FXUS64 KFWD 301113 AAA
AFDFWD
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE FORT WORTH TX
513 AM CST MON NOV 30 2009
.AVIATION...
/12Z TAFS/
VFR CONDITIONS TO CONTINUE. BROKEN TO OVERCAST HIGH CLOUDS WILL
PERSIST. WINDS WILL GRADUALLY SHIFT FROM THE NORTH TO NORTHEAST
TONIGHT...AND EVENTUALLY TO THE EAST BY MID MORNING TUESDAY. CLOUD
DECKS WILL GRADUALLY LOWER TUESDAY MORNING...BUT SHOULD REMAIN VFR
THROUGH 12Z AT WACO AND 18Z AT METROPLEX SITES. RAIN SHOWERS ARE
LIKELY AT WACO AFTER 12Z TUESDAY...MOVING INTO THE METROPLEX BY
MIDDAY.
&&
.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 / 20 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 / 10 10 70 80 40
TEMPLE, TX 54 44 47 38 50 / 30 30 90 80 20
&&
.FWD WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
