FXUS64 KJAN 221737 CCA
AFDJAN
AREA FORECAST DISCUSSION...CORRECTED AVIATION
NATIONAL WEATHER SERVICE JACKSON MS
1105 AM CST TUE DEC 22 2009
...POWERFUL STORM LINING UP FOR DAYTIME ON CHRISTMAS EVE...
.UPDATE...A MOSTLY THIN LAYER OF HIGH LEVEL CLOUDS SPREADING EWD
THROUGH THE LOWER MS VALLEY REGION THIS MORNING AS A SURFACE HIGH
REMAINED POSITIONED OVER SRN GA. A LIGHT RETURN SLY LOW LEVEL FLOW
SENT MANY LOCATIONS IN THE MIDDLE 50S BY LATE MORNING WITH DEWPOINTS
CREEPING UPWARD IN THE 40S. A RATHER WEAK WARM FRONT FORMING IN THE
NWRN GULF OF MEXICO WILL BE EDGING NWD LATER TONIGHT AS MOISTURE
CONTINUES TO BUILD AHEAD OF OUR POWERFUL STORM SYSTEM NOW DIVING
INTO THE SRN ROCKIES. HAVE MADE MINOR ADJUSTMENTS TO SKY COVER
...TEMPS AND DEWPOINTS FOR THE SHORT TERM AND UPDATES SHOULD BE
AVAILABLE.
LATEST GUIDANCE STILL SUGGESTING THAT LIGHT RAINS WILL BREAK OUT OVER
OUR WRN CWFA DURING THE EVENING HOURS AND EXPAND TO MUCH OF THE AREA
AFTER MIDNIGHT. QPF AMOUNTS LIKELY TO AVERAGE ONE HALF TO ONE INCH
AND SHOULD BE CONFINED TO LOCATIONS NW OF THE NATCHEZ TRACE PARKWAY
BEFORE NOON ON WEDNESDAY WITH A FEW RUMBLES OF ELEVATED TSRA
POSSIBLE. /40/
REST OF PREVIOUS DISCUSSION FOLLOWS: 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./03/
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 CONDS WILL PREVAIL THIS AFTN WITH INCREASING MID-
UPPER LVL CLDS XPCTD THRU THE DAY. A WARM FRONT WILL MOVE ACROSS THE
AREA FM THE SW THIS EVENING BRINGING RAIN CHANCES TO AREAS W THE MS
RIVER AFTER 00Z. PDS OF RAIN WITH MVFR/IFR CIGS AND VIS WILL PLAGUE
ALL AIRFIELDS FROM WEST TO EAST AFTER 03Z...WITH THE EXCEPTION BEING
HBG AND POSSIBLY MEI. SERLY WNDS WILL PICK UP THIS AFTN AND INCREASE
INTO THE EVENING AS THE SFC PRES GRAD TIGHTENS. A COLD FRNT WILL
MOVE INTO WRN AREAS THURS MORNING WITH A GOOD CHANCE FOR SEVERE TS
ALONG AND AHEAD OF THE FRNT. /BK/
&&
.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.
&&
$$
BK
