FXUS64 KJAN 300337 AAA
AFDJAN
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON MS
937 PM CST SUN NOV 29 2009
.UPDATE...
SURFACE COLD FRONT AT 30/0300 UTC EXTENDS FROM JUST WEST OF MEMPHIS
TENNESSEE ACROSS SOUTHEAST AND SOUTH CENTRAL ARKANSAS INTO NORTHWEST
LOUISIANA. STRONGER PRE-FRONTAL ISENTROPIC UPGLIDE NOTED AT LEVELS
BELOW 295K HAS MOVED NORTH OF THE CWA...AND RESULTING SCATTERED
SHOWERS HAVE MOVED NORTH OF THE AREA. THUS...POPS PRIOR TO MIDNIGHT
HAVE BEEN REDUCED ACROSS THE SOUTHEASTERN TWO-THIRDS OF THE CWA.
AREA RADARS INDICATE THAT A NEARLY SOLID BAND OF MODERATE RAIN WITH
EMBEDDED THUNDERSTORMS IS ALONG AND JUST BEHIND THE SURFACE FRONT.
ALL OF THE ASSOCIATED CONVECTION HAS BECOME ELEVATED AS SBCAPES HAVE
FALLEN WITH LOSS OF DAYTIME HEATING. HOWEVER...A RESERVOIR OF
MUCAPES OVER 250 J/KG WILL BE FOUND ALONG AND BEHIND THE SURFACE
FRONT...SPECIFICALLY FOR A PARCEL OF AIR LIFTED FROM 900 MB. GIVEN
THAT THE FRONTAL CIRCULATION WILL EXTEND ABOVE 900 MB...ELEVATED
CONVECTION AND ISOLATED THUNDERSTORMS WILL BE POSSIBLE ALONG AND
BEHIND THE FRONT ACROSS MUCH OF THE AREA. THE FORECAST HAS BEEN
UPDATED TO EXPAND THE COVERAGE OF ISOLATED THUNDERSTORMS TO MUCH OF
THE CWA TONIGHT INTO MONDAY MORNING...WITH THE 30/0000 UTC NAM
INDICATING 250-500 J/KG OF MUCAPE FOLLOWING THE SURFACE FRONT
THROUGH MONDAY MORNING...AND SREF IS REPORTING AT LEAST 50 PERCENT OF
ITS MEMBERS GENERATING AT LEAST 250 J/KG OF MUCAPE. THE BAND OF RAIN
AND ISOLATED THUNDERSTORMS IS EXPECTED TO REACH THE NORTHWESTERN
PORTION OF THE CWA BY MIDNIGHT...AND THEN BE ORIENTED ALONG THE
NATCHEZ TRACE PARKWAY AROUND 6 AM...BEFORE REACHING SOUTHEAST
MISSISSIPPI BY LATE MORNING. GIVEN THE MORE CONVECTIVE NATURE OF THE
PRECIPITATION...QPF TOTALS HAVE BEEN INCREASED TO THE ONE-HALF TO ONE
INCH RANGE NORTHWEST OF THE NATCHEZ TRACE PARKWAY...PER LATEST HPC
GUIDANCE...FOR THE MIDNIGHT-MONDAY MORNING TIME PERIOD.
RECENT SATELLITE IMAGERY INDICATES HIGHER COVERAGE OF CLOUDS MOVING
INTO SOUTHEAST MISSISSIPPI...WHERE CLOUDS ARE EXPECTED TO FURTHER
INCREASE THROUGH THE NIGHT. THUS...CLOUD COVERAGE HAS BEEN INCREASED
ACROSS THIS AREA FOR TONIGHT. LOW TEMPS TONIGHT HAVE BEEN INCREASED
BY A FEW DEGREES OVER THE SOUTHEASTERN TWO-THIRDS OF THE CWA...WHERE
INCREASED CLOUD COVERAGE WILL INHIBIT RADIATIONAL COOLING...AND
WHERE POST-FRONTAL COLD AIR ADVECTION WILL ARRIVE THE LATEST.
FOR THE TUESDAY NIGHT-WEDNESDAY SYSTEM DESCRIBED BELOW...IT APPEARS
THAT THERE IS INCREASING POTENTIAL FOR HEAVY RAINFALL ACROSS
SOUTHEASTERN PORTIONS OF THE CWA...PARTICULARLY SOUTHEAST OF THE
NATCHEZ TRACE PARKWAY. UNCERTAINTY IN THE TRACK OF THE SURFACE LOW
YIELDS SOME CONCERN FOR HOW MUCH RAINFALL WILL ACCUMULATE...BUT
CURRENT NWP MODEL CONSENSUS IS FOR 1-3 INCHES OF RAIN SOUTHEAST OF
THE PARKWAY. THE 30/0000 UTC NAM HAS COME IN WITH EVEN HIGHER TOTALS
EAST OF THE TRACK OF THE SURFACE LOW ACROSS THE EASTERN THIRD OF THE
CWA...WHERE MUCH GREATER GULF MOISTURE TRANSPORT WILL OCCUR GIVEN A
FURTHER WESTWARD SURFACE LOW TRACK. THE HWO HAS BEEN UPDATED TO
ACCOUNT FOR THIS TREND...AND ISOLATED THUNDERSTORMS HAVE BEEN
INCLUDED IN THE TUESDAY NIGHT FORECAST ACROSS EASTERN AREAS WHERE
ELEVATED INSTABILITY WILL BE ENHANCED. /COHEN/
&&
.PREV DISCUSSION... /ISSUED 311 PM CST SUN NOV 29 2009/
PREVIOUSLY...TONIGHT THROUGH MONDAY NIGHT...RAIN CHANCES WILL
INCREASE ACROSS THE ENTIRE FORECAST AREA FROM WEST TO EAST THROUGH
THE OVERNIGHT HOURS AS A COLD FRONT...WHICH CURRENTLY STRETCHES
SOUTHWEST FROM THE GREAT LAKES REGION THROUGH NORTHWEST ARKANSAS AND
SOUTHEAST OKLAHOMA...INTO NORTH CENTRAL AND CENTRAL TEXAS...MOVES
INTO WESTERN PORTIONS OF THE ARKLAMISS REGION LATE TONIGHT. AHEAD
OF THE FRONT...DECENT ISENTROPIC UPGLIDE WILL CONTINUE TO PRODUCE
PATCHES OF LIGHT...TO OCCASIONALLY MODERATE...RAIN ACROSS LOCATIONS
NORTH OF THE INTERSTATE 20 CORRIDOR...WHILE CLOUDS CONTINUE TO
INCREASE FROM WEST TO EAST ACROSS THE REGION. A COMBINATION OF ALL
THE ABOVE WILL ONCE AGAIN RESULT IN A MILD NIGHT AS OVERNIGHT LOWS
WILL RANGE FROM THE AROUND 50 ACROSS THE DELTA TO THE MID 50S ACROSS
SOUTHEAST MISSISSIPPI.
THE FRONT WILL BEGIN PUSHING SOUTHEAST INTO THE NORTHWEST HALF OF
THE FORECAST AREA AFTER MIDNIGHT TONIGHT...AND SHOULD EXIT SOUTHEAST
MISSISSIPPI DURING THE LATE MORNING/EARLY AFTERNOON HOURS MONDAY.
RAIN WILL GRADUALLY TAPPER OFF FROM NORTHWEST TO SOUTHEAST THROUGH
THE DAY...AND FINALLY COME TO AN END ACROSS SOUTHEAST MISSISSIPPI BY
MONDAY EVENING. BEHIND THE FRONT...SKIES WILL GRADUALLY CLEAR AS
COOLER DRIER AIR QUICKLY BEGINS FILTERING INTO THE CWA FROM THE
NORTHWEST...RESULTING IN A COOLER FEEL TO THE AIR OVER MUCH OF THE
FORECAST AREA MONDAY NIGHT./19/
TUESDAY THROUGH SUNDAY...THIS SHOULD LEAVE MOST OF THE REGION FAIRLY
DRY ON TUESDAY. THERE COULD BE SOME LIGHT RAIN BEGINNING ON TUESDAY
AFTERNOON DUE TO ISENTROPIC LIFT ACROSS THE SOUTH AND HAVE INCLUDED
SOME POPS IN DURING THIS TIME PERIOD BUT LEFT NORTHERN SECTIONS DRY.
TIMING AND PLACEMENT DIFFERENCES BETWEEN MODELS LEAVE MUCH
UNCERTAINTY WITH MOST OF THE EXTENDED BUT IT LOOKS LIKE MOST OF THE
ARKLAMISS WILL SEE SOME RAIN WITH WED LOOKING TO BE THE WETTEST DAY.
MODELS INDICATE THAT THE HEAVIER/BULK OF THE RAIN WILL OCCUR
GENERALLY ALONG AND SOUTHEAST OF THE NATCHEZ TRACE WITH LESSER
AMOUNTS ACROSS THE MS DELTA. BY WED. MORNING...THE ECMWF AND OTHER
MODELS CONTINUE TO SHOW THE SFC LOW JUST TO OUR SOUTHWEST WITH THE
GFS FASTER WITH THE LOW ACROSS NW FL/S AL WITH THE MID LEVEL LOW
STILL ACROSS EAST CENTRAL TEXAS.
BY WEDNESDAY NIGHT....THE BULK OF THE RAIN SHOULD MOVE OFF TO
LOCATIONS MUCH FARTHER EAST OF THE CWA AS THE MID LEVEL LOW ENTERS
OUR REGION. LINGERING LIGHT RAIN COULD AFFECT THE CWA THROUGH THURS.
MORNING AND HAVE TAPERED THIS FOR THE EAST/NORTHEAST WITH ONLY
SLIGHT CHANCES IN THE WEST PRIOR TO MIDNIGHT AND LEAVING ONLY SLIGHT
CHANCES IN THE EAST/NORTHEAST THROUGH DAYBREAK. CONDITIONS SHOULD
REMAIN FAIRLY DRY BEGINNING DURING THE DAY THURSDAY THROUGH MOST OF
THE REST OF THE PERIOD.
FOR THU-FRI. THE LARGER SCALE TROUGH SWINGS ON THROUGH AND COLD
HIGH PRESSURE RESUMES AT THE SURFACE. MODELS DIFFER ONCE AGAIN PAST
THIS POINT. THE GFS QUICKLY MOVES THE SFC HIGH OFF TO THE EAST WITH
SOUTHERLY FLOW RETURNING LATE FRIDAY INTO SATURDAY AND THE ECMWF
DOES NOT MOVE THE UPPER TROUGH THROUGH AS FAST AND LINGERS NORTHERLY
FLOW. WITH THE ECMWF THE RETURN FLOW AND EASTWARD PUSH OF THE HIGH
DOES NOT OCCUR UNTIL LATE SUNDAY. GFS WANTED TO BRING RAIN CHANCES
BACK WITH THE NEXT SYSTEM BY SATURDAY BUT HAVE OPTED TO KEEP THESE
OUT OF THE FORECAST UNTIL THERE IS A LITTLE BETTER AGREEMENT.
OVERALL...TRIED TO STAY CLOSE TO MAV/MEX NUMBERS GIVEN UNCERTAINTIES
IN THE EXTENDED. HOWEVER...DID INCREASE POPS FOR TUES-WED IN THE
SOUTH WHERE THE BETTER POTENTIAL FOR RAIN EXISTS AND CUT NORTHERN
POPS DOWN SOME. TRIED TO FOLLOW THE SLIGHTLY SLOWER TIMING OF THE
ECMWF/SREF WHICH WAS ALSO A LITTLE WETTER. UPDATED TEMPS HAVE BEEN
TRENDED TOWARD THE ENSEMBLE MEANS WITH SUBFREEZING OVERNIGHT
READINGS THURSDAY NIGHT AND FRIDAY NIGHT. THE 12Z RUNS OF BOTH
GFS/ECMWF SHOW A NEARLY 1030MB SURFACE HIGH CROSSING THE LOWER MS
VALLEY WITH PLENTY OF DRY AIR FOR THE RADIATIONAL COOLING LOWS TO BE
ACHIEVED. /28/40/
&&
.AVIATION...
FOR TONIGHT...A COLD FRONT WILL BEGIN MOVING SOUTHWARD ACROSS THE
REGION...WITH ONE OR MORE BANDS OF MODERATE SHOWERS ALONG AND JUST
BEHIND THE FRONT. CEILINGS WILL LOWER TO IFR NEAR THIS ACTIVITY...WITH
MVFR TO LOCALLY IFR VISIBILITIES AS WELL. ADDITIONALLY...WINDS WILL
ABRUPTLY SHIFT TO NORTHWEST TO NORTH AND INCREASE TO 10 TO 15 KT WITH
GUSTS TO 20 KT IN THE WAKE OF THE FRONT. THE FRONT IS EXPECTED TO
REACH KGLH AND KGWO BETWEEN 08 AND 10 UTC...KGTR AND KJAN BETWEEN 12
AND 14 UTC...AND KMEI AND KHBG BETWEEN 13 AND 16 UTC. ISOLATED
THUNDERSTORMS WILL BE POSSIBLE ALONG AND JUST BEHIND THE COLD
FRONT...BUT THE RISK FOR THUNDERSTORMS IMPACTING ANY TAF SITE IS TOO
LOW FOR MENTION IN THE TAFS AT THIS TIME. AFTER THE MODERATE RAIN
MOVES THROUGH...TWO TO THREE HOURS LIGHT RAIN WILL OCCUR WITH MVFR
CEILINGS AND VISIBILITIES. LOW CLOUDS WITH MVFR CEILINGS WILL
CONTINUE THROUGH MONDAY AFTERNOON...WITH CLEARING EXPECTED TO BEGIN
FROM NORTHWEST TO SOUTHEAST LATE MONDAY AFTERNOON INTO MONDAY
EVENING. WINDS WILL BEGIN TO SUBSIDE LATE MONDAY AFTERNOON AS WELL.
/COHEN/
&&
.PRELIMINARY POINT TEMPS/POPS...
JACKSON 55 58 39 57 / 74 65 3 47
MERIDIAN 55 61 35 57 / 57 75 3 44
VICKSBURG 54 58 40 56 / 89 50 3 47
HATTIESBURG 57 65 40 57 / 24 82 11 64
NATCHEZ 56 57 41 55 / 76 64 8 65
GREENVILLE 50 53 38 56 / 100 30 2 23
GREENWOOD 50 54 37 59 / 100 41 2 23
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...NONE.
LA...NONE.
AR...NONE.
&&
$$
COHEN/19/28/40
