FXUS64 KJAN 150429
AFDJAN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
1015 PM CST MON DEC 14 2009
.UPDATE...LATEST SURFACE ANALYSIS HAS THE QUASI-STATIONARY BOUNDARY
OVER SOUTHERN LOUISIANA AND SOUTHERN MISSISSIPPI...A LITTLE FARTHER
SOUTH THAN THIS AFTERNOON AND THE MAIN AREA OF HEAVY RAIN HAS
SHIFTED SOUTHEAST OF OUR CWA. SFC ANALYSIS ALSO SHOWED A COLD FRONT
MOVING INTO SOUTHEAST ARKANSAS. THIS COLD FRONT IS A LITTLE SLOWER
THAN THE GFS SUGGESTED BUT FASTER THAN THE NAM PROGGED. THE COLD
FRONT WILL BE PUSHED SOUTH TONIGHT AND TUESDAY MORNING BY A DECENT
1030MB HIGH OVER THE CENTRAL PLAINS ALTHOUGH THE FLOW ALOFT WILL
REMAIN SOUTHWESTERLY AHEAD OF THE FRONT DUE TO THE SHORTWAVE
TROUGHING OVER THE DESERT SOUTHWEST. THUS...ALTHOUGH THERE IS A
BREAK IN THE RAIN OVER OUR CWA THIS EVENING...RAIN CHANCES WILL
REMAIN OVERNIGHT AS THE COLD FRONT MOVES INTO THE AREA AND WEAK
DISTURBANCES IN THE SW FLOW ALOFT COMBINE WITH THE AVAILABLE
MOISTURE. SOME ELEVATED INSTABILITY IS INDICATED IN THE MODELS IN
OUR SOUTHERN MOST ZONES WHERE WL MAINTAIN MENTION OF THUNDER. THE
FLASH FLOOD WATCH IN THE SOUTH WILL REMAIN IN EFFECT DUE TO THE
RECENT HEAVY RAINFALL AND THE POSSIBILITY OF ADDITIONAL HEAVY
RAINFALL THROUGH TUESDAY. TEMPERATURES AND DEW POINTS WERE RUNNING
HIGHER THAN EXPECTED DUE TO THE SLOWER APPROACH OF THE COLD FRONT.
PATCHY DENSE FOG HAS BEEN REPORTED OVER THE AREA BUT WIDESPREAD
DENSE FOG IS NOT EXPECTED WITH ADDITIONAL RAINFALL IN THE SOUTH AND
THE COLD FRONT MOVING INTO THE NORTHWEST. GUSTY WINDS ARE EXPECTED
BEHIND THE COLD FRONT TUESDAY THAT WILL MEET LOCAL LAKE WIND
ADVISORY CRITERIA OVER THE AREA LAKES. HAVE HOISTED THE LIMIT AREA
LAKE WIND ADVISORY THIS EVENING FOR TUESDAY. UPDATES HAVE BEEN
POSTED. /22/
&&
.AVIATION...
THE MAIN AREA OF CONVECTION HAS SHIFTED EAST THIS EVENING BUT
ADDITIONAL SHOWERS WILL BE POSSIBLE REMAINDER OF TONIGHT MAINLY S OF
THE NATCHEZ TRACE CORRIDOR. A COLD FRONT WAS NOTED OVER SOUTHEAST
ARKANSAS. THIS COLD FRONT WILL MOVE ACROSS THE AREA TONIGHT AND
TUESDAY MORNING. OCCASIONAL LIFR CIGS WILL OCCUR AHEAD OF THE COLD
FRONT WITH WIDESPREAD MVFR BKN-OVC DECKS FROM 1500-3000 FEET
PREVAILING ELSEWHERE. IN ADDITION...AREAS OF FOG WILL REDEVELOP
OVERNIGHT AHEAD OF THE COLD FRONT. MOST AREAS WILL REMAIN FROM 1-3
MILES BUT LOCALLY DENSE FOG WILL ALSO BE POSSIBLE. CONDITIONS WILL
IMPROVE EARLY TUESDAY AS FOG ERODES AND CIGS LIFT DURING THE
MORNING. OCNL IFR CIGS WILL PERSIST LONGEST OVER SRN ZONES WHERE
RAINFALL CHANCES WILL BE HIGHEST. /22/
&&
.PREV DISCUSSION... /ISSUED 408 PM CST MON DEC 14 2009/
SHORT TERM...TONIGHT THROUGH WEDNESDAY NIGHT...LOCAL RADARS ARE
SHOWING NUMEROUS SHOWERS AND THUNDERSTORMS ACROSS MUCH OF THE
SOUTHERN SECTIONS OF MY CWA. A LINE OF THUNDERSTORMS HAS BEEN MOVING
THROUGH THE PINE BELT REGION WHILE ANOTHER HAS BEEN MOVING THROUGH
SOUTHERN LOUISIANA AND INTO AROUND THE NATCHEZ AREA. LOCATIONS IN
BETWEEN HAVE NOT SEEN AS MUCH RAIN BUT THIS SHOULD CHANGE AS RAIN
LOOKS TO BE FILLING IN. LOCATIONS FURTHER NORTH OF THE HIGHWAY 84
CORRIDOR HAVE NOT SEEN AS MUCH CONTINUOUS RAIN AND
THUNDERSTORMS...THOUGH HEAVY DOWNPOURS HAVE OCCURRED IN AND AROUND
THUNDERSTORMS ALONG THE I-20 CORRIDOR. FURTHER NORTH OF THE I-20
CORRIDOR HAS BEEN PRETTY MUCH DRY AND THIS IS LIKELY DUE TO THE
RELATIVELY DRIER AIR IN PLACE OVER THAT REGION. RADAR ESTIMATED
RAINFALL AMOUNTS HAVE BEEN IN EXCESS OF 2 INCHES AROUND THE
HATTIESBURG AREA. THIS IS NOT GOOD NEWS AS THIS IS THE AREA THAT HAS
BEEN THE MOST SATURATED FROM RAINFALL OVER THE WEEKEND.
A WARM FRONT IS SITUATED ROUGHLY AROUND THE HIGHWAY 98 CORRIDOR AND
SHORTWAVES MOVING THROUGH THE WARM SECTOR HAVE BEEN CONTRIBUTING TO
CONVECTION. ALL OF THIS COMES AHEAD OF A COLD FRONT THAT LOOKS TO BE
DRAPED ACROSS CENTRAL ARKANSAS THIS AFTERNOON. PWAT VALUES WERE
PROGGED TO INCREASE THIS AFTERNOON IN THE SOUTH UP TO AROUND 1.8
INCHES. THIS IS THE AREA THAT HAS SHOWN THE BEST MOISTURE TRANSPORT
AND CONVERGENCE.
NOT MUCH HAS CHANGED IN HOW THE REST OF TONIGHT INTO TUESDAY WILL
EVOLVE. MODELS STILL DEPICT RAIN AND THUNDERSTORMS TO CONTINUE THIS
AFTERNOON AND EVENING FOR MAINLY SOUTH OF I-20. AS THE FRONT MOVES
THROUGH THE REGION TONIGHT...RAIN CHANCES WILL COME TO AN END FROM
NORTH TO SOUTH. HOWEVER...MODELS CONTINUE TO HANG THE FRONT UP IN
THE SOUTH AND ALLOW FOR A FEW MORE WAVES/DISTURBANCES TO RIDE ALONG
THE FRONT THROUGH TUESDAY AFTERNOON. THIS WILL BRING ADDITIONAL
RAINFALL TO ALREADY SATURATED GROUNDS IN THE SOUTHEAST. THE FRONT
FINALLY PUSHES THROUGH TUESDAY AFTERNOON AS THE SHORTWAVE MID LEVEL
TROUGH SWINGS THROUGH THE REGION. HIGH PRESSURE WILL FILTER INTO THE
ARKLAMISS AND BRING COOLER AND DRIER CONDITIONS TO THE ARKLAMISS
THROUGH THE MIDDLE OF THE WEEK. BEHIND THE FRONT...THERE WILL BE
GUSTY WINDS ON TUESDAY DUE TO A TIGHTENING PRESSURE GRADIENT. A LAKE
WIND ADV WILL LIKELY BE NEEDED DURING THIS TIME. CONDITIONS LOOK
MARGINAL RIGHT NOW FOR AREAS OTHER THAN THE MAJOR LAKES AND WILL LET
FUTURE SHIFTS EVALUATE THE NEED FOR AN ADV FOR TUESDAY.
AS HAS BEEN THE CASE...THE MAIN CONCERNS WILL BE FROM FLOODING
ACROSS THE AREAS GENERALLY ALONG THE HIGHWAY 84 CORRIDOR. A STRONG
TO SVR STORM CANNOT BE COMPLETELY RULED OUT BUT IS A LESSER RISK
WITH THIS SYSTEM. CAPE VALUES ARE NOT VERY MUCH AND DEEP LAYER SHEAR
IS NOT IMPRESSIVE AS WELL. UNIDIRECTIONAL WIND PROFILES WILL ALLOW
FOR THE THREAT OF TRAINING TO REMAIN UNTIL THE FRONT MOVES THROUGH
TUESDAY AFTERNOON/EVENING. THAT BEING SAID...PREVIOUSLY ISSUED FLASH
FLOOD WATCH LOOKS TO REMAIN IN GOOD SHAPE AND WILL CONTINUE IT
THROUGH 00Z WED. MODELS STILL DIFFER ON QPF AMOUNTS THROUGH THE TIME
PERIOD WITH THE GFS AGAIN SHOWING THE HIGHEST AMOUNTS. THIS COULD BE
BROUGHT ABOUT BY SOME FEEDBACK ISSUES BUT LOCATIONS IN THE SOUTH
COULD STILL SEE ABOUT 2-3 INCHES OVERALL BEFORE EVERYTHING IS SAID
AND DONE WITH SOME LOCALLY HIGHER AMOUNTS.
ADJUSTMENTS TO GUI WERE MAINLY MADE TO POPS IN THE SOUTH TO INCREASE
THEM FOR TONIGHT INTO TUESDAY. COULD SEE SOME LIGHT RAIN THE NORTH
AS THE FRONT MOVES THROUGH SO LEFT SMALL CHANCE POPS. /28/
LONG TERM...WEDNESDAY THROUGH THURSDAY...
THE SRN EXTENT OF A CHILLY POLAR AIRMASS WILL SURGE SOUTHWARD INTO
THE FORECAST AREA TUES NIGHT/WEDNESDAY. GFS MOS IS LIKELY NOT
HANDLING THE SHALLOW NATURE OF THE AIRMASS AND LOOKS TOO WARM WHEN
COMPARED TO EXPLICIT OUTPUT...PARTICULARLY FOR WED/THURS HIGHS AND
LOWERED THEM A BIT. THE POSITION OF THE SFC HIGH CENTER...WHICH WILL
SHIFT EWD ACROSS THE MIDWEST AND OH VALLEY...WILL NOT BE IDEAL FOR
FOR SFC RADIATIONAL COOLING AND PERIODS OF HIGH CIRRUS MAY INTERRUPT
COOLING AS WELL SO WILL NOT CUT GFS MOS LOWS.
THURSDAY NIGHT THROUGH SUNDAY...
THE FORECAST FOR THE LONGER RANGE PERIODS IS OF LOWER THAN AVERAGE
CONFIDENCE GIVEN INCONSISTENCIES BETWEEN THE GFS AND ECMWF MODELS.
THE OPERATIONAL GFS IS KEEPING THE THE FORECAST AREA UNDER DRY
NORTHWEST FLOW AS WE GO FROM LATE WEEK INTO THE WEEKEND...AND IT
DE-EMPHASIZES SRN STREAM SHORTWAVE ENERGY THEREBY KEEP ANY GULF LOW
DEVELOPMENT SUPPRESSED WELL TO OUR SOUTH. THE 00Z ECMWF ON THE OTHER
HAND CONTINUES TO SUGGEST THAT SRN STREAM SHORTWAVE ENERGY WILL DIG
SWD OVER NRN MEXICO AND HELP INDUCE A NW GULF LOW THAT WOULD BRING
LIGHT-MDT RAINFALL TO THE SRN HALF OF THE FORECAST AREA FROM THURS
NIGHT AND FRIDAY. THE ECMWF IS ALSO MORE AGGRESSIVE IN DIGGING NRN
STREAM SHORTWAVE ENERGY SWD THROUGH THE PLAINS THUS BRINGING COLDER
AIR AND THE POTENTIAL FOR A FEW SNOW SHOWERS AS WE GO INTO SUNDAY.
WHILE THE THE ECMWF LOOKS A BIT EXTREME...IT HAS SUPPORT FROM
SEVERAL GFS ENSEMBLE MEMBERS AND THE UKMET IN AN EL NINO YEAR. SO
WE HAVE RAISED GFS MOS GUIDANCE POPS A LITTLE FOR THE FRI TO SAT
NIGHT PERIOD AND HAVE INDICATED A SMALLER HIGH/LOW TEMPERATURE RANGE
THAN GFS MOS BASED ON GREATER CLOUD COVERAGE EXPECTED. ANY
PRECIPITATION IS EXPECTED TO LIGHT IF IT OCCURS...AND TEMPERATURES
COULD GET VERY CHILLY AS WE GO THROUGH THE WEEKEND IF THE 00Z ECMWF
VERIFIES. /EC/
&&
.PRELIMINARY POINT TEMPS/POPS...
JACKSON 52 52 36 57 / 68 40 0 0
MERIDIAN 55 56 33 56 / 72 54 0 0
VICKSBURG 50 51 36 54 / 66 35 0 0
HATTIESBURG 59 59 37 60 / 82 97 9 0
NATCHEZ 52 51 37 54 / 81 84 10 0
GREENVILLE 44 49 32 51 / 24 13 0 0
GREENWOOD 46 51 32 54 / 23 15 0 0
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...FLASH FLOOD WATCH THROUGH TUESDAY AFTERNOON FOR MSZ052-054>066-
072>074.
LAKE WIND ADVISORY FROM 7 AM TO 4 PM CST TUESDAY FOR MSZ026-030-
031-043-049-052.
LA...FLASH FLOOD WATCH THROUGH TUESDAY AFTERNOON FOR LAZ024-026.
LAKE WIND ADVISORY FROM 7 AM TO 4 PM CST TUESDAY FOR LAZ009.
AR...LAKE WIND ADVISORY FROM 7 AM TO 4 PM CST TUESDAY FOR ARZ075.
&&
$$
22/28/EC
