SWODY1
SPC AC 200500
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1200 AM CDT FRI MAR 20 2009
VALID 201200Z - 211200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
RIDGING ALOFT IS FCST TO DRIFT EWD ACROSS HIGH PLAINS AS ERN
TROUGHING SHIFTS EWD...AND TROUGH AMPLIFICATION/PROGRESSION BEGINS
OVER NERN PACIFIC. POSITIVELY TILTED SHORTWAVE TROUGH -- INITIALLY
ANALYZED FROM ST LAWRENCE VALLEY SWWD ACROSS OH -- WILL MOVE
OFFSHORE MID-ATLANTIC STATES AND SRN NEW ENGLAND DURING FIRST 6-12
HOURS OF PERIOD. IN ITS WAKE...BROAD ZONE OF NWLY TO WNWLY FLOW
ALOFT WILL COVER MUCH OF CENTRAL/SRN CONUS...PERTURBED ONLY BY VERY
WEAK SHORTWAVE RIPPLES. SRN STREAM SHORTWAVE TROUGH -- NOW EVIDENT
IN MOISTURE CHANNEL IMAGERY W OF BAJA BETWEEN 120W-125W -- SHOULD
LIFT NEWD ACROSS NRN SONORA AND SRN AZ BY 21/00Z THEN ERN NM BY
21/12Z. MEANWHILE...MID-UPPER SPEED MAX WILL DIG SSEWD ALONG
UPSTREAM SIDE OF TROUGH THAT WILL BE AMPLIFYING W OF NRN CA/ORE/WA
COAST.
AT SFC...COLD FRONT -- ANALYZED FROM ERN SC TO SRN AL...CENTRAL LA
AND N-CENTRAL TX -- SHOULD BECOME DIFFUSE OVER MUCH OF GULF COAST
REGION AMIDST ELY/NELY FLOW ON BOTH SIDES. WRN PORTION OF FRONT
WILL REORGANIZE/REDEVELOP NWD AS WARM FRONT BY 21/12Z...EXTENDING
SEWD FROM STRENGTHENING LEE-SIDE LOW OVER SERN CO.
...CENTRAL PLAINS...
WIDELY SCATTERED TO SCATTERED TSTMS SHOULD DEVELOP AFTER DARK AS
CONTINUING WAA REGIME ACQUIRES PROGRESSIVELY MORE MOISTURE THROUGH
ADVECTION/TRANSPORT ASSOCIATED WITH NOSE OF 35-45 KT LLJ. STRONGEST
LIFT -- WITH PARCELS ISENTROPICALLY REACHING LFC AND REALIZING
MUCAPE 500-1000 J/KG -- IS POSSIBLE ACROSS PORTIONS SERN KS FOR A
FEW HOURS BEGINNING AROUND 21/06Z. ACTIVITY THEN SHOULD MOVE/EXPAND
EWD...GENERALLY WEAKENING WITH TIME DURING LATTER 3-4 HOURS OF
PERIOD...BUT STILL POSING GEN THUNDER THREAT INTO WRN MO. MODIFIED
ETA-KF FCST SOUNDINGS SUGGEST WEAK EFFECTIVE SHEAR OVER MOST OF
REGION BECAUSE OF FAILURE OF UPPER REACHES OF BUOYANT LAYER TO
EXTEND INTO BOTTOM PORTIONS OF 55-70 KT UPPER JET MAX. HOWEVER...A
FEW CELLS WITH GREATEST CAPE/DEPTH BRIEFLY MAY EXPERIENCE FAVORABLE
DEEP-LAYER ENVIRONMENTAL SHEAR TO DEVELOP MRGL HAIL THREAT. ATTM
PROBABILITIES APPEAR TOO CONDITIONAL/MRGL FOR AOA 5-PERCENT SVR
CONTOUR.
...CENTRAL/SRN ROCKIES...
LOW-LEVEL MOISTURE IS EXPECTED TO GENERALLY INCREASE WITH SWD EXTENT
RELATED TO RECENT FROPA ACROSS CENTRAL/SRN PLAINS...AND RESIDUAL
MOISTURE FROM UPSLOPE TRANSPORT. WITH DIURNAL HEATING AND RELATED
WEAKENING OF CINH...SFC THETAE AND OROGRAPHIC LIFT SHOULD BE
SUFFICIENT TO SUPPORT ISOLATED TO WIDELY SCATTERED CB OVER THIS
REGION. LOW LEVEL WAA...AND POSSIBLY INCREASING DPVA AHEAD OF
EJECTING SRN STREAM PERTURBATION...MAY MAINTAIN CONVECTIVE POTENTIAL
OVER PORTIONS CENTRAL/SRN NM AND FAR W TX AFTER SUNDOWN. WEAK
DEEP-LAYER FLOW...INVOF MEAN RIDGE ALOFT...WILL PRECLUDE SVR RISK.
..EDWARDS.. 03/20/2009
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