Thursday, March 18, 2010

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 190052
SWODY1
SPC AC 190051

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0751 PM CDT THU MAR 18 2010

VALID 190100Z - 191200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
IN MID-UPPER LEVELS...PATTERN TRANSITION IS UNDERWAY AS SERN CONUS
CYCLONE WEAKENS AND MOVES EWD OFFSHORE SERN ATLANTIC COAST...AND
HEIGHTS FALL ACROSS MUCH OF ROCKY MOUNTAIN REGION. SHORTWAVE TROUGH
-- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY OVER SERN CORNER BC AND
ADJACENT PORTIONS MT/AB -- IS FCST TO CONTINUE DIGGING SSEWD ACROSS
NRN ROCKIES TO NERN UT AND SWRN WY BY END OF PERIOD. THIS SYSTEM
WILL BE MAIN CONTRIBUTOR TO SIGNIFICANT CYCLONE AFFECTING
S-CENTRAL/SERN CONUS THIS WEEKEND...SEE DAY-2 AND DAY-3 OUTLOOKS.
INITIALLY SEPARATE PERTURBATION OVER CENTRAL/SWRN NV IS EXPECTED TO
MOVE SSEWD TO SERN CA AND NRN BAJA. BROAD ZONE OF SWLY FLOW ALOFT
THEREFORE WILL CONTINUE DOWNSTREAM ACROSS SRN ROCKIES AND
CENTRAL/SRN GREAT PLAINS.

IN LOW LEVELS...EXPECT CONTINUED LEE-SIDE TROUGHING FROM NRN MEX NWD
TO INTERSECTION WITH CENTRAL PLAINS COLD FRONT. RELATED
PRESSURE/HEIGHT FALLS WILL SUPPORT STG LOW LEVEL WAA REGIME ACROSS
MUCH OF SRN/CENTRAL PLAINS. MOISTURE RETURN...HOWEVER...WILL BE
LIMITED BY UNFAVORABLY LOW-THETAE TRAJECTORIES EMANATING FROM
CONTINENTAL ANTICYCLONE...WITH MINIMAL TO NO RESIDENCE TIME OVER
GULF. FARTHER W...COLD FRONT WILL CONTINUE TO MOVE SEWD ACROSS
REMAINDER SRN AND ERN GREAT BASIN REGION....AHEAD OF AFOREMENTIONED
MID-UPPER PERTURBATIONS.

AT SFC...SLOWLY DEPARTING CYCLONE OFFSHORE NC...AND BROAD AREA OF
CONTINENTAL HIGH PRESSURE IN WAKE OF TRAILING SFC COLD FRONT -- WILL
KEEP AIR MASS TOO DRY AND STABLE FOR TSTMS ACROSS MOST OF CONUS E OF
ROCKIES.

...GREAT BASIN...CENTRAL ROCKIES TO CENTRAL HIGH PLAINS...
LOW-LEVEL FRONTAL FORCING...DIABATIC HEATING OF NEAR-FRONTAL AND
PREFRONTAL LAND SFC...STEEP LAPSE RATES ATOP FRONTAL PROCESS...AND
MRGL MOISTURE HAVE CONTRIBUTED TO SPORADIC/ISOLATED TSTMS OVER
PORTIONS CENTRAL/SRN NV AND SWRN UT. THIS REGIME MAY YIELD EPISODIC
THUNDER FOR A FEW MORE HOURS...BEFORE BUOYANCY BECOMES TOO WEAK FOR
10% UNCONDITIONAL THUNDER COVERAGE PROBABILITIES.

MORE DOUBTFUL IS OVERNIGHT TSTM THREAT FARTHER E ACROSS CENTRAL
PLAINS. ROUGHLY HALF OF SREF MEMBERS PRODUCE LITTLE OR NO
CONVECTIVE PRECIP ACROSS THIS REGION BY 12Z. MODEL FCST SOUNDINGS
-- EVEN THIS CLOSE TEMPORALLY -- ARE DRASTICALLY DIFFERENT FROM ONE
ANOTHER AT THE SAME VALID TIMES REGARDING PRESENCE OR LACK OF
ELEVATED CAPE. GIVEN THESE INCONSISTENT PROGS...AND DRYNESS/LOW
THETAE OF LOW-LEVEL AIR MASS EVIDENT UPSTREAM...PRIND THUNDER
POTENTIAL IS TOO CONDITIONAL/ISOLATED TO MAINTAIN OUTLOOK E OF
MOUNTAINS.

..EDWARDS.. 03/19/2010

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