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000
FXUS64 KFWD 040525 AAD
AFDFWD

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE FORT WORTH TX
1125 PM CST TUE DEC 3 2013

.AVIATION...
/06Z TAFS/

CONCERNS...ARRIVAL OF FRONT AT THE DFW TAF SITES TOMORROW AFTERNOON.

AN ARCTIC FRONT IS QUICKLY MAKING ITS WAY DOWN THE PLAINS AND WILL
ARRIVE IN NORTH TEXAS SEVERAL HOURS SOONER THAN PREVIOUSLY
THOUGHT. THROUGH TONIGHT...SOUTH TO SOUTHWEST WINDS BELOW 10 KTS
WILL PREVAIL. IN THE DFW AREA...THE WINDS WILL BECOME MORE
WESTERLY AROUND 16Z. THE LEADING EDGE OF THE FRONT WILL SLOWLY
AND QUIETLY SEEP THROUGH DFW AROUND 20-21Z TOMORROW AFTERNOON.
THE WINDS MAY ACTUALLY BE LIGHT AND VARIABLE FOR A FEW HOURS AS
THE FRONT STALLS NEAR THE I-20 CORRIDOR BUT NORTH WINDS SHOULD
PREVAIL BY THE EVENING HOURS. WIND SPEEDS WILL INCREASE OVERNIGHT
WITH STRONGER WINDS BETWEEN 15-20 KTS ON THURSDAY.

THE FRONT WILL NOT REACH KACT IN THIS TAF PERIOD AND EXPECT SOUTH
TO SOUTHWEST WINDS TO PREVAIL THROUGH THE PERIOD. THE FRONT WILL
ARRIVE TOMORROW NIGHT...JUST BEYOND THE TIMING OF THIS TAF PERIOD.

IN THE EXTENDED...FROZEN PRECIPITATION NOW APPEARS MORE LIKELY AT
THE DFW TAF SITES AS EARLY AS THURSDAY EVENING AND IS A
POSSIBILITY AT WACO EARLY FRIDAY MORNING.

82/JLD

&&

.UPDATE...
THE MAIN UPDATE ISSUE OF INTEREST IS THAT WE HAVE EXPANDED THE
WINTER STORM WATCH TO COVER THE NW HALF OF NORTH TEXAS. BUT FOR
TONIGHTS FORECAST HAVE LOWERED TEMPERATURES IN A FEW AREAS WHERE
DRY AIR AND GOOD RADIATIONAL COOLING ARE EXPECTED. HAVE ALSO ADDED
A MENTION OF FOG TO THE EAST AND SOUTHEAST ZONES WHERE
TEMPERATURES WILL COOL TO REACH THE DEWPOINTS.

WITHOUT EVEN LOOKING AT THE MODEL DATA THE 0Z UPPER AIR ANALYSIS
FOREBODES AN OMINOUS SETUP FOR WINTER WEATHER FOR NORTH TEXAS. THE
UPPER PATTERN SUGGESTS THAT AT SOME POINT IN THE NEXT FEW
DAYS...EITHER THURSDAY NIGHT/FRIDAY AND/OR THIS WEEKEND THE
COMBINATION OF COLD AIR AND MOISTURE/LIFT ARE GOING TO COME INTO
PLAY TO CREATE A WINTRY MIX OVER MUCH OF THE AREA.

WHILE SURFACE TEMPS ARE THE GO-TO FOR SEEING HOW COLD AN AIR MASS
IS...IT IS ACTUALLY BETTER TO ANALYZE THE LOW-MID LEVEL TEMPS
UPSTREAM TO SEE HOW COLD THE AIR IS THERE. THIS IS BECAUSE AIR
BEHIND A COLD FRONT UNDERGOES SLOW SUBSIDENCE AS IT MAKES ITS WAY
SOUTH FROM THE ARCTIC. BACKWARD TRAJECTORIES OF PAST COLD FRONTS
SHOW US TO CHECK 500-700MB TEMPS IN THE ARCTIC REGION SEVERAL DAYS
OUT...AND 700-850MB TEMPS ACROSS SOUTHERN CANADA 2 TO 3 DAYS OUT
TO GET A ROUGH IDEA ON HOW COLD IT IS GOING TO GET. THUS IT IS
CONCERNING THAT THE UPPER AIR ANALYSIS FROM 00Z REVEALS
EXCEPTIONALLY COLD AIR AT 700MB-850MB ACROSS MONTANA AND INTO
ALBERTA. GREAT FALLS MONTANA HAD A 700MB TEMP OF -24C AND -20C AT
850MB. THESE TEMPS ARE RUNNING 2 TO 3 STANDARD DEVIATIONS BELOW
NORMAL...WHICH IS AKIN TO SAYING THIS WOULD BE NEAR RECORD COLD
IF WE KEPT RECORDS AT THIS POINT IN SPACE. MODEL GUIDANCE HAS BEEN
2-4 DEG C TOO WARM WITH 6-12 HOUR FORECAST TEMPS AT THIS LEVEL AS
WELL...BUT IS BEGINNING TO CATCH ON.

MEANWHILE THE SURFACE ANALYSIS IS SHOWING THE COLD FRONT
BARRELING SOUTH THROUGH THE PLAINS...AND AHEAD OF SCHEDULE...NOW
CROSSING THROUGH MOST OF WESTERN KANSAS. ALL MODELS EXCEPT FOR THE
RAP/NAM ARE MUCH TOO SLOW IN THEIR 3-6 HOUR FORECASTS. THIS IS A
COMMON ISSUE WITH ARCTIC FRONTS WHEN THE 500MB PATTERN IS SITUATED
IN THIS FASHION. LEE SIDE COLD AIR DAMMING IN THE FRONT RANGE OF
THE ROCKIES CAUSES THE SURFACE HIGH TO BUILD FARTHER SOUTH AND
ALLOWS FOR STRONGER EQUATOR-WARD TRANSPORT OF ARCTIC AIR THAN
FORECAST. HIGH RESOLUTION MODELS DO A BETTER JOB AT FORECASTING
THIS...AND THE NAM/WRF MODELS ARE ABOUT THE BEST WE HAVE IN THE
SHORT-MEDIUM TIME RANGE. THE RAP IS EXCELLENT IN THIS SITUATION AS
WELL...BUT ONLY GOES OUT 18 HOURS. THE NAM AND RAP MODELS ARE
INDICATING THE FRONT WILL REACH THE NORTHWEST ZONES AFTER
SUNRISE...AND WILL LIKELY STALL ALONG OR JUST NORTH OF THE I-20
CORRIDOR WEDNESDAY AFTERNOON. THE AIR BEHIND THIS FRONT WILL BE
VERY SHALLOW...AND SUNSHINE WILL MODERATE THE LEADING EDGE OF THIS
AIR GREATLY. THUS HAVE BUMPED UP THE TIMING OF THE FRONT SEVERAL
HOURS AND LOWERED HIGHS INTO THE 60S IN THE NORTHERN ZONES.
WOULD NOT BE SURPRISED TO SEE THE FRONT MOVE THROUGH THE METROPLEX
IN THE AFTERNOON HOURS BUT AGAIN...THE CHANGE IN TEMPS AND WINDS
WILL NOT BE ALL THAT DRASTIC AT FIRST. THE REAL COLD AIR WILL
GRADUALLY INVADE THE REGION THROUGH THE OVERNIGHT HOURS.

THE NEW 00Z NAM HAS COME IN COLDER THURSDAY...AND ESSENTIALLY ALL
GUIDANCE BUT THE SREF IS INDICATING TEMPERATURES NEAR FREEZING
ACROSS THE NORTHWEST ZONES THURSDAY AFTERNOON AS PRECIPITATION
BEGINS TO DEVELOP. SINCE THE AIR IS SO COLD UPSTREAM IN THE SOURCE
REGION...AND THESE FRONTS TEND TO RUN A LITTLE COLDER THAN
MODEL FORECASTS...HAVE BUMPED UP THE TIMING OF THE FREEZING RAIN
AND WINTER STORM WATCH TO THURSDAY AFTERNOON OVER THE NORTHWEST
ZONES. IT IS TOO TOUGH TO SAY WHETHER IMPACTS WILL BEGIN
IMMEDIATELY THURSDAY AFTERNOON...BUT FELT THAT THE WATCH STARTING
AT 0Z WAS CUTTING IT TOO CLOSE.

AGAIN THERE IS GOOD MODEL AGREEMENT REGARDING THE FORECAST FOR
THURSDAY NIGHT AND FRIDAY. HAVE NOT CHANGED ANY OF THE FORECASTED
SENSIBLE WEATHER FROM THE PREVIOUS FORECAST AS IT ALL LOOKS
GOOD. HOWEVER...THERE MAY END UP BEING MORE SLEET THAN FREEZING
RAIN OVER THE NORTHWEST ZONES BUT IT IS TOO EARLY TO TELL FOR
SURE. HOWEVER PLACING A PERCENT LIKELIHOOD OF WINTER STORM WARNING
CRITERIA BEING MET IS TOUGH AT THIS POINT. WPC NOW INDICATES THE
DFW METROPLEX AND NORTHEAST INTO PARIS HAVE A 50-60 PERCENT CHANCE
OF A QUARTER INCH OF ICE ACCUMULATION THURSDAY NIGHT AND FRIDAY
MORNING. WATCH CRITERIA THRESHOLD IS A 50 PERCENT CONFIDENCE LEVEL
WHILE WARNING IS 80 PERCENT. SO GOING BY THIS PIECE OF GUIDANCE WE
SHOULD ISSUE A WATCH NOW. HOWEVER IT IS CONCERNING THE SREF IS
STILL FORECASTING A MARGINAL FREEZING RAIN EVENT FOR THIS REGION
WHICH LOWERS OUR CONFIDENCE. IT IS ALSO CONCERNING THAT THE WARM
NOSE WILL BE VERY WARM...AND RAIN DROPS WILL LIKELY TRANSPORT WARM
AIR TO THE SURFACE...WHICH WOULD INHIBIT ICE ACCUMULATION AND
IMPACTS. ON THE FLIP SIDE IT IS VERY CONCERNING THAT THE AIR
TEMPERATURES MAY STAY BELOW FREEZING FOR MUCH OF THE CWA FRIDAY
AND SATURDAY WITH CLOUDY SKIES. THIS MEANS IF ICE AND/OR SLEET IS
SIGNIFICANT THURSDAY NIGHT AND FRIDAY MORNING...ICE ON ROADS MAY
LINGER INTO SATURDAY OR SUNDAY WHEN COINCIDENTALLY ANOTHER SHOT AT
WINTER PRECIP ARRIVES. THE ISSUE IS THAT THIS EVENT UNLIKE THE
LAST MARGINAL/NON-EVENT DOES HAVE THE POTENTIAL FOR PROLONGED
WINTRY IMPACTS WHICH IS MORE REASON TO RAISE PUBLIC AWARENESS NOW
AND GO AHEAD AND EXPAND THE WATCH SOUTHEASTWARD TO INCLUDE MORE
AREA.

NOTE THIS DOES NOT MEAN THE ENTIRE WATCH AREA WILL BE UPGRADED TO
A WARNING...BUT AT THIS POINT WE BELIEVE THE ENTIRE WATCH AREA
WILL BE IN AT LEAST A WINTER WEATHER ADVISORY THURSDAY NIGHT AND
FRIDAY MORNING. IT IS TOO EARLY TO FINE TUNE ACCUMULATION AMOUNTS
OR ENTERTAIN WHO WILL SEE WHAT IMPACTS...AND THOSE WILL COME LATER
AS CONFIDENCE INCREASES FURTHER.

TR.92



&&

.PREV DISCUSSION... /ISSUED 356 PM CST TUE DEC 3 2013/

WE ARE ISSUING A WINTER STORM WATCH FROM AREAS ALONG AND NORTHWEST
OF A BRECKENRIDGE TO GAINESVILLE LINE FOR THURSDAY NIGHT THROUGH
FRIDAY. CONFIDENCE IS HIGH ENOUGH WITHIN THIS AREA TO MEET
WARNING CRITERIA OF 1/4 INCH OR MORE OF ICE.

THE ARCTIC FRONT WILL MOVE SOUTH OF THE RED RIVER WEDNESDAY
EVENING AND OUT OF THE SOUTHERN COUNTIES BY MIDDAY THURSDAY.
TEMPERATURES WILL FALL RAPIDLY BEHIND THE FRONT AS TEMPERATURES
UPSTREAM ARE IN THE LOW TEENS OVER WYOMING AND IN THE SINGLE
DIGITS IN CANADA.

PRECIPITATION WILL BE MOSTLY POST-FRONTAL THURSDAY NIGHT-FRIDAY
WITH MODERATE RAINFALL POSSIBLE ALONG A COMANCHE TO PARIS LINE
WHERE RICK ELEVATED MOISTURE MOVES OVER THE ELEVATED FRONTAL
BOUNDARY. THE RAIN WILL CHANGE TO FREEZING RAIN OVER THE
NORTHWEST COUNTIES THURSDAY EVENING AND PROGRESS SOUTHEASTWARD
WITH THE 32F ISOTHERM TO NEAR A SULPHUR SPRINGS TO GOLDTHWAITE
LINE ON FRIDAY. DUE TO UNCERTAINTY IN THE DEPTH OF THE COLD
AIR...WARM SOILS/STREETS...LATENT HEAT RELEASE OF RESIDUAL WATER
FROM RAINFALL AND THE STRENGTH OF THE WARM NOSE ALOFT...THE
LOCATION OF THE RAIN/FREEZING RAIN TRANSITION ZONE WAS HARD TO
DETERMINE... BUT CONFIDENCE WAS HIGH ENOUGH TO ISSUE A WATCH FOR
THE NORTHWEST COUNTIES WITH THIS PACKAGE. THE WATCH MAY BE PUSHED
FURTHER SOUTHEAST IF FUTURE MODEL RUNS PRODUCE HIGHER CONFIDENCE
THAT SIGNIFICANT ICE ACCUMULATIONS WILL OCCUR ELSEWHERE.

THERE WILL BE A LULL IN THE PRECIPITATION FRIDAY NIGHT AS THE
UPPER DISTURBANCE MOVES EAST OF THE REGION. ISENTROPIC UPGLIDE AND
ANOTHER UPPER DISTURBANCE WILL BRING PRECIPITATION BACK TO THE
REGION SATURDAY THROUGH SUNDAY. THIS PRECIPITATION WILL BE LIGHTER
THAN THE PREVIOUS ROUND...BUT WILL BE SLEET AND FREEZING RAIN
DURING THE OVERNIGHT HOURS...BUT GENERALLY LIQUID WHERE DAYTIME
TEMPS WARM ABOVE FREEZING.

THIS WILL BE THE COLDEST AIR OF THE SEASON SO FAR WITH LOWS IN THE
TEENS AND 20S ON SEVERAL NIGHTS. DAYTIME TEMPS WILL TREND WARMER
SUNDAY AND MONDAY...BUT A REINFORCING SHOT OF ARCTIC AIR IS
EXPECTED TO SEND US BACK INTO THE ICEBOX BY TUESDAY MORNING.

75



&&


.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX  55  77  38  44  28 /   0   5  20  60  90
WACO, TX              49  80  50  52  31 /   0   5  20  50  90
PARIS, TX             49  74  39  45  29 /   0   5  20  70  90
DENTON, TX            49  72  36  39  26 /   0   5  20  60  80
MCKINNEY, TX          48  75  38  42  27 /   0   5  20  60  90
DALLAS, TX            56  79  38  45  28 /   0   5  20  60  90
TERRELL, TX           52  77  42  47  29 /   0   5  20  60  90
CORSICANA, TX         54  77  50  50  31 /   0   5  20  60  90
TEMPLE, TX            52  81  56  56  32 /   0   5  20  50  80
MINERAL WELLS, TX     47  76  36  40  25 /   0   5  20  60  80

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM THURSDAY EVENING THROUGH FRIDAY
AFTERNOON FOR TXZ094-095-104>107-118>120-130>133-141>144.

WINTER STORM WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY
AFTERNOON FOR TXZ091>093-100>103-115>117-129.


&&

$$

82/92