Flash Flood Warning 7, NWS Jackson, MS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
350 AM CST FRI MAR 2 2001

CONVECTION OVER LA/CENTRAL AND SRN MS THIS AM...AS SURFACE BOUNDARY
STRETCHING FROM NRN GULF MX THROUGH N CENTRAL MS. HEAVIER RAINFALL
TRAINING OVER SRN ZONES. SHOWERS BEGINNING TO BE WEAKEN...YET
CONDITIONS CONDUCIVE TO FLASH FLOODS...ESPECIALLY S MS. RAIN AMOUNTS
OVER NE LA/CENTRAL AND SRN MS AVERAGING LESS THAN .2 INCH/HOUR AT
MOST SITES...BUT LOCAL AMOUNTS TO 1.0 INCH HAVE OCCURRED. REGIONAL
RADARS CONFIRMING SATELLITE IMAGERY...WHICH SHOWS MORE PRECIP WILL
PUSH INTO FA. WV SATELLITE IMAGERY SHOWS PLUME OF PACIFIC MOISTURE
INTO LOWER MS RIVER VALLEY...WITH MOISTURE RE-ENFORCEMENT FROM GULF
MX AS LOWER-/MID-LEVEL FLOW BECOMING MORE SRLY.

500 MB PATTERN AMPLIFIES THROUGH SAT. AT 500 MB...SWRN CLOSED LOW
PRESSURE AREA SHIFTS FROM BAJA ACROSS OLD MX. SYSTEM DEEPENS AS IT
SWINGS E THROUGH NEXT 48 HRS...WITH OPEN WAVE AT 06Z CLOSING OFF
OVER MX BY 12Z TODAY. BY 06Z SAT...CLOSED LOW BEGINS FILLING/SHIFTS
TOWARD NWRN GULF MX. THROUGHOUT PROCESS...SERIES OF SHORTWAVES
CONTINUOUSLY RIPPLE THROUGH STRONG SW FLOW/SPUR CONVECTION. 500 MB
TROUGH SHIFTS OUT OF CWFA BY 12Z SUN...WHILE 700 MB TROUGH SEEMS TO
DRAG SLIGHTLY BEHIND. WITH SIGNIFICANT LAYER RH UNTIL 18Z SUN...
EXPECT CLEARING DURING AFTERNOON FROM W.

IN ALL MODELS...BEST CHANCE OF PRECIP DEVELOPS ALONG/N OF BOUNDARY.
WITH SHORTWAVES RIPPLING ALONG FRONT...SOUNDINGS MORE UNSTABLE AFTER
00Z SAT. N OF FRONT...AVN/ETA HELICITY VALUES BIG DUE MAINLY TO
DIRECTIONAL SHEAR AS SURFACE WINDS FROM NE WITH MID-LEVEL SW WINDS.
MORE CONCERNED ABOUT HELICITY VALUES OVER CENTRAL/SRN ZONES OF CWFA.
PEAK HELICITY VALUES IN 300S SAT IN STRONG SE-SW FLOW. GIVEN STRONG
SHEAR...SHOULD ANY BREAKS IN CLOUDS ALLOW INSOLATION...CONCERN S OF
BOUNDARY IN WARM SECTOR WOULD BE INCREASED INSTABILITY DUE TO
HEATING. LOW WET-BULB ZERO VALUES INTO SAT COULD FOSTER DEVELOPMENT
OF HAIL IN ANY THUNDERSTORMS.

ALL MODELS SIMILAR...WITH MANLY TEMPORAL DIFFERENCES. AVN MOST
CONSISTENT OVER LAST SEVERAL DAYS. THEREFORE PREFER AVN...AS IT
HOLDS PRECIP SLIGHTLY LONGER INTO SUN. THIS SOLUTION ACCEPTABLE
SINCE FRONT BECOMING NEAR STATIONARY AROUND CENTRAL ZONES 06Z FRI TO
06Z SAT. AFTER 06Z SAT...SURFACE LOW DEVELOPS OVER NWRN GULF AND
THEN SHIFTS INTO CWFA BY 18Z SAT IN AVN/NGM. ETA FASTER ON THIS
FEATURE WITH LOW OVER CENTRAL AL BY 18Z. AVN HOLDS PRECIP WATER
VALUES OVER 1 UNTIL 06Z SUN...THEN AIRMASS STARTS DRYING. ETA ABOUT
6 HRS FASTER ON THIS FEATURE. GIVEN ACCEPTABLE AVN/NGM SYNOPTIC
PROGS...WILL KEEP SOME CHC PRECIP OVER AREA THROUGH SUN MORNING.

WITH AMPLE TROPICAL MOISTURE FROM PACIFIC/GULF MX...MODELS CRANKING
COPIOUS PRECIP THROUGH EARLY SUN. ANTICIPATE SHORT LULL IN RAINFALL
THIS AM...THEN SHOWERS/THUNDERSTORMS DEVELOPING AGAIN. PRECIP WATER
VALUES RUNNING AROUND 1.5 OVER CWFA THIS AM...PROGGED TO INCREASE
TO NEAR 1.75 OVER CENTRAL/SRN ZONES OF CWFA AFTER 00Z SAT. MID-
LEVEL PATTERN CHANGES LITTLE INTO SAT...WHILE FRONT BECOMING NEARLY
PARALLEL TO FLOW. CONVECTION WILL DEVELOP/REDEVELOP OVER SAME AREAS.
NEW 1-HR FLASH FLOOD GUIDANCE VALUES OVER SEVERAL ZONES ALREADY AOB
1.0...WITH 3-HR VALUES DANGEROUSLY LOW AS WELL. EXPECT EXCESSIVE
RAIN WILL CONTINUE TO PRODUCE SOME FLASH FLOODS/COULD FURTHER PUSH
MAINSTEM RIVERS ALREADY AT/OVER CRITICAL STAGES. FLASH FLOOD WATCH
WILL BE EXTENDED THROUGH TONIGHT FOR ENTIRE CWFA.

.EXTENDED FORECAST...
IN AVN...SURFACE LOW PRESSURE STRENGTHENS OVER GA THEN PUSHES OUT TO
SEA MON. RIDGE AXIS AROUND NM/W TX WILL SHIFT E SUN INTO MON. IN NW-N
FLOW OVER CWFA AFTER 12Z SUN...AIRMASS DRIES OUT. FAIR FORECAST
THROUGH WED...AS HIGH PRESSURE RIDGES BUILDING OVER PLAINS AT 500
MB/700 MB.

PRELIM NUMBERS:
JAN 63/54/63/46 9+95
MEI 66/56/66/48 9+96

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

ARZ074-075-LAZ007>009-015-016-023>026-MSZ018-019-025>066-072>
074-031200-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE JACKSON MS
600 AM CST FRI MAR 2 2001

...THUNDERSTORMS...
ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE TODAY AND TONIGHT SOUTH OF
A VICKSBURG...YAZOO CITY...CARTHAGE...DEKALB LINE. ISOLATED TORNADOES
AND DAMAGING THUNDERSTORM WINDS ARE POSSIBLE THIS AFTERNOON AND
EVENING ALONG AND SOUTH OF A NATCHEZ TO MERIDIAN LINE. LARGE HAIL
WILL BE POSSIBLE NORTH OF THE LINE.

AN OLD FRONTAL BOUNDARY WILL REMAIN DRAPED OVER SOUTHEAST MISSISSIPPI
THROUGH TONIGHT. MEANWHILE...A SERIES OF UPPER LEVEL DISTURBANCES
WILL PASS OVER THE BOUNDARY TODAY AND TONIGHT. AS THESE DISTURBANCES
APPROACH THE REGION...WIDESPREAD AREAS OF RAIN AND THUNDERSTORMS WILL
DEVELOP AND MOVE EAST. THE NEXT DISTURBANCE WILL APPROACH THE AREA
BY MID MORNING WITH THUNDERSTORMS INCREASING BY THIS TIME.

...FLOODING...
A FLASH FLOOD WATCH IS IN EFFECT THROUGH TONIGHT SOUTH OF A CROSSETT
ARKANSAS...CLEVELAND...GRENADA...COLUMBUS MISSISSIPPI LINE.

IN ADDITION TO THE EXPECTED THUNDERSTORM DEVELOPMENT...HEAVY RAIN
WILL BE OF CONCERN AS WELL. ABUNDANT RAINFALL OF THE PAST FEW DAYS
HAS RESULTED IN GROUNDS BEING SATURATED AND STREAM AND CREEKS AT
BANKFULL. HEAVY RAINFALL IS EXPECTED TODAY AND TONIGHT WITH AMOUNTS
NEAR THREE INCHES POSSIBLE BY SATURDAY MORNING. THESE ADDITIONAL
AMOUNTS WILL SERVE TO AGGRAVATE ONGOING RUNOFF PROBLEMS.

FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE AT
WWW.SRH.NOAA.GOV/JAN. THIS INCLUDES THE GRAPHICAL HAZARDOUS WEATHER
OUTLOOK.