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

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FXUS64 KFWD 260410 AAC
AFDFWD

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE FORT WORTH TX
1010 PM CST THU DEC 25 2014

.UPDATE...
FORECAST IS IN GOOD SHAPE...BUT SOME MINOR ADJUSTMENTS TO
OVERNIGHT LOWS AND HOURLY TEMPERATURES HAVE BEEN MADE IN A FEW
AREAS TO ACCOUNT FOR CURRENT TRENDS. TR.92

&&

.AVIATION...
/ISSUED 531 PM CST THU DEC 25 2014/

CONCERNS...BEGINNING AND DURATION OF MVFR CIGS.

WE WILL ALLOW THE KDFW AIRPORT WEATHER WARNING FOR HIGH GUSTS TO
EXPIRE AT 26/00Z OR 6 PM CST THIS EVENING.

STRONG SOUTHERLY AFTERNOON WINDS WILL DIMINISH DURING THE FIRST
HOUR OR SO OF THE TAF WITH SPEEDS GENERALLY 17 KNOTS THIS EVENING
AND OVERNIGHT...AND 15+ KNOTS ON FRIDAY. A STRONG LLJ OF 45-55
KNOTS WILL DEVELOP TONIGHT AND ADVECT LOW END MVFR
STRATUS...OVC015... ACROSS KACT BY 08Z AND THE METROPLEX BY 10Z.
CURRENTLY...DO NOT THINK CIGS WILL BECOME IFR AROUND DAYBREAK OR
SHORTLY AFTER...BUT THERE IS A LOW CHANCE OF THIS HAPPENING. WILL
RE-EVALUATE THIS POTENTIAL FOR THE 03Z AND 06Z ISSUANCES LATER THIS
EVENING. AS STATED PREVIOUSLY... EXPECTING MVFR CIGS TO LIFT TO OR
SLIGHTLY ABOVE BKN022 FOR FRIDAY AFTERNOON. HOWEVER THEY WILL COME
BACK DOWN TO OVC014 FOR THE KDFW EXPENDED PERIOD. 75


&&


.PREV DISCUSSION... /ISSUED 339 PM CST THU DEC 25 2014/

THE LARGE UPPER LEVEL TROUGH CURRENTLY ACROSS THE GREAT BASIN WILL
CONTINUE TO SLIDE SOUTH AND EAST CLOSER TOWARDS THE GREAT PLAINS.
50-60 KNOT FLOW AT 500 MB WILL CONTINUE TO AID IN LEE-SIDE
CYCLOGENESIS ACROSS THE FRONT RANGE OF COLORADO. SOUTH TO SOUTHWEST
SUSTAINED WINDS OF 25 TO 35 MPH HAVE BEEN REPORTED ACROSS THE REGION
IN RESPONSE TO THE STIFF PRESSURE GRADIENT AND DAYTIME MIXING. THE
SLIGHT DOWNSLOPING COMPONENT HAS ALLOWED TEMPERATURES TO CLIMB
QUICKLY INTO THE 50S AND AFTERNOON HIGH TEMPERATURES IN THE 60S ARE
STILL EXPECTED.

.SHORT TERM.../TONIGHT THROUGH SATURDAY/...

DIURNAL MIXING SHOULD GRADUALLY DECREASE AS THE BOUNDARY LAYER
PARTIALLY DECOUPLES THIS EVENING. THE STIFF PRESSURE GRADIENT
WILL STILL ALLOW FOR WINDS OF AROUND 10 TO 15 MPH ACROSS MOST
AREAS. THIS IN CONJUNCTION WITH THE LOW LEVEL WARM/MOIST ADVECTION
SHOULD SERVE TO KEEP TEMPERATURES RELATIVELY MILD AS COMPARED TO
THE PREVIOUS NIGHTS. A STRENGTHENING LOW LEVEL JET WILL HELP TO
TRANSPORT MOISTURE NORTHWARD TONIGHT AND STRATUS IS EXPECTED TO
DEVELOP ACROSS MUCH OF NORTH AND CENTRAL TX. THE MORE
PRONOUNCED/DEEPER WARM AIR ADVECTION IS EXPECTED TO OCCUR ALONG
THE EASTERN FRINGES OF THE CWA AND THUS OVERNIGHT TEMPERATURES
WILL REMAIN SLIGHTLY WARMER HERE ALONG WITH THE SLIGHTLY THICKER
CLOUDS.

INTRODUCED A 20 POP ACROSS THE EASTERN 2-3 COLUMNS OF COUNTIES IN
THE CWA FOR FRIDAY MORNING WHERE THE STRONGER WAA REGIME IS
PROGGED TO SET UP. FORECAST SOUNDINGS INDICATE THAT MOST OF THE
MOISTURE IS CONFINED GENERALLY BELOW 850MB AND AS A RESULT...
RAINFALL AMOUNTS WILL REMAIN LIGHT WITH TOTALS GENERALLY LESS THAN
A TENTH OF AN INCH. TRICKY TEMPERATURE FORECAST FOR FRIDAY AS WAA
AND DIABATIC HEATING WILL COMBAT WIDESPREAD CLOUD COVER. SW FLOW
AROUND 850MB WEST OF I-35 SUGGESTS THAT ANY MOISTURE AT 850MB
MOISTURE THAT LIFTS NORTHWARD OVERNIGHT WILL BE SCOURED OUT BY
RELATIVELY DRIER AIR...WHILE TO THE EAST..PERSISTENT WARM/MOIST
ADVECTION WILL HELP KEEP LOW LEVEL MOISTURE IN PLACE FOR CLOUDS.
AS A RESULT...HAVE KEPT WARMEST TEMPERATURES ACROSS THE WESTERN
/LESS CLOUDY AND SLIGHT DOWNSLOPING COMPONENT/ AREAS WITH COOLER
TEMPERATURES FURTHER EAST /MORE CLOUDS/. FAR SOUTHERN ZONES WILL
BE THE BENEFICIARIES OF STRONG LOW LEVEL WAA AND TEMPS ACROSS THIS
REGION MAY CLIMB INTO THE MID TO UPPER 60S. SOME MODEL GUIDANCE
/THE 12Z NAM/ IS AGGRESSIVE WITH EVEN 70 DEGREE AIR ACROSS THIS
REGION.

RAIN CHANCES ACROSS THE AREA WILL INCREASE AS A SURFACE COLD FRONT
IS EXPECTED TO ENTER THE NW ZONES AROUND MIDNIGHT SATURDAY. THIS
FRONT WILL PLUNGE SOUTHWARD THROUGHOUT THE DAY ON SATURDAY. CLOUDS
WILL GRADUALLY RETURN ACROSS WESTERN ZONES AS UPGLIDE ALONG THE
925/850 MB FRONT INCREASES. THE AIRMASS ACROSS WESTERN ZONES STILL
APPEARS TO BE FAIRLY DRY ALOFT AND AS A RESULT...HAVE TRIMMED BACK
POPS A BIT FOR THIS AREA. STIFF NORTH WINDS AND COOL TEMPERATURES
WILL RESULT IN A RAW DAY ON SATURDAY WITH HIGH TEMPERATURES IN THE
40S AND 50S. FAR SOUTHEASTERN PORTIONS OF THE CWA MAY STILL CLIMB
INTO THE 60S BEFORE THE FRONT ARRIVES HOWEVER.

15-BAIN

&&

.LONG TERM.../SATURDAY NIGHT THROUGH NEW YEAR`S DAY/...

ON SUNDAY...FORECAST MODELS CONSISTENTLY SHOW THAT THE FINAL PIECE
OF UPPER LEVEL ENERGY ASSOCIATED WITH THE STRONG UPPER TROUGH
CURRENTLY OVER THE GREAT BASIN WILL MOVE EAST OVER TEXAS. AT THIS
TIME...MODELS INDICATE THAT THIS SHORTWAVE TROUGH WILL MOVE OVER
TEXAS POSITIVELY TILTED...WHICH WILL LIKELY RESULT IN LOW-LEVEL
FLOW REMAINING VEERED IN NATURE ALONG THE ELEVATED FRONTAL
BOUNDARY IN PLACE OVER THE REGION. WHILE SOME WARM AIR ADVECTION
AND FORCING FOR ASCENT WILL OCCUR OUT AHEAD OF THIS TROUGH...THE
VEERED FLOW ALOFT WITH THE FRONT WELL SOUTHEAST OF THE CWA IS
EXPECTED TO RESULT IN WEAK LIFT OVER NORTH AND CENTRAL TEXAS. AS A
RESULT...CUT BACK POPS ON SUNDAY TO 20 TO 30 PERCENT...REMAINING
EAST OF INTERSTATE 35. FOR LOCATIONS THAT DO RECEIVE RAIN ON
SUNDAY...RAINFALL AMOUNTS ARE EXPECTED TO REMAIN VERY LIGHT.
TEMPERATURES ON SUNDAY ARE EXPECTED TO BE WARMER WEST OF
INTERSTATE 35 WHERE CLOUD COVER IS MOST LIKELY TO BREAK UP BEFORE
SUNSET. HIGHS WILL APPROACH THE LOW 50S OUT WEST...AND REMAIN IN
THE MID 40S UNDER MOSTLY CLOUDY SKIES.

TAKING A STEP BACK FROM LOCAL AREA WEATHER...ELSEWHERE ON
SUNDAY...A STRONG UPPER TROUGH IS EXPECTED TO DIG SOUTH ACROSS
WESTERN CANADA AND MOVE OVER THE NORTHERN CONUS ROCKIES. THIS IS
IN RESPONSE TO A VERY STRONG UPPER LEVEL RIDGE THAT ALL MODEL
GUIDANCE INDICATES WILL AMPLIFY OVER THE YUKON AND OVER THE
ALASKA/CANADIAN BORDER. CONFIDENCE IN THIS PATTERN VERIFYING IS
HIGH AT THIS TIME AS THE NAEFS AND ECMWF ENSEMBLE MEANS ALL
STRONGLY POINT TO THIS SOLUTION. THE UPPER TROUGH APPEARS TO BE
STRONG...AND WAS LOCATED SOUTH OF DUTCH HARBOR ALASKA EARLY THIS
AFTERNOON PER WATER VAPOR SATELLITE IMAGERY.

ASSUMING THIS STRONG UPPER TROUGH MOVES OVER THE YUKON...AND THEN
DIVES SOUTH AS UPPER RIDGING AMPLIFIES THIS WEEKEND...THIS APPEARS
TO BE A VERY FAVORABLE LARGE SCALE UPPER AIR PATTERN THAT WILL
RESULT IN AN ARCTIC OUTBREAK FOR THE SOUTHERN PLAINS NEXT WEEK.
THE CONSENSUS OF 12Z MODEL GUIDANCE CERTAINLY SEEMS TO SUPPORT
THIS SOLUTION...SO THINK THAT THE POTENTIAL FOR ARCTIC AIR TO
BUILD ACROSS THE SOUTHERN PLAINS ON TUESDAY IS VERY HIGH AT THIS
TIME. THE STRENGTH OF THIS ARCTIC AIRMASS...ONCE IN PLACE...WILL
HAVE A LARGE IMPACT ON THE FORECAST FOR NEW YEAR`S EVE AND DAY AS
PRECIPITATION IS EXPECTED TO BEGIN TO BUILD OVER THE REGION ABOUT
24 HOURS AFTER THIS ARCTIC AIR IS IN PLACE.

MODELS SEND A SHALLOW ARCTIC AIRMASS SOUTH ALONG THE HIGH PLAINS
RAPIDLY MONDAY NIGHT INTO TUESDAY MORNING. THIS AIRMASS IS THEN
EXPECTED TO BUILD A BIT SLOWER TO THE EAST...ALMOST SPREADING
ITSELF FROM WEST TO EAST ACROSS THE CWA INSTEAD OF RUSHING IN
BEHIND A WELL DEFINED FRONTAL BOUNDARY. MODELS INDICATE THAT THIS
AIRMASS WILL SEND TEMPERATURES BELOW FREEZING FOR MOST LOCATIONS
BY WEDNESDAY MORNING...HOWEVER THIS COULD OCCUR MUCH FASTER IF
MODELS ARE UNDER DOING THE STRENGTH OF THE SHALLOW ARCTIC AIRMASS.
THIS IN SHORT IS THE PRIMARY FORECAST CHALLENGE MOVING FORWARD...
HOW STRONG AND EXPANSIVE WILL THE ARCTIC AIR BE WHEN IT MOVES INTO
THE REGION ON TUESDAY?

THE LOW-LEVEL AIRMASS THAT MOVES OUR WAY APPEARS TO BE IN NORTHERN
CANADA RIGHT NOW. MODELS ARE CURRENTLY DOING A DECENT JOB HANDLING
LOW-LEVEL TEMPERATURES THERE FOR NOW...BUT THAT DOES NOT MEAN
MODELS ARE NOT UNDER-FORECASTING THE STRENGTH OF THE COLD AIR
ONCE IT ARRIVES IN TEXAS. THE LOW-LEVEL CANADIAN AIRMASS WILL
MODIFY AS IT MOVES SOUTH ACROSS THE PLAINS EARLY NEXT WEEK...BUT
BY HOW MUCH? ONE OF THE KEY INGREDIENTS TO LOOK FOR IN TERMS OF
ARCTIC AIRMASS MODIFICATION POTENTIAL IS MODEL MID-LEVEL WIND
FIELDS. STRONG WESTERLY MID-LEVEL FLOW OVER THE ROCKIES BEHIND AN
ARCTIC AIRMASS WILL TEND TO ADIABATICALLY WARM THE ARCTIC AIR AS
IT MOVES SOUTH. THIS IS SIMPLY DUE TO WARMING AIR ASSOCIATED WITH
DOWNSLOPE WINDS IN THE LEE OF THE ROCKIES. AT THIS TIME...WHILE
THE ARCTIC AIRMASS IS MOVING SOUTH MONDAY AND TUESDAY...MOST
MODELS SHOW WEAK 700 MB FLOW...BUT MAYBE MORE
IMPORTANTLY...SUGGEST EASTERLY WINDS AS OPPOSED TO WESTERLY WINDS.
EASTERLY MID-LEVEL WINDS WILL TEND TO HELP KEEP THE ARCTIC AIRMASS
COLD BY PROVIDING CLOUD COVER AND COLD AIR DAMMING AGAINST THE
HIGH TERRAIN WHICH MAY ACTUALLY SPEED THE ARCTIC AIR UP. THE 12Z
ECMWF SOLUTION SEEMED TO HANDLE THIS PROCESS THE BEST...SO WENT
AHEAD AND NUDGED THE FORECAST TOWARDS THIS SOLUTION FOR TUESDAY
THROUGH THURSDAY.

IN GENERAL THE ECMWF SOLUTION IS A BIT FASTER WITH THE ARRIVAL OF
THE ARCTIC AIR ON TUESDAY...AND IS COLDER IN GENERAL WITH THE
FORECAST ONCE THE ARCTIC AIR IS IN PLACE. BOTH THE ECMWF AND GFS
INDICATE THAT THE DUTCH HARBOR UPPER TROUGH WILL CLOSE OFF INTO AN
UPPER LEVEL LOW OVER SOUTHERN CALIFORNIA BY TUESDAY NIGHT.
ASSUMING THIS OCCURS...THIS WOULD RESULT IN SOUTHWEST FLOW ALOFT
OVER THE SOUTHERN PLAINS...WHICH WOULD INDUCE A LONG PERIOD OF
WARM AIR ADVECTION OVER THIS SHALLOW ARCTIC AIRMASS BY THE EARLY
MORNING HOURS OF NEW YEAR`S EVE...ALL THE WAY THROUGH JANUARY 2ND.
WITH HIGHER CONFIDENCE IN SHALLOW ARCTIC AIR IN PLACE...BUT LOW
CONFIDENCE ON THE EXACT DETAILS OF THE VERTICAL TEMPERATURE
PROFILE 6-7 DAYS OUT...WENT AHEAD AND MENTIONED A 20 TO 30 PERCENT
CHANCE OF FREEZING RAIN OR LIGHT RAIN IN THE FORECAST OVER MUCH OF
NORTH AND CENTRAL TEXAS.

CONFIDENCE IN THE AMOUNT OF LIFT AVAILABLE FOR PRECIPITATION OVER
THE ARCTIC AIRMASS...AS WELL AS AVAILABLE MOISTURE FOR
PRECIPITATION REMAIN LOW AT THIS TIME FOR NEW YEAR`S EVE AND
NEW YEAR`S DAY. CONFIDENCE IN LIFT AND AVAILABLE MOISTURE
INCREASES QUITE A BIT ON JANUARY 2ND WHEN MODELS SUGGEST THE DUTCH
HARBOR UPPER LOW WILL MOVE OVER NEW MEXICO AND SPREAD STRONG LARGE
SCALE FORCING FOR ASCENT OVER THE ENTIRE CWA. UNFORTUNATELY AS
CONFIDENCE IN PRECIPITATION RISES...CONFIDENCE IN THE SHALLOW
ARCTIC AIRMASS REMAINING IN PLACE DECREASES. GFS AND ECMWF DYNAMIC
TROPOPAUSE MAPS INDICATE THAT THE CUT OFF UPPER LOW IS ISOLATED
FROM THE POLAR JET STREAM BY THE TIME IT MOVES EAST OVER THE
SOUTHWEST CONUS AND TOWARDS TEXAS ON NEW YEAR`S DAY AND JANUARY
2ND. ONCE THIS OCCURS...DOWNSTREAM AIRMASS MODIFICATION BECOMES
INCREASINGLY LIKELY...WHICH REALLY JUST MEANS THE ARCTIC AIR IS
MORE LIKELY TO WARM UP BECAUSE IT WILL NOT BE REINFORCED BY ANY
MORE COLD AIR FROM THE NORTH.

AT ANY RATE THE BASIC THREAT TO THE REGION FOR WINTRY WEATHER
LOOKS LIKE THIS:

ARCTIC AIR WILL BUILD IN TUESDAY/TUESDAY NIGHT WHILE VERY LIGHT
RAIN/DRIZZLE CHANCES INCREASE INTO THE MORNING HOURS ON NEW YEAR`S
EVE. WHEREVER LIGHT RAIN/DRIZZLE SETS UP...IT HAS A GOOD CHANCE AT
FREEZING UPON CONTACT WITH ELEVATED SURFACES.

CONFIDENCE IN PRECIPITATION AND PRECIPITATION AMOUNTS INCREASES
THROUGH JANUARY 2ND WHILE THE SHALLOW ARCTIC AIRMASS WILL SLOWLY
WARM UP. RAINFALL CHANCES LOOK TO BE HIGHEST WHILE ARCTIC AIR IS
STILL PROBABLY COLD ENOUGH TO FREEZE THINGS ON NEW YEAR`S DAY. BY
JANUARY 2ND...WIDESPREAD PRECIPITATION IS LIKELY...BUT IT MAY TEND
TO ALL FALL IN LIQUID FORM BY THAT TIME.

IN GENERAL...CONFIDENCE REMAINS TOO LOW TO EXPECT ANY MAJOR WINTER
WEATHER EVENT ACROSS NORTH OR CENTRAL TEXAS AT THIS TIME.
HOWEVER...WE WILL CONTINUE TO WATCH THIS PERIOD CLOSELY MOVING
FORWARD AS THE POTENTIAL FOR WINTRY IMPACTS ARE CERTAINLY THERE
FOR THE REGION DURING NEW YEAR`S EVE/NEW YEAR`S DAY FESTIVITIES.

CAVANAUGH


&&


.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX  49  63  46  47  34 /   5  10  30  30  10
WACO, TX              48  66  51  51  35 /   5  10  30  30  10
PARIS, TX             43  59  50  50  34 /  10  20  40  40  30
DENTON, TX            47  62  42  45  31 /   5  10  20  20  10
MCKINNEY, TX          47  61  46  46  32 /  10  20  30  30  10
DALLAS, TX            50  63  48  48  35 /  10  10  30  30  10
TERRELL, TX           47  62  51  51  35 /  10  20  30  30  20
CORSICANA, TX         49  64  54  54  36 /  10  20  30  30  20
TEMPLE, TX            49  67  53  53  35 /   5  10  30  30  20
MINERAL WELLS, TX     46  64  39  44  29 /   5  10  20  20  10

&&

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

&&

$$




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