FXUS64 KFWD 021240
AFDFWD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
640 AM CST WED DEC 2 2009
.UPDATE...
CHANGE OVER TO ALL SNOW HAS OCCURRED ACROSS THE NW CWA AS TEMPS
HAVE COOLED DOWN TO NEAR FREEZING. PRECIPITATION BAND IS EXTENSIVE
AND IS RESULTING IN CONTINUED MODERATE SNOW ESPECIALLY OVER
MONTAGUE...WISE COUNTIES. UPDATED FORECAST TO INCLUDE SOME
ACCUMULATION OF 1 INCH OR SO IN THE FORECAST FOR THESE COUNTIES.
MOST OF THE SNOW IS MELTING ON CONTACT OF ROAD SURFACES...BUT WE
ARE GETTING SOME REPORTS OF SLUSH IN A FEW SPOTS. VERY CLOSE TO
DOING A 2-3 COUNTY WINTER ADVISORY...BUT NO DECISION MADE YET DUE
TO LOCALIZED NATURE. OTHERWISE...THE SNOW LINE IS KNOCKING ON THE
NW DOOR OF THE METROPLEX...AND IT IS CONCEIVABLE THAT CHANGE OVER
WILL OCCUR IN METROPLEX WITH CONTINUED PRECIPITATION WORKING ON
COOLING THE LOW LEVEL THERMAL PROFILES. UPDATES SENT.
TR.92
&&
.AVIATION...
/12Z TAFS/
LIGHT RAIN AND POSSIBLY A FEW FLURRIES AT METRO TAF SITES THIS
MORNING WILL TAPER OFF BY 15Z. NORTHWEST WINDS WILL INCREASE TO
15-20 KTS AT ALL SITES BY LATE MORNING...CONTINUING THROUGH THE
AFTERNOON HOURS. IFR CIGS EARLY THIS MORNING WILL LIFT INTO MVFR
BY MID MORNING...FINALLY BECOMING VFR NEAR/SHORTLY AFTER 00Z.
NOTICE...EFFECTIVE AT 15Z THURSDAY DEC 3RD THE NWS IN FORT WORTH
WILL BEGIN 3-HOURLY TAF ISSUANCES FOR KDFW...KDAL...KFTW...KAFW
AND KACT AIRPORTS. THE INTERMEDIATE TAF ISSUANCES AT
03Z...09Z...15Z AND 21Z WILL BE ISSUED AS AMENDMENTS TO THE TAFS
ISSUED AT 00Z...06Z...12Z AND 18Z. THE INTERMEDIATE TAFS WILL BE
ISSUED DURING A 20-MINUTE WINDOW BETWEEN 50 MINUTES AFTER THE HOUR
AND 10 MINUTES AFTER THE HOUR. UPDATED AVIATION FORECAST
DISCUSSIONS WILL BE ISSUED WHENEVER THERE IS A SIGNIFICANT CHANGE
TO THE FORECAST.
&&
.PREV DISCUSSION... /ISSUED 445 AM CST WED DEC 2 2009/
POWERFUL UPPER LEVEL LOW CONTINUES TO TRACK ACROSS TEXAS WITH
IMPRESSIVE BAND OF WRAP AROUND PRECIPITATION AFFECTING THE
NORTHERN HALF OF THE CWA. SNOW HAS FALLEN OVERNIGHT IN THE
ABILENE AREA...BUT SO FAR SURFACE TEMPS HAVE REMAINED WARM ENOUGH
TO PREVENT ANY SNOW IN THE WESTERN PARTS OF THE CWA. AS LOW TRACKS
FARTHER EAST...BELIEVE THERMAL PROFILES WILL COOL SUFFICIENTLY
ACROSS THE NW CWA FOR SNOW TO MIX WITH THE RAIN. BEFORE THE SNOW
REACHES THE GROUND WE WILL SEE SURFACE TEMPS WHICH HAVE BEEN STUCK
AROUND 40 START TO FALL...AS COOLING OCCURS FROM MELTING SNOW
ALOFT ABSORBING HEAT DURING THE PHASE CHANGE. NAM/RUC PARTIAL
THICKNESS AND SOUNDING PROFILES SUGGEST SNOW MAY MIX IN AS FAR
EAST AS THE METROPLEX...BUT WE WILL CONTINUE THE FORECAST OF THE
LAST SEVERAL DAYS AND MENTION IT GENERALLY NW OF A COMANCHE TO
SHERMAN LINE. WILL MONITOR TRENDS IN THE NEXT FEW HOURS FOR ANY
AMENDMENTS TO THIS THINKING.
AS THE UPPER LEVEL LOW PULLS AWAY DURING THE DAY...WRAP AROUND
PRECIPITATION PRIMARILY AFFECTING THE NORTHERN CWA WILL RAPIDLY
COME TO AN END. ISENTROPIC DOWNGLIDE WILL ALSO ASSIST IN ERODING
CLOUD COVER...BUT INCREASING NW WINDS WILL RESULT IN STRONG COLD
ADVECTION. THEREFORE HIGHS WILL REMAIN ON THE COLD SIDE TODAY.
ALTHOUGH WINDS STAY AROUND 5 TO 10 MPH TONIGHT AND CIRRUS CLOUDS
WILL BE MOVING BACK INTO THE AREA...MANY LOCATIONS ACROSS NORTH
TEXAS WILL FALL TO FREEZING AS COLD ADVECTION CONTINUES THROUGH
THE OVERNIGHT HOURS. THIS WILL BE THE FIRST FREEZE FOR LOCATIONS
GENERALLY ALONG AND EAST OF I-35. ALTHOUGH WACO/DENTON ALREADY
FROZE...THEY ARE INCLUDED IN THE FREEZE WARNING FOR AESTHETICS.
BY THURSDAY...MUCH OF THE CONTINENT WILL BE UNDER THE INFLUENCE OF
A LARGE UPPER LEVEL TROUGH THAT WILL SEND A COLD CANADIAN AIRMASS
SOUTHWARD INTO THE PLAINS. MODELS CONTINUE TO ADVERTISE A PACKET
OF POTENTIAL VORTICITY DROPPING SOUTHWARD ON THE WESTERN SIDE OF
THE UPPER TROUGH. AS THIS ENERGY ROUNDS THE BASE OF THE TROUGH
EARLY FRIDAY...RATHER STRONG DYNAMIC LIFT WILL SPREAD OVER THE
REGION. INTENSIFYING ISENTROPIC LIFT WILL LEAD TO SATURATION AND
PRECIPITATION OVER THE AREA BEGINNING FRIDAY MORNING. THERMAL
PROFILES ARE PLENTY COLD ENOUGH FOR SNOW...WHICH MAKES THE PRECIP
TYPE EASY TO FORECAST. THE UNCERTAIN PART OF THE FORECAST IS DUE
TO QUESTIONS ON THE QUALITY OF MOISTURE AND SNOWFALL AMOUNTS. AS A
FORECASTING RULE OF THUMB...MOST OF THE SIGNIFICANT SNOW WILL FALL
GENERALLY TO THE SOUTH OF THE 700 MB FRONT...WHICH IS FORECAST TO
BE DRAPED ALONG I-20. MODELS ARE KEYING IN ON ACCUMULATIONS AND
QPF SOUTH OF THIS FEATURE...WITH THE GREATEST AMOUNTS ACROSS OUR
SOUTHERN ZONES AND FARTHER SOUTH. EVEN THOUGH MODELS DO NOT SHOW
QPF FOR THE NORTHERN ZONES...WE WILL FORECAST LIGHT SNOW THERE TOO
BECAUSE ISENTROPIC LIFT WILL BE OCCURRING ABOVE THE FRONTAL
INVERSION AT 500-700MB. MOISTURE CONTENT GETS LOWER THE HIGHER UP
AND THUS...ACCUMULATIONS/SIGNIFICANT SNOW IS NOT ANTICIPATED...BUT
WE DO EXPECT PERIODS OF VERY LIGHT SNOW TO OCCUR. ACROSS THE
SOUTHERN HALF OF THE CWA...EXPECT GENERALLY 1 INCH OF SNOW...WHICH
AGREES WITH HPC/NAM/SREF MEAN FORECASTS.
SKIES WILL RAPIDLY CLEAR OUT FRIDAY EVENING AND A VERY COLD NIGHT
IS EXPECTED WITH TEMPS DROPPING INTO THE 20S AREA WIDE. AIRMASS
WILL GRADUALLY MODERATE INTO THE WEEKEND AND NEXT WEEK...BUT AGAIN
THE MEX MOS IS LIKELY TRENDING TOWARD CLIMO AND IS TOO QUICK WITH
THE WARM UP. THERE WILL BE A LOW CHANCE OF SHOWERS IN THE EAST ON
SUNDAY AS A SHORTWAVE MOVES ACROSS. ANOTHER CHANCE OF RAIN IS
POSSIBLE ON TUESDAY...BUT MODEL CONSISTENCY IS LOW.
TR.92
&&
.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX 49 33 48 35 41 / 90 0 0 10 20
WACO, TX 50 32 50 34 38 / 30 0 0 10 60
PARIS, TX 45 31 46 30 44 / 100 0 0 10 10
DENTON, TX 48 31 47 31 41 / 100 0 0 10 20
MCKINNEY, TX 47 31 47 31 42 / 100 0 0 10 10
DALLAS, TX 47 34 48 36 41 / 90 0 0 10 20
TERRELL, TX 47 32 48 33 41 / 90 0 0 10 20
CORSICANA, TX 48 32 48 34 40 / 60 0 0 10 40
TEMPLE, TX 52 32 51 34 38 / 20 0 0 10 60
&&
.FWD WATCHES/WARNINGS/ADVISORIES...
FREEZE WARNING FROM 3 AM TO 9 AM CST THURSDAY FOR TXZ092>095-
103>107-118>123-133>135-145>148-158>162-174-175.
&&
$$
21/92
