SWODY2
SPC AC 081730
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM CDT SUN MAY 08 2011
VALID 091200Z - 101200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE NORTHERN PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE
MIDWEST...
...SYNOPSIS...
AN INCREASINGLY AMPLIFIED/BLOCKY LONGWAVE UPPER FLOW REGIME WILL
PREVAIL INTO MONDAY OVER THE CONUS...WITH A NEARLY STATIONARY CLOSED
LOW OVER THE WESTERN ATLANTIC AND A BROAD TROUGH OVER THE WESTERN
STATES. IN REGARDS TO THE WESTERN CONUS UPPER TROUGH...A LEAD
SHORTWAVE PORTION OF THIS TROUGH IS EXPECTED TO ADVANCE
NORTHEASTWARD FROM THE CENTRAL ROCKIES TO THE NORTHERN HIGH PLAINS
ON MONDAY...WHILE THE BASAL PORTION OF THE WEST TROUGH DIGS
SOUTHWARD OVER SOUTHERN CA AND THE LOWER CO RIVER VALLEY.
...NORTHERN PLAINS...
AN INFLUX OF LOW LEVEL MOISTURE WILL CONTINUE TO SURGE CYCLONICALLY
ON THE EASTERN/NORTHERN PERIPHERY OF A DEEPENING/GRADUAL
EAST-NORTHEASTWARD SHIFTING NORTH-CENTRAL HIGH PLAINS SURFACE
LOW...AS A WARM FRONT BECOMES INCREASINGLY ESTABLISHED NORTHWARD
INTO EXTREME NORTHERN NEB AND SOUTHERN/CENTRAL SD. WITH INCREASING
DYNAMIC FORCING FOR ASCENT AS AIDED BY A LEAD SHORTWAVE TROUGH
ADVANCING FROM THE CENTRAL ROCKIES TO THE NORTHERN HIGH
PLAINS...SURFACE BASED TSTMS ARE LIKELY TO DEVELOP/INCREASE BY
MID/LATE AFTERNOON...INITIALLY IN THE LEE OF THE ROCKIES FRONT RANGE
AND/OR VICINITY OF THE BLACK HILLS. A SUBSEQUENT UPSWING IN DEEP
CONVECTIVE COVERAGE/VIGOR IS ANTICIPATED INTO EARLY/MID EVENING AS
STORMS DEVELOP EAST-NORTHEASTWARD ACROSS SD IN VICINITY OF THE WARM
FRONT/LOW-LEVEL MOIST AXIS. INCREASINGLY STRONG/DIFFLUENT FLOW ALOFT
WILL SUPPORT SUPERCELLS CAPABLE OF LARGE HAIL...IN ADDITION TO THE
POSSIBILITY OF TORNADOES. A NOCTURNALLY STRENGTHENING LOW LEVEL
JET/ISENTROPIC LIFT REGIME NORTH OF THE WARM FRONT WILL SUPPORT AT
LEAST AN ISOLATED SEVERE HAIL THREAT CONTINUING THROUGH THE NIGHT
FROM THE EASTERN DAKOTAS INTO MN.
...MIDWEST/MS VALLEY/LOWER OH VALLEY...
SPREAD AMONGST NUMERICAL GUIDANCE AND THE POTENTIAL DEGREE OF
AFTERNOON CAPPING CONTINUES TO LIMIT FORECAST CONFIDENCE FOR MONDAY.
THAT SAID...THE MOST LIKELY SCENARIO IS FOR CLUSTERS OF ELEVATED
TSTMS TO BE ONGOING ACROSS PORTIONS OF IA AND/OR IL/EASTERN MO
MONDAY MORNING...WITH SOME OF THESE STORMS CAPABLE OF SEVERE HAIL. A
VEERING LOW LEVEL JET WILL PROBABLY MAINTAIN AT LEAST ELEVATED
STORMS EAST-NORTHEAST TOWARD THE GREAT LAKES REGION DURING THE DAY.
THEREAFTER...THE ELEVATED MIXED LAYER NEAR THE WARM FRONT WILL ONLY
STRENGTHEN DURING THE DAY...WITH CONSIDERABLE UNCERTAINTY REGARDING
THE LIKELIHOOD OF SURFACE BASED TSTM DEVELOPMENT DURING THE
AFTERNOON/EARLY EVENING. THAT SAID...THERE IS CONDITIONAL-TYPE
CONCERN THAT ISOLATED SURFACE BASED TSTMS COULD DEVELOP SOMEWHERE IN
A NEAR WARM FRONTAL CORRIDOR FROM IA INTO CENTRAL IL. AT LEAST IN A
CONDITIONAL SENSE...VERY STEEP MID LEVEL LAPSE RATES AND FAVORABLE
EFFECTIVE SHEAR WOULD BE FAVORABLE FOR SUPERCELLS CAPABLE OF LARGE
HAIL/DAMAGING WINDS AND PERHAPS A FEW TORNADOES.
...SOUTHEAST STATES...
BACKDOOR FRONTAL BOUNDARY WILL CONTINUE TO SETTLE SOUTHWESTWARD FROM
SC TO GA/FAR NORTH FL ON MONDAY. GIVEN A WEAK CAP...SCATTERED TSTMS
ARE LIKELY TO DEVELOP ALONG/JUST SOUTHWEST OF THE SURFACE FRONT
DURING THE AFTERNOON WITHIN A MOIST/MODERATELY UNSTABLE BOUNDARY
LAYER. AIDED BY 20-30 KT NORTHWESTERLY MID LEVEL FLOW...THESE
MULTICELLULAR TSTMS MAY ORGANIZE INTO SOUTHWARD-MOVING LINEAR
CLUSTERS CAPABLE OF DAMAGING WINDS/SOME SEVERE HAIL.
...WEST-CENTRAL TX...
12Z BASED NUMERICAL GUIDANCE IMPLIES THAT GRADUAL HEIGHT FALLS WILL
OCCUR ON MONDAY IN ASSOCIATION WITH A LEAD IMPULSE ACROSS WEST TX.
VARIOUS NUMERICAL GUIDANCE SUCH AS THE 12Z WRF-NAM AND VARIOUS 09Z
SREF MEMBERSHIP IMPLY ISOLATED TSTM DEVELOPMENT IS POSSIBLE IN
VICINITY OF THE DRYLINE MONDAY LATE AFTERNOON/EARLY
EVENING...ALTHOUGH SOME OF THIS MAY PARTIALLY BE ATTRIBUTABLE TO THE
CAP BEING AGGRESSIVELY ERODED BY THE BMJ SCHEME VIA MID LEVEL
MOISTENING. REGARDLESS...AT LEAST A LOW PROBABILITY OF TSTMS SEEMS
WARRANTED...AND THIS REGION WILL BE SUBSEQUENTLY REEVALUATED FOR
WHAT COULD BE AN ISOLATED SEVERE RISK IN THE FORM OF HAIL IN
VICINITY OF THE DRYLINE.
..GUYER.. 05/08/2011
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