
SURFACE WAVE MAY BE IN THE PROCESS OF SHIFTING INTO/ACROSS MID
ATLANTIC COASTAL AREAS EARLY IN THE DAY THURSDAY. IN THE WAKE OF
THIS FEATURE...FORCING/FOCUS FOR STORM DEVELOPMENT IS STILL UNCLEAR.
IT MAY BE THAT OROGRAPHY BECOMES THE PRIMARY CONTRIBUTOR TO STORM
INITIATION...AS WEAK TO MODERATE BOUNDARY LAYER DESTABILIZATION
OCCURS NEAR THE CENTRAL/SOUTHERN APPALACHIANS. MODESTLY SHEARED
30-40 KT MEAN WESTERLY LOWER/MID TROPOSPHERIC FLOW WILL SUPPORT AT
LEAST LOW SEVERE PROBABILITIES...BUT IT IS NOT YET CERTAIN THAT
STORM COVERAGE WILL BECOME SUFFICIENT TO SUPPORT A CATEGORICAL
SLIGHT RISK.

..KERR.. 04/25/2012

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