Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 261613 AAA
AFDJAN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON MS
1013 AM CST FRI DEC 26 2014

.UPDATE...
MORNING SFC ANALYSIS INDICATES 1028MB SFC HIGH OVER THE APPALACHIANS
WITH INCREASING LOW-LEVEL RETURN FLOW IN OUR REGION. UPPER AIR
ANALYSIS INDICATES ~590DM H5 RIDGE OVER SE FL WITH DEEP LONGWAVE
TROUGH DEVELOPING OVER THE ROCKIES. THIS SETUP IS AIDING IN
INCREASING ISENTROPIC LIFT AND FAVORABLE FOR RAIN CHANCES TO INCREASE
THIS AFTERNOON INTO TONIGHT. 12Z KJAN SOUNDING INDICATES DRY
ENVIRONMENT WITH ONLY ~0.2-0.3 INCH PW`S WHILE DEEPER MOISTURE
~0.7-0.8 INCH PW`S ARE SITUATED IN SRN LA. EXPECT PW`S TO CLIMB TO
~1.2-1.4 INCHES IN NE LA/SW MS THROUGH THE DAY AS ISENTROPIC ASCENT IN
THE 310-325K LAYER FROM S/WV OVER THE AREA HELPS MOISTEN THE
ATMOSPHERE THROUGHOUT THE AFTERNOON. DUE TO VERY DRY MID-
LEVELS...EXPECT IT TO TAKE MOST OF THE AFTERNOON TO REALLY MOISTEN
THE ATMOSPHERE UP. THUS...KEPT POPS THE SAME AND QPF LOW IN NE LA/SW
MS DUE TO MUCH OF THE RAINFALL NOT REACHING THE GROUND THROUGH THE
AFTERNOON. FOR FORECAST ELEMENTS...HIGHS LOOK GOOD DUE TO CLOUDY TO
OVERCAST SKIES ACROSS THE REGION FOR THE DAY. ONLY ADJUSTED HOURLY
TEMPS/DEWPOINTS/SKY GRIDS TO CURRENT TRENDS.

NEW GUIDANCE COMING IN IS STILL INDICATIVE OF HEAVY RAINFALL POTENTIAL
THIS WEEKEND. MORE WILL BE DISCUSSED IN THE AFTERNOON PACKAGE. /DC/

&&

.AVIATION...DESPITE PATCHES OF MVFR CIGS THIS MORNING...EXPECT
MOSTLY VFR CONDITIONS TODAY WITH MID AND HIGH LEVEL CLOUDINESS.
LATER TONIGHT...MVFR CIGS AND VSBY DUE TO RAIN WILL DEVELOP. THESE
CONDITIONS WILL CONTINUE AND POSSIBLY WORSEN BETWEEN 12Z AND 18Z
SAT. /SW/

&&

.PREV DISCUSSION... /ISSUED 439 AM CST FRI DEC 26 2014/

SHORT TERM...TODAY THROUGH SATURDAY NIGHT...MULTIFACETED FORECAST
PROBLEM TO DEAL WITH THIS MORNING IN THE SHORT TERM. AT PRESENT...IR
IMAGERY SHOWING CIRRUS STREAMING ACROSS THE REGION IN STEADILY
INCREASING SW FLOW ALOFT. THIS AHEAD OF A POTENT MID/UPPER LEVEL WAVE
OVER THE FOUR CORNERS REGION THAT WILL IMPACT THE SOUTHERN CONUS AS
IT MOVES EAST OVER THE NEXT FEW DAYS. WHILE SW FLOW IS ONLY TAPPING
HIGH LEVEL MOISTURE AT THE MOMENT...THE BLENDED TOTAL PRECIPITABLE
WATER IMAGERY IS SHOWING VALUES NEAR 1.5 INCHES (130% OF NORMAL)
POISED OVER THE WESTERN GULF AND PRESENTLY SHOWING SOME SIGNS OF A
NORTHWARD JOG. ALSO OF NOTE EARLY THIS MORNING IS THE LIGHT RAIN
BEGINNING TO DEVELOP OVER SW LA IN RESPONSE TO INCREASING SOUTHERLY
FLOW OUT OVER THE GULF RISING UP AND OVER THE COASTAL BAROCLINIC
ZONE.

MODELS ARE IN GOOD AGREEMENT THAT WIDESPREAD RAIN WITH A ZONE OF
HEAVY RAIN WILL OVERSPREAD THE AREA FROM SW TO NE OVERNIGHT INTO
SATURDAY. ONE OF THE FORECAST PROBLEMS WILL BE WHERE THE ZONE OF
HEAVY RAIN SETS UP. ECMWF SHOWING THE AXIS OF HEAVIEST RAINFALL
OCCURRING OVER THE BIG BLACK RIVER BASIN...WHILE THE GFS/CANADIAN IS
INDICATING SOUTHEAST MISSISSIPPI. THE NAM ACTUALLY HAS BOTH THOSE
AREAS...AS WELL AS THE SREF WHICH SEEMS TO BE JUST A BROAD BRUSH OF
BOTH. MODELS AGREE THAT PW VALUES WILL BE IN THE 99TH PERCENTILE FOR
THIS TIME OF YEAR WITH VALUES AROUND 1.75 INCHES OVER THE SE HALF OF
THE FORECAST AREA. SLOWLY PULLING AWAY COOL/DENSE AIRMASS IN PLACE
WILL SET STAGE FOR STRONG ISENTROPIC FORCING AS WIND FIELDS INCREASE
AND CONTINUE TO PULL THE MOISTURE RICH AIR NORTHWARD FROM THE GULF
OF MEXICO. WILL OUTLOOK A LIMITED THREAT FOR FLOODING FOR
SATURDAY/SATURDAY NIGHT WITH A FFA POSSIBLY NEEDING TO BE CONSIDERED
LATER. HIGH MOISTURE CONTENT WILL ALLOW FOR VERY EFFICIENT RAINFALL
PRODUCTION...ESPECIALLY IF THE ATMOSPHERE CAN CONVECT...WHICH BRINGS
THE NEXT FORECAST PROBLEM.

THERE REMAINS GOOD AGREEMENT IN THE MODELS WITH A NORTHWARD SURGE IN
THE WARM SECTOR SATURDAY WITH MID 60S DEWPOINTS PUNCHING INTO NORTH
CENTRAL LA/SW MS AHEAD OF SURFACE COLD FRONT. THIS JUICY AIR DOES
NOT SURGE AS FAR NORTH OVER MS AS PREVIOUS RUNS INDICATED...PROBABLY
A RESULT OF THE INCREASED RAINFALL AREA. BUFR SOUNDINGS ARE SHOWING
A NARROW CORRIDOR OF ~500 J/KG OF MU CAPE OVER SW SECTIONS SATURDAY
AFTERNOON/EARLY EVENING...BUT TRAILING OFF RAPIDLY TO THE EAST. WILL
CONTINUE TO OUTLOOK A LIMITED SEVERE THREAT...BUT WILL SHRINK AREA
TO COINCIDE WITH BEST CAPE/SHEAR./26/

LONG TERM...SUNDAY THROUGH THURSDAY...THE RISK FOR HEAVY RAINFALL
WILL CONTINUE INTO SUNDAY WITH ANOMALOUS PRECIPITABLE WATER IN EXCESS
OF 1.5 INCHES (NAEFS STANDARDIZED ANOMALIES 2 - 2.5) CONVERGING ALONG
AND AHEAD OF A SLOW-MOVING COLD FRONT THAT IS FORECAST TO ROUGHLY
BISECT THE FORECAST AREA SUNDAY MORNING. THE SEVERE WEATHER RISK AREA
WILL DIMINISH WITH SURFACE BASED INSTABILITY BECOMING MORE SUPPRESSED
WITH TIME. IN THE HAZARDOUS WEATHER OUTLOOK...WILL CONTINUE THE
MENTION OF HEAVY RAIN/LIMITED FLOOD THREAT AND INDICATE A DECREASING
SEVERE WEATHER THREAT IN THE HAZARDOUS WEATHER OUTLOOK.

EXPECT COOLER AND DRIER WEATHER BEHIND THE FRONT FOR THE MON NIGHT
THROUGH TUES NIGHT PERIOD WITH TEMPERATURES GENERALLY NEAR SEASONAL
AVERAGES. AS WE GO INTO MID WEEK...MODELS ARE IN GENERAL AGREEMENT
THAT A MASSIVE ARCTIC AIRMASS WILL SURGE SOUTHWARD THROUGH THE
PLAINS AND EXPAND INTO THE LOWER MS VALLEY REGION NEW YEAR`S EVE.
THE LARGEST TEMPERATURE ANOMALIES ARE EXPECTED TO STAY WEST OF THE
ARKLAMISS BASED ON THE PRESSURE PATTERN...BUT IT WILL BE SUCH A
STRONG HIGH PRESSURE CENTER THAT SUFFICIENTLY COLD AIR FOR WINTER
WEATHER POTENTIAL MAY EXIST INTO NORTHERN PORTIONS OF THE AREA AS
SOUTHWEST FLOW JUXTAPOSES THE SHALLOW MODIFYING ARCTIC AIR.

ALTHOUGH GFS/ECMWF ARE BEARISH WITH QPF FOR MID/LATE WEEK...THE
AIRMASS OVER THE GULF WILL CONTINUE TO BE UNSEASONABLY MOIST AND
PRIME FOR QUICK NORTHWARD TRANSPORT WITH THE SLIGHTEST DISTURBANCE
AND BACKING OF LOW LEVEL FLOW GIVEN THE STRONG GULF COAST BAROCLINIC
ZONE. GEFS ENSEMBLE MEAN QPF IS SLIGHTLY HEAVIER...AND HAVE INCLUDED
A SMALL CHANCE FOR -RA/-SN FOR NOW BASED ON EXPLICIT MODEL BLEND
TEMP/POP FORECASTS FOR NEW YEARS EVE. IT DOES NOT APPEAR THE
ARKLAMISS WILL EXPERIENCE OVERLY COLD TEMPERATURES GIVEN THE TREND
FOR INCREASING SOUTHERN STREAM SEPARATION/DOMINANCE AND NRN STREAM
RETREAT. /EC/

&&

.PRELIMINARY POINT TEMPS/POPS...
JACKSON       61  52  65  54 /  17  65 100  94
MERIDIAN      62  48  61  56 /   7  30 100  95
VICKSBURG     62  53  68  52 /  22  65 100  92
HATTIESBURG   62  50  67  59 /   8  34 100  95
NATCHEZ       62  56  70  50 /  27  65 100  94
GREENVILLE    58  51  62  45 /  17  61 100  89
GREENWOOD     61  53  63  49 /  15  53 100  92

&&

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

$$

DC/SW/26/EC





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