FXUS64 KJAN 232231 AAA
AFDJAN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
431 PM CST WED DEC 23 2009
SYNOPSIS...WARM FRONTAL ZONE LIES ROUGHLY ALONG KSHV-KGPT LINE WHILE
THE FIRST BAND OF RAINFALL LIFTING AWAY TO THE NE. RAIN AMOUNTS OF 2
TO 2.5 INCHES HAVE OCCURRED OVER PORTIONS OF THE DELTA ALREADY. EXPECT
THE BOUNDARY TO CONTINUE CREEPING NWD TONIGHT AS MORE UPPER LEVEL
ENERGY MOVES THROUGH CENTRAL AND SRN TX AND A SURFACE LOW(1000MB)
FORMING IN TX BEGINS TO DEEPEN OVER NE TX BY MORNING. THE DEEPENING
SURFACE LOW(995MB) THURSDAY MORNING OVER SERN AR MOVES DROPS TO
990MB BY NOON OVER N AR AND 987MB BY 6PM OVER SRN MO. AS PREVIOUSLY
NOTED...THIS TRACK HAS BEEN NOTORIOUS FOR PRODUCING SVR WX INCLUDING
TORNADOES IN MS AS THE TRAILING FRONT/SQUALL LINE SWEEPS EWD.
IN THE SHORT TERM...EXPECT SCATTERED TO NUMEROUS SHRA/ISOLATED
ELEVATED TSRA TO CONTINUE MAINLY N AND W PORTIONS OF THE CWFA THIS
EVENING BUT BECOMING MORE CONCENTRATED AFTER MIDNIGHT. MOSTLY
ISOLATED ACTIVITY ELSEWHERE BEFORE MIDNIGHT. AS THE WARM FRONT SLIDES
NWD WITH INCREASING SLY WINDS AREAWIDE. WE HAVE CONTINUED LAKE WIND
ADVISORIES FOR THE WRN HALF THIS EVENING AND THEN EXPANDED THESE TO
INCLUDE THE ENTIRE CWFA AFTER MIDNIGHT LASTING THROUGH THE FROPA ON
THURSDAY. WINDS SHOULD GET EVEN STRONGER ALONG THE MS RIVER CHANNEL
FROM 06-18Z AND HAVE UPGRADED THESE LOCATIONS TO WIND ADVISORY FOR
GUSTS OF 40-45 MPH POSSIBLE. MEANWHILE...THE FLASH FLOOD WATCH FOR
LOCATIONS WEST OF A GRENADA TO NATCHEZ LINE TONIGHT WILL BE EXPANDED
TO INCLUDE THE REST OF THE HIGHWAY 82 CORRIDOR ON THURSDAY AS PWATS
OF 1.5-1.7 INCHES SURGE N AND INCREASE RAINFALL PRODUCTION.
AS A SQUALL LINE EVOLVES JUST AHEAD OF THE FRONT OVER AR/LA LATER
TONIGHT...IT SHOULD BEGIN ACCELERATING EWD TOWARD OUR AREA BY DAYBREAK.
THE PRIMARY TIMING FOR THE STRONGEST STORMS ON THURSDAY SHOULD BE FROM
AROUND 4-8AM IN NE LA/SE AR SWEEPING EWD THROUGH THE MS RIVER
COUNTIES/PARISHES DURING THE MORNING HOURS TO AROUND I-55 BY 11AM-2PM
AND THEN 3-6 PM FOR ERN MS. SEVERE WEATHER PARAMETERS HAVE HELD QUITE
CONSISTENT WITH THIS STORM SYSTEM AND PREFER THE OVERALL GFS TIMING
AS THE NAM TOO SLOW AND THE LOCAL WRFS APPEARING A BIT FAST.
AS SURFACE PRESSURE GRADIENTS TIGHTEN DURING THE OVERNIGHT AND
THURSDAY MORNING...THE ONLY QUESTIONABLE FACTOR REMAINS THE DEGREE OF
QUALITY BOUNDARY LAYER MOISTURE AND ULTIMATE INSTABILITY FOR SEVERE
STORMS. MLCAPE VALUES 400J/KG EDGING INTO THE SW CORNER OF THE CWFA BY
4-6AM WHICH EXPANDS RAPIDLY TO 7-900J/KG BY MID MORNING OVER SRN HALF
ACCELERATING EWD ACROSS THE AREA THROUGH MID AFTERNOON. PRE-SQUALL
DEEP LAYER SHEAR MORE THAN SUFFICIENT WITH 0-3KM HELICITY VALUES
4-600 IN PROGGED SOUNDINGS AND 0-1KM HELICITIES 3-400. THEN...A MID
LEVEL SPEED MAX OF 85+KTS AT 700MB BLASTS DOWN THE HIGHWAY 84
CORRIDOR ABOUT MIDDAY AND REALLY KICKS THE SQUALL LINE EAST.
ALTHOUGH DAMAGING WIND AND TORNADOES LOOK TO BE THE PREDOMINANT
SEVERE RISK WITH THIS EPISODE...LARGE HAIL WILL ALSO BE POSSIBLE.
RAINFALL AMOUNTS FROM 2 TO 3 INCHES ARE EXPECTED LATE TONIGHT AND
THURSDAY. THESE AMOUNTS CURRENTLY FALL BELOW FLOOD GUIDANCE NUMBERS
FOR E AND S PORTIONS...BUT THAT COULD CHANGE OVERNIGHT. PERIODS OF
HEAVY RAINFALL WILL BE POSSIBLE ACROSS THE ENTIRE FORECAST AREA
DURING THE DAY THURSDAY AND LOCALIZED FLOODING PROBLEMS WILL BE
POSSIBLE BUT HAVE CONCENTRATED ON NRN AND WRN ZONES FOR NOW DUE TO
THEIR PROXIMITY TO THE UPPER TROUGH AND BEST UVVS.
ALL ACTIVITY QUICKLY EXITS EARLY THURSDAY EVENING IN TIME FOR A MUCH
QUIETER AND COLDER CHRISTMAS WITH TEMPS BACK BELOW NORMALS FOR LATE
DECEMBER GOING INTO THE WEEKEND./40/
LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY...A STRETCH OF BELOW
NORMAL TEMPERATURES THAT SHOULD LAST THROUGH THE WEEKEND. STRONG CAA
IS EXPECTED THURSDAY NIGHT BEHIND THE COLD FRONT AND FRIDAY MORNING
LOWS WILL BOTTOM OUR NEAR FREEZING IN THE WESTERN MOST ZONES.
VIRTUALLY ALL PRECIPITATION WILL HAVE ENDED LONG BEFORE TEMPERATURES
GET DOWN INTO THE LOWER 30S BUT A FEW FLURRIES WILL NOT BE TOTALLY
OUT OF THE QUESTION IN PORTIONS OF THE DELTA EARLY FRIDAY MORNING. WL
NOT INCLUDE MENTION OF FLURRIES THIS PACKAGE THOUGH. MODELS SUGGEST
LOW CLOUDS WILL LINGER THROUGH MOST OF FRIDAY MORNING BUT HIGH
PRESSURE AT THE SURFACE IS EXPECTED TO SHIFT EAST OVER OUR AREA BY
AFTERNOON AND BRING SOME SUNSHINE. STILL MOST SITES WILL STRUGGLE TO
REACH THE UPPER 40S. THE LARGE UPPER VORTEX WILL BE CENTERED OVER THE
MID MISSISSIPPI VALLEY FRIDAY NIGHT WITH A SURFACE RIDGE AXIS ALONG
THE GULF COAST. LESS THAN IDEAL RADIATIVE COOLING WILL OCCUR BUT
TEMPERATURES SHOULD DROP BELOW FREEZING ACROSS MOST OF THE AREA BY
SATURDAY MORNING. THIS PATTERN WILL CHANGE VERY LITTLE THROUGH SUNDAY
AND OVERALL THIS RUN OF THE GFS IS COOLER AND DRIER THROUGH THE
WEEKEND. HIGHS WILL GENERALLY BE IN THE UPPER 40S AND OVERNIGHT LOWS
AROUND 30 SATURDAY...SUNDAY AND MONDAY. SUNDAY INTO MONDAY THE LARGE
UPPER VORTEX WILL FINALLY LIFT OUT TO THE NORTHEAST BUT ANOTHER LARGE
CLOSED LOW WILL BE DROPPING SOUTH DOWN THE WESTERN CONUS. SHORTWAVE
RIDGING SURFACE AND ALOFT IS EXPECTED OVER OUR REGION MONDAY INTO
TUESDAY. THIS SHOULD BRING US SOME WARMER TEMPS TUESDAY. THE GFS AND
ECMWF DIFFER SIGNIFICANTLY ON THE EVOLUTION OF THIS LOW THOUGH. THE
ECMWF IS MORE PROGRESSIVE THAN THE GFS THIS RUN AND MOVES RAIN BACK
INTO OUR CWA FROM THE SW BY TUESDAY AFTERNOON WHILE THE GFS HANGS THE
CLOSED LOW BACK OVER THE DESERT SOUTHWEST THROUGH TUESDAY NIGHT. BY
WEDNESDAY THOUGH THIS SYSTEM IS EXPECTED TO BRING THE NEXT BEST
CHANCE FOR WIDESPREAD RAIN TO OUR REGION. MAV GUIDANCE TEMPS WERE
STUCK CLOSE TO BUT THE SLIGHT CHANCE POPS WERE CUT FRIDAY THROUGH
MONDAY. POPS WERE INCREASED TUESDAY INTO WEDNESDAY TO ACCOUNT FOR A
LITTLE FASTER EASTWARD PROGRESSION OF THE NEXT LOW. /22/
&&
.AVIATION...
STRONG SFC WINDS AND ASSOC TURBULENCE WILL BE THE FOCUS
FOR THIS AFTN...ACCOMPANIED BY PRIMARILY VFR CONDS ALTHOUGH
INTERMITTENT MVFR WILL BE PSBL OVR ERN AREAS. EARLY THIS EVENING
XPCT GRADUAL DETERIORATION TO IFR CONDS IN THE E AS LOW LEVELS
CONTINUING MOISTENING IN SRLY FLOW. RAIN/TS CHANCES WILL RETURN LATE
TONIGHT...ACCOMPANIED BY INCREASING COVERAGE OF IFR CONDS AS A COLD
FRONT APPROACHES THE AREA. THE FRONT IS RATHER STRONG AND A SQUALL
LINE IS XPCTD TO BE SWEEPING THE AREA IN THE MORNING...WITH DAMAGING
WINDS AND ISOLD TORNADOES BEING THE PRIMARY RISK. SFC WINDS WILL BE
STRONG AND SERLY AHEAD OF THE FRONT SHIFTING TO STRONG AND SWRLY
RIGHT BEHIND THE FRONT. /BK/
&&
.PRELIMINARY POINT TEMPS/POPS...
JACKSON 58 64 35 47 / 100 100 24 14
MERIDIAN 55 65 35 51 / 72 100 63 14
VICKSBURG 58 61 34 48 / 100 100 15 14
HATTIESBURG 58 67 35 50 / 79 100 35 14
NATCHEZ 59 63 30 48 / 100 100 12 14
GREENVILLE 56 59 34 44 / 100 100 22 14
GREENWOOD 56 61 35 47 / 100 100 25 14
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...LAKE WIND ADVISORY FROM MIDNIGHT TONIGHT TO 2 PM CST THURSDAY
FOR MSZ029>033-037>039-044>046-050>052-055>058-063>066-
072>074.
FLASH FLOOD WATCH FROM THURSDAY MORNING THROUGH THURSDAY
AFTERNOON FOR MSZ028>033-037>039.
LAKE WIND ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR MSZ018-034-040-
041-047-053-059-060.
FLASH FLOOD WATCH FROM MIDNIGHT CST TONIGHT THROUGH THURSDAY
AFTERNOON FOR MSZ018-019-025>027-034>036-040>042-047-053-
059-060.
WIND ADVISORY FROM MIDNIGHT TONIGHT TO NOON CST THURSDAY FOR
MSZ018-034-040-041-047-053-059-060.
LAKE WIND ADVISORY UNTIL 2 PM CST THURSDAY FOR MSZ019-025>028-
035-036-042-043-048-049-054-061-062.
LA...LAKE WIND ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR LAZ007>009-015-
016-023>026.
FLASH FLOOD WATCH FROM MIDNIGHT CST TONIGHT THROUGH THURSDAY
AFTERNOON FOR LAZ007>009-015-016-023>026.
WIND ADVISORY FROM MIDNIGHT TONIGHT TO NOON CST THURSDAY FOR
LAZ007>009-015-016-023>026.
AR...LAKE WIND ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR ARZ074-075.
FLASH FLOOD WATCH FROM MIDNIGHT CST TONIGHT THROUGH THURSDAY
AFTERNOON FOR ARZ074-075.
WIND ADVISORY FROM MIDNIGHT TONIGHT TO NOON CST THURSDAY FOR
ARZ074-075.
&&
$$
