FXUS64 KJAN 230249 AAA
AFDJAN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
850 PM CST TUE DEC 22 2009
.UPDATE...SHOWERS ARE MOVING ACROSS THE DELTA THIS EVENING AND THE
SHOWERS WILL CONTINUE TO INCREASE IN COVERAGE MAINLY FOR AREAS ALONG
AND WEST OF THE RIVER THROUGH THE OVERNIGHT HOURS. MADE A FEW
ADJUSTMENTS TO THE HOURLY GRIDS BUT OTHER THAN THAT THE FORECAST
LOOKS ON TRACK...SO NO UPDATES ARE NEEDED AT THIS TIME. AS FAR AS
THURSDAY GOES THE MODELS ARE STILL PRETTY CONSISTENT WITH THE TIMING
OF THE STORM SYSTEM ACROSS THE AREA...WITH THE BEST INSTABILITY
CONTINUING TO BE ALONG AND SOUTH OF THE I-20 CORRIDOR. /15/
...POWERFUL STORM SYSTEM TO IMPACTING THE AREA FOR CHRISTMAS EVE...
.SYNOPSIS...A POWERFUL STORM SYSTEM BUILDING OVER THE SWRN STATES
TONIGHT WILL BE HEADING INTO THE SRN PLAINS WEDNESDAY AND THEN BE
IMPACTING THE LOWER MS VALLEY REGION MAINLY ON CHRISTMAS EVE DAY.
THE PRIMARY TIME FRAME FOR TORRENTIAL RAINS AND SEVERE STORMS WITH
DAMAGING WINDS AND POSSIBLE TORNADOES APPEARS TO BE FROM ABOUT 3AM
UNTIL 3PM THURSDAY AND RESIDENTS SHOULD BE URGED TO STAY TUNED FOR
LATER UPDATES.
SHORT TERM(TONIGHT AND WEDNESDAY)...WARMER AIR WILL CONTINUE
STREAMING INTO THE REGION ON SSELY WINDS TONIGHT AS A RESULT OF A
GRADUALLY TIGHTENING E-W PRESSURE GRADIENT. THIS GRADIENT OF 4MB
TONIGHT REACHES 6MB WEDNESDAY MORNING AND 8MB BY WEDNESDAY EVENING
AS PRESSURE FALLS INCREASE TO OUR W. 925MB WINDS PROGGED TO RAMP UP
TO 30-35KTS MIDDAY WEDNESDAY OVER THE WRN HALF OF OUR CWFA AND WILL
GO AHEAD WITH A LAKE WIND ADVY FOR THOSE LOCATIONS. MEANWHILE...
LATEST GUIDANCE STILL SUGGESTING THAT AND AREA OF LIGHT RAINS WILL
BREAK OUT OVER NERN LA/SERN AR LATER THIS EVENING AND EXPAND TO AT
LEAST THE NWRN THIRD OF OUR CWFA AFTER MIDNIGHT. QPF AMOUNTS LIKELY
TO AVERAGE ONE HALF TO ONE INCH AND SHOULD BE CONFINED TO LOCATIONS
NW OF A WINNSBORO TO GRENADA LINE WITH A FEW RUMBLES OF ELEVATED
TSRA POSSIBLE IN DECENT 850MB MOISTURE TRANSPORT AHEAD OF THE WARM
FRONT LIFTING NWD FROM THE NW GULF. SHRA ALREADY STARTING TO PICK UP
IN THE SABINE RIVER VALLEY INTO THE UPPER TX COAST AND THE RUC TAKES
THESE INTO OUR DELTA REGION BY 03-06Z. EXPECT ANY TSRA TO BE VERY
TRANSIENT AS STORM MOTIONS INCREASE TO ABOVE 40KTS AFTER MIDNIGHT
HOWEVER A QUICK ONE HALF TO ONE INCH QPF POSSIBLE THROUGH MIDDAY
WEDNESDAY AS THE WARM FRONT PASSES. EVEN THOUGH THE BETTER DYNAMICS
REMAIN WEST OF THE FA DURING THE DAY WEDNESDAY...THE 850MB JET AXIS
TRACKING FROM NERN TX INTO THE MID SOUTH SENDS A 50KT CORE GRAZING
OUR NWRN COUNTIES 09-15Z FOR THE LOCAL DOWNPOURS.
THEN...AS THE INITIAL MID-UPPER LEVEL ENERGY EJECTS INTO THE TX
PANHANDLE WEDNESDAY AFTERNOON...OUR FIRST ROUND OF RAINFALL SHOULD
EASE OFF AS THE WARM FRONT LIFTS JUST N OF OUR REGION. A LULL IN THE
UVV FIELDS WEDNESDAY EVENING WILL BE ACCOMPANIED BY INCREASING LOW
LEVEL WINDS HOWEVER. THE LAKE WIND ADVY WILL PROBABLY HAVE TO BE
EXTENDED/EXPANDED WITH A POTENTIAL FOR WRN PORTIONS OF THE AREA
NEEDING A WIND ADVY GOING INTO LATER WEDNESDAY NIGHT. SURFACE
CYCLOGENESIS SHOULD BE UNDERWAY ALONG A STEADILY MOVING COLD FRONT
CROSSING THE ARKLATEX EARLY THURSDAY MORNING. THE MODELS HAVE BEEN
QUITE CONSISTENT IN DEVELOPING THIS LOW(999-995MB) WITH MINOR
DIFFERENCES IN EXACT LOCATION AND TIMING. THIS TYPE/TRACK OF THIS
SYSTEM RELATES RATHER WELL PAST SEVERE WEATHER EPISODES IN OUR AREA
DURING THE COLD SEASONS. LOCAL CHECKLISTS/PARAMETERS SUPPORT SEVERE
STORMS FOR WHAT HAS BEEN ONLY MINOR INSTABILITY FLUCTUATIONS FROM
MODEL RUN TO RUN. THE GFS BRINGS 600-700J/KG OF MLCAPE UP TO THE
I-20 CORRIDOR AND 200 J/KG TO THE NORTHERN PORTION OF THE AREA
HOWEVER MODIFIED RAOBS WERE ABOUT 500J/KG HIGHER. THE MODELS HAVE NOT
FLUCTUATED MUCH WITH THE AMOUNT OF FORCING AND SHEAR WITH THE SYSTEM
INDICATING 50KTS OF 0-6 BULK SHEAR AND 0-3KM HELICITIES OF 400-600
M^2/S^2 THURSDAY MORNING INTO THE AFTERNOON AHEAD OF THE FRONT. AS A
SQUALL LINE DEVELOPS ALONG THE FRONT THURSDAY MORNING W OF THE MS
RIVER...THE RISK FOR DAMAGING WINDS(65-75KTS) WILL BECOME GREATER/
MORE WIDESPREAD AS IT SWEEPS THROUGH THE REGION BEFORE MID AFTERNOON.
EXACT LOCATIONS OF THE GREATEST RISKS ARE STILL SOMEWHAT QUESTIONABLE
AT THIS TIME HOWEVER SUPERCELL STRUCTURES AHEAD OF THE LINE WILL BE
BEST ABLE TO GENERATE TORS. ONE LIMITING FACTOR REMAINS THE QUALITY
OF THE BOUNDARY LAYER AIR(65F+ DEWPOINTS) WHICH COULD TEND TO GET
PINCHED OFF OVER OUR SRN COUNTIES AS THE SYSTEM MOVES EAST./40/
REST OF THE PREVIOUS DISCUSSION...LONG TERM...THURSDAY NIGHT THROUGH
TUESDAY...VIGOROUS STORM SYSTEM STILL ON TRACK TO PUSH THROUGH THE
ARKLAMISS THURSDAY. THE COLD FRONT WILL SWEEP OUT OF THE AREA
THURSDAY NIGHT. 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 CONTINUE TO PREVAIL THIS EVENING WITH
INCREASING MID-UPPER LVL CLDS XPCTD. A WARM FRONT WILL MOVE
ACROSS THE AREA FM THE SW LATER TONIGHT 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
STRONG COLD FRNT WILL MOVE INTO WRN AREAS THURS MORNING WITH A GOOD
CHANCE FOR SEVERE TS ALONG AND AHEAD OF THE FRNT AS IT PASSES OVER
THE ARKLAMISS. /BK/
&&
.PRELIMINARY POINT TEMPS/POPS...
JACKSON 50 64 56 65 / 44 72 78 100
MERIDIAN 44 62 53 66 / 19 48 63 100
VICKSBURG 53 66 58 61 / 70 89 86 99
HATTIESBURG 47 67 57 68 / 15 34 62 99
NATCHEZ 53 69 59 63 / 64 72 89 99
GREENVILLE 50 62 56 60 / 93 100 91 99
GREENWOOD 49 60 56 63 / 67 98 82 100
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...LAKE WIND ADVISORY FROM 11 AM TO 6 PM CST WEDNESDAY FOR MSZ018-
019-025>028-034>036-040>043-047>049-053-054-059>062.
LA...LAKE WIND ADVISORY FROM 11 AM TO 6 PM CST WEDNESDAY FOR
LAZ007>009-015-016-023>026.
AR...LAKE WIND ADVISORY FROM 11 AM TO 6 PM CST WEDNESDAY FOR ARZ074-
075.
&&
$$
