FXUS64 KJAN 260344 CCA
AFDJAN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
929 PM CST WED NOV 25 2009
.DISCUSSION...LOW TEMPERATURES FOR TONIGHT HAVE BEEN ADJUSTED
SLIGHTLY IN THE UPDATE AND HAVE BEEN LOWERED A FEW DEGREES PER THE
LATEST OBSERVATIONS. WINDS HAVE CALMED OVER MUCH OF THE ARKLAMISS
AND CLOUD DECKS ACCOMPANYING THE APPROACHING FRONT HAVE CONTINUED TO
DECREASE IN COVERAGE. WILL SEE TEMPS DROP NEAR THE FREEZING MARK IN
LOCALLY COOLER AREAS TONIGHT WITH MID 30S EXPECTED OVER MOST ZONES.
ADDED PATCHY FROST AS A RESULT OF THIS. THE QUESTION MARK AS FAR AS
TEMPS ARE CONCERNED TONIGHT INVOLVES THE INCREASING PRESSURE
GRADIENT EXPECTED TOWARD MORNING BUT WITH SUCH RAPID COOLING
CURRENTLY UNDERWAY LOWER MINS LOOK IN ORDER. ALSO OF NOTE ARE GUSTY
NW WINDS THAT DEVELOP IN COLD AIR ADVECTION IN THE WAKE OF THE FRONT
TOMORROW. CURRENT INDICATIONS ARE THAT LAKE WIND ADVISORY CRITERIA
MAY BE REACHED ON AREAS LAKES DURING THE DAY ON THANKSGIVING. THIS
WILL BE EXAMINED MORE CLOSELY ON THE NEXT MODEL RUN.
&&
.PREV DISCUSSION...235 PM CST WED NOV 25 2009(TONIGHT THROUGH
FRIDAY NIGHT)...LATEST SATELLITE IMAGERY SHOWS A COOL UPPER TROUGH
OVER THE REGION ON THIS THANKSGIVING EVE. AN UPPER VORT AXIS WAS WAS
PUSHING THROUGH THE MID TO UPPER MISSISSIPPI VALLEY. SURFACE HIGH
PRESSURE(1024 MB) CENTERED OVER THE SOUTHERN PLAINS WAS PROVIDING
CLEAR SKIES TO THE REGION. TEMPERATURES AS OF MID AFTERNOON WERE IN
THE 60S.
AN UPPER LEVEL CLOSED LOW WILL PIVOT THE UPPER TROUGH AXIS INTO THE
MISSISSIPPI VALLEY FOR TONIGHT BEFORE IT SWEEPS THROUGH THE OHIO
VALLEY ON THANKSGIVING DAY. THIS TROUGH WILL BRING REINFORCING
SURFACE HIGH PRESSURE FROM THE CENTRAL ROCKIES SEWD INTO THE SRN
PLAINS TO INCREASE OUR GRADIENT NWLY WINDS FOR THE HOLIDAY.
MODERATE COLD AIR ADVECTION FOR THIS AFTERNOON WILL RELAX TONIGHT
FOR PARTIAL RADIATIONAL COOLING AND LOWS 34-39F. STRONGER COOLING
ARRIVES EARLY THURSDAY AND HOLDS READINGS DOWN TO BETWEEN 54-60F AS
THE REINFORCING TROUGH RIDES SEWD THROUGH THE TENNESSEE/OHIO
VALLEYS. BY THURSDAY NIGHT...THE TEXAS SURFACE HIGH WILL BUILD
EASTWARD ALONG THE GULF COAST AND WE SHOULD END UP WITH GOOD
RADIATIONAL COOLING CONDITIONS WITH A DRYER GROUND SOIL AND LIGHT
WINDS. LOOKING AT SURFACE DEWPOINTS...SREF WILL RANGE FROM
28-30F...GFS 30-32F...AND NAM 25-27F. SREF <0 CELSIUS PROBS LOOK TO
BE AROUND 20 TO 35 PERCENT IN THE EAST FOR FRIDAY MORNING. SO
CURRENT THINKING IS THAT THE EAST WILL BE ABLE TO DIP TO AROUND 32
OR SLIGHTLY BELOW FOR PERHAPS 1-2 HOURS...WHILE THE WEST WOULD
PROBABLY STAY JUST ABOVE FREEZING OR BARELY TOUCH IT IN THE COOLER
LOCATIONS. SO WITH THE CURRENT THIRD PERIOD TIME LINE FOR THURSDAY
NIGHT WILL ISSUE A FREEZE WATCH FOR THE EAST. SINCE IT WILL BE THE
FIRST ONE FOR THIS LATE IN THE FALL SEASON. ALSO CONSIDERABLE FROST
WILL BE AN ISSUE FOR AT LEAST THE CENTRAL AND EASTERN PORTIONS OF
MISSISSIPPI FOR THURSDAY NIGHT. AS WE GET INTO FRIDAY THE
GFS/ECMWF/GEFS ARE IN GOOD AGREEMENT SHOWING UPPER RIDGING BUILDING
OVER THE REGION AS THE UPPER TROUGH LIFTS EAST OFF THE ATLANTIC
SEABOARD. THIS WILL PLACE THE ARKLAMISS IN DRY NORTHWESTERLY FLOW
ALOFT ALLOWING CLEAR SKIES AND SEASONABLE HIGH TEMPS THROUGH FRIDAY.
COOL TEMPS CAN BE EXPECTED SAT MORNING DUE TO EFFICIENT RADIATIONAL
COOLING ASSOCIATED WITH CLEAR SKIES AND LIGHT WINDS
EXPECTED...COUPLED WITH THE COLD AIRMASS THAT WILL BE IN PLACE. LOW
TO MID 30S EAST OF I-55 LOOK VERY POSSIBLE. USUALLY THIS TIME OF
YEAR A FREEZE WILL HAVE OCCURRED MAKING MENTION OF FROST IN THE
FORECAST UNNECESSARY HOWEVER CONSIDERING WE HAVEN'T SEEN ONE YET
THIS YEAR WILL GO AHEAD AND INCLUDE FROST EAST OF I-55 SAT MORNING.
AS FAR AS TEMPS ARE CONCERN...FOR TONIGHT THE MAV/NAM/GFS WERE A
LITTLE WARM WITH MID 30S TO 40S. GMOS LOOKED A LITTLE BETTER WITH
LOWS FROM THE LOWER 30S EAST TO THE UPPER 30S WEST. MADE SLIGHT
ADJUSTMENTS TO IT. FOR FRIDAY...THE NAM...MAV...ESPECIALLY THE
GFS(UPPER 40S TO MIDDLE 50S) LOOKED TO BE TOO COOL WITH THE FULL
SUNSHINE AND COLD AIR ADVECTION CONTINUING. WENT WITH GMOS TEMPS
WHICH RANGE FROM THE MIDDLE 50S NORTH TO NEAR 60 SOUTH. FOR FRIDAY
NIGHT WITH THE GOOD RADIATION COOLING WENT CLOSE TO MAV GUIDANCE.
ONLY MADE SLIGHT ADJUSTMENTS SO THAT THE FREEZING TEMPS WILL BE EAST
OF INTERSTATE 55. GFS WAS A LITTLE WARM...WHILE THE GMOS HAD THE
FREEZING TEMPS ACROSS I-55 AND SOUTH MISSISSIPPI. FOR FRIDAY HIGHS
WILL BE IN THE UPPER 50S TO LOWER 60S. WENT CLOSE TO MAV GUIDANCE.
NAM...ESPECIALLY THE GFS (50-55) WAS TOO COOL. FOR FRIDAY NIGHT THE
SURFACE HIGH CENTER WILL PUSH EAST OF THE REGION. CURRENT GUIDANCE
LOOKED A LITTLE WARM...ESPECIALLY THE NAM WITH LOWS IN THE 40S. SO
KEPT THE CURRENT FORECAST WITH LOWS IN THE LOWER TO UPPER 30S./17/
&&
.PREVIOUS LONG TERM...SATURDAY THROUGH WEDNESDAY...
A LOW CONFIDENCE FORECAST ENSUES SUNDAY THROUGH WEDNESDAY AS LONG
RANGE MODEL GUIDANCE CONTINUES TO SHOW CONSIDERABLE SOLUTION SPREAD.
A S/WV CROSSING THE DESERT SOUTHWEST EARLY SUNDAY WILL MOVE INTO THE
SOUTHERN PLAINS BY MONDAY WITH AN ATTENDANT SURFACE LOW/COLD FRONT
INTENSIFYING OVER EASTERN TX MONDAY AFTERNOON. MODELS DIVERGE FROM
THERE AS TO THE PROGRESSION OF THIS SYSTEM WITH THE GFS DEVELOPING A
DEEP, CLOSED UPPER LEVEL CIRCULATION BY LATE MONDAY WHILE THE ECMWF
MAINTAINS AN OPEN WAVE THROUGH THIS TIME. THE ECMWF DOES EVENTUALLY
CLOSE OFF A CIRCULATION BY TUESDAY AFTERNOON ALTHOUGH NOT NEARLY AS
DEEP AS THE GFS. IMPLICATIONS TO THE FORECAST ARE SIMILAR THROUGH
MONDAY WITH RAIN CHANCES INCREASING FROM WEST TO EAST SUNDAY AS THE
COLD FRONT APPROACHES THE REGION. THE FRONT WILL PASS OVER THE
ARKLAMISS MONDAY MOVING INTO AL SOMETIME IN THE LATE
AFTERNOON/EVENING. SOUTHERLY FLOW AHEAD OF THE FRONT WILL GRADUALLY
INCREASE GULF MOISTURE ACROSS THE REGION BEFORE THE FRONT
PASSES...WITH GFS SHOWING AN AREA OF 100-300J/KG MUCAPE DEVELOPING
ALONG AREAS SOUTH OF I-20. A 100KT+ JET OVER THE CWA WILL PROVIDE
ADDITIONAL LIFT SUPPORT AND WILL KEEP THE SLIGHT CHANCE OF THUNDER
GOING ACROSS SOUTHERN AREAS AS THE FRONT PASSES. FROM HERE GUIDANCE
VARIATIONS SPELL GREAT UNCERTAINTY IN THE FORECAST. THE SLOWER GFS
HANGS ITS DEEP, CLOSED CIRCULATION IN THE TN VALLEY THROUGH WED
MORNING...AND IF THIS PANS OUT...WOULD MEAN A GREATER CHANCE OF
PRECIP ACROSS AREAS NORTH OF I-20 AS LOW LEVEL MOISTURE WRAPS AROUND
THE LOW. THE ECMWF ON THE OTHER HAND SLIDES A MUCH WEAKER, MORE
PROGRESSIVE S/WV INTO THE TN VALLEY BY WED MORNING KEEPING PRECIP
CHANCES LIMITED TO AREAS EAST OF OUR REGION. TRIED TO GO WITH A
BLEND IN TERMS OF THE FORECAST AT THIS TIME WITH MEN POPS LOOKING
REASONABLE AS THEY KEEP A SLIGHT CHANCE OF PRECIP ACROSS NORTHERN
ZONES WITH DRY CONDITIONS ELSEWHERE.
MEX TEMPS GENERALLY ACCEPTED ALTHOUGH SOME LOWERING TOWARD MEN
GUIDANCE WAS NEEDED OVER THE WEEKEND WITH BOTH HIGH AND LOW TEMPS.
/BK/
&&
.AVIATION...VFR CONDITIONS UNDER MAINLY CLEAR SKIES WILL PREVAIL
ACROSS THE ARKLAMISS THROUGH THE PERIOD. ANOTHER COLD FRONT WILL
SWEEP ACROSS THE AREA DURING THE EARLY MORNING THURSDAY BRINGING
MAINLY ANOTHER REINFORCING SHOT OF COOL AIR./15/
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...FREEZE WATCH FROM LATE THURSDAY NIGHT THROUGH FRIDAY MORNING
FOR MSZ029>033-037>039-044>046-050>052-056>058-065-066-073-074.
LA...NONE.
AR...NONE.
&&
$$
17/15
03
