SWODY2
SPC AC 171730
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM CDT MON SEP 17 2007
VALID 181200Z - 191200Z
..THERE IS A SLGT RISK OF SVR TSTMS PORTIONS KS TO UPPER MS
VALLEY...
..SYNOPSIS...
IN MID/UPPER LEVELS...LARGE SCALE PATTERN WILL CONTINUE TO INCLUDE
MEAN WRN TROUGH...AND POSITIVELY TILTED RIDGING FROM SE TX TO QUE.
PRONOUNCED SHORTWAVE TROUGH IS EVIDENT ATTM IN MOISTURE CHANNEL
IMAGERY OVER GREAT BASIN REGION. THIS PERTURBATION IS FCST TO
DEAMPLIFY AND ACCELERATE NEWD ACROSS CENTRAL/NRN PLAINS AND
MID/UPPER MS VALLEY. SHORTWAVE TROUGH NOW EMBEDDED WITHIN UPSTREAM
LONGWAVE RIDGE -- OVER AK -- IS EXPECTED TO PHASE WITH PERTURBATIONS
NOW OVER NRN/WRN BC AND DIG SSEWD...EVOLVING INTO CLOSE LOW OVER
WA/ORE BY 19/12Z. MEANWHILE...ELONGATED CYCLONIC SHEAR ZONE ALOFT
WILL PERSIST FROM CUBA ACROSS FL TO NEAR COASTAL NC. EMBEDDED/WEAK
UPPER CYCLONE NOW INVOF HAT MAY PERSIST..WHILE ANOTHER DEVELOPS OVER
ERN/SRN FL IN SUPPORT OF GEN TSTM POTENTIAL THERE.
AT SFC...CYCLONE NOW ANALYZED OVER CENTRAL SD SHOULD MOVE NEWD AND
WEAKEN. ANOTHER LOW -- INITIALLY OVER S-CENTRAL SASK -- SHOULD MOVE
GENERALLY ESEWD THEN EWD JUST N OF CANADIAN BORDER...ALONG WARM
FRONT NOW LIFTING NWD ACROSS ND AND MN. CONSIDERABLE DIFFERENCES
EXIST AMONG SHORT-RANGE GUIDANCE...INCLUDING SREF
MEMBERS...REGARDING STRENGTH OF THIS LOW. ACCOMPANYING COLD FRONT
SHOULD MOVE SEWD ACROSS NRN PLAINS AND CENTRAL HIGH PLAINS. BY
19/00Z...FRONT SHOULD EXTEND FROM MN/ONT BORDER AREA LOW SWWD ACROSS
FSD/SUX REGION...S-CENTRAL NEB...WRN KS...E-CENTRAL/SERN CO...WITH
DRYLINE FROM NWRN/W-CENTRAL KS FRONTAL INTERSECTION SSWWD ACROSS TX
PANHANDLE.
..CENTRAL PLAINS TO UPPER MS VALLEY...
SCATTERED TSTMS IN BANDS OR CLUSTERS SHOULD DEVELOP ALONG/AHEAD OF
SFC COLD FRONT THROUGHOUT DAY AND EVENING. DEEP-LAYER SHEAR AND
LARGE SCALE ASCENT...AHEAD OF EJECTING SWRN TROUGH...EACH SHOULD
SPREAD OVER MUCH OF SFC COLD FRONTAL ZONE...AS WELL AS OVER
FOREGOING WARM SECTOR. MEANWHILE LOW LEVEL LAPSE RATES WILL STEEPEN
THROUGH DAY...AWAY FROM THICKLY CLOUDED AREAS...RELATED TO
INSOLATION. MEAN WIND APPEARS TO BE MORE PARALLEL TO FRONTAL
ORIENTATION FROM NEB NEWD...WHEREAS POTENTIAL FOR RELATIVELY
DISCRETE STORMS AND SUPERCELLS MAY BE GREATER OVER KS PORTION OF
OUTLOOK WITH STRONGER CAP IN PLACE. SFC DEW POINTS GENERALLY
MID/UPPER 60S...LOCALLY LOW 70S F...SHOULD CONTRIBUTE TO MLCAPES
AROUND 2000 J/KG...JUXTAPOSED WITH 35-45 KT EFFECTIVE SHEAR.
PRIND DEEP-LAYER VERTICAL SHEAR WILL BE FAVORABLE FOR SVR ACROSS
MUCH OF MN/WI...ALONG/AHEAD OF SFC FRONT...HOWEVER PROBABLE PRESENCE
OF CLOUDS/PRECIP AND LACK OF PRECURSORY/AMBIENT HIGH THETAE IN
BOUNDARY LAYER EACH WILL SUBSTANTIALLY LIMIT BUOYANCY. THIS RENDERS
SVR PROBABILITIES HIGHLY CONDITIONAL -- AND MORE SO WITH NWD EXTENT
-- ACROSS THIS REGION.
.EDWARDS.. 09/17/2007
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