SWODY1
SPC AC 020059
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0759 PM CDT THU SEP 01 2011
VALID 020100Z - 021200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS MN/WI/LS/WRN UPPER
MI...
...SYNOPSIS...
BROAD AREA OF HIGH HEIGHTS ALOFT...FROM GA-MO-AZ...REMAINS DOMINANT
UPPER-AIR FEATURE. POSITIVELY TILTED TROUGHING FROM SRN SK TO NRN
CA LINKS AT LEAST TWO DISTINCT SHORTWAVE TROUGHS AND EMBEDDED
VORTICITY MAXIMA...FIRST OVER CENTRAL MT AND SECOND OVER CENTRAL NV.
NRN SHORTWAVE TROUGH IS FCST TO MOVE ENEWD OVERNIGHT AND DEAMPLIFY
SOMEWHAT...REACHING NRN MN BY 12Z. SRN TROUGH WILL DRIFT GENERALLY
EWD TOWARD UT BORDER THROUGH REMAINDER PERIOD. FARTHER
E...TROUGHING CURRENTLY EVIDENT FROM ERN NY SSWWD TO COASTAL
MID-ATLANTIC AND DELMARVA REGIONS WILL MOVE OFFSHORE
OVERNIGHT...LEAVING BEHIND DIFLUENT NNWLY FLOW FIELD ALOFT.
AT SFC...23Z ANALYSIS SHOWED LOW OVER SWRN MN NEAR MVE...WARM FRONT
EWD ACROSS MSP AREA THEN SEWD OVER SERN WI. COLD FRONT WAS DRAWN
FROM EXTREME N-CENTRAL MN SWWD THROUGH LOW THEN SWWD ACROSS SERN SD
TO BBW AREA. THIS BOUNDARY BECAME QUASISTATIONARY OR SLIGHTLY
WARM-FRONTAL WNWWD TO ANOTHER SFC LOW NEAR DGW. SEPARATE
FRONTAL/CONVERGENCE ZONE...DEMARCATING NRN FRINGE OF VERY
HOT/WELL-MIXED AIR TO ITS S...WAS DRAWN FROM LOW N LAA EWD ACROSS
NRN KS TO BETWEEN MHK-STJ. MN SFC LOW SHOULD MOVE NEWD ACROSS LS
OVERNIGHT AND WEAKEN...WHILE COLD FRONT MOVES SEWD TO NWRN
IA...S-CENTRAL NEB AND NERN CO.
...UPPER MIDWEST TO CENTRAL PLAINS...
SVR THREAT IS BECOMING MORE CONDITIONAL WITH TIME OVER REMAINDER OF
OUTLOOK AREA...GIVEN STRENGTH OF MLCINH EVIDENT IN 00Z MPX RAOB AND
UNCERTAINTIES REGARDING FRONTAL ASCENT. VIS IMAGERY SHOWS SOME
TOWERS INVOF SFC FRONT OVER CENTRAL MN...THOUGH WINDOW FOR SFC-BASED
DEVELOPMENT WILL CLOSE FAIRLY RAPIDLY AFTER ABOUT 02Z. ATTM...WILL
RETAIN SHRUNKEN 15% HAIL AREA...AND RATCHET WIND PROBABILITIES DOWN
TO 5% GIVEN LIKELIHOOD THAT DIABATICALLY STABILIZING BOUNDARY LAYER
WILL FURTHER INCREASE MLCINH AND WEAKEN DCAPE.
...CENTRAL PLAINS...
SCATTERED TSTMS HAVE DEVELOPED IN REGIME OF DIURNAL/DIABATIC HEATING
AND UPSLOPE FLOW N OF FRONT...ACROSS PORTIONS SWRN WY...NEB
PANHANDLE AND SWRN SD. POTENTIAL WILL EXIST FOR ANOTHER FEW HOURS
FOR STG-SVR GUSTS FROM A FEW OF THESE TSTMS...PER MODIFIED 00Z LBF
RAOB SHOWING DRY SUBCLOUD LAYER. THOUGH MOISTURE IS MRGL IN CURRENT
CONVECTIVE REGIME...SOME OF THIS ACTIVITY MAY PERSIST INTO MORE
ROBUST LOW-LEVEL THETAE ACROSS NRN NEB AND SD. ISOLATED HAIL NEAR
SVR LEVELS IS POSSIBLE...AMIDST ROUGHLY 50-KT EFFECTIVE SHEAR
MAGNITUDES. ADDITIONAL DEVELOPMENT MAY OCCUR OVER SWRN/CENTRAL NEB
AT SIMILAR RELATIVE DISTANCES FROM FRONT AS IT MOVES FARTHER SEWD
OVERNIGHT...ROOTED IN ELEVATED PARCELS LIFTED FRONTALLY TO
LFC...ALSO WITH ISOLATED SVR HAIL/GUST POTENTIAL. THREAT APPEARS
TOO ISOLATED/SHORT-LIVED FOR CATEGORICAL SVR AREA.
...INTERIOR MID-ATLANTIC TO LOWER GREAT LAKES...
ISOLATED TO WIDELY SCATTERED TSTMS OVER PORTIONS WRN NY AND PA MAY
PERSIST THROUGH EVENING...MOVING SEWD IN REGIME OF WEAK MLCINH AND
FAVORABLE SFC THETAE WITH SFC DEW POINTS MID-60S F. DEEP-LAYER
SHEAR IS AT LEAST MRGLLY FAVORABLE FOR SVR WITH EFFECTIVE SHEAR
MAGNITUDES 35-45 KT DERIVED FROM MODIFIED PIT RAOB AND RUC
SOUNDINGS...AND MLCAPE UP TO ABOUT 1000 J/KG. ISOLATED DAMAGING
GUSTS AND HAIL NEAR SVR LEVELS MAY OCCUR...AND A TORNADO CANNOT BE
COMPLETELY RULED OUT GIVEN SUPPORTIVE STORM-SCALE PROCESSES. SLOWLY
STABILIZING BOUNDARY LAYER IS EXPECTED THROUGH REMAINDER
EVENING...GRADUALLY ELEVATING INFLOW LAYER ABOVE SFC...ESPECIALLY
AFTER ABOUT 04Z.
...COASTAL LA...
NHC HAS CLASSIFIED T.D. 13 IN NRN GULF...LOCATED NEAR 26.6N 91.4W AS
OF 00Z. ALTHOUGH THIS SYSTEM REMAINS RATHER BROAD AND POORLY
ORGANIZED ATTM...STRONGEST WINDS JUST ABOVE SFC APPEAR DISPLACED
WELL AWAY FROM CENTER IN PORTIONS NRN/ERN SEMICIRCLES...WITH 25-30
KT ELYS EVIDENT IN .5-3 KM AGL LAYER IN LIX VWP. HODOGRAPHS MAY
ENLARGE OVERNIGHT...ESPECIALLY IF T.D. 13 INTENSIFIES OR CENTER
RELOCATES FARTHER N. LOW-LEVEL SHEAR MAY BECOME AT LEAST MRGLLY
FAVORABLE FOR SHALLOW SUPERCELLS AND CONDITIONAL TORNADO POTENTIAL N
THROUGH NE OF GULF SFC LOW. REF NHC ADVISORIES FOR LATEST
TRACK/INTENSITY FCST GUIDANCE ON THIS SYSTEM.
..EDWARDS.. 09/02/2011
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