Severe Thunderstorm Warning 227, NWS Jackson, MS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
230 PM CDT WED MAY 9 2001

SURFACE BOUNDARY BARELY DISCERNIBLE. USING VISIBLE SATELLITE...BACK
EDGE OF EARLIEST CUMULUS DEVELOPMENT SUGGESTED THAT DIFFUSE BOUNDARY
NEAR KGTR-KMLU-KLFK AT 15Z. SURFACE DEWPOINTS GENERALLY IN THE
MIDDLE 60S/MSAS LI'S RUNNING -3 TO -5 THIS AFTERNOON. WITH SRLY FLOW
OVER REGION TODAY...APPEARS SUFFICIENT MOISTURE IN PLACE FOR
CONVECTION.  ALTHOUGH NO MAJOR LIFTING MECHANISM AROUND...SOME WEAK
NET ISENTROPIC LIFT APPEARS IN ETA/AVN MODELS FROM
300K-320K...MAINLY OVER E MS/LA TODAY. WIDELY SCATTERED SHOWERS
POPPING UP GENERALLY ALONG DIFFUSE BOUNDARY.

WHILE MID-LEVEL FLOW BECOMING MORE ZONAL N OF CWFA...SOME BROAD
TROUGHINESS REMAINS OVER LOWER MS RIVER VALLEY THROUGH 60 HRS. ETA
EVEN DEVELOPS CLOSED 500 MB/SURFACE LOW OVER GULF BY 12Z FRI.

IN SHORT-TERM...AVN MODEL STARTED WITH SHORTWAVES OVER TX/MO THIS AM
AS SHORTWAVE OVER S MS PUSHED E THROUGH AFTERNOON. ETA STARTED WITH
BROADER/WEAKER FIELDS; PREFER AVN SOLUTION. AIRMASS UNSTABLE AGAIN
THIS AFTERNOON...WITH FORECAST CAPE VALUES 1200-1800 CENTRAL/SRN
ZONES. EARLIER MODEL RUNS LIMITED MOISTURE TO LOWEST 700 MB...WITH
DRY AIR ABOVE. THIS RUN OF MODELS PRODUCES SLIGHTLY DEEPER MOISTURE
TO NEAR 600 MB...WITH DRY AIR STILL ENTRENCHED ABOVE. WILL STILL SEE
CONVECTION THROUGH EARLY EVENING HOURS.

WEAK NET ISENTROPIC LIFT APPEARS IN ETA/AVN FROM 300K-320K OVER N
CENTRAL MS/DELTA AGAIN THU. IN MESO-ETA THIS SAME TREND APPEARS IN
OMEGA FIELDS...WITH RAINFALL INITIATING THESE SAME AREAS. MODEL
CAPES AGAIN IN 1200-2000 J/KG RANGE. IN AVN...WEAK 500 MB TROUGH/
VORT MAX STILL OVER CWFA WITH CONSIDERABLE MOISTURE OVER CENTRAL/SRN
ZONES. WILL KEEP SOME CHANCE SHOWERS FOR THU AFTERNOON/EVENING...
MAINLY CENTRAL/S. DIURNAL HEATING WILL HELP PROVIDE INITIAL LIFT.

MODELS CONCUR THAT FRONTOGENESIS OCCURRING FROM GREAT LAKES INTO W
TX AFTER 00Z FRI. THIS FRONT WILL APPROACH LOWER MS RIVER VALLEY FRI
AFTERNOON. AIRMASS GRADUALLY DRIES OUT FRI IN BOTH ETA/AVN. EXPECT
HIGH PRESSURE TO DOMINATE WEATHER OVER SE...AS SURFACE RIDGE
STRENGTHENS. THIS HIGH PRESSURE BECOMES CENTERED OFF SERN COAST...
PRODUCING E TO SE SURFACE FLOW ACROSS NRN GULF INTO CWFA. SOME
MOISTURE FILTERS INTO REGION/PROVIDE WEAK MOISTURE CONVERGENCE BY
18Z FRI. MESO-ETA CONTINUES TO DEVELOP WEAK OMEGA/PRECIP IN 15Z-18Z
FRI TIME FRAME. AVN ALSO CRANKS OUT PRECIP OVER NRN ZONES BY 18Z
FRI. SLIGHT CHANCE PRECIP...MAINLY NRN ZONES.

MODEL TEMP GUID LOOKS OK; WILL VARY AROUND.

.EXTENDED FORECAST...
AVN INDICATES WEAK LOW PRESSURE SYSTEM OVER GULF MX FRI NIGHT BUT
LOSES FEATURE BY SAT. MESO-ETA TOTALLY DIFFERENT. AFTER 00Z FRI...
500 MB GULF SYSTEM DEEPENS/BECOMES CLOSED LOW PRESSURE AREA. FRI
MESO-ETA PUSHES 500 MB LOW/MOISTURE N ACROSS GULF. WITH SRLY FLOW
OVER REGION AHEAD OF FRONT APPROACHING FROM PLAINS AND WHATEVER
HAPPENS IN GULF MX...ABUNDANT MOISTURE OVER CWFA FRI NIGHT. MAY BE
SLIGHT CHANCE PRECIP NRN ZONES FRI NIGHT. FRONT PUSHES IN SAT/
APPEARS TO SLOW DOWN BIT SAT NIGHT. SHOWERS/THUNDERSTORMS OVER CWFA
SAT/SAT EVENING...POSSIBLY WITH HEAVY RAINFALL SINCE DEEP MOISTURE
IN PLACE.

BY EARLY SUN...COLD FRONT ERODING AS LARGE AREA OF HIGH PRESSURE
BUILDS OVER ERN STATES. HIGH PRESSURE BECOMES CENTERED AROUND
APPALACHIANS/DOMINATES WEATHER OVER SE THROUGH TUE. MRF SUGGESTS
BACKDOOR COLD FRONT WILL SLIDE DOWN ATLANTIC COAST AND COULD IMPACT
NRN CWFA BY WED...AS NE LOW PRESSURE SYSTEM SLIDES TO ATLANTIC
COAST. WILL NOT MENTION PRECIP ATTM FOR WED.

PRELIM NUMBERS:
JAN 61/83 61/85  2311
MEI/ 60/83 60/84  2311

.JAN...
MS...NONE.
LA...NONE.
AR...NONE.