ACUS01 KWNS 180556
SWODY1
SPC AC 180554
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1254 AM CDT TUE SEP 18 2007
VALID 181200Z - 191200Z
..THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE CENTRAL
PLAINS TO THE UPPER MS VALLEY...
..SYNOPSIS...
A MID/UPPER LEVEL TROUGH CURRENTLY MOVING EWD THROUGH THE FOUR
CORNERS REGION IS EXPECTED TO REMAIN PROGRESSIVE AS IT TRACKS NEWD
FROM CO/SRN ROCKIES AT THE START OF DAY 1 TO THE MID MO VALLEY BY
EARLY THIS EVENING...AND THEN REACH THE UPPER GREAT LAKES/NRN
ONTARIO BY 12Z WEDNESDAY. ATTENDANT MID LEVEL JET STREAK WILL
MAINTAIN BAND OF 50-60 KT SWLY FLOW AND STRONG DEEP LAYER SHEAR FROM
THE CENTRAL PLAINS TO WRN GREAT LAKES.
IN THE LOW LEVELS...A COLD FRONT EXTENDING FROM NRN MN SWWD INTO NRN
NEB WILL MOVE EWD THROUGH THE UPPER MS VALLEY TO WRN GREAT LAKES
REGION TODAY...WITH SRN EXTENT SHIFTING SWD ACROSS NEB TO NRN KS.
THIS BOUNDARY SHOULD EXTEND FROM ERN MN SWWD THROUGH NWRN IA TO SWRN
NEB TOWARD 19/00Z. A SURFACE WAVE...ATTENDANT TO PROGRESSIVE CO/SRN
ROCKIES UPPER TROUGH...IS FORECAST TO DEVELOP NEWD ALONG THE COLD
FRONT REACHING EAST CENTRAL MN/NWRN WI BY EARLY THIS EVENING. BY
LATE AFTERNOON...A DRY LINE IS EXPECTED TO EXTEND FROM FRONTAL
INTERSECTION IN SRN NEB/NRN KS SSWWD INTO THE TX PANHANDLE.
..CENTRAL PLAINS TO UPPER MS VALLEY...
AN EXPANSIVE...PRE-FRONTAL CONVECTIVE BAND IS EXPECTED TO BE ONGOING
AT 12Z TODAY FROM THE UPPER MS VALLEY SWWD INTO CENTRAL/ERN NEB TO
PARTS OF WRN KS...AND PERHAPS INTO NWRN OK AND THE TX/OK PANHANDLES.
GIVEN THE LIKELIHOOD FOR AN EXTENSIVE CLOUD SHIELD ASSOCIATED WITH
THIS ONGOING CONVECTION...THE STRONGEST SURFACE HEATING SHOULD OCCUR
TODAY IN THE VICINITY OF THE DRY LINE NWD INTO SRN NEB. HERE...
STEEP MID LEVEL LAPSE RATES SHOULD SUPPORT MODERATE INSTABILITY.
ALTHOUGH MID LEVEL LAPSE RATES ARE EXPECTED TO BE WEAKER
ELSEWHERE...SURFACE HEATING/DESTABILIZATION WILL BE POSSIBLE S OF
THE CLOUD SHIELD INTO ERN IA TO SWRN/CENTRAL WI...AND ALSO NEWD
ALONG THE COLD FRONT THROUGH WRN INTO NRN MN.
NEW TSTM DEVELOPMENT IS EXPECTED IN BANDS OR CLUSTERS ALONG AND
AHEAD OF THE COLD FRONT...AND SWD ALONG THE DRY LINE AS UPWARD
FORCING FOR ASCENT SPREADS NEWD AHEAD OF CO/SRN ROCKIES IMPULSE.
TSTMS MAY RE-INTENSIFY ALONG SRN PERIPHERY OF CLOUD SHIELD FROM NERN
KS TO PARTS OF WI AS BOUNDARY LAYER DESTABILIZES. STRONG DEEP LAYER
SHEAR VECTORS ORIENTED PARALLEL TO THE COLD FRONT AND DIFFERENTIAL
HEATING BOUNDARIES NEWD FROM ERN NEB TO UPPER MS VALLEY SHOULD
RESULT IN MAINLY BOWING STRUCTURES...BUT STRENGTH OF SHEAR MAY ALSO
SUPPORT SUPERCELLS. MEANWHILE...SHEAR VECTOR ORIENTATION FARTHER S
INTO SRN NEB/KS SUGGESTS GREATER POTENTIAL FOR DISCRETE STORMS AND
SUPERCELLS. IN ADDITION TO THREAT FOR DAMAGING WINDS AND HAIL...LOW
LEVEL SHEAR IS EXPECTED TO BE ENHANCED ACROSS SERN MN INTO WEST
CENTRAL WI ALONG TRACK OF SURFACE LOW AS SWLY LLJ STRENGTHENS THIS
AFTERNOON/EVENING. THUS...A TORNADO THREAT WILL BE POSSIBLE ACROSS
THIS AREA FROM LATE AFTERNOON INTO THE EARLY EVENING.
FARTHER N ACROSS CENTRAL INTO NRN MN...TSTMS ARE EXPECTED TO DEVELOP
ALONG THE COLD FRONT AS IT PROGRESSES EWD...BUT WEAKER INSTABILITY
SHOULD LIMIT THE COVERAGE OF THE SEVERE WEATHER THREAT.
.PETERS/BOTHWELL.. 09/18/2007
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