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

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FXUS64 KFWD 230513
AFDFWD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
1113 PM CST MON DEC 22 2014

.AVIATION...
A NARROW SWATH OF LIGHT TO MODERATE PRECEPITATION CONTINUES TO
NOSE EASTWARD INTO NORTH TEXAS TONIGHT AS A SHORTWAVE TROUGH
SWINGS EASTWARD ACROSS WEST-CENTRAL TEXAS...AROUND THE BASE OF A
MUCH LARGER UPPER TROUGH CURRENTLY RESIDING OVER THE PLAINS. LIFT WILL
BE ON THE INCREASE DURING THE OVERNIGHT HOURS AS THE FEATURE
TRAVERSES NORTH TEXAS AND ITS RESIDENT TAF LOCATIONS.

RADAR TRENDS INDICATE THAT PRECIPITATION WILL BEGIN SOON IN THE
DALLAS-FORT WORTH METROPLEX. WE WILL CONTINUE WITH THE ONSET OF -RA
AT 08Z AT ALL METRO AREA TAF SITES. TOP-DOWN MOISTENING WILL LEAD
TO LOWERING CIGS DURING THE OVERNIGHT HOURS...BUT HIGH MVFR OR LOW
IFR IS ABOUT AS BAD AS WE ARE FORECASTING AT THIS TIME BASED ON
THE LATEST GUIDANCE. PRECIPITATION WILL END AROUND 21Z WITH
IMPROVING CIGS THEREAFTER. SIMILAR TIMING CAN BE EXPECTED AT
KACT...WITH PERHAPS AN HOUR OR DELAY IN ONSET/CESSATION. THERE IS
A SLIM CHANCE OF A LATE ROUND OF SPRINKLES TUESDAY NIGHT AS THE
CORE OF THE UPPER LOW PASSES OVERHEAD...BUT AT THIS TIME IT LOOKS
AS THOUGH MOISTURE WOULD BE TOO LACKING FOR ANY MEASURABLE
PRECIPITATION.

30

&&

.UPDATE...
PRECIPITATION CONTINUES TO BE ON THE INCREASE OVER AREAS WEST AND
NORTHWEST OF NORTH TEXAS THIS EVENING AS GOOD ASCENT ASSOCIATED WITH
A SHORTWAVE TROUGH OVER WEST TEXAS ROUNDS THE BASE OF THE LONGWAVE
TROUGH SITUATED OVER THE PLAINS. AREAS OF LIGHT TO MODERATE RAIN
SHOULD ARRIVE ACROSS MOST OF NORTH TEXAS AFTER MIDNIGHT
TONIGHT...WITH PERIODS OF RAIN ONGOING THROUGH THE MORNING HOURS
TUESDAY. RAIN SHOULD COME TO AN END TUESDAY AFTERNOON AS THE
SHORTWAVE ACCELERATES OFF TO THE NORTHEAST...WITH A FEW SPRINKLES
LINGERING TUESDAY NIGHT AS THE CORE OF THE UPPER LOW PASSES
OVERHEAD. THE CURRENT FORECAST IS IN GOOD SHAPE WITH NO MAJOR GRID
CHANGES PLANNED AT THIS TIME.

30

&&

.PREV DISCUSSION... /ISSUED 400 PM CST MON DEC 22 2014/
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

&&


.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.

&&

$$






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