SWODY2
SPC AC 181729
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1229 PM CDT TUE SEP 18 2007
VALID 191200Z - 201200Z
..NO SVR TSTM AREAS FORECAST...
..SYNOPSIS...
IN MID/UPPER LEVELS...LARGE SCALE PATTERN WILL CONTINUE TO INCLUDE
TROUGHING OVER W COAST STATES...AND POSITIVELY TILTED RIDGE FROM
NWRN GULF TO NEW ENGLAND. UPPER LOW -- NOW LOCATED OVER CENTRAL FL
-- IS EXPECTED TO DRIFT ERRATICALLY OVER FL PENINSULA THROUGH MOST
OF PERIOD BEFORE MOVING GENERALLY WWD IN PHASE WITH LOW LEVEL
TROPICAL WAVE. INCREASINGLY WELL DEFINED MANIFESTATION OF MID-UPPER
LOW AT SFC IS PROGGED BY MANY OPERATIONAL/SREF GUIDANCE PACKAGES.
REF NHC TROPICAL OUTLOOK -- WMO HEADER ABNT20 KNHC -- FOR ADDITIONAL
DISCUSSION. THIS SYSTEM WILL CONTRIBUTE TO TSTM POTENTIAL OVER FL.
FARTHER NW...MID/UPPER LEVEL SHORTWAVE TROUGH -- NOW LOCATED OVER
CENTRAL PLAINS -- IS FCST TO EJECT NEWD ACROSS UPPER GREAT LAKES AND
NRN ONT EARLY IN PERIOD.
SERIES OF LOW-AMPLITUDE PERTURBATIONS AND SPEED MAXIMA -- NOW
EVIDENT IN MOISTURE CHANNEL IMAGERY AND UPPER AIR ANALYSES BETWEEN
SEA AND SWRN YUKON -- ARE FCST TO PHASE AND DIG SSEWD THROUGH DAY-2.
THIS SHOULD RESULT IN CLOSED LOW BY 19/12Z CENTERED INVOF
PDX/AST...MOVING SWD OVER COAST RANGES AND ACROSS NWRN CA BY END OF
PERIOD. ASSOCIATED SFC CYCLOGENESIS IS EXPECTED OVER NRN ROCKIES
AND NRN GREAT BASIN REGIONS. BENEATH SWLY FLOW ALOFT...LEESIDE
PRESSURE FALLS SHOULD OCCUR FROM ERN CO NWD ACROSS WY/NEB BORDER
REGION. COLD FRONT -- NOW MOVING SWD ACROSS CENTRAL HIGH
PLAINS...SERN SD AND NWRN MN -- SHOULD BECOME QUASISTATIONARY OVER
LOWER MO RIVER VALLEY...WHILE LIFTING NWD ACROSS NRN KS AND WRN NEB
AS WARM FRONT. ERN PORTION OF THIS FRONT WILL MOVE EWD OVER UPPER
GREAT LAKES REGION...REACHING SERN ONT...SRN INDIANA AND SRN IL BY
20/12Z.
..CENTRAL HIGH PLAINS...AFTERNOON/EVENING...
WIDELY SCATTERED TO SCATTERED TSTMS MAY DEVELOP INVOF SFC FRONTAL
ZONE -- PARTICULARLY DURING AFTERNOON/EARLY EVENING...BETWEEN OH AND
NWRN KS/SERN NEB REGION. PRIND VERTICAL SHEAR...LAPSE RATES AND
PEAK AFTERNOON SBCAPE EACH WILL INCREASE WITH WWD EXTENT ACROSS THIS
CORRIDOR...SUCH THAT AT LEAST CONDITIONAL SVR PROBABILITIES ARE
WARRANTED OVER PORTIONS CENTRAL HIGH PLAINS.
ALONG AND N OF NWRN KS/WRN NEB FRONTAL SEGMENT...BACKED/ELY BOUNDARY
LAYER WIND COMPONENT WILL ADVECT FAVORABLE LOW LEVEL MOISTURE INTO
REGION...AS WELL AS ENHANCE BOTH LOW LEVEL HODOGRAPHS AND DEEP-LAYER
SHEAR VECTORS. 40-50 KT EFFECTIVE BULK SHEAR MAGNITUDES...AND 0-1
KM SRH 150-200 J/KG...ARE POSSIBLE. MAIN CAVEAT APPEARS TO BE
DEGREE OF THERMODYNAMIC SUPPORT ABOVE SFC...WITH STRONG ELEVATED
MIXED-LAYER AIR MASS CAUSING ROBUST CAPPING. ADDITIONALLY...STABLE
LAYER INVOF 400-500 MB -- OBSERVED IN 18/12Z RAOBS FROM CENTRAL HIGH
PLAINS SWWD ACROSS NM/AZ -- IS EXPECTED TO BE MAINTAINED OVER THIS
REGION PER WRF/NAM-KF FCST SOUNDINGS...REDUCING MID-UPPER LEVEL
BUOYANCY. ANY TSTM DEVELOPING INVOF THIS SEGMENT OF FRONT MAY
ROTATE AND PRODUCE LARGE HAIL AND DAMAGING GUSTS...HOWEVER COVERAGE
SHOULD BE GREATLY LIMITED BY CINH.
..NRN PLAINS...AFTER 20/00Z...
ISOLATED TO WIDELY SCATTERED TSTMS MAY DEVELOP AFTER DARK...WITH
POTENTIAL FOR HAIL. STRONG/ELEVATED LOW LEVEL WAA IS EXPECTED
THROUGHOUT MOST OF PERIOD IN REGIME OF LEE-SIDE PRESSURE/HEIGHT
FALLS...WHILE NARROW PLUME OF AT LEAST MRGLLY FAVORABLE MOISTURE
RETURN WILL OCCUR AFTER ABOUT 20/03Z OVER NRN HIGH PLAINS.
ASSOCIATED DESTABILIZATION OF LOW-MIDDLE LEVEL LAPSE RATES...AND
REDUCTION OF ELEVATED MUCINH...MAY LEAD TO PROGRESSIVELY MORE
PARCELS ISENTROPICALLY BOOSTED TO LFC WITH TIME. MODIFIED NAM-KF
FCST SOUNDINGS SUGGEST ELEVATED MUCAPES 500-1000 J/KG MAY DEVELOP
OVER PORTIONS WRN DAKOTAS AND/OR ERN MT FROM APPROXIMATELY 20/06Z
ONWARD...AMIDST 40-50 KT EFFECTIVE SHEAR. CONVECTIVE COVERAGE IS IN
QUESTION...WITH MOST MODELS INDICATING VERY LITTLE EXCEPT OVER WRN
SD AND PERHAPS NERN MT.
.EDWARDS.. 09/18/2007
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