DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 191727
SWODY2
SPC AC 191726

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1226 PM CDT SAT MAY 19 2007

VALID 201200Z - 211200Z

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

..SYNOPSIS...
MID/UPPER LEVEL TROUGH IS EXPECTED TO AMPLIFY AS IT MOVES ACROSS THE
PACIFIC NW INTO THE NRN INTERMOUNTAIN REGION ON SUNDAY AS UPSTREAM
HEIGHTS RISE ACROSS THE NERN PACIFIC. 12Z NAM IS NOW FASTER AND A
LITTLE STRONGER /BETTER AGREEMENT WITH GFS/ TRANSLATING A MID LEVEL
IMPULSE NEWD FROM ORE TO CENTRAL/ERN MT BY LATE SUNDAY AFTERNOON
/TOWARD 21/00Z/.

AT THE SURFACE...A COLD FRONT IS EXPECTED TO MOVE EWD INTO THE NRN
HIGH PLAINS SUNDAY AFTERNOON AND SHOULD EXTEND FROM THE MT/ND BORDER
SWWD TO THE WY/MT BORDER AREA BY 21/00Z. SURFACE LOW LOCATED IN THE
VICINITY OF NERN WY/SERN MT IS FORECAST TO DEEPEN IN RESPONSE TO THE
HEIGHT FALLS. A BOUNDARY INITIALLY EXTENDING EWD FROM THE LOW
THROUGH SRN SD TO ALONG THE MN/IA BORDER WILL RETREAT NWD AS A WARM
FRONT DUE TO STRENGTHENING SLY LOW LEVEL WINDS ACROSS THE PLAINS.
DESPITE THESE SLY WINDS...SURFACE RIDGING INTO THE WRN GULF WILL
CONTINUE TO LIMIT GULF MOISTURE RETURN FARTHER N THIS FORECAST
PERIOD.

..NRN HIGH PLAINS...
AT 12Z SUNDAY...TSTMS MAY BE ONGOING ACROSS PARTS OF ND. THIS
ACTIVITY WILL BE ASSOCIATED WITH A MID LEVEL IMPULSE TOPPING THE
RIDGE AND SHOULD PERSIST WITHIN WAA REGIME INTO ERN ND/NRN MN AND
ADJACENT PARTS OF CANADA. SEVERE WEATHER THREAT WILL BE MINIMAL DUE
TO WEAK ELEVATED INSTABILITY.

FARTHER W ACROSS THE SLIGHT RISK AREA...STRONG SURFACE HEATING
EXPECTED IN THE WARM SECTOR AND WWD FROM THE SURFACE LOW ALONG THE
COLD FRONT INTO SRN MT SHOULD RESULT IN MLCAPE VALUES UP TO 1500-
2000 J/KG...GIVEN STEEP LAPSE RATES AND SURFACE DEWPOINTS IN THE
50S. STRONGEST SWLY MID LEVEL FLOW IS EXPECTED TO EXTEND FROM ID/MT
INTO SRN CANADA AS UPPER TROUGH AMPLIFIES. ALTHOUGH SURFACE TO AT
LEAST 1 KM WINDS SHOULD GENERALLY BE WEAK ACROSS MT/WY...INCREASING
AND VEERING WINDS WITH HEIGHT WILL SUPPORT EFFECTIVE SHEAR OF 30-40
KT FAVORING SUPERCELLS.

TSTMS ARE EXPECTED TO INITIATE SUNDAY AFTERNOON ALONG THE COLD FRONT
IN SRN TO ERN MT. GIVEN STEEP MID LEVEL LAPSE RATES AND DRY
ADIABATIC PROFILES IN THE LOWEST 1-2 KM...BOTH SEVERE WIND AND HAIL
CAN BE EXPECTED WITH THESE STORMS. MODELS ALSO SUGGEST TSTM
DEVELOPMENT IN THE VICINITY OF THE SURFACE LOW AND EWD ALONG THE SD/
ND BORDER NEAR THE WARM FRONT BY LATE SUNDAY AFTERNOON. HAIL AND
STRONG WINDS WILL BE THE PRIMARY THREAT WITH THIS ACTIVITY.
HOWEVER...AN INCREASING SLY LLJ INTO THE DAKOTAS BY EARLY SUNDAY
EVENING AND RESULTANT INCREASING LOW LEVEL HODOGRAPH SIZE SUGGESTS
THE THREAT FOR ISOLATED TORNADOES.

ACTIVITY OVER MT MAY GROW UPSCALE INTO AN MCS SUNDAY EVENING AS IT
TRACKS ENEWD INTO ND AND ADJACENT PARTS OF SRN CANADA.
STRENGTHENING DAKOTAS SLY LLJ WILL MAINTAIN A FEED OF SUFFICIENT
ELEVATED INSTABILITY FOR A CONTINUED SEVERE THREAT SUNDAY NIGHT.

ELSEWHERE...HIGH BASED STORMS ARE POSSIBLE ACROSS EXTREME ERN WY/
FAR NWRN NEB TO THE SOUTH OF THE SURFACE LOW LATE SUNDAY AFTERNOON.
40+F SURFACE TEMPERATURE/DEWPOINT SPREADS WOULD BE SUPPORTIVE OF
STRONG WIND GUSTS...BUT ACTIVITY SHOULD BE DIURNAL AND GENERALLY
ISOLATED IN COVERAGE.

.PETERS.. 05/19/2007

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