Wednesday, April 18, 2007

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 190100
SWODY1
SPC AC 190058

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0758 PM CDT WED APR 18 2007

VALID 190100Z - 191200Z

..THERE IS A SLGT RISK OF SVR TSTMS PORTIONS NERN WY...ERN MT...

..SYNOPSIS...
HIGHLY AMPLIFIED UPPER AIR PATTERN EXISTS ACROSS
CONUS...CHARACTERIZED PRIMARILY BY UPPER LOW CENTERED OVER SRN
ID...RIDGING FROM NWRN ONT HIGH SSWWD TO LOWER TX COAST...AND NEARLY
ZONALLY ORIENTED ERN TROUGH. TROUGH ASSOCIATED WITH ID LOW WILL
BECOME PROGRESSIVELY MORE NEGATIVELY TILTED THROUGH REMAINDER
PERIOD...REACHING WRN CO AND CENTRAL WY WHILE PARENT CYCLONE ONLY
SLOWLY EJECTS TOWARD YELLOWSTONE AREA. MOISTURE CHANNEL IMAGERY
INDICATES MID/UPPER LOW OVER NRN INDIANA...ASSOCIATED WITH LARGER
SCALE ERN TROUGH. THIS FEATURE IS FCST TO MOVE SEWD ACROSS OH RIVER
TO NRN KY BY 12Z AND SUPPORT ISOLATED TSTMS...WHILE DOWNSTREAM
SHORTWAVE NOW OVER GA COAST AND SC EJECTS RAPIDLY EWD OVER ATLANTIC.


AT SFC...SEVERAL LOWS ARE EVIDENT ALONG PRONOUNCED FRONTAL ZONE THAT
EXTENDS FROM E-CENTRAL MT SWD THROUGH CENTRAL WY...THEN SWWD ACROSS
SERN UT AND WRN AZ. THIS FRONT IS FCST TO SURGE EWD THROUGH CENTRAL
ROCKIES OVERNIGHT AS PRIMARY SFC CYCLONE CONSOLIDATES ACROSS SERN
MT.

..NRN/CENTRAL HIGH PLAINS...
WIDELY SCATTERED TO SCATTERED TSTMS IN CLUSTERS -- SOME SVR -- WILL
CONTINUE FOR SEVERAL MORE HOURS ACROSS PORTIONS ERN MT...BECOMING
ISOLATED TO WIDELY SCATTERED FARTHER S ACROSS WY WHERE LOW LEVEL
FORCING IS SOMEWHAT WEAKER. ACTIVITY WILL REMAIN RATHER HIGH BASED
GIVEN SFC DEW POINTS UPPER 30S TO MID 40S. LARGE HAIL AND STG-SVR
GUSTS WILL REMAIN POSSIBLE. AS MID-UPPER TROUGH BECOMES MORE
NEGATIVELY TILTED...MEAN WIND VECTOR WILL BACK AND ATTAIN MORE
PRONOUNCED ELY COMPONENT...FROM NERN WY NWD THROUGH ERN MT. THIS IN
TURN WILL SUPPORT MERIDIONAL TO NWWD STORM MOTIONS -- MODULATED
SOMEWHAT BY SFC FORCING ASSOCIATED WITH NEWD-DIRECTED OUTFLOW POOLS
-- AND BY EXTENSION...KEEP SVR POTENTIAL FROM SPREADING MUCH FARTHER
EWD ACROSS NRN HIGH PLAINS.

SVR POTENTIAL WILL BE MORE SPORADIC WITH SWD EXTENT INTO CENTRAL
HIGH PLAINS...HOWEVER STRENGTHENING WIND FIELDS ALOFT AHEAD OF
MIDLEVEL TROUGH WILL ENSURE SUFFICIENT VERTICAL SHEAR FOR
SUPERCELLS. HOWEVER...ACTIVITY IS STRONGLY DIURNALLY DRIVEN...WITH
HEATING AND RESULTANT VERTICAL MIXING OF BOUNDARY LAYER REDUCING
CINH ENOUGH TO SUPPORT DEVELOPMENT. SBCINH SHOULD AGAIN INCREASE
RAPIDLY AS RELATIVELY DRY SFC AIR COOLS RAPIDLY AFTER SUNSET.
THERFORE TIME WINDOW WILL BE SHORT FOR SVR POTENTIAL FROM HIGH-BASED
TSTMS -- NOW EVIDENT IN VIS IMAGERY E OF FRONT/LARAMIE RANGES.
GIVEN LIMITED COVERAGE/DURATION OF POTENTIAL...WILL KEEP
PROBABILITIES MRGL.

.EDWARDS.. 04/19/2007

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