SPC Day 1 Thunderstorm Outlook Issued 12Z 20030928


ZCZC SPCSWODY1 ALL
ACUS01 KWNS 280524
SPC AC 280524

DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
1224 AM CDT SUN SEP 28 2003

VALID 281200Z - 291200Z

THERE IS A SLGT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM 25 S
ILM 30 W OAJ 20 NE RWI 35 ESE RIC 25 ENE SBY.

GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 20 ESE CHS 40 N CRE
30 S RDU DAN 20 N PSK 15 S LEX 20 SW BMG 35 N DNV 30 SSE MKE 50 SSE
ESC 60 N ANJ ...CONT... 20 WSW CTY 30 NNW GNV 25 S SSI.

GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 30 SSE ELP 20 E SAF
40 W TAD 15 WNW LHX 25 ENE LAA 30 SSW GCK 30 WNW GAG 20 N CDS 15 NW
DRT.

...THERE IS A SLGT RISK OF SVR TSTMS OVER ERN PARTS OF NC AND VA...

...SYNOPSIS...
HIGH-AMPLITUDE LARGE-SCALE PATTERN WILL PERSIST THROUGH THE FORECAST
WITH THE PRIMARY FEATURE OF INTEREST BEING DEEP MID-LEVEL TROUGH
OVER THE ERN CONUS. THIS TROUGH WILL GRADUALLY BECOME NEGATIVELY
TILTED AS STRONG MID/UPPER-LEVEL JET STREAKS --NOW OVER THE CNTRL
PLAINS/MID MS VALLEY-- EMERGE FROM THE TROUGH BASE AND LIFT NEWD
ACROSS THE MIDDLE ATLANTIC STATES INTO NEW ENGLAND.

IN THE LOW-LEVELS...PRIMARY SYNOPTIC FRONT WILL PROGRESS EWD ACROSS
THE NERN U.S. AND MIDDLE ATLANTIC STATES BEFORE MOVING INTO THE
ATLANTIC BY MONDAY MORNING.

...ERN PARTS OF VA/NC...
CURRENT SURFACE OBSERVATIONS INDICATE A VERY MOIST LOW-LEVEL AIRMASS
ALREADY IN PLACE ACROSS THE AREA WITH DEWPOINTS IN THE UPPER 60S TO
LOWER 70S. THIS MOISTURE COUPLED WITH LIMITED DAYTIME HEATING SHOULD
CONTRIBUTE TO POCKETS OF MODERATE INSTABILITY LATER TODAY WITH
MLCAPES APPROACHING 1000-1500 J/KG. TSTMS ARE EXPECTED TO DEVELOP BY
AFTERNOON AS APPROACHING COLD FRONT ENCOUNTERS THE UNSTABLE AIRMASS.
VERTICAL WIND SHEAR WILL CONCURRENTLY INCREASE AS AFOREMENTIONED
MID/UPPER-LEVEL WIND MAXES ROUND THE TROUGH BASE ACROSS THE
SRN/CNTRL APPALACHIANS. FORECAST HODOGRAPHS INDICATE LARGELY
UNIDIRECTIONAL WLY WINDS ACROSS THE WARM SECTOR...HOWEVER
SUFFICIENTLY STRONG DEEP-LAYER SPEED SHEAR WILL EXIST FOR ORGANIZED
TSTMS. DAMAGING WINDS WILL BE THE PRIMARY SEVERE WEATHER THREAT WITH
THE MOST INTENSE STORMS...ESPECIALLY WITH ANY BOWING SEGMENTS/LEWP
STRUCTURES.

FARTHER N FROM MD/DE NWD INTO SRN NEW ENGLAND...IT APPEARS THAT
INSTABILITY WILL REMAIN RATHER WEAK AND WILL EFFECTIVELY LIMIT THE
SEVERE WEATHER POTENTIAL. NONETHELESS...WIND FIELDS WILL REMAIN
QUITE STRONG AHEAD OF SURFACE FRONT AND IF IT BECOMES APPARENT THAT
MORE INSTABILITY WILL BE REALIZED...AN UPGRADE TO SLIGHT RISK MAY BE
REQUIRED IN SUBSEQUENT OUTLOOKS.

...WRN TX...
LOW-AMPLITUDE SHORTWAVE TROUGH OVER THE PACIFIC NW WILL CROSS THE
CNTRL ROCKIES TODAY PRIOR TO MOVING INTO THE SRN HIGH PLAINS LATE
TONIGHT. A 30-40KT SLY LLJ IS FORECAST TO DEVELOP OVERNIGHT FROM WRN
TX INTO SWRN NEB IN RESPONSE TO THE APPROACH OF THIS FEATURE. A
PLUME OF STEEP MID-LEVEL LAPSE RATES /7-8 C/KM/ WILL ACCOMPANY THE
SHORTWAVE TROUGH...AND WHEN COUPLED WITH THE NWD ADVECTION OF
LOW-LEVEL MOISTURE ALONG LLJ AXIS...WILL CONTRIBUTE TO MUCAPES OF
500-1000 J/KG. ENHANCED WAA/ISENTROPIC ASCENT ALONG LLJ MAY BE
SUFFICIENT TO INITIATE A FEW TSTMS LATE TONIGHT ACROSS THE TX S
PLAINS/TX PNHDL. RELATIVELY LOW WBZ HEIGHTS OF 8-9KFT SUGGEST THE
POTENTIAL FOR SOME HAIL WITH THE STRONGEST STORMS.

..MEAD/BROYLES.. 09/28/2003

...NOTICE...
FOR USERS DECODING THE POINTS PARAGRAPH HEREIN...LATITUDE AND
LONGITUDE POINTS FOR THE CATEGORICAL AND PROBABILISTIC OUTLOOK
GRAPHICS ALSO ARE LOCATED IN A SEPARATE PRODUCT UNDER THE WMO
HEADINGS WUUS01 PTSDY1...WUUS02 PTSDY2...AND WUUS03 PTSDY3.  THE
INCLUSION OF POINTS IN THIS PRODUCT WILL EVENTUALLY BE DISCONTINUED.

$$