Area Forecast Discussion
Issued by NWS Dallas/Fort Worth, TX

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000
FXUS64 KFWD 222200
AFDFWD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
400 PM CST MON DEC 22 2014

.DISCUSSION...
A COLD FRONT IS SWEEPING THROUGH NORTH TEXAS. POSTFRONTAL
TEMPERATURES HAVE FALLEN INTO THE 50S NORTH AND NORTHWEST OF THE
DALLAS/FORT WORTH METROPLEX. AHEAD OF THE BOUNDARY...WHERE WINDS
HAVE VEERED TO THE SOUTHWEST...TEMPERATURES HAVE SOARED INTO THE
70S. THE WARM SUNNY WEATHER WILL BE SHORT-LIVED...WITH COLD AIR
FILTERING INTO CENTRAL AND EAST TEXAS THIS EVENING.

A STRONGLY AMPLIFIED MID-LEVEL TROUGH IS DIGGING INTO WEST TEXAS.
THE EXPANDING CANOPY OF MID CLOUDS IS EVIDENCE OF THE LIFT
ASSOCIATED WITH THIS FEATURE. THIS TROUGH WILL SWING THROUGH THE
LONE STAR STATE TONIGHT AND TUESDAY...WITH COLD AIR INVADING AT
THE SURFACE. AT A GLANCE...THIS MIGHT APPEAR TO HAVE THE MAKINGS
OF A WINTER WEATHER EVENT. BUT EVEN WITH SATURATION AND ADEQUATE
LIFT WITHIN THE DENDRITIC GROWTH ZONE...THE POSTFRONTAL AIR IN THE
LOW-LEVELS STILL APPEARS TO BE TOO WARM FOR SNOW AT THE SURFACE.
ACROSS OKLAHOMA AND KANSAS...LATE MORNING TEMPS HAD ALREADY
EXCEEDED NORMAL HIGHS FOR THIS TIME OF YEAR DESPITE GUSTY
NORTHERLY WINDS. ALTHOUGH MID CLOUDS HAVE SOMEWHAT OBSCURED THE
SUN...CONSIDERABLE MODERATING OF THE POSTFRONTAL AIR MASS
CONTINUES...WITH AFTERNOON TEMPERATURES ALSO ABOVE SEASONAL
NORMALS. BASED ON THESE TRENDS UPSTREAM...IT APPEARS SUFFICIENTLY
COLD LOW-LEVEL AIR IS UNLIKELY TO BE IN PLACE DURING THIS EVENT.

12Z GUIDANCE WAS MUCH MORE BULLISH ON THE INTENSITY AND AREAL
COVERAGE OF THE RESULTING PRECIPITATION...WITH THE 18Z RUNS
CONCURRING. WITH INCREASING CONFIDENCE...RAIN CHANCES HAVE BEEN
SIGNIFICANTLY INCREASED. PRECIPITATION ABOVE THE 850MB FRONT WILL
ENTER WESTERN ZONES AS EARLY AS THIS EVENING...SPREADING EASTWARD
ACROSS NORTH TEXAS TUESDAY MORNING. STRONG FRONTOGENETIC FORCING
850-700MB WILL RESULT IN BANDED PRECIPITATION THAT WILL PIVOT
COUNTERCLOCKWISE AS THE DAY PROGRESSES. ALTHOUGH THERMAL PROFILES
ARE UNSUPPORTIVE OF DEEP UPRIGHT CONVECTION...THIS SLANTWISE
INSTABILITY CAN ENHANCE PRECIPITATION EFFICIENCY. QPF AMOUNTS
GENERALLY RANGE FROM 1/10 TO 1/2 INCH...WITH THE HIGHEST AMOUNTS
ALONG THE I-20 CORRIDOR WHERE THE DURATION OF PRECIPITATION IS
EXPECTED TO BE MAXIMIZED.

WHEN UPDRAFTS OCCUR IN AN ENVIRONMENT OF ELEVATED CAPE SUFFICIENT
TO PRODUCE LIGHTNING...THIS THERMAL PROFILE COULD SUPPORT A
SLEET/HAIL HYBRID OF ICE PELLETS IN THE STRONGER CELLS. HOWEVER...
IN PRECIP BANDS RESULTING FROM CONDITIONAL SYMMETRIC INSTABILITY
(CSI)...THE VERTICAL MOTIONS ARE LESS VIGOROUS. EVEN IN THE
PRESENCE OF GRAUPEL...LIGHTNING IS UNLIKELY TO OCCUR. HOWEVER...
SNOW WILL BE GENERATED IN LARGE QUANTITIES IN THESE UPDRAFTS.
WHILE IT IS POSSIBLE THAT SOME OF THESE WET FLAKES COULD REACH THE
SURFACE...IT WILL BE DIFFICULT TO OVERCOME THE WARMER BOUNDARY
LAYER. AT THIS TIME...IT APPEARS THESE SLOW-FALLING FLAKES WILL
HAVE A LONG JOURNEY THROUGH A 3000-4000FT LAYER OF AIR WITHIN
WHICH TEMPS WILL BE ABOVE FREEZING. DURING THE PRECIPITATION...
SURFACE TEMPS WILL BE GENERALLY IN THE 40S. AS A RESULT...WE HAVE
MAINTAINED A FORECAST WITH ONLY LIQUID RAIN.

AFTER THE SHORTWAVE SWINGS PAST...ANOTHER REINFORCING SHOT OF COLD
AIR WILL INVADE. CLOUD COVER MAY LINGER TUESDAY NIGHT...BUT THERE
IS THE POTENTIAL FOR A FREEZE IN WESTERN COUNTIES WEDNESDAY
MORNING. A MORE WIDESPREAD FREEZE LIKELY CHRISTMAS MORNING. DESPITE
THE CHILLY START TO THE DAY ON THURSDAY...AFTERNOON TEMPERATURES
SHOULD REACH THE 60S ACROSS NEARLY ALL OF NORTH AND CENTRAL TEXAS.
RELATIVE HUMIDITY VALUES WILL FALL BELOW 35 PERCENT REGIONWIDE...
WITH GUSTY SOUTH WINDS. EVEN WITH A WETTING RAIN ON TUESDAY...
DORMANT VEGETATION COULD BE SUFFICIENTLY DRIED TO BE CONDUCIVE TO
FIRE INITIATION AND SPREAD.

THE PROGRESSIVE PATTERN WILL CONTINUE WITH ANOTHER COLD FRONT
ARRIVING FRIDAY OR FRIDAY NIGHT. CURRENT FORECAST FAVORS THE
FASTER GFS/CANADIAN...WITH A FRIDAY AFTERNOON FROPA. A TRAILING
SHORTWAVE WILL SWING THROUGH ON SATURDAY...WITH CHILLY POSTFRONTAL
TEMPERATURES. ALTHOUGH FORECAST LOWS MAY DIP TO NEAR FREEZING IN
NORTHWEST ZONES...WILL KEEP ALL OF THE PRECIPITATION IN LIQUID
FORM AT THIS TIME. THE PRECIPITATION SHOULD COME TO AN END BEFORE
TEMPERATURES FALL BELOW FREEZING ACROSS MUCH OF THE REGION SUNDAY
MORNING.

25

&&

.AVIATION...
/ISSUED 1155 AM CST MON DEC 22 2014/

FOR THE 18Z TAFS...TIMING THE WIND SHIFT ASSOCIATED WITH A COLD
FRONTAL PASSAGE AT THE START OF THE FORECAST PERIOD...AND TIMING
THE ONSET OF RAIN TOMORROW MORNING ARE THE PRIMARY FORECAST
CHALLENGES.

A COLD FRONT WAS MOVING ACROSS THE DFW AREA BETWEEN 17 AND
18Z...SO STARTED THE TAFS OFF ASSUMING THE FRONT HAD JUST PASSED
THROUGH MOST LOCAL AREA AIRPORTS BEGINNING AT 18Z. WINDS WILL
INITIALLY BE WEST-NORTHWEST BEHIND THE LEADING EDGE OF THE
FRONT...BUT SHOULD VEER TO THE NORTHWEST A COUPLE OF HOURS BEHIND
THE FRONT. THE STRENGTH OF THE WINDS WHILE OUT OF THE WEST-
NORTHWEST ARE EXPECTED TO BE WEAK ENOUGH TO PREVENT SIGNIFICANT
CROSSWIND ISSUES. 10-15 KT WINDS ARE EXPECTED DURING THIS TIME.
WINDS WILL LIKELY PICK UP TO 15 KTS WITH SOME HIGHER GUSTS ONCE
WINDS VEER TO THE NORTHWEST LATER THIS AFTERNOON.

THE CONSENSUS OF 12Z MODEL DATA HAS CAUSED A SIGNIFICANT INCREASE
IN THE FORECAST CONFIDENCE FOR RAIN ACROSS THE DFW AREA TOMORROW
MORNING. MORNING DETERMINISTIC MODEL RUNS ALL SHOW A VERY STRONG
BAND OF FRONTOGENETIC FORCING FROM 850 TO 700 MB SLOPED OVER THE
DFW AREA TOMORROW MORNING. MODELS ALSO SHOW THAT THE ATMOSPHERE IS
CONDITIONALLY UNSTABLE TO SLOPED VERTICAL MOTIONS ALONG THIS
ELEVATED FRONT...SO EXPECT BANDED LIGHT TO MODERATE RAIN SHOWER
ACTIVITY TO IMPACT THE TAFS FOR MUCH OF THE PERIOD BETWEEN 12 AND
18Z TOMORROW.

MODELS ARE COLD ENOUGH FOR SNOW FROM NEAR THE 850 MB LEVEL
UPWARDS...SO ONCE AIRCRAFT CLIMB ABOVE THE 850 MB LEVEL...THEY
WILL BE DOING SO THROUGH LIGHT TO MODERATE SNOWFALL. HOWEVER...ALL
MODEL GUIDANCE HAS THE ATMOSPHERE BELOW THE 850 MB LEVEL WELL
ABOVE FREEZING...SO ALL SNOW IS EXPECTED TO MELT BEFORE REACHING
THE GROUND AT THIS TIME. MODEL DEW POINTS AT THE SURFACE ARE IN
THE LOWER 40S...SO CONFIDENCE IN ALL ALL-LIQUID FORECAST IS FAIRLY
HIGH. ALSO...UPSTREAM SURFACE OBSERVATIONS ACROSS THE CENTRAL
PLAINS ARE IN THE MID-40S...SO THERE`S REALLY NO REASON FOR
SIGNIFICANT COOLING IN THE LOWER ATMOSPHERE OVER THE NEXT 24
HOURS.

RAINFALL IS EXPECTED TO END FROM NORTHWEST TO SOUTHEAST ACROSS THE
REGION TOMORROW AFTERNOON. FORECAST SOUNDINGS SHOW CIGS HOLDING AT
VFR LEVELS AT THIS TIME...ALTHOUGH PERIODS OF MVFR CIGS CANNOT BE
RULED OUT DURING HEAVIER BANDS OF RAINFALL.

CAVANAUGH



&&

.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX  44  53  38  50  34 /  60  60   0   0   0
WACO, TX              49  50  35  52  31 /  50  60   0   0   0
PARIS, TX             44  46  36  48  31 /  20  50  10   5   0
DENTON, TX            44  54  36  49  30 /  60  50   0   0   0
MCKINNEY, TX          42  52  35  50  30 /  50  60   5   0   0
DALLAS, TX            46  53  38  50  35 /  60  60   0   0   0
TERRELL, TX           45  47  37  49  31 /  50  60   5   0   0
CORSICANA, TX         49  50  38  51  33 /  50  60   5   0   0
TEMPLE, TX            46  47  34  53  31 /  30  60   0   0   0
MINERAL WELLS, TX     41  53  32  49  28 /  70  50   0   0   0

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

69/25





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