FXUS64 KFWD 300024 AAB
AFDFWD
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE FORT WORTH TX
624 PM CST SUN NOV 29 2009
.AVIATION...
A COLD FRONT HAS MOVED TO THE SOUTH OF THE TAF SITES...EXTENDING
SOUTH OF A KSLR...KACT...KBMQ LINE AS OF 00Z. SHOWERS AND
THUNDERSTORMS WILL CONTINUE TO MOVE NORTHEAST ALONG AND EAST OF
THE FRONT. BEHIND THE FRONT...MVFR CONDITIONS ARE EXPECTED
THROUGH 12Z...WITH SOME HIGH END IFR CONDITIONS POSSIBLE IN LIGHT
RAIN THROUGH 02-04Z. NORTHERLY WINDS OF 15 TO 20 KNOTS WILL
PREVAIL WITH WIND SPEEDS DECREASING DURING THE DAY MONDAY.
&&
.UPDATE...
606 PM CST SUN NOV 29 2009
RAN A QUICK UPDATE TO INCLUDE THE 20 POPS NORTHWARD TO COVER
AREAS NORTH OF I-20 FOR THE OVERNIGHT HOURS. MODELS ARE HOLDING ON
TO THE MOISTURE FROM THE SURFACE UP TO ABOUT 750 MB AND POCKETS OF
LIGHT RAIN/SPRINKLES WILL BE POSSIBLE THROUGH AT LEAST MIDNIGHT.
MADE NO CHANGES TO THE FORECAST FOR THE REST OF THE CWA. POP
CONFIGURATION FOR AREAS ALONG THE FRONT LOOK GOOD FOR THE
REMAINDER OF THE NIGHT.
85/NH
&&
.PREV DISCUSSION... /ISSUED 354 PM CST SUN NOV 29 2009/
TONIGHT THROUGH MONDAY NIGHT...AT 21Z THE COLD FRONT WAS NEAR A
LAMPASAS TO EMORY LINE WITH A BROKEN LINE OF RAIN SHOWERS WITH
EMBEDDED THUNDERSTORMS RUNNING JUST BEHIND ITS LEADING EDGE. FOR
THE MOST PART RAIN SHOWER ACTIVITY HAS BEEN LIGHT...HOWEVER
EMBEDDED THUNDERSTORMS HAVE BEEN PRODUCING RAINFALL AMOUNTS OF A
QUARTER INCH TO HALF INCH PER HOUR. THE COLD FRONT AS ASSOCIATED
RAIN SHOWER/TSTM ACTIVITY IS EXPECTED TO CONTINUE SOUTHEAST THIS
EVENING...EVENTUALLY SLOWING DOWN AS IT MOVES TOWARDS SOUTHEASTERN
COUNTIES OF THE CWA AFTER MIDNIGHT. KEPT LIKELY TO CATEGORICAL
POPS GOING FOR THE AREAS EXPECTED TO REMAIN SOUTHEAST OF THE FRONT
AFTER 00Z...AND THEN STARTED TAPERING OFF PRECIP CHANCES QUICKLY
FROM NORTHWEST TO SOUTHEAST AS LOW LVL DRY AIR BEGINS TO MOVE INTO
NORTH TX. LOW LVL DRY AIR MOVING IN SHOULD KEEP MOST OF NORTH TX
DRY FOR MONDAY...ONLY REAL CHANGE TO THE PERIOD WAS TO INCREASE
CLOUD COVERAGE A BIT...LOW CLOUDS ARE NOT MUCH OF A
CONCERN...HOWEVER 21Z WATER VAPOR IMAGERY CONTINUES TO INDICATE
SUBTROPICAL JET IN THE BASE OF THE CUT OFF LOW OVER THE
SOUTHWESTERN CONUS...AND WOULD EXPECT MID TO HIGH LVL CLOUDINESS
TO REMAIN OVER MOST AREAS. BY MONDAY NIGHT THE UPPER LOW IS
PROGGED TO BEGIN ITS PUSH EAST NORTHEAST INTO THE SOUTHERN
PLAINS...AND BEGAN INCREASING POPS FROM SOUTHWEST TO NORTHEAST AS
UPPER LVL POSITIVE PV ADVECTION AND H850 POSITIVE MOISTURE
ADVECTION RAMP UP OVER THE FORECAST AREA.
TUESDAY THROUGH WEDNESDAY...LOOKING AT THE 310 THETA E
SURFACE...GULF MOISTURE BEGINS TO RETURN OVER NORTH TX TUESDAY
MORNING AND CONTINUES THROUGHOUT THE DAY AS THE POWERFUL UPPER
LEVEL TROUGH MOVES NORTHEAST TOWARDS THE CWA. UNLIKE TYPICAL GULF
MOISTURE RETURN DO NOT EXPECT TO SEE THE AT THE SURFACE...BUT
EXPECT THE COLD...DRY LOW LVL AIRMASS BEHIND TODAY'S COLD FRONT
WILL SERVE TO STEEPEN LOW LVL ISENTROPIC SFCS...ALLOWING GULF
MOISTURE TO INITIALLY RETURN AT AND ABOVE THE H850 LVL. THE
COMBINATION OF THE MOISTURE RETURN ALOFT...THE LOWER LVL
ISENTROPIC LIFT AND THE INCREASE OF LARGE SCALE FORCING FOR ASCENT
OVER NORTH TX ASSOCIATED WITH THE APPROACHING TROUGH ALL RAISE
CONFIDENCE IN WIDESPREAD PRECIPITATION DURING THE PERIOD.
INCREASED POPS INTO THE 60 TO 80 PERCENT RANGE FROM SOUTHWEST TO
NORTHEAST BEGINNING TUESDAY AFTERNOON AND HOLDING THROUGH THE
OVERNIGHT HRS. GFS/ECMWF BOTH INDICATE THAT THE UPPER LOW WILL
TRACK DIRECTLY OVER THE CWA DURING THE PERIOD...WITH THE DRY SLOT
MOVING INTO OUR SOUTHEASTERN ZONES TUESDAY EVENING. AS THIS OCCURS
THE MODELS DEPICT THE CYCLONIC BRANCH OF THE WARM CONVEYOR BELT
WILL WRAP UP OVER OUR RED RIVER COUNTIES AND CYCLONICALLY ASCEND
BEHIND THE UPPER LOW AS IT CONTINUES NORTHEAST TUESDAY NIGHT. THIS
WOULD BRING THE CLASSIC TROWAL FEATURE LARGELY OVER CENTRAL/NORTH
CENTRAL TX AS COLD...CANADIAN AIR PUSHES SOUTH BEHIND THE SYSTEM.
WHAT THIS MEANS FOR NORTH TX IS THAT THE BEST CHANCE FOR
BANDED/CONVECTIVE PRECIPITATION BEHIND THE UPPER LOW LOOKS TO
REMAIN JUST WEST OF OUR CWA. CROSS SECTIONS INDICATE THAT
FRONTOGENETIC FORCING IN THE 6-700 MB LAYER FAVORABLY LIE BENEATH
A BROAD ZONE CHARACTERIZED BY EITHER CONVECTIVE OR SLANTWISE
POTENTIAL INSTABILITY. AT THIS TIME THE STRONGEST FRONTOGENETIC
FORCING LOOKS TO REMAIN NEAR A WICHITA FALLS TO ABILENE LINE.
THERMAL PROFILES HERE BECOME MORE FAVORABLE FOR SNOWFALL TOWARDS
12Z WEDNESDAY MORNING AS LOW LVL COLD AIR ADVECTION CONTINUES.
BECAUSE OF THE PLACEMENT OF THE TROWAL...AND THE SOMEWHAT LATE
ADVECTION OF COLD AIR INTO THE WESTERN PORTIONS OF NORTH
TX...THINK THAT A CHANGEOVER TO ALL SNOW IS UNLIKELY AT THIS TIME.
WENT AHEAD AND KEPT THE MENTION OF A RAIN/SNOW MIX FOR AREAS ALONG
AND WEST OF JACKSBORO TO LAMPASAS LINE FROM 06Z TO 15Z WEDNESDAY.
AT THIS TIME DO NOT EXPECT ANY ACCUMULATION WITHIN OUR CWA AS SNOW
WILL LIKELY MELT AS IT FALLS OVER OUR WESTERN COUNTIES. THIS
TROWAL REGION MOVES EAST AS THE UPPER LOW CONTINUES NORTHEAST ON
WEDNESDAY...HOWEVER BY THEN EXPECT ANY LINGERING PRECIPITATION TO
FALL IN LIQUID FORM...AND DO NOT EXPECT A LOT OF QPF AS LARGE
SCALE FORCING FOR SUBSIDENCE BEGINS TO DOMINATE MESOSCALE FORCING
FOR ASCENT ASSOCIATED WITH THE TROWAL. BIGGEST CONCERNS FOR NORTH
TX MAY ACTUALLY BE IN THE FORM OF FLOODING AS AREA VEGETATION HAS
LARGELY ENTERED DORMANT PHASE...ENHANCING POTENTIAL RUNOFF FROM
THE HEAVIER RAINFALL EXPECTED TO FALL TUESDAY AFTERNOON THROUGH
THE EVENING HRS. NOT ENOUGH CONFIDENCE IN THIS THREAT TO ISSUE A
FLOOD WATCH AT THIS TIME...BUT SOMETHING TO KEEP AN EYE ON AS THIS
SYSTEM EVOLVED. OF COURSE...ANY CHANGES IN THE POSITION OF THE
TROWAL WILL HAVE A LARGE IMPACT ON THE FORECAST.
EXTENDED...ONLY CHANGE MADE TO THE REST OF THE FORECAST PACKAGE
WAS TO INCLUDE A SLIGHT CHANCE FOR RAIN SHOWERS ON SUNDAY WHERE
THE ECMWF BRINGS A SHORTWAVE TROUGH THROUGH THE SOUTHERN PLAINS.
CAVANAUGH
&&
.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX 42 55 40 49 40 / 30 5 10 60 80
WACO, TX 45 56 38 49 39 / 80 10 30 80 50
PARIS, TX 43 55 37 51 38 / 40 5 10 40 80
DENTON, TX 41 54 37 49 37 / 20 5 10 60 80
MCKINNEY, TX 43 55 38 50 39 / 30 5 10 60 80
DALLAS, TX 43 55 39 50 40 / 30 5 10 60 80
TERRELL, TX 45 56 40 51 40 / 40 5 10 60 80
CORSICANA, TX 46 57 39 52 39 / 80 5 10 70 70
TEMPLE, TX 45 57 42 49 38 / 80 20 40 80 50
&&
.FWD WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
58/85
