Flash Flood Warning 105, NWS Jackson, MS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
345 AM CST THU DEC 13 2001

PREFRONTAL CONVECTION BAND STALLING OUT THIS MORNING ALONG A KMEI-KBTR
LINE AND SHOWING SIGNS OF RETREATING ON LATEST RADAR/SATELLITE
LOOPS. ACTUAL SURFACE FRONT ALONG A KCRP-KSHV-KMEM LINE WILL REMAIN
STATIONARY TODAY AS STRONG UPPER LOW NEAR KELP LIFTS NEWD. ALL OF
CWFA IN WARM SECTOR WITH 65-70F SURFACE DEWPOINTS PUSHING NWD INTO
THE LOWER MS VALLEY.

SHORT TERM REMAINS WET AS 250-300% OF NORMAL PRECIPITABLE WATER
VALUES(1.7-1.9) ENGULF THE AREA THROUGH THIS EVENING. MAIN FORECAST
CONCERNS WILL BE REPOSITIONING FFA AS ADDITIONAL RAINFALL AMOUNTS OF
2-5 ARE POSSIBLE ACROSS AREAS THAT JUST HAD 2-3 IN THE PAST 24 HRS
AS PREFER THE NGM/06Z MESOETA SCENARIOS FOR SURFACE WAVE DEVELOPING
ON THE QSTNRY FRONT ALONG THE TX COAST. ALREADY SEEING SUPPORT FOR
THIS WAVE AS PROFILERS AT PALESTINE...WINFIELD AND LAKE CHARLES VWP
BACKING THE WINDS IN LOWER 5K FEET AT 08Z. LOOK FOR SURFACE LOW
FORMING NEAR KVCT TO TRACK NEAR KMLU BY LATE AFTERNOON AND KUOX BY
MIDNIGHT. A MID LEVEL JET STREAK(85-95KTS) MEETS THE LOW AS IT
CROSSES THE DELTA REGION BETWEEN 00Z AND 06Z. INCREASING LOW LEVEL
JET OF 40-50KT AT 850MB(328K THETA-E AIR)TEAMS WITH RIGHT ENTRANCE
REGION OF 150-170KT 300MB JET CORE IN THE OH VALLEY TO CREATE A
CLASSIC FRONTAL/SYNOPTIC FLASH FLOOD EVENT.

WILL PLACE MUCH OF CWFA IN FFA NW OF ABOUT A MERIDIAN TO MONTICELLO
LINE AS MODELS OF CHOICE HAVE RAIN DEVELOPING NWWD INTO THE DELTA
BEFORE NOON. WILL MENTION SEVERE TSRA FOR AREAS ROUGHLY SE OF THE
NATCHEZ TRACE WHERE STORM RELATIVE HELICITIES PROGGED TO REACH
350-400 IN COMBINATION WITH CAPES OF 1000-2000J/KG BETWEEN 21Z-03Z.
SPC ALSO CONSIDERING UPGRADE TO MODERATE RISK IN SERN MS.

ONCE THE UPPER LOW EJECTS NEWD LATE TONIGHT...RAINFALL ENDS RATHER
QUICKLY FROM WEST TO EAST LEAVING FRIDAY AND SATURDAY MOSTLY DRY.
NEXT UPSTREAM SYSTEM WILL PROBABLY HOLD OFF UNTIL SATURDAY NIGHT AND
SUNDAY AS MODELS TENDING TO CLOSE OFF  THIS SYSTEM BY THE TIME IT
REACHES THE SRN PLAINS(I.E. ANOTHER SLOWER AND STRONGER TREND THAN
THE MODELS). THE EXTENDED PERIOD ENDS UP IN A TRANSITION TO ZONAL
FLOW PATTERN ACROSS THE CONUS AND THUS DRYING OUT FOR A FEW DAYS.

JAN 68/47/57/40/64 ++-01
MEI 70/51/59/39/66 ++100

.JAN...
MS...FFA ALONG/NW OF A MERIDIAN-MONTICELLO LINE THROUGH MIDNIGHT.
LA...FFA ALL NE ZONES THROUGH MIDNIGHT.
AR...FFA ALL EXTREME SE ZONES THROUGH MIDNIGHT.