FXUS64 KJAN 290324 AAA
AFDJAN
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON MS
924 PM CST SAT NOV 28 2009
.UPDATE...
29/0100 UTC SURFACE ANALYSIS DEPICTS DEPARTING SURFACE HIGH
PRESSURE...CURRENTLY CENTERED OVER THE FLORIDA PANHANDLE...AND AN
APPROACHING FRONTAL SYSTEM OVER THE CENTRAL PLAINS. THIS LEAVES THE
ARKLAMISS IN A SOUTH-SOUTHEASTERLY RETURN FLOW PATTERN...WITH SURFACE
DEWPOINTS GRADUALLY INCREASING INTO THE LOWER 40S ACROSS THE AREA.
GREATER LOW/MID-LEVEL MOISTURE IS FOUND FARTHER WEST TOWARD THE
ARKLATEX REGION...WITH THE 29/0000 UTC SHREVEPORT SOUNDING INDICATING
MOIST LAYER EXTENDING UP TO 600 MB WITH A PWAT OF 1.03 INCHES. THIS
AIRMASS WILL BE APPROACHING THE ARKLAMISS DURING THE NEXT DAY IN
ADVANCE OF THE AFOREMENTIONED FRONTAL SYSTEM...WITH LOW/MID-LEVEL
CLOUD COVERAGE INCREASING OVER WESTERN AREAS THROUGH THE NIGHT. CLOUD
COVERAGE HAS BEEN INCREASED WEST OF INTERSTATE 55 THROUGH THE NIGHT
TO ACCOUNT FOR THESE TRENDS...AS EVIDENT IN RECENT 11-3.9 MICRON
SATELLITE IMAGERY. FARTHER TO THE EAST...MID/HIGH-LEVEL CLOUDS WILL
BE RETREATING EASTWARD IN ASSOCIATION WITH A DEPARTING MID/UPPER-
LEVEL SHEAR AXIS. AS SUCH...SKY COVERAGE HAS BEEN TAPERED DOWN TO
PARTLY CLOUDY OVER EASTERN MISSISSIPPI THROUGH THE NIGHT. THIS WILL
RAISE THE CONCERN FOR SOME PATCHY FOG DEVELOPMENT OVER SOUTHEAST
MISSISSIPPI LATE TONIGHT AS WINDS BECOME LIGHT IN RESPONSE TO
BOUNDARY LAYER DECOUPLING...THOUGH ENOUGH CLOUDS WILL BE PRESENT TO
MITIGATE SIGNIFICANT FOG POTENTIAL. ADDITIONALLY...LATEST NWP MODEL
GUIDANCE IS INDICATING INCREASING ISENTROPIC UPGLIDE FOR LEVELS AT
AND BELOW 310K LEVEL AFTER 29/0600 UTC TONIGHT...PARTICULARLY WEST OF
INTERSTATE 55. A SLIGHT CHANCE OF SPRINKLES HAS BEEN ADDED TO THE
FORECAST FOR LATE TONIGHT ALONG AND WEST OF THE MISSISSIPPI
RIVER...WHERE THE ASCENT WILL COMBINE WITH RELATIVE HUMIDITY VALUES
STEADILY INCREASING INTO THE 70-90 PERCENT RANGE BELOW H85. AS THE
ASSOCIATED MOISTURE PLUME WORKS ITS WAY EASTWARD THROUGH
SUNDAY...RAIN CHANCES HAVE BEEN INCREASED NORTHWEST OF THE NATCHEZ
TRACE PARKWAY FOR SUNDAY MORNING. AS FOR TEMPERATURES...LOW TEMP
FORECAST FOR TONIGHT REMAINS UNCHANGED...THOUGH HOURLY TEMPERATURES
WERE DECREASED A FEW DEGREES PRIOR TO MIDNIGHT ACROSS THE
SOUTHEAST...WHERE REDUCED CLOUD COVERAGE HAS PROMOTED AN EARLY FALL
IN TEMPERATURES. /COHEN/
&&
.PREV DISCUSSION... /ISSUED 314 PM CST SAT NOV 28 2009/
DISCUSSION...TONIGHT THROUGH SUNDAY NIGHT...HIGH PRESSURE WILL
CONTINUE TO SLIDE EAST OF THE FORECAST AREA TONIGHT ALLOWING MID AND
LOW LEVEL WINDS TO BECOME MORE SOUTHERLY. THE COMBINATION OF DECENT
ISENTROPIC UPGLIDE AND A STORM SYSTEM APPROACHING THE LOWER
MISSISSIPPI RIVER VALLEY FROM THE WEST THROUGH THE DAY SUNDAY WILL
KEEP SOME CLOUDS OVER THE CWA THROUGH THE OVERNIGHT HOURS. THIS
WILL ALL RESULT IN A SLIGHTLY MILDER NIGHT...COMPARED TO PREVIOUS
NIGHT...ACROSS THE FORECAST AREA TONIGHT AS TEMPERATURES RANGE FROM
THE UPPER 40S WEST OF THE MISSISSIPPI RIVER TO AROUND 40 ACROSS EAST
MISSISSIPPI.
RAIN CHANCES WILL BE ON THE INCREASE THROUGH THE DAY SUNDAY AS AN
UPPER LEVEL TROUGH DROPS SOUTHEAST OUT OF THE NORTHERN PLAINS...
ACROSS THE MID MISSISSIPPI RIVER VALLEY...AND TOWARDS THE SOUTHEAST
UNITED STATES. THIS SYSTEM WILL DRAG A COLD FRONT INTO AND
EVENTUALLY THROUGH THE FORECAST AREA LATE SUNDAY NIGHT INTO MONDAY
MORNING. GOOD ISENTROPIC UPGLIDE AHEAD OF THE FRONT THOUGH COULD
CAUSE SOME LIGHT RAIN TO DEVELOP ACROSS MAINLY WESTERN PORTIONS OF
THE AREA AS EARLY AS SUNDAY AFTERNOON. THE BETTER RAIN CHANCES
HOWEVER WILL EXIST AREA WIDE SUNDAY NIGHT INTO MONDAY MORNING AS THE
FRONT MOVES ACROSS THE FORECAST AREA.
THE PREVIOUS LONG TERM FORECAST DISCUSSION FOLLOWS. /19/
MONDAY THROUGH NEXT SATURDAY...COLD FRONT TRAVERSING THE REGION
MONDAY WILL CONTINUE TO SLIDE TO THE SOUTHEAST THROUGH THE MORNING
HOURS AND EXIT THE CWA IN THE AFTERNOON. NORTHERLY WINDS WILL
INCREASE BEHIND THE FRONT AND WILL LIKELY NEED A LAKE WIND ADVISORY
FOR AREA LAKES AFTER FROPA. MEX POPS LOOKED GOOD MON KEEPING LIKELY
WORDING FOR MOST OF THE AREA AND A CHANCE OF RAIN FOR THE
NORTHWESTERN TIER COUNTIES. LOW LEVEL WARM/MOIST ADVECTION AHEAD OF
THE FRONT STRUGGLES TO DEVELOP ANY SIGNIFICANT INSTABILITY DUE TO
THE DRY BL CONDITIONS PRESENT ALONG THE GULF COAST...AS WELL AS OVER
THE NORTHERN GULF AND WILL MAINTAIN ZERO THUNDER CHANCES IN THE
FORECAST THROUGH MONDAY.
FROM HERE THE FORECAST CONCERN IS CENTERED ON SFC LOW PRESSURE IN
THE WESTERN GULF DEVELOPING MONDAY NIGHT ALONG THE FRONTAL
BOUNDARY...AHEAD OF AN APPROACHING SRN STREAM S/WV...AND THE
ASSOCIATED HEAVY RAIN AND THUNDER CHANCES FOR THE ARKLAMISS THROUGH
WEDNESDAY. GFS/ECMWF/GEFS ARE IN DECENT AGREEMENT WITH THE
DEVELOPMENT OF THE LOW LATE MONDAY OUT OVER THE WESTERN GULF. FROM
HERE THE GUIDANCE DIFFERS A BIT AS THE GFS/00Z OUTRUNS ITS ENSEMBLE
MEAN AS WELL AS THE ECMWF/00Z WITH THE PROGRESSION OF THIS SYSTEM.
GFS ADVANCES THE UPPER LOW INTO CENTRAL LA BY 12Z WED...WITH THE
ECMWF KEEPING THE UPPER LOW BACK OVER THE FORT WORTH AREA 12Z WED.
THE GEFS SHOWS MORE SUPPORT FOR THE ECMWF SOLUTION MAKING FOR LOWER
CONFIDENCE IN THE GFS. FOR NOW...WILL GRADUALLY REINTRODUCE POPS
MONDAY NIGHT BUT NOT QUITE AS FAST AS GFS SUGGESTS BASED ON THE
PREFERRED SLOWER SOLUTION. RAIN CHANCES WILL CONTINUE INCREASING FROM
SOUTH TO NORTH THROUGH THE DAY TUESDAY AS THE SFC LOW TRACKS TOWARD
THE GULF COAST. HAVE INTRODUCED SOME THUNDER CHANCES STARTING OVER
WESTERN AREAS TUESDAY NIGHT AS WARM/MOIST AIR IS LIFTED OVER THE BL
AHEAD OF THE LOW(MODELS INDICATE A SWATH OF 200-400J/KG MUCAPE
SLIDING ACROSS NORTHERN AREAS)...COMBINED WITH APPROACHING DEEP LAYER
LIFT/STRENGTHENING JET SUPPORT IN ADVANCE OF THE UPPER S/WV. WILL
KEEP THUNDER CHANCES ACROSS NORTHERN AND EVENTUALLY NORTHEASTERN
ZONES THROUGH THE MORNING HOURS WEDNESDAY BEFORE COOL/DRY ADVECTION
DEVELOPS ACROSS THE ARKLAMISS IN WAKE OF THE LOW THAT HAS NOW PASSED
EAST OF THE AREA. ONE ITEM OF NOTE IS THE DISCREPANCY BETWEEN THE
GFS/ECMWF WITH REGARDS TO RAIN TOTALS WITH THIS SYSTEM. THE MORE
PROGRESSIVE GFS POSITIONS A SWATH OF 4 TO 6IN OF RAIN WELL EAST OF
OUR CWA WHILE THE ECMWF/00Z SHOWS A SWATH OF 4 TO 5IN FALLING OVER
FAR SOUTHEASTERN AREAS OF THE ARKLAMISS BY 12Z WED. CONSIDERING THE
UNCERTAINTY IN THE TRACK OF THE LOW AT THIS POINT WILL FORGO MENTION
OF HEAVY RAIN IN THE HWO. THIS WILL BE MONITORED AS THE SITUATION
EVOLVES.
RAIN CHANCES WILL TAPER OFF WEDNESDAY AFTERNOON INTO THE EVENING AS
THE LOW MOVES EAST BUT DID NOT DECREASE RAIN CHANCES QUITE AS FAST
AS THE GFS SUGGESTS WITH SLIGHT CHANCE POPS CARRIED OVER
NORTHEASTERN ZONES INTO WEDNESDAY EVENING. FROM HERE MODELS
GENERALLY AGREE COLD HIGH PRESSURE WILL SETTLE OVER THE REGION FOR
THE REMAINDER OF THE WEEK KEEPING RAIN CHANCES OUT...AND BELOW
NORMAL TEMPS IN THE FORECAST THROUGH SATURDAY.
MEX TEMPS LOOKED REASONABLE THROUGH THE PERIOD ALTHOUGH SOME
ADJUSTMENTS TOWARD MEN GUID WERE MADE LATE IN THE WEEK. /BK/
&&
.AVIATION...
MID/HIGH-LEVEL CLOUD COVERAGE OVER EASTERN MISSISSIPPI WILL CONTINUE
TO DECREASE THROUGH TONIGHT AS AN UPPER LEVEL DISTURBANCE MOVES
AWAY FROM THE REGION. GENERALLY VFR CONDITIONS ARE EXPECTED
TONIGHT...THOUGH SOME PATCHY FOG COULD IMPACT SOUTHEAST MISSISSIPPI
INCLUDING KHBG FROM 29/1000 UNTIL 29/1300 UTC...WHICH WOULD RESULT IN
VISIBILITIES FALLING TO THE MVFR CATEGORY. RELATIVELY LOW CONFIDENCE
EXISTS IN THE FOG FORECAST DUE TO THE POTENTIAL FOR LINGERING CLOUD
COVERAGE. OTHERWISE...LIGHT WINDS ARE EXPECTED TONIGHT. FOR
SUNDAY...SOUTHERLY WINDS WILL INCREASE TO 5 TO 10 KT...AS SURFACE LOW
PRESSURE AND AN ASSOCIATED COLD FRONT APPROACH THE AREA. AHEAD OF THE
FRONT...SCATTERED SHOWERS ARE EXPECTED THROUGH THE DAY ON SUNDAY
ALONG AND NORTHWEST OF THE NATCHEZ TRACE PARKWAY...WHERE CEILINGS
WILL FALL TO THE MVFR CATEGORY. THE COVERAGE OF SHOWERS AND LOWERED
CEILINGS WILL EXPAND ACROSS THE ENTIRE AREA SUNDAY NIGHT AS THE FRONT
MOVES THROUGH. THE RAIN WILL BE LIGHT TO MODERATE IN INTENSITY...WITH
VISIBILITIES OCCASIONALLY REDUCED TO MVFR NEAR THE MODERATE RAIN.
/COHEN/
&&
.PRELIMINARY POINT TEMPS/POPS...
JACKSON 46 68 52 57 / 1 21 48 59
MERIDIAN 39 68 50 59 / 0 13 35 56
VICKSBURG 48 69 52 55 / 5 32 58 60
HATTIESBURG 43 71 52 65 / 1 7 16 53
NATCHEZ 49 70 55 57 / 6 20 45 67
GREENVILLE 48 64 49 54 / 7 52 79 43
GREENWOOD 45 65 49 54 / 3 45 72 45
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...NONE.
LA...NONE.
AR...NONE.
&&
$$
COHEN/19/BK
