FXUS64 KJAN 120948
AFDJAN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
348 AM CST SAT DEC 12 2009
.SHORT TERM...TODAY THROUGH SUNDAY NIGHT...WIDESPREAD ISENTROPIC
UPGLIDE UNDERWAY ON THE W SIDE OF A LARGE 1034MB SURFACE HIGH
CURRENTLY CENTERED IN ERN NC. INCREASING SWLY FLOW ALOFT IN THE RIGHT
ENTRANCE REGION OF A 170+KT 200MB JET STREAK OVER THE MID ATLANTIC
REGION WILL HELP IN THE DEVELOPMENT OF A SURFACE LOW IN THE NWRN GULF
ALONG A BAROCLINIC ZONE. AS THE GULF LOW TRANSLATES NEWD INTO LA THIS
AFTERNOON...AN EXPANDING CLUSTER OF ELEVATED TSRA SHOULD MOVE INTO
OUR SRN CWFA IN RICH 330K 850MB THETA E AIR. MLCAPES REACH
400-500J/KG THIS EVENING AND IN RESPONSE... PWATS BEGIN RISING TOWARD
1.5 INCHES ACROSS LOCATIONS S OF I-20 FOR LOCALLY HEAVY RAINS. EVEN
BETTER SURFACE-BASED INSTABILITY SHOULD STAY CONFINED FARTHER TO OUR
S. POPS KEPT AT NEAR 100 PERCENT THROUGH MIDNIGHT BEFORE STARTING TO
TAIL OFF FROM W TO E. QPF VOLUMES OF 1 TO 2 INCHES APPEAR PROBABLE
WITH THIS FIRST SYSTEM... ESPECIALLY FOR OUR SRN HALF BEFORE MIDDAY
SUNDAY. THESE RAINFALL TOTALS COULD RESULT IN PONDING OF WATER IN
LOW-LYING AND POOR- DRAINAGE AREAS. HOWEVER... FLASH FLOOD GUIDANCE
VALUES ARE HIGH ENOUGH IN THIS AREA TO PRECLUDE A FLASH FLOOD CONCERN
BUT WE COULD BE PRIMING THE PUMP FOR THE NEXT SYSTEM EARLY NEXT WEEK.
TEMPERATURES SHOULD STRUGGLE TO WARM MUCH TODAY IN ONGOING RAIN
SHIELD AND HAVE CUT MAV MOS NUMBERS CLOSER TO NAM12 GUIDANCE.
READINGS TONIGHT SHOULD HOLD RATHER STEADY AS WAA OFFSETS MUCH OF
THE NOCTURNAL COOLING. READINGS SHOULD MODIFY NICELY SUNDAY
AFTERNOON AS MODELS PRETTY MUCH IN AGREEMENT FOR ENDING THE RAINS
FOR ABOUT 18-24 HOURS STARTING MIDDAY SUNDAY AS DRIER SURGE ALOFT
MOVES IN BEHIND THE DEPARTING SHORTWAVE. LOWER LEVEL CLOUDS WILL BE
A LITTLE MORE DIFFICULT TO BREAK UP COMPLETELY INTO SUNDAY NIGHT BUT
IF SKIES MANAGE TO CLEAR...THEN FOG WOULD BECOME A CONCERN AFTER
MIDNIGHT. WILL INCLUDE PATCHY FOG FOR NOW WITH LOWS IN THE UPPER 40S
AND LOWER 50S...OUR FAVORITE FOGGY BOTTOM TEMPERATURE RANGE./40/
.LONG TERM...MONDAY THROUGH SATURDAY...MOIST SOUTHERLY FLOW WILL
PREVAIL ACROSS THE AREA ON MONDAY WITH ISENTROPIC LIFT INCREASING OUT
AHEAD OF A SERIES SHORTWAVES THAT WILL BEGIN TO MOVE THROUGH THE
ARKLAMISS MONDAY NIGHT AND TUESDAY. PWATS WILL RISE ON MONDAY NEAR
1.4 INCHES AND EVENTUALLY WILL RISE ABOVE 1.5 INCHES OVER MOST OF
THE AREA MONDAY NIGHT. THE GFS/EURO CONTINUE TO INDICATE SOME
INSTABILITY ESPECIALLY ALONG AND SOUTH OF I-20 MONDAY NIGHT INTO
TUESDAY WITH ML CAPES RANGING FROM AROUND 200-600 J/KG AND H700-H500
LAPSE RATES NEAR 6.0 C/KM. SHEAR PROFILES ARE ALSO MARGINAL WITH
MAINLY A UNIDIRECTIONAL FLOW AND DEEP LAYER SHEAR OF AROUND 30 TO
35KTS. SEVERE POTENTIAL LOOKS MARGINAL...BUT AN ISOLATED STRONG TO
SEVERE STORM CANNOT BE RULED OUT. HEAVY RAINFALL LOOKS TO BE THE
MAIN CONCERN AND THIS COMBINED WITH THE RAINFALL OVER THE WEEKEND
MAY CREATE FLASH FLOODING CONCERNS. WILL CONTINUE MENTION HEAVY
RAINFALL/FLOODING POTENTIAL IN THE HWO FOR MONDAY AND TUESDAY.
A COLD FRONT WILL SWING SOUTH ACROSS THE AREA ON TUESDAY AND MOST OF
THE RAIN SHOULD BE EAST/SOUTH OF THE AREA BY MID AFTERNOON. THE REST
OF THE WEEK LOOKS MAINLY DRY AS COOL HIGH PRESSURE AS A 1038MB HIGH
SHIFTS ACROSS THE OHIO VALLEY. THE GFS/EURO DIFFER ON THE STRENGTH
OF THE SURFACE HIGH WITH THE EURO BEING STRONGER...BUT EITHER WAY A
COLDER DRIER AIRMASS WILL BE IN PLACE FOR LATE IN THE WEEK. GFS
GUIDANCE HAS COME IN WARMER THAN PREVIOUS RUNS...BUT AFTER LOOKING
AT H850/H925 TEMPS FROM BOTH THE GFS/EURO HAVE DECIDED TO CUT BELOW
GUIDANCE FOR HIGHS ON WEDNESDAY AND MORNING LOWS BOTH THURSDAY AND
FRIDAY. /15/
&&
.AVIATION...VFR CEILINGS 4-8K FEET THIS MORNING ARE EXPECTED TO
LOWER TO MVFR FROM S TO N BY MIDDAY AS WIDESPREAD LIGHT RAINS
GRADUALLY INCREASE WITH EAST WINDS AT 7-11KTS. THERE WILL BE A
SLIGHT CHANCE FOR LIGHT SLEET OR LIGHT FREEZING RAIN INITIALLY MIXED
IN WITH THE RAIN OVER NERN MS CHANGING OVER TO ALL RAIN BY 16Z.
UPGLIDE MOISTURE BEING TRANSPORTED INTO THE REGION WILL RESULT IN
LOWERING MVFR CONDITIONS THIS AFTERNOON TO IFR FROM S TO N ACROSS
THE AREA BEFORE EVENING WITH LOCALLY HEAVY DOWNPOURS...MAINLY SRN
MISSISSIPPI. ISOLATED TSRA OVER SRN MS THIS AFTERNOON SHOULD SPREAD
N AND BECOME SCATTERED TONIGHT OVER THE S PORTIONS. WIDESPREAD IFR
RAINS WILL AFFECT THE ENTIRE AREA TONIGHT...WITH A CHANCE FOR TSRA
UNTIL EARLY SUNDAY MORNING WHEN THE UPPER TROUGH AXIS BEGINS
SHIFTING ACROSS THE REGION. CONDITIONS WILL IMPROVE FROM W TO E
SUNDAY AFTERNOON AS THE RAINS END. /40/
&&
.PRELIMINARY POINT TEMPS/POPS...
JACKSON 46 44 63 51 / 100 96 20 7
MERIDIAN 46 44 65 48 / 100 100 46 5
VICKSBURG 46 44 64 52 / 100 80 11 8
HATTIESBURG 51 49 69 54 / 100 93 46 13
NATCHEZ 50 48 68 54 / 100 76 13 12
GREENVILLE 44 41 59 50 / 100 75 8 5
GREENWOOD 45 41 59 49 / 100 90 13 4
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...NONE.
LA...NONE.
AR...NONE.
&&
$$
40/15
