SPC AC 270643
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1243 AM CST SUN FEB 27 2011
VALID 281200Z - 011200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS LOWER-MID MS VALLEY TO
CAROLINAS/MID-ATLANTIC REGION...
...SYNOPSIS...
MID-UPPER LEVEL CYCLONE -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY
OVER SRN CA -- IS FCST TO DEVOLVE TO OPEN-WAVE TROUGH AND ASSUME STG
POSITIVE TILT DAY-1 AS IT ACCELERATES ENEWD ACROSS SRN PLAINS. BY
START OF PERIOD...500-MB TROUGH SHOULD EXTEND FROM MO SWWD ACROSS
N-CENTRAL TX. THOUGH MINOR/MESOSCALE DIFFERENCES EXIST IN
TIMING...STG CONSENSUS OF SREF AND OPERATIONAL PROGS INDICATES
TROUGH SHOULD DEAMPLIFY GRADUALLY AND MOVE OFFSHORE MID-ATLANTIC
COAST DURING 01/06Z-01/12Z TIME FRAME.
AT SFC...DOMINANT LOW BY 28/12Z SHOULD BE LOCATED OVER LE/WRN
NY/NWRN PA REGION...WITH SECONDARY/FRONTAL-WAVE LOW POSSIBLE OVER
SERN MO/SRN IL REGION ALONG TRAILING SFC COLD FRONT. FRONT SHOULD
EXTEND FROM THAT LOW SWWD TO NEAR MID/UPPER TX COAST. EXPECT MAIN
LOW TO MOVE ENEWD ACROSS NEW ENGLAND DURING LATE
AFTERNOON/EVENING...WITH 01/00Z COLD-FRONTAL POSITION NEAR
PVD...IAD...ATL...LAF LINE. FRONT WILL SWEEP OFFSHORE ALL BUT GA/FL
ATLANTIC COASTS BY END OF PERIOD...WHILE CROSSING FL PANHANDLE FROM
NE-SW.
...LOWER-MID MS VALLEY TO CAROLINAS/MID-ATLANTIC REGION...
SVR EVENT DISCUSSED IN DAY-1 OUTLOOK WILL BE ONGOING INTO THIS
PERIOD ACROSS WRN PORTIONS OUTLOOK AREA...AND MAY FAN OUT TO AFFECT
BROAD SWATH OF ERN STATES THROUGH AFTERNOON/EVENING. DAMAGING WIND
WILL BE MAIN THREAT...WITH AT LEAST A FEW TORNADOES POSSIBLE.
CORRIDOR OF GREATER RISK AND MORE ENHANCED PROBABILITIES IS POSSIBLE
WITHIN THIS SWATH...BUT TOO DEPENDENT ON MESOSCALE PROCESSES TO
NARROW DOWN SPECIFICALLY ATTM.
SFC ANALYSIS SHOWS 60S F SFC ISODROSOTHERM ALREADY INLAND TO RED
RIVER VALLEY REGION OF S-CENTRAL/SE OK AND N-CENTRAL/NE TX AS OF
27/05Z...WITH MID-60S CENTRAL TX AND COASTAL PLAIN. RELATED MOIST
PLUME IS FCST TO ADVECT NEWD ACROSS OZARKS AND LOWER-MID MS VALLEY
DAY-1...LEADING EDGE OF WHICH MAY BE SUPPORTING AT LEAST MRGL SVR
HAIL POTENTIAL IN TSTMS ROOTED ABOVE SFC OVER PORTIONS NRN
INDIANA/OH BY 28/12Z. FARTHER S ACROSS WARM SECTOR...MORNING
BOUNDARY LAYER WILL CONTAIN CHARACTERISTIC TEMPORAL MAX IN STATIC
STABILITY IN SHALLOW/NEAR-SFC LAYER. HOWEVER...THETAE ADVECTION
WILL HELP TO OFFSET THIS TENDENCY ENOUGH TO YIELD SVR THREAT FROM
QLCS AND/OR EMBEDDED SUPERCELL MODES. FCST MORNING SOUNDINGS SHOW
MAGNITUDE/DEPTH OF STABLE LAYER TOO SMALL TO PRECLUDE EFFECTIVE
LIFTED PARCELS FROM BEING SFC-BASED...OR VERY NEARLY SO. MAIN
UNCERTAINTIES FOR EARLY IN PERIOD INVOLVE WHETHER ANY
EMBEDDED/PRECURSORY SUPERCELLS WILL BE PRESENT IN ADDITION TO
DOMINANT LINEAR CONVECTIVE MODE...AND HOW FAR SWD INITIAL BAND OF
MAY BACKBUILD INTO MORE STRONGLY CAPPED...ELEVATED MIXED-LAYER AIR.
ADDITIONAL DEVELOPMENT AND/OR BACKBUILDING OF INITIAL/MORNING
ACTIVITY IS EXPECTED DURING DAY ACROSS PORTIONS TN VALLEY REGION AND
AL INTO SRN APPALACHIANS...WHILE ACTIVITY ALONG/AHEAD OF COLD FRONT
FARTHER N MOVES EWD-ENEWD UP OH VALLEY AND INTO CENTRAL
APPALACHIANS. BROAD AREA OF FAVORABLE DEEP-LAYER SHEAR IS EXPECTED
ACROSS AT LEAST MRGLLY UNSTABLE WARM SECTOR...WITH MID-UPPER FLOW
STRENGTHENING JUST AHEAD OF COLD FRONT AS SHORTWAVE TROUGH APCHS.
STRONGEST ISALLOBARIC FORCING WILL BE SHIFTING NEWD ACROSS ST.
LAWRENCE VALLEY AND NY/NEW ENGLAND...AHEAD OF WARM
SECTOR...RESULTING IN SWLY SFC WINDS OVER MOST OF OUTLOOK AREA.
HOWEVER...FCST SOUNDINGS SUGGEST SLGT VEERING WITH HEIGHT IN LOWEST
1-2 KM...COMBINED WITH STG SPEED SHEAR...WILL PRODUCE FAVORABLY
ENLARGED HODOGRAPHS FOR BOWS...AS WELL AS SUPERCELLS EITHER EMBEDDED
WITHIN OR AHEAD OF CONVECTIVE BANDS. BROAD SWATHS OF DAMAGING WIND
APPEAR QUITE POSSIBLE...HENCE LARGE SIZE OF AOA 30% SVR
PROBABILITIES.
INSTABILITY WILL BE WEAKER WITH NWD EXTENT...BUT WITH AT LEAST
NEUTRAL TO WEAKLY POSITIVE BUOYANCY AS FAR N AS OH/PA IN SUPPORT OF
SVR THREAT. SRN EXTENT OF ORGANIZED SVR POTENTIAL REMAINS RATHER
UNCERTAIN ATTM...THEREFORE PROBABILITIES ARE TAPERED SWD TOWARD GULF
AND SEWD TOWARD COASTAL CAROLINAS.
..EDWARDS.. 02/27/2011
CLICK TO GET WUUS02 PTSDY2 PRODUCT
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
|
