SWODY2
SPC AC 300631
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1231 AM CST FRI NOV 30 2007
VALID 011200Z - 021200Z
..NO SVR TSTM AREAS FORECAST...
..SYNOPSIS...
MODELS SUGGEST THAT A STRONG PACIFIC JET WILL UNDERCUT A HIGH
LATITUDE OMEGA BLOCK DEVELOPING IN THE UPPER FLOW PATTERN ACROSS THE
NORTHEASTERN PACIFIC/ALASKA/AND WESTERN CANADA LATER TODAY THROUGH
SATURDAY. AS THIS OCCURS...SPLIT DOWNSTREAM POLAR JETS OVER THE
U.S. ARE PROGGED TO CONSOLIDATE AND BECOME MORE ZONAL.
WITHIN ONE OF THESE STREAMS...A COUPLE OF SIGNIFICANT SHORT WAVE
IMPULSES...NOW DIGGING ALONG BRITISH COLUMBIA/NORTHERN PACIFIC
COASTAL AREAS..ARE PROGGED TO MIGRATE INLAND...ACROSS THE
INTERMOUNTAIN WEST/ROCKIES/AND PLAINS. THE LEAD IMPULSE IS FORECAST
TO BE ACCOMPANIED BY THE INLAND ACCELERATION OF A CLOSED LOW...NOW
WEST OF BAJA. AND...THE REMNANTS OF THE LOW ARE FORECAST TO LIFT
NORTHEAST OF THE FOUR CORNERS EARLY SATURDAY...BEFORE CONTINUING
RAPIDLY ACROSS THE UPPER MISSISSIPPI VALLEY/GREAT LAKES REGION BY
12Z SUNDAY...AS THE UPSTREAM SHORT WAVE ADVANCES ACROSS THE SOUTHERN
PLATEAU/SOUTHERN ROCKIES INTO THE SOUTH CENTRAL HIGH PLAINS.
THE INTERACTION BETWEEN THE IMPULSES WITHIN THE MERGING STREAMS OF
FLOW IS A SOURCE OF UNCERTAINTY AMONG THE MODELS. BUT...GUIDANCE
GENERALLY INDICATES THAT FAIRLY SIGNIFICANT SURFACE CYCLOGENESIS
WILL OCCUR FROM THE LEE OF THE CENTRAL ROCKIES THROUGH THE UPPER
GREAT LAKES REGION. THIS IS EXPECTED TO BE ACCOMPANIED BY A RETURN
FLOW OF MOISTURE OFF THE WESTERN GULF OF MEXICO INTO THE CENTRAL
STATES...FOLLOWED BY A COLD INTRUSION TO THE LEE OF THE ROCKIES.
..CNTRL PLAINS INTO MID/UPPER MISSISSIPPI VALLEY...
STRONG LOWER/MID TROPOSPHERIC WARM ADVECTION AND THE LEADING EDGE OF
MOISTURE RETURN APPEAR LIKELY TO ACCOMPANY THE REMNANTS OF THE
CLOSED LOW AS IT ACCELERATES NORTHEAST OF THE CENTRAL ROCKIES
THROUGH THE UPPER MIDWEST. HOWEVER...MODEL FORECAST SOUNDINGS ARE
SUGGESTIVE THAT WEAK MID-LEVEL LAPSE RATES WILL MINIMIZE
DESTABILIZATION...AND LIMIT THE RISK OF THUNDERSTORM ACTIVITY...WITH
THE INITIAL ZONE OF STRONGER FORCING SHIFTING NORTHEAST OF THE LOWER
MISSOURI VALLEY DURING THE DAY SATURDAY.
A BETTER CHANCE FOR THUNDERSTORMS APPEARS TO EXIST IN THE WARM
SECTOR OF THE SURFACE LOW LATER SATURDAY/SATURDAY NIGHT...WITH THE
ONSET OF AT LEAST WEAK MID-LEVEL COOLING...AND THE APPROACH OF THE
NEXT IMPULSE FROM THE SOUTHWESTERN STATES. CAPE MAY INCREASE INTO
THE 500-1000 J/KG RANGE...GENERALLY BASED IN A MOIST LAYER ABOVE A
NEAR SURFACE STABLE LAYER...ACROSS PARTS OF THE EAST CENTRAL PLAINS
INTO THE LOWER MISSOURI VALLEY. IF THIS OCCURS...STRONG DEEP LAYER
SHEAR COULD CONTRIBUTE TO SOME HAIL APPROACHING OR BRIEFLY EXCEEDING
SEVERE LIMITS IN THE MOST VIGOROUS CELLS.
..FOUR CORNERS STATES...
DESTABILIZATION BENEATH A COOL MID-LEVEL ENVIRONMENT ACROSS THE
HIGHER TERRAIN IS EXPECTED TO SUPPORT SCATTERED THUNDERSTORM
ACTIVITY. THIS WILL BE AIDED BY LARGE-SCALE FORCING ASSOCIATED WITH
THE SHORT WAVE TROUGH WHICH IS PROGGED TO SHIFT EAST OF THE LOWER
COLORADO VALLEY SATURDAY AFTERNOON/EVENING.
..PACIFIC NORTHWEST...
MOIST LOW-LEVEL ONSHORE FLOW INTO THE WESTERN SLOPES OF THE NORTHERN
CASCADES IS FORECAST TO STRENGTHEN SATURDAY AFTERNOON INTO SATURDAY
NIGHT...ASSOCIATED WITH AN UPPER IMPULSE PIVOTING THROUGH CYCLONIC
FLOW NEAR THE BRITISH COLUMBIA COAST. THIS IS EXPECTED TO OCCUR
BENEATH A LINGERING COLD MID-LEVEL AIR MASS... WHICH MAY SUPPORT
SUFFICIENT DESTABILIZATION FOR WIDELY SCATTERED WEAK THUNDERSTORM
ACTIVITY.
.KERR.. 11/30/2007
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