SWODY2
SPC AC 131730
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM CDT WED AUG 13 2008
VALID 141200Z - 151200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS CENTRAL/SRN PLAINS...
...SYNOPSIS...
BROAD/PERSISTENT CYCLONIC GYRE -- NOW CENTERED OVER CENTRAL/SRN QUE
-- IS FCST TO REMAIN QUASISTATIONARY THROUGH PERIOD...BUT WITH STG
SHORTWAVE TROUGH DIGGING SEWD AROUND ITS SWRN SEMICIRCLE. THIS
TROUGH -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY OVER JAMES BAY
AREA -- SHOULD SWIVEL SWD-SEWD OVER LH...SRN ONT AND LOWER GREAT
LAKES DAY-2. MEAN SYNOPTIC TROUGHING WILL BE MAINTAINED SWD ACROSS
CENTRAL APPALACHIANS TO ERN GULF COAST.
UPPER LOW -- NOW MEANDERING SLOWLY/ERRATICALLY ACROSS S-CENTRAL SASK
-- IS FCST BY STG CONSENSUS OF OPERATIONAL/SREF GUIDANCE TO DIG SWD
TOWARD SERN MT/NRN WY BY END OF PERIOD...CONSIDERABLY MORE WWD
POSITION THAN IN MOST PROGS FROM PREVIOUS DAYS. AS THIS
OCCURS...GEN NWLY-WNWLY FLOW REGIME WILL BE MAINTAINED FROM NRN
ROCKIES REGION TO GULF COAST STATES...BUT WITH TIGHTER HEIGHT
GRADIENTS OVER MOST OF CENTRAL/NRN ROCKIES REGION. SHORTWAVE TROUGH
-- CURRENTLY WEAK OVER NRN ID AND WRN MT -- IS FCST TO AMPLIFY AS IT
MOVES SEWD ACROSS CENTRAL ROCKIES DAY-1. THIS TROUGH THEN SHOULD
DECELERATE ACROSS CENTRAL PLAINS DAY-2...AMIDST BROADER REGIME OF
DIFLUENT FLOW DOWNSTREAM FROM UPPER CYCLONE.
AT SFC...WEAK FRONTAL-WAVE LOW INITIALLY OVER GA IS FCST TO
MOVE/REDEVELOP OFFSHORE NC COAST...AS ASSOCIATED/TRAILING FRONTAL
ZONE BECOMES WEAKER AND QUASISTATIONARY NEAR GULF COAST WWD TO S TX.
RATHER MUDDLED PATTERN EXISTS ELSEWHERE ATTM...WITH WEAK AND
ILL-DEFINED SFC FEATURES ACROSS MUCH OF MS VALLEY...GREAT PLAINS AND
INTERMOUNTAIN REGIONS. SFC FRONTOGENESIS -- NOW EVIDENT OVER ERN MT
-- SHOULD EXTEND SWD ACROSS CENTRAL HIGH PLAINS THROUGH EARLY DAY-2
THEN DECELERATE WITH DISTANCE FROM MID/UPPER WAVES OVER ROCKIES. BY
15/00Z...EXPECT SLOW-MOVING BAROCLINIC ZONE FROM N-CENTRAL NM ENEWD
ACROSS TX-OK PANHANDLES...SWRN-CENTRAL KS...E-CENTRAL PORTIONS
NEB/SD...AND ERN ND...PERHAPS ACCOMPANIED BY WEAK LOWS OVER NERN NM
AND ERN ND.
...PORTIONS CENTRAL/SRN PLAINS...
ONE OR TWO WEAKENING TSTM CLUSTERS MAY BE ONGOING AT BEGINNING OF
PERIOD BETWEEN WRN/CENTRAL NEB AND AREA CONTAINING ERN TX
PANHANDLE/WRN OK. SCATTERED AFTERNOON TSTMS SHOULD DEVELOP...AS STG
SFC HEATING WEAKENS SBCINH. SOME OF THIS ACTIVITY MAY PRODUCE SVR
HAIL AND GUSTS...WITH ANOTHER MCS OR TWO POSSIBLE LATE IN PERIOD.
ALTHOUGH FCST MID-UPPER LEVEL FLOW IS LESS THAN IDEAL FOR
SUSTAINED/CYCLIC SUPERCELLS...HEAVY-PRECIP STORMS ARE POSSIBLE...AND
THOSE INTERACTING WITH BOUNDARIES MAY POSE TORNADO THREAT AS WELL.
NWLY FLOW ALOFT WILL CONTRIBUTE TO VERY STG DEEP-LAYER DIRECTIONAL
SHEAR...ALONG WITH ENLARGED HODOGRAPHS AND 35-45 KT EFFECTIVE SHEAR
FAVORABLE FOR SUPERCELLS INVOF BOUNDARIES. DPVA/UVV PRECEDING
SHORTWAVE TROUGH WILL HELP TO MAINTAIN/ENHANCE LAPSE RATES ALOFT
OVER CENTRAL PLAINS. LOCATION/STRENGTH OF SPECIFIC BOUNDARY FOCI
APPEAR NEBULOUS ATTM...AS DOES BAROCLINIC ZONE ITSELF BECAUSE OF
PRIOR CONVECTIVE INFLUENCES POSSIBLE FROM LATE DAY-1 INTO THIS
PERIOD. BECAUSE OF THESE MESOSCALE DEPENDENCIES...ONLY
BROAD-BRUSHED 15-PERCENT AREA WILL BE MAINTAINED ATTM...THOUGH
NARROWER CORRIDOR OF RELATIVELY DENSE SVR REPORTS IS EXPECTED WITH
ANY SUSTAINED MCS THAT CAN DEVELOP AND MOVE SWD/SEWD ACROSS THIS
REGION DURING EVENING/OVERNIGHT HOURS.
...SRN HIGH PLAINS TO FAR W TX...
DIURNAL AXIS OF BUOYANCY SHOULD EXTEND SWWD FROM CENTRAL PLAINS
ACROSS ERN NM TOWARD FAR W TX...RESULTING FROM STG SFC HEATING OF
AIR MASS CONTAINING 50S TO LOW 60S F SFC DEW POINTS. BY LATE
AFTERNOON INTO EARLY EVENING...WELL-MIXED BOUNDARY LAYERS MAY
SUPPORT POTENTIAL FOR STG-SVR GUSTS IN ANY TSTMS THAT CAN ORGANIZE
COLD POOLS AND PROPAGATE SWD/SWWD ACROSS THIS AREA. SRN BRANCH
UPPER JET SHOULD EXTEND FROM CENTRAL NM EWD...ALSO AIDING IN STORM
ORGANIZATION OVER PARTS OF THIS AREA.
...UPPER MIDWEST TO OH VALLEY...
WIDELY SCATTERED TO SCATTERED TSTMS ARE POSSIBLE WITHIN ARC-SHAPED
CORRIDOR E OF FRONTAL ZONE...FROM PORTIONS MN SEWD ACROSS IL THEN
EWD OVER OH VALLEY. ACTIVITY SHOULD BE SUPPORTED BY WEAK LOW LEVEL
WAA...DIURNAL/DIABATIC SFC HEATING AND WEAKENING SBCINH WITHIN CLOUD
BREAKS...AND SFC DEW POINTS GENERALLY 60S F...YIELDING MLCAPES IN
1000-2000 J/KG RANGE IN NAM-KF FCST SOUNDINGS. AREA FROM MN-IL WILL
CORRESPOND TO ZONE OF ENHANCED HEIGHT GRADIENTS IN UPPER LEVELS SW
OF AMPLIFYING ERN GREAT LAKES SHORTWAVE...RESULTING IN SMALL 250 MB
JET MAX 70-80 KT. ALTHOUGH BOTH MAGNITUDES AND DIRECTIONAL CHANGE
OF LOW-MIDLEVEL WINDS WILL REMAIN WEAK...ENHANCED UPPER FLOW MAY AID
IN MULTICELLULAR STORM ORGANIZATION. ISOLATED SVR HAIL/GUSTS ARE
POSSIBLE.
..EDWARDS.. 08/13/2008
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