FXUS64 KJAN 221242 CCA
AFDJAN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
452 AM CST TUE DEC 22 2009
.SHORT TERM...THE AIR MASS REMAINS DRY THIS MORNING WITH SURFACE
DEWPOINTS IN THE 30S BENEATH FAIR SKIES ACROSS THE AREA. A WARM
FRONT IS PERCHED NEAR THE COAST AND WILL SLOWLY LIFT NWD WITH TIME.
THIS FEATURE BECOMES DIFFUSE AND DIFFICULT TO LOCATE WITH TIME. LOW
LEVEL MOISTURE RETURN WILL BEGIN TODAY BUT WILL BE SLOW. THE FORECAST
AREA WILL REMAIN ON THE WRN FRINGES OF LOW LEVEL RIDGING TODAY.
ALTHOUGH LOW LEVEL FLOW WILL INCREASE AND BEGIN TO BACK OVER WRN
ZONES LATE TODAY...CURRENT OBSERVATIONS INDICATE A RELATIVELY DRY AIR
MASS OVER THE GULF THIS MORNING WITH REPORTED DEWPOINTS IN THE MID
40S TO LOWER 50S OVER THE ERN GULF. UPPER FLOW WILL RANGE FROM ZONAL
TO FLAT RIDGING TODAY AHEAD OF THE DEEP UPPER LOW DIGGING NEAR THE
WEST COAST...GRADUALLY BACKING WITH TIME OVER THE ARKLAMISS. A WEAK
SHORTWAVE WILL PUSH INTO THE REGION LATE TODAY BUT MOISTURE WILL
REMAIN UNORGANIZED AND RELATIVELY SHALLOW...BARELY DEEPENING TO 700
MBS OVER NWRN ZONES BY SUNSET. ISENTROPIC FLOW ALSO BEGINS TO
INCREASE OVER AREAS W OF THE MS RIVER. HAVE MAINTAINED SLIGHT CHANCE
POPS EXTREME NWRN ZONES LATER TODAY...OTHERWISE LOOK FOR DRY WEATHER
OVER THE REGION. INCREASED HIGHS TEMPS SLIGHTLY AT A FEW LOCATIONS.
LOW LEVEL FLOW BACKS TO THE S ACROSS THE REGION BY SUNRISE
WEDNESDAY...CONTINUING TO INCREASE AS THE UPSTREAM LOW PRESSURE
SYSTEM CONTINUES TO MOVE THIS WAY. WILL SEE A GRADUAL INCREASE IN
LOW LEVEL MOISTURE OVER WRN AND SRN ZONES BUT THE ADVECTION OF DRIER
AIR CONTINUES FROM THE EAST ON THE WRN FRINGES OF THE DOWNSTREAM LOW
LEVEL RIDGE THAT MAINTAINS A WEDGE OF DRIER AIR JUST TO OUR EAST.
MODELS ALSO AGREE THAT A LOBE OF DRIER AIR AROUND 850 MB WILL PIVOT
ACROSS THE NRN GULF LATE TONIGHT AND LIFT INTO LA/SRN MS EARLY
WEDNESDAY MORNING. MID AND UPPER MOISTURE IS FORECAST TO INCREASE
LATE TONIGHT AS A HEALTHIER SHORT WAVE MOVES INTO THE AREA. THIS
FEATURE IS ASSOCIATED WITH BETTER VERTICAL MOTION/QVECTOR DIV AND
BETTER UPPER JET SUPPORT.
THE LOW LEVEL JET CONTINUES TO INTENSIFY WEDNESDAY WITH 30-40 KTS
EXPECTED AT 850 MB BY LATE AFTERNOON. THE BETTER DYNAMICS REMAIN
WEST OF THE FORECAST AREA DURING THE DAY WEDNESDAY WITH THE 850 MB
JET CORE TRACKING FROM ERN TX ACROSS THE ARKLATX. THE ADVECTION OF
BETTER MOISTURE IS DELAYED UNTIL THE LOBE OF DRIER AIR LIFTS NWD
ACROSS THE REGION WITH SURFACE DEWPOINTS FORECAST INTO THE UPPER 50S
OVER SWRN ZONES BY 00Z THU AS THE BETTER PUSH OF MOISTURE BEGINS TO
SET UP AHEAD OF THE APPROACHING LOW. HOWEVER THE EFFECTS OF
DOWNSTREAM RIDGING PERSIST WITH ERN MS DEWPOINTS FORECAST TO LINGER
IN THE 40S THROUGH WEDNESDAY AFTERNOON. INCREASING WIND FIELDS WILL
TRANSLATE INTO GUSTY SLY WIND ACROSS THE AREA AND LAKE WIND
ADVISORIES MAY BE NEEDED FOR AREA LAKES AND NWRN LAND AREAS FOR
WEDNESDAY. INSTABILITY INCREASES VERY GRADUALLY OVER THE NEXT COUPLE
OF DAYS AND WILL LIMIT THE MENTION OF THUNDER MAINLY TO WRN ZONES
FOR TONIGHT INTO WEDNESDAY.
.LONG TERM...WEDNESDAY NIGHT THROUGH TUESDAY...VIGOROUS STORM SYSTEM
STILL ON TRACK TO PUSH THROUGH THE ARKLAMISS THURSDAY. THE MODELS ARE
IN REAL GOOD AGREEMENT ON THE TIMING OF THE COLD FRONT ACROSS THE
AREA. THE MODELS CONTINUE TO FLUCTUATE A BIT ON THE INSTABILITY FROM
RUN TO RUN WITH THE GFS BEING THE MOST UNSTABLE BRINGING 500-600 J/KG
OF ML CAPE UP TO THE I-20 CORRIDOR AND 200 J/KG TO THE NORTHERN
PORTION OF THE AREA. THE MODELS HAVE NOT FLUCTUATED MUCH WITH THE
AMOUNT OF FORCING AND SHEAR WITH THE SYSTEM INDICATING 50KTS OF 0-6
BULK SHEAR AND 0-3 HELICITIES OF 400 TO 600 M^2/S^2 THURSDAY MORNING
INTO THE AFTERNOON AHEAD OF THE BOUNDARY. THE MODE LOOKS TO BE MAINLY
A SQUALL LINE SWEEPING ACROSS THE AREA WITH DAMAGING WINDS...BUT WITH
THE AMOUNT OF SHEAR THAT WILL BE PRESENT AND DEPENDING ON THE AMOUNT
OF INSTABILITY...TORNADOES CONTINUE TO BE A POSSIBILITY.
THE COLD FRONT WILL SWEEP ACROSS THE AREA THURSDAY AND WILL EXTEND
ACROSS ALABAMA BY THE EVENING HOURS. A FEW REMNANT SHOWERS WILL BE
POSSIBLE...BUT MOST OF THE ACTIVITY WILL SHIFT WELL TO THE EAST
DURING THE OVERNIGHT HOURS. SURFACE HIGH PRESSURE RIDGING WILL BUILD
IN FRIDAY WITH TEMPERATURES HOLDING IN THE 40S UNDER STRONG COLD AIR
ADVECTION. THE COOL CONDITIONS WILL CONTINUE THROUGH MUCH OF THE
WEEKEND INTO MONDAY WITH THE GFS DEVELOPING ANOTHER PRETTY STRONG
SHORT WAVE AND ASSOCIATED LOW IN THE GULF TRACKING IT ACROSS THE
NORTHERN GULF ON TUESDAY. DEPENDING ON THE STRENGTH OF THE HIGH IN
THE MIDWEST...THERE ARE SOME INDICATIONS OF THE POSSIBLE OF WINTRY
PRECIPITATION FOR THE NORTHERN PORTIONS OF THE AREA...BUT THIS IS
STILL A LONG WAY OUT.
MADE A FEW ADJUSTMENTS TO GUIDANCE THROUGH THE PERIOD MAINLY WITH
TEMPERATURES. ADJUSTED TEMPERATURES WELL BELOW GUIDANCE THROUGH THE
WEEKEND. THE H925/H850 TEMPERATURES FROM BOTH THE GFS/EURO AND BUFR
SOUNDINGS WOULD INDICATE COOLER HIGHS AND LOWS THAN GUIDANCE IS
INDICATING. THE EURO IS ALSO INDICATING COOLER TEMPS THAN MEX
GUIDANCE ALSO. STUCK PRETTY CLOSE TO MEX POPS THROUGH THE
PERIOD...BUT DID MAKE SOME SLIGHT ADJUSTMENTS UP FOR THURSDAY AS THE
MODELS ARE IN PRETTY GOOD AGREEMENT ON THE TIMING OF THE FRONT.
STUCK PRETTY CLOSE TO GUIDANCE FOR THE REMAINING PERIODS...BUT DID
CUT BELOW POPS FOR THE WEEKEND AS MEX GUIDANCE CONTINUES TO KEEP 20
POPS ACROSS THE AREA WHEN WE SHOULD BE DRY. /15/
&&
.AVIATION...VFR SKY CONDITIONS WILL CONTINUE TODAY WITH HIGHER CLOUD
DECKS ABOVE 10K FEET AND SCT DECKS FROM 3-5K FEET THIS AFTERNOON.
AREAS OF MORNING FOG CAN BE EXPECTED. POCKETS OF HEAVIER FOG WILL
LOCALLY LOWER VSBYS FROM 1-3 MILES. FOG WILL CLEAR QUICKLY AFTER
SUNRISE. ISOLD SHOWERS WILL BE POSSIBLE OVER NWRN ZONES DURING THE
AFTERNOON. RAINFALL WILL INCREASE FROM THE WEST OVERNIGHT. VFR TO
MVFR DECKS WILL DEVELOP TONIGHT WITH MVFR VSBYS POSSIBLE IN PERIODS
OF RAIN AND FOG.
&&
.PRELIMINARY POINT TEMPS/POPS...
JACKSON 66 50 64 57 / 5 44 49 74
MERIDIAN 65 42 62 52 / 1 19 29 54
VICKSBURG 65 52 66 58 / 10 64 64 83
HATTIESBURG 68 48 68 57 / 1 15 20 56
NATCHEZ 67 54 69 60 / 9 59 52 84
GREENVILLE 62 50 62 54 / 13 79 85 81
GREENWOOD 62 49 60 56 / 8 61 73 71
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...NONE.
LA...NONE.
AR...NONE.
&&
$$
15/03
