SPC AC 221245
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0745 AM CDT SAT MAY 22 2010
VALID 221300Z - 231200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE NRN PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE CAROLINAS...
...SYNOPSIS...
UPPER AIR PATTERN THIS PERIOD WILL BE DOMINATED BY A BELT OF FAST
SWLY FLOW FROM THE LOWER CO RIVER VALLEY TO THE DAKOTAS/MN ON THE
ERN FLANK OF A LARGE SCALE TROUGH ESTABLISHED OVER THE WRN U.S. THIS
STRONGER FLOW WILL COINCIDE WITH A SLOW-MOVING DEEP-LAYER FRONTAL
ZONE ALONG WHICH THE MOST SIGNIFICANT PERTURBATION WILL TRACK OUT OF
THE INTERMOUNTAIN REGION AND OVER THE DAKOTAS LATER TODAY.
DOWNSTREAM FROM THE WRN U.S. TOUGH...UPPER RIDGE WILL BUILD ACROSS
THE MS VALLEY AND GREAT LAKES AS A WEAKENING UPPER TROUGH IS SHUNTED
EWD ACROSS THE APPALACHIANS/MID ATLANTIC.
...NRN PLAINS...
POTENT LOW LEVEL JET OF 50-60KT WAS CONTINUING TO TRANSPORT HIGH
THETA-E AIR NWD ACROSS THE GREAT PLAINS THIS MORNING BENEATH
WELL-DEFINED CAP/ELEVATED MIXED LAYER EMANATING FROM THE HIGHER
TERRAIN UPSTREAM /REF LBF RAOB WITH OBSERVED 8.6C PER KM 700-500MB
LAPSE RATE...0.84 INCH PW...AND 14C TEMP AT 700MB/.
ONGOING MCS ACROSS ERN SD WAS BEING FUELED BY THIS PLUME OF ELEVATED
INSTABILITY AND SUSTAINED BY MASS AND MOISTURE INFLUX ON THE NOSE OF
60KT LOW LEVEL JET. ADDITIONAL/RECENT DEVELOPMENT HAS OCCURRED ON
THE EDGE OF THE CAP ACROSS ERN NEB AND IS FORECAST TO DRIFT INTO IA
THIS MORNING PERHAPS POSING A THREAT FOR ISOLATED LARGE HAIL /REF
SWOMCD NUMBER 660/.
ANOTHER ROUND OF ROBUST CONVECTIVE DEVELOPMENT IS EXPECTED LATER
TODAY ACROSS PARTS OF ERN WY AND THE ADJACENT HIGH PLAINS AS A
LOW-AMPLITUDE SHORT WAVE TROUGH EMERGES ACROSS THE HIGH PLAINS AND
ACTS ON WARM AND VERY UNSTABLE AIR MASS FROM NEB NWD ACROSS THE
DAKOTAS. BY LATE AFTERNOON EXPECT MLCAPE VALUES IN THIS AREA TO
EXCEED 3000 J PER KG. WHILE CAP WILL LIKELY HOLD ACROSS MUCH OF THE
PLAINS SOUTH OF NEB...COMBINATION OF SURFACE HEATING AND WEAK HEIGHT
FALLS WITH APPROACHING SHORT WAVE SHOULD BE SUFFICIENT TO OVERCOME
REMAINING INHIBITION AND SUPPORT THUNDERSTORM INITIATION IN STRONGLY
SHEARED DEEP-LAYER FLOW.
THUNDERSTORMS WILL OCCUR COINCIDENT WITH WEAK FRONTAL WAVE TRACKING
NEWD ALONG THE SURFACE FRONT...AND A DRY LINE NOSING ENEWD NEAR THE
SD/NEB BORDER. MODEST LOW LEVEL HODOGRAPH CURVATURE AND MAGNITUDE OF
INSTABILITY SUGGEST THAT A COUPLE OF TORNADOES AND VERY
LARGE/DAMAGING HAIL WILL BE POSSIBLE WITH DISCRETE
STORMS/SUPERCELLS. THIS ACTIVITY MAY STRUGGLE TO BECOME MORE
WIDESPREAD INITIALLY DUE TO STRONG CAPPING AND TENDENCY FOR STORMS
TO TAKE ON MORE LINEAR CHARACTERISTICS AND BE UNDERCUT ALONG THE
FRONTAL ZONE WHERE STRONGEST MESOSCALE FORCING CAN ACT TO FURTHER
ERODE THE CAP.
FORCING ALONG THE EDGE OF THE CAP THROUGH THE EVENING AND THEN
STRENGTHENING NOCTURNAL LOW LEVEL JET SHOULD CONTRIBUTE TO SEVERE
MCS EVOLVING ACROSS SD...AND PERHAPS PARTS OF ND...AND THEN
SPREADING ENEWD INTO MN THROUGH EARLY SUNDAY MORNING.
...NC PIEDMONT TO SC MIDLANDS...
MODEST NW FLOW OF 20-30KT AND GRADUAL DIURNAL DESTABILIZATION...WITH
SBCAPE RANGING FROM 1000 TO 2000 J PER KG BY AFTERNOON...MAY SUPPORT
INCREASING SEVERE STORM POTENTIAL THESE AREAS. FORCING FOR LARGER
SCALE ASCENT WILL BE SUBTLE BUT IT APPEARS REGION WILL COME UNDER
THE INFLUENCE OF WEAK HEIGHT FALLS FROM THE TROUGH PASSING NORTH OF
THE AREA AND LEE-TROUGH WILL BECOME COINCIDENT WITH AXIS OF GREATEST
FORECAST DESTABILIZATION.
EFFECTIVE BULK SHEAR ON THE ORDER OF 30KT WILL FURTHER AID STORM
PERSISTENCE AND ORGANIZATION WITH A FEW HAILSTONES POSSIBLY
EXCEEDING ONE INCH ALONG WITH LOCALLY DAMAGING WIND GUSTS.
...WEST TX...
HOT TEMPERATURES EXCEEDING 90F...TERRAIN INFLUENCES...AND DRY LINE
MIXING MAY PROVE SUFFICIENT TO OVERCOME WARM EML AND RESULT IN
ISOLATED STORM DEVELOPMENT LATE THIS AFTERNOON AS INDICATED IN SOME
NUMERICAL GUIDANCE. CHANCES FOR NUMEROUS STORMS APPEAR LOW BUT
ABUNDANT CAPE AND ADEQUATE SHEAR THIS REGION SUGGEST A CONDITIONAL
LOW PROBABILITY OF SEVERE HAIL/WIND IS WARRANTED.
..CARBIN/ROGERS.. 05/22/2010
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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