River Flood Warning 161, NWS Jackson, MS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
447 AM CST FRI DEC 18 2009

.SHORT TERM...TODAY AND FRIDAY...RAIN WILL EXIT TO THE EAST BY THE MID
TO LATE MORNING HOURS...AND SATELLITE TRENDS INDICATE THAT RAPID
CLEARING WILL TAKE PLACE FOLLOWING THE RAIN. WEAK HIGH PRESSURE WILL
BUILD OVER THE ARKLAMISS DURING THE AFTERNOON BRINGING QUIET WEATHER
WITH SEASONABLY COOL TEMPERATURES.

FRIDAY NIGHT THROUGH SATURDAY NIGHT...

A MOSTLY DRY BUT BRISK WEATHER REGIME IS FORECAST FOR THE WEEKEND
AS STRONG POLAR STREAM SHORTWAVE ENERGY DIVES SOUTHEAST INTO THE ERN
CONUS. THE 00Z GFS/GEFS/ECMWF ARE NEARLY PERFECT MATCHES ON THEIR
DEPICTION OF THIS WAVE...AND IT LOOKS LIKE THE BEST LOW LEVEL COLD
ADVECTION WILL KICK IN LATE FRIDAY NIGHT AND EARLY SATURDAY MORNING.
A STRATUS DECK WILL ACCOMPANY THE COLD ADVECTION WITH THE
POSSIBILITY FOR SPRINKLES/FLURRIES OVER THE COLUMBUS AREA SATURDAY.
WHILE IT IS QUESTIONABLE IF THE DEPTH OF THE MOISTURE WILL BE DEEP
ENOUGH FOR ICE PRODUCTION...WET BULB ZERO HEIGHTS WILL BECOME
SUFFICIENTLY LOW FOR ANY FLURRIES TO REACH THE GROUND. HAVE
CONTINUED THE TREND OF CUTTING GFS MOS HIGHS BY A FEW DEGREES FOR
SATURDAY GIVEN THE CONSIDERABLE STRATUS EXPECTED. CLEARING SKIES
WILL ALLOW MOST LOCATIONS TO EXPERIENCE A LIGHT FREEZE SATURDAY
NIGHT. /EC/

.LONG TERM...SUNDAY THROUGH THURSDAY...QUIET WEATHER FOR THE FIRST
PORTION OF THE EXTENDED FORECAST. HIGH PRESSURE AT THE SURFACE AND
NORTHWESTERLY FLOW ALOFT THROUGH TUESDAY WILL LEAVE THE CWA DRY BUT
CHILLY. SUNDAY LOOKS TO BE A LITTLE WARMER THAN SATURDAY GIVEN
CLEARING CONDITIONS. WITH HIGH PRESSURE OVERHEAD....SUNDAY NIGHT
WILL BE ANOTHER COLD ONE AS GOOD RADIATIONAL COOLING WILL TAKE
PLACE. HOWEVER...THE MAIN FEATURE OF THE LONG TERM IS WITH THE NEXT
STORM SYSTEM PROGGED TO AFFECT THE REGION JUST BEFORE CHRISTMAS.

AS SFC HIGH PRESSURE BEGINS TO SLIDE OFF TO THE EAST ON
MONDAY...SOUTHERLY FLOW RETURNS TO THE WESTERN PORTIONS OF
THE CWA. MOISTURE BEGINS TO INCREASE SLOWLY WITH PWAT VALUES
INCREASING DURING THE DAY ON TUESDAY TO NEAR 1 INCH ACROSS MY
WESTERN ZONES. AS THIS OCCURS...THE UPPER FLOW BECOMES MORE ZONAL
AND AN UPPER TROUGH BEGINS TO DEVELOP ACROSS THE WESTERN U.S. THIS
WILL BRING AN INCREASE IN HIGH LEVEL CLOUDS OVER THE AREA. IN
ADDITION...TEMPERATURES SHOULD BEGIN TO MODERATE AS HIGHS WILL WARM
INTO THE UPPER 50S AND LOWER 60S MONDAY AND TUESDAY.

AS THE UPPER TROUGH BEGINS TO DIG FURTHER SOUTH AND HEAD TOWARD THE
EAST...A SFC LOW DEVELOPS ACROSS THE LEE SIDE OF THE ROCKIES AND MOVES
IN OUR DIRECTION AS WELL. RAIN CHANCES BEGIN TO INCREASE ACROSS THE
WEST TUESDAY NIGHT AS THE MID LEVEL FLOW BECOMES MORE SOUTHWESTERLY
AND THERE MAY BE SOME WEAK ISENTROPIC LIFT/WAA OCCURING. BY WEDNESDAY
PWAT VALUES PEAK AROUND 1.3-1.5 INCHES JUST AHEAD OF THE APPROACHING
STORM SYSTEM.

WHILE THIS SYSTEM IS STILL ABOUT 5 TO 6 DAYS OUT...MODELS HAVE COME
INTO MUCH BETTER AGREEMENT AS COMPARED TO LAST NIGHTS RUNS. THE
ECMWF IS NOW IN BETTER ALIGNMENT WITH THE GFS AND GFES.
HOWEVER...THE GFS STILL REMAINS MORE ROBUST IN THE DEVELOPMENT OF
THE SFC LOW AS COMPARED TO THE OTHER TWO MODELS. AS THE UPPER TROUGH
CONTINUES TO DIG SOUTH AND THE SFC LOW MOVES CLOSER TO THE
EAST...RAIN WILL CONTINUE TO INCREASE ON WEDNESDAY AHEAD OF THIS
SYSTEM THAT SHOULD MOVE THROUGH ON WEDNESDAY NIGHT/EARLY THURSDAY
WITH ASSOCIATED COLD FRONT THROUGH THE CWA BY MIDDAY ON THURSDAY.
AGAIN WHILE THIS IS CONSIDERABLY FAR OUT IN THE FORECAST...THIS IS
AN INTERESTING SYSTEM TO WATCH. WITHOUT GETTING TOO DETAILED...IT
LOOKS LIKE THERE COULD BE SOME DECENT INSTABILITY ASSOCIATED WITH
THIS AS MLCAPES AND VERTICAL TOTALS ARE NOT TOO SHABBY ALONG WITH
DECENT FORCING AND SHEAR WEDNESDAY NIGHT...AS ADVERTISED BY THE GFS.
THE TRACK OF THE SFC LOW IS ALSO MUCH FURTHER NORTH THIS RUN THAN
LAST NIGHT AND THAT WOULD ALSO INDICATE A BETTER SCENARIO FOR SOME
SVR WX...AS WOULD THE NEGATIVE TILT THAT THE UPPER TROUGH LOOKS TO
BE TAKING ON. NOT ONLY DO WE HAVE TO KEEP AN EYE OUT FOR THIS
POTENTIAL BUT ALSO FOR MODERATE TO HEAVY RAIN. ALL OF THIS WOULD
DEPEND ON THE TRACK AND DEPTH OF THE LOW AS THE ECMWF IS DEFINITELY
NOT AS DEEP AS THE GFS. ALL SOMETHING TO KEEP AN EYE OUT FOR OVER THE
NEXT SEVERAL MODEL RUNS.

AFTER THURSDAY...THE AREA SHOULD DRY OUT AS THE UPPER TROUGH/LOW
MOVES NORTH OVER THE GREAT LAKES AND INTO CANADA. TEMPS ON THURSDAY
SHOULD NOT WARM TOO MUCH AS CAA WILL MOVE IN AND CLOUDY CONDITIONS
SHOULD REMAIN AND KEEP TEMPS LOW. CHRISTMAS DAY WILL ALSO BE CHILLY
AND FEEL MORE LIKE WINTER(AS OPPOSED TO THE SPRING LIKE TEMPS THAT
WE WILL HAVE SEEN JUST A FEW DAYS EARLIER).

OVERALL KEPT CLOSE TO MEX NUMBERS AS THEY CAME IN HIGH AND
REASONABLE FOR POPS. DID CUT FROM GUI FOR CHRISTMAS DAY AS WE SHOULD
BE DRY BY THAT POINT. ONLY MADE SLIGHT ADJUSTMENTS TO TEMPS DURING
THE PERIOD. /28/

&&

.AVIATION...MVFR/IFR RESTRICTIONS IN RAIN EARLY THIS MORNING OVER
CNTRL/ERN MS WILL IMPROVE QUICKLY FROM MID TO LATE MORNING. BY THIS
AFTERNOON...EXPECT VFR CONDITIONS AT ALL LOCATIONS AS WEAK HIGH
PRESSURE BUILDS OVER THE AREA. COLDER AIR WILL MOVE INTO THE AREA
LATE TONIGHT AND SATURDAY...AND THIS WILL BE ACCOMPANIED BY A BROKEN
TO SOLID STRATUS DECK WITH CEILINGS IN THE 1500 TO 2500 FT. /EC/

&&

.PRELIMINARY POINT TEMPS/POPS...
JACKSON       56  35  45  30 /  11   4   4   2
MERIDIAN      54  35  46  30 /  48   6   5   4
VICKSBURG     56  36  47  31 /   3   4   3   2
HATTIESBURG   57  36  49  31 /  21   5   6   4
NATCHEZ       56  35  49  29 /   3   4   3   1
GREENVILLE    55  36  46  30 /   2   6   3   2
GREENWOOD     52  35  44  30 /  11   7   5   4

&&

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

EC/28/

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