DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 240101
SWODY1
SPC AC 240059

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0759 PM CDT SUN SEP 23 2007

VALID 240100Z - 241200Z

..THERE IS A SLGT RISK OF SVR TSTMS ACROSS OF THE NRN PLAINS AND
CNTRL HIGH PLAINS...

..NRN PLAINS AND CNTRL HIGH PLAINS...
A HIGH-AMPLITUDE UPPER-LEVEL TROUGH IS EVIDENT ON WATER VAPOR
IMAGERY ACROSS THE WRN STATES. AT THE SFC...A COLD FRONT EXTENDS SWD
ACROSS THE CNTRL DAKOTAS INTO WRN NEB. LOW-LEVEL CONVERGENCE HAS
MARKEDLY INCREASED ACROSS WRN NEB AND CNTRL SD AND SCATTERED STRONG
THUNDERSTORMS ARE DEVELOPING ALONG AND JUST AHEAD OF THE FRONT. THE
AIRMASS AHEAD OF THE BOUNDARY IS MODERATELY UNSTABLE ACCORDING TO
OBJECTIVE ANALYSIS AND THUNDERSTORMS SHOULD EXPAND IN COVERAGE WITH
THE DEVELOPMENT OF SEVERAL MCS/S POSSIBLE THIS EVENING.

A 75 KT MID-LEVEL JET CURRENTLY OVER NW CO AND SRN WY WILL CONTINUE
TO EJECT NEWD TOWARD THE REGION. AHEAD OF THE JET...STRONG VERTICAL
SHEAR IS ALREADY IN PLACE AND THUNDERSTORMS SHOULD BECOME
INCREASINGLY ORGANIZED THIS EVENING ACROSS THE SLIGHT RISK AREA.
INITIALLY...SUPERCELLS WITH LARGE HAIL AND WIND DAMAGE WILL BE
POSSIBLE ESPECIALLY ACROSS ERN ND AND FAR NW MN WHERE INSTABILITY IS
MAXIMIZED AND 0-6 KM SHEAR VALUES LIKELY EXCEED 60 KT. IN
ADDITION...LOW-LEVEL CONVERGENCE IS STRONG ALONG THE BOUNDARY FROM
CNTRL SD TO WRN NEB AND OBJECTIVE ANALYSIS SHOWS STEEP LOW-LEVEL
LAPSE RATES ALONG THIS CORRIDOR. THIS MAY BE FAVORABLE FOR AN
ENHANCED WIND DAMAGE THREAT ESPECIALLY IF A LINEAR MCS CAN ORGANIZE
THIS EVENING BEHIND THE FRONT WHERE SFC WINDS ARE VEERED AND
UNIDIRECTIONAL BOUNDARY LAYER WINDS EXIST. THE GREATEST SEVERE
THREAT SHOULD OCCUR OVER THE NEXT 2 TO 3 HOURS BEFORE INSTABILITY
WEAKENS AND A CAPPING INVERSION STRENGTHENS ACROSS THE REGION.

..COASTAL LA...
A CLUSTER OF THUNDERSTORMS IS FORECAST TO ORGANIZE OFF THE COAST OF
LA TONIGHT ASSOCIATED WITH A PLUME OF MOISTURE ACROSS THE NRN GULF
OF MEXICO. BOTH THE NAM AND GFS MODELS INCREASE LOW-LEVEL FLOW IN
THE VICINITY OF THIS MCS AND SHEAR PROFILES MAY BE SUFFICIENT FOR
ROTATING STORMS...SOME OF WHICH MAY APPROACH THE LA COAST LATE
TONIGHT. HOWEVER...THE STRONGEST LOW-LEVEL SHEAR IS FORECAST TO
REMAIN OFFSHORE SUGGESTING THE SEVERE THREAT SHOULD REMAIN SOUTH OF
THE LA COAST.

.BROYLES.. 09/24/2007

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