000
FXUS64 KJAN 210927
AFDJAN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
327 AM CST SAT NOV 21 2009

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT...PRIMARY FORECAST CONCERNS
FOR THIS PERIOD WILL BE RAINFALL ASSOCIATED WITH SLOWLY DEEPENING LOW
PRESSURE OVER THE GULF...ALONG WITH THE ASSOCIATED WINDS. EARLY
MORNING SURFACE ANALYSIS PLACES A 1008 MB SURFACE LOW OVER THE
NORTHWEST GULF OF MEXICO...ABOUT 120 MILES SOUTHEAST OF HOUSTON
TEXAS. THIS LOW CONTINUES TO DEVELOP AS VIGOROUS DEEP-LAYER ASCENT
DOWNSTREAM OF A SHORTWAVE TROUGH EMBEDDED WITHIN THE SOUTHERN JET
STREAM CONTINUES TO INTERACT WITH A BAROCLINIC ZONE OVER THE WESTERN
GULF. AMONG MULTI-MODEL GUIDANCE...THE GFS/NAM/SREF/UKMET APPEAR TO
INITIALIZE THE DEPTH AND POSITION OF THE LOW QUITE WELL. BY THIS
EVENING...THE NAM SHOWS THE LOW ASSUMING MORE OF A NORTHWARD HEADING
WHILE ELONGATING THE LOW FROM NORTHWEST TO SOUTHEAST...AND FOLLOWING
A TRACK SIMILAR TO THE ECMWF. TIGHT CLUSTERING AMONGST GFS ENSEMBLE
MEMBERS AROUND THE OPERATIONAL GFS/UKMET/SREF TRACK SOLUTIONS GIVES
HIGHER CREDIBILITY TOWARD THESE SOLUTIONS...AND THUS THE MORE
SOUTHERN LOW TRACK IS THE PREFERRED SOLUTION. THIS CALLS FOR THE LOW
TRACKING EAST-NORTHEASTWARD SOUTH OF THE GULF COASTLINE THROUGH
SUNDAY MORNING BEFORE MAKING LANDFALL OVER THE WESTERN FLORIDA
PANHANDLE.

GIVEN THE MORE SOUTHERN LOW TRACK...THE NORTHWARD EXTENT OF PRECIP
COVERAGE TODAY IS IN QUESTION...AND LOCAL HIGH-RES WRF ENSEMBLE
MEMBERS THAT USE PREFERRED GFS PARAMETERS AS INPUT SUGGEST THAT RAIN
COVERAGE ACROSS NORTHERN AREAS WILL NOT BE AS WIDESPREAD AS
PREVIOUSLY ANTICIPATED. THUS...POPS WERE TRENDED DOWNWARD TO LIKELY
OVER THE NORTHERN THIRD OF THE CWA...CONSISTENT WITH LATEST MAV
GUIDANCE. HOWEVER...ALL WRF MEMBERS INDICATE MEASURABLE PRECIPITATION
OCCURRING ALONG AND SOUTH OF INTERSTATE 20...WHERE POPS WERE
INCREASED ABOVE MAV GUIDANCE TO 100 PERCENT FOR TODAY. THE OTHER
IMPLICATION OF THE MORE SOUTHERN LOW TRACK IS THAT THE PROBABILITY OF
MEETING LAKE WIND ADVISORY CRITERIA ON ROSS BARNETT RESERVOIR AND
OKATIBBEE LAKE HAS DECREASED. THE TOTAL SOUTH-TO-NORTH PRESSURE
DIFFERENCE ACROSS THE CWA IS NOT EXPECTED TO EXCEED 3.5 MB TODAY OR
TONIGHT...SUPPORTING SUSTAINED NORTHEAST WINDS OF 10 TO 15 MPH ON THE
LAKES. FORECAST SOUNDINGS FROM THE GFS INDICATE MAXIMUM FLOW BELOW H7
REMAINING AT OR BELOW 25 KT...AND EVEN WINDS THIS STRONG WILL
STRUGGLE REACHING THE SURFACE AS GUSTS GIVEN STABLE THERMAL PROFILE
BELOW H7. GUSTS ARE EXPECTED TO REMAIN BELOW 25 MPH. IN FACT...WRF
ENSEMBLE NOW INDICATES LESS THAN 15 PERCENT CHANCE OF LAKE WIND
ADVISORY CRITERIA BEING MET ON THE LAKES...AND THUS THE ADVISORY HAS
BEEN CANCELLED. THE STRONGER LOW-LEVEL WIND FIELD SUGGESTED BY THE
NAM APPEARS UNLIKELY GIVEN THE ANTICIPATED SOUTHERN LOW TRACK.
ADDITIONALLY...ELEVATED INSTABILITY SUPPORTING MUCAPES FROM 200 TO
500 J/KG WILL AFFECT THE SOUTHEASTERN THIRD OF THE FORECAST AREA THIS
AFTERNOON AND EVENING...WHERE ISOLATED THUNDERSTORMS ARE POSSIBLE.
NEAR ZERO SBCAPES WILL PRECLUDE PRESENCE OF SURFACE-BASED CONVECTION
OR RISK FOR STRONG THUNDERSTORMS. HIGH TEMPERATURES TODAY MOSTLY
FOLLOWED MAV GUIDANCE...THOUGH THEY WERE RAISED A COUPLE DEGREES
ACROSS NORTHERN AREAS...WHERE ONSET OF RAIN WILL BE THE LATEST.

FOR TONIGHT...RAIN WILL CONTINUE TO SPREAD ACROSS THE EASTERN HALF
OF THE CWA...WHERE POPS HAVE BEEN RAISED ABOVE MAV GUIDANCE TO 100
PERCENT WITH HIGH CONFIDENCE OF MEASURABLE PRECIP FROM THE SREF.
TOTAL RAINFALL AMOUNTS THROUGH TONIGHT OF ONE-HALF TO ONE INCH ARE
EXPECTED...WHICH WILL BE TOO LOW FOR FLASH FLOODING. MEANWHILE...
DRIER AIR WRAPPING INTO THE SOUTHWESTERN SEMICIRCLE OF THE LOW WILL
LIMIT PRECIP CHANCES OVER THE SOUTHWESTERN CWA...WHERE RAIN IS
EXPECTED TO END DURING THE EVENING. ON SUNDAY...THE SURFACE LOW WILL
BEGIN FILLING AS THE SUPPORTING MID/UPPER-LEVEL SHORTWAVE TROUGH
BECOMES ABSORBED INTO THE LARGE-SCALE JET STREAM AND DECOUPLES FROM
THE SURFACE CIRCULATION. AS SUCH...PRECIP CHANCES AND WIND SPEEDS
WILL DECREASE...THOUGH ENOUGH MOISTURE WEST OF THE LOW WILL SUPPORT
A CHANCE FOR RAIN OVER EASTERN AREAS SUNDAY MORNING PER MAV
GUIDANCE. BY SUNDAY EVENING...MOST OF THE RAIN IS EXPECTED TO HAVE
TAPERED OFF. SKIES WILL BEGIN CLEARING FROM SOUTHWEST TO NORTHEAST
ON SUNDAY...AND THUS TEMPS WERE INCREASED A COUPLE DEGREES ABOVE MAV
GUIDANCE ACROSS THE SOUTHWEST. THEN FOR SUNDAY NIGHT...CLEARING
SKIES COMBINED WITH THE MOIST GROUND WILL SET THE STAGE FOR PATCHY
FOG DEVELOPMENT...PARTICULARLY ACROSS THE SOUTHERN PORTION OF THE
CWA WHERE HIGHEST RAINFALL TOTALS THROUGH SUNDAY ARE EXPECTED.
/COHEN/

.LONG TERM...A RATHER FLAT ZONAL FLOW PATTERN WILL TRANSITION BACK TO
RIDGING IN THE WRN CONUS AND TROUGHING IN THE E DURING THE COMING
HOLIDAY WEEK. THE PRIMARY FEATURE FOR THE WEEK APPEARS TO BE A WEAK
FRONTAL SYSTEM PASSING THROUGH THE LOWER MS VALLEY TUESDAY AND
TUESDAY NIGHT WITH MINIMAL RAINFALL CHANCES. THIS BOUNDARY IS
FOLLOWED BY TWO REINFORCING TROUGHS WEDNESDAY NIGHT AND LATER ON
SATURDAY TO KEEP US COOLER THAN CLIMATOLOGY.

QUITE MILD CONDITIONS BEGIN THE WEEK ON MONDAY WITH FOGGY LOWS IN
THE 40S AND HIGHS RECOVERING NICELY INTO THE M-U60S WITH CONSIDERABLE
SUNSHINE. THE GFS IS NOW MUSTERING UP 0.75-1.0 INCH PWATS ALONG THE
TUESDAY FRONT BEFORE RETURNING TO 0.25 INCHES ON WEDNESDAY. PRE
FRONTAL LOW LEVEL RIDGING ALONG THE GULF COAST SHOULD PREVENT MUCH
MOISTURE RETURN AND DO NOT SEE MUCH MOISTURE CONVERGENCE WITH THE
BOUNDARY SO WILL KEEP MENTION TO LIGHT RAIN. THE ECMWF IS ACTUALLY A
LITTLE WETTER WITH THIS FRONT AS IT SHOWS A TENTH OF AN INCH QPFS
HANGING ON INTO TUESDAY EVENING OVER THE SERN PORTIONS OF OUR CWFA.
BEYOND THAT...A QUICK REINFORCING DRY TROUGH SWEEPS THROUGH THE AREA
WITH A FEW CLOUDS FOR WEDNESDAY NIGHT. THIS SETS UP A CHILLY CAA
CELEBRATION FOR THANKSGIVING DAY WITH MOST LOWS IN THE U30S AND HIGHS
IN THE 50S.

A 1020MB SURFACE HIGH OVER SERN TX FRIDAY MOVES ALONG THE GULF COAST
FOR FRIDAY NIGHT AND SATURDAY WITH SOME MOISTURE RETURN FOR SATURDAY
NIGHT. ANOTHER WEAK FRONT COULD REACH THE AREA BY THAT TIME BUT IT
ALSO IS APPEARING RATHER DRY WITH THE SURFACE HIGH OFF THE COAST OF
NW FL. WILL HAVE TO MONITOR THIS TIME FRAME AS THE ECMWF AGAIN A
LITTLE MORE ROBUST WITH THE MASS FIELDS AND HIGHER RAIN CHANCES.

ALL IN ALL...THE HOLIDAY WEEK SHOULD BE QUITE DRY AND ALSO SEASONABLE
IN THE TEMPERATURE DEPARTMENT. THE ENSEMBLE MOS GUIDANCE STAYS WITHIN
1-2 STANDARD DEVIATIONS AND IN MOST CASES THE MEANS ARE CLOSE TO THE
OPERATIONAL NUMBERS./40/

.AVIATION...RAIN WILL SPREAD FROM SOUTHWEST TO NORTHEAST ACROSS THE
AREA TODAY...AS AN UPPER LEVEL DISTURBANCE AND SURFACE LOW PRESSURE
APPROACH THE REGION. RAINFALL INTENSITY IS EXPECTED TO BE LIGHT TO
MODERATE...WITH THE GREATEST COVERAGE OF RAIN ACROSS CENTRAL AND
SOUTHERN MISSISSIPPI TODAY. FOR TONIGHT...THE GREATEST COVERAGE OF
RAIN WILL BE ACROSS EASTERN MISSISSIPPI. MVFR CONDITIONS DUE TO
CEILING RESTRICTIONS AND OCCASIONAL VISIBILITY RESTRICTIONS WILL
AFFECT MUCH OF THE AREA BY THIS AFTERNOON...WITH OCCASIONAL IFR
CEILINGS AND VISIBILITIES POSSIBLE AT KHBG AND KMEI NEAR THE MODERATE
RAIN. AN ISOLATED THUNDERSTORM WILL ALSO BE POSSIBLE ACROSS SOUTHEAST
MISSISSIPPI THIS AFTERNOON AND EVENING...THOUGH THE CHANCE OF
THUNDERSTORMS OCCURRING AT ANY TAF SITE IS TOO LOW FOR MENTION IN THE
TAFS AT THIS TIME. NORTHEAST TO EAST WINDS ARE EXPECTED TO INCREASE
TO 7 TO 12 KT BY THIS AFTERNOON...BUT WILL SLOWLY DIMINISH LATE
TONIGHT. /COHEN/

.PRELIMINARY POINT TEMPS/POPS...
JACKSON       57  49  61  45 / 100  83  15   9
MERIDIAN      57  47  62  44 / 100  98  35  15
VICKSBURG     58  47  62  42 / 100  48  15   7
HATTIESBURG   59  49  64  46 / 100  96  15   9
NATCHEZ       56  48  63  43 / 100  47  10   3
GREENVILLE    59  47  62  44 /  59  50  15   7
GREENWOOD     60  47  61  44 /  62  89  30  10

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...NONE.
LA...NONE.
AR...NONE.