FXUS64 KFWD 301745
AFDFWD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
1145 AM CST MON NOV 30 2009
.AVIATION...
FOR THE 18Z TAFS...VFR CONDITIONS LOOK TO HOLD OVER TAF SITES OVER
THE NEXT 24 HRS...AFTER WHICH CONDITIONS ARE EXPECTED TO
DETERIORATE FOR ALL SITES IN NORTH TX. AN APPROACHING UPPER LVL
STORM SYSTEM WILL LIKELY KEEP SOME MID TO HIGH LVL CLOUDS OVER TAF
SITES THROUGHOUT THE PERIOD. THIS SYSTEM BEGINS TO MOVE NORTHEAST
TOWARDS TAF SITES DURING THE DAY ON TUESDAY...SPREADING
PRECIPITATION CHANCES FROM SOUTHWEST TX NORTHEAST TOWARDS TAF
SITES PROGRESSIVELY THROUGHOUT THE DAY. ACT LOOKS TO BEGIN SEEING
RAIN CHANCES JUST BEFORE SUNRISE...WITH NEAR STEADY PRECIPITATION
MOVING OVER THE AIRPORT TOWARDS 18Z. PRECIP CHANCES LOOK TO BEGIN
AT THE METROPLEX SITES JUST BEFORE 18Z...BECOMING LIKELY AFTER
21Z. WHEN PRECIPITATION BECOMES WIDESPREAD OVER NORTH TX FLIGHT
CATEGORIES ARE EXPECTED TO DETERIORATE RAPIDLY. LOW MVFR TO IFR
CONDITIONS BECOME LIKELY FOR ACT AFTER 18Z AND THEN FOR METROPLEX
SITES AFTER 00Z WED.
TODAY...VFR.
TONIGHT...VFR. CIGS WILL LOWER THRU SUNRISE BUT REMAIN VFR.
TUESDAY...STARTING OFF VFR. PRECIP LIKELY AT ACT AOA 18Z. MVFR/IFR
CIGS AND VSBY POSSIBLE ONCE RAIN SHOWER ACTIVITY BEGINS.
CAVANAUGH
&&
.UPDATE...
OVERALL THE CURRENT FORECAST IS ON TRACK. DID MAKE A FEW MINOR
ADJUSTMENTS TO MAXIMUM TEMPERATURES IN THE SOUTH WHERE
OVERCAST/BROKEN CLOUD COVER IS EXPECTED TO PERSIST FOR MUCH OF THE
DAY...LIMITING THE AMOUNT OF HEATING IN THAT AREA. WIDESPREAD
LIGHT RAIN CONTINUES ACROSS THE SOUTHERN HALF OF TEXAS WITH
ADDITIONAL LIGHT RAIN DEVELOPING IN WEST AND SOUTHWEST TEXAS. SOME
LIGHT RAIN IS STILL POSSIBLE IN THE FAR SOUTHERN COUNTIES OF NORTH
TEXAS FOR THE REMAINDER OF THE DAY...BUT MOST OF THE PRECIPITATION
IS EXPECTED TO REMAIN SOUTH OF THE CWA.
82/JLD
&&
.PREV DISCUSSION... /ISSUED 422 AM CST MON NOV 30 2009/
COLD FRONT HAS MOVED THROUGH AND LOW-MID LEVEL MOISTURE/CLOUDS ARE
GRADUALLY ERODING FROM NORTH TO SOUTH AS ISENTROPIC DOWNGLIDE
OCCURS IN THE WAKE OF YESTERDAY/S COLD FRONT. HOWEVER...THE FAR
SOUTHERN ZONES WILL HAVE A LOW CHANCE OF SOME LIGHT RAIN OR
SPRINKLES TODAY AS ISENTROPIC LIFT AT 310K /OR NEAR 600 MB/
CONTINUES THERE. MEANWHILE UPPER LEVEL LOW OVER BAJA HAS TAPPED
INTO THE SUBTROPICAL PACIFIC AND WILL KEEP CIRRUS STREAMING IN
ACROSS THE AREA. HIGH TEMPS TODAY ARE LARGELY A FUNCTION OF
SUNSHINE...AND THUS EXPECT THE COOLEST TEMPS TO BE IN THE SOUTH.
UPPER LEVEL LOW OVER BAJA WILL GRADUALLY MOVE EASTWARD TODAY...AND
AS IT GETS CLOSER...FLOW ON ALL THE ISENTROPIC SURFACES FROM
310K DOWN TO 290K WILL BEGIN TO SLOPE UPWARD. CLOUDS AT SEVERAL
LEVELS WILL DEVELOP AND THICKEN AS SATURATION IS REACHED. EXPECT
RAIN TO FORM OVER THE SW ZONES LATE TONIGHT AND SPREAD INTO NORTH
TEXAS FROM SOUTHWEST TO NORTHEAST TUESDAY. RAIN CHANCES LOOK GOOD
TUESDAY AFTERNOON INTO TUESDAY NIGHT OVER THE ENTIRE AREA AS
FAVORABLE MOISTURE FLUX AND LIFT OCCURS AHEAD OF THE UPPER LEVEL
LOW. QPF OF 1-2 INCHES IS EXPECTED...WHICH MAY BE SUFFICIENT FOR
HYDROLOGIC RESPONSES IN AREA STREAMS/RIVERS...BUT FLASH FLOODING
THREAT SHOULD BE LIMITED BY EVENT OF LOW INTENSITY/LONG DURATION.
THE UPPER LEVEL LOW WILL FINALLY LUMBER ACROSS NORTH TEXAS
WEDNESDAY MORNING. MODELS CONTINUE TO SHOW THICKNESS VALUES COLD
ENOUGH FOR SNOW IN THE CORE AND NORTHERN SIDE OF THE UPPER LEVEL
LOW. HOWEVER...CLOSER INSPECTION SHOWS SURFACE TEMPS /AND WET
BULBS/ WILL BE SEVERAL DEGREES ABOVE FREEZING TUESDAY NIGHT AHEAD
OF THE LOW. THERE IS NO SHORTAGE OF COLD AIR IN THE MID-UPPER
LEVELS FOR SNOW...THE INHIBITING FACTOR IS THE WARM LOW LEVEL
TEMPS. SINCE THERE WILL BE LITTLE WET BULB COOLING OR COLD
ADVECTION TUESDAY NIGHT...THE ONLY MECHANISM LEFT TO FORCE LOW
LEVEL TEMPS COLDER IS LATENT HEAT ABSORPTION CAUSED BY THE MELTING
OF FALLING SNOW. TYPICALLY THIS REQUIRES A FAIRLY LARGE AMOUNT OF
MELTING SNOW...AND THUS ONLY OCCURS IN HEAVY PRECIPITATION AREAS.
SIGNIFICANT CLOUD LEVEL SNOW IS EXPECTED TO OCCUR MAINLY ON THE
BACKSIDE OR NW SIDE OF THE UPPER LEVEL LOW...WHICH SUGGESTS THE
WESTERN AND NORTHWESTERN ZONES OF NORTH TEXAS WILL HAVE THE BEST
CHANCES OF SEEING ANY SNOW REACH THE GROUND LATE TUESDAY NIGHT AND
WEDNESDAY MORNING. EVEN IF SNOW DOES REACH THE GROUND IN THESE
LOCATIONS...SIGNIFICANT ACCUMULATIONS ARE NOT EXPECTED.
AS THE LOW CLEARS THE AREA ON WEDNESDAY...STRONG NW WINDS...COLD
ADVECTION AND RAPID CLEARING IS EXPECTED BY THE AFTERNOON WITH A
WIDESPREAD FREEZE LIKELY WEDNESDAY NIGHT. MODELS BEGIN TO DIVERGE
WITH THE EVOLUTION OF THE UPPER PATTERN ACROSS NORTH AMERICA.
BELIEVE THE GFS IS TOO QUICK TO MOVE THE UPPER TROUGH OFF TO THE
EAST AS THE NEXT WAVE FORMS OVER THE NORTHERN ROCKIES. THUS THE
GFS WARMS US UP VERY QUICKLY AND EVEN SHOWS ENOUGH MOISTURE RETURN
FOR RAIN BY SATURDAY. AT THIS TIME...FAVORING THE ECMWF/CANADIAN
WHICH SHOW A COLD AND DRY FORECAST THROUGH THE WEEKEND AS CANADIAN
HIGH SETTLES IN THE REGION. HAVE UNDERCUT THE MEX MOS TEMPS 5-10
DEGREES ACROSS THE BOARD WEDNESDAY THROUGH MONDAY.
TR.92
&&
.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX 57 39 51 39 48 / 0 5 70 80 40
WACO, TX 56 42 47 39 47 / 10 20 80 80 20
PARIS, TX 59 35 53 39 47 / 0 0 40 70 70
DENTON, TX 57 36 51 38 48 / 0 5 70 80 50
MCKINNEY, TX 58 35 52 39 48 / 0 0 60 80 50
DALLAS, TX 58 41 51 40 47 / 0 5 70 80 40
TERRELL, TX 58 38 51 40 47 / 0 5 70 80 50
CORSICANA, TX 58 41 50 40 48 / 5 10 70 80 40
TEMPLE, TX 54 44 47 38 50 / 30 30 90 80 20
&&
.FWD WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
