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

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000
FXUS64 KFWD 181524
AFDFWD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
924 AM CST THU DEC 18 2014

.UPDATE...

WILL UPDATE ZONES TO KEEP CLOUDS IN THROUGH THE DAY ACROSS MOST OF
THE AREA. WESTERLY WINDS WILL HELP TO ERODE THE CLOUDS OUT WEST
BUT HIGH RES MODEL GUIDANCE SHOWS MOISTURE TRAPPED AROUND THE
925MB LEVEL WILL HANG TOUGH OUTSIDE OF THE WESTERN AREAS. ALSO
SINCE WE ARE WITHIN A WEEK OF THE WINTER SOLSTICE...LOW SUN ANGLE
NOT GOING TO BE MUCH OF A HELP FOR TODAY.

HAVE LOWERED TEMPS SEVERAL DEGREES FOR TODAY. HIGH TEMPS WILL LIKELY
ONLY BE ABOUT THREE TO FIVE DEGREES WARMER THAN WHERE WE ARE RIGHT
NOW DUE TO THE CLOUDS...BUT WILL WORK THEIR WAY WELL INTO THE 50S
TO NEAR 60 OUT WEST WHERE MORE SUNSHINE WILL PREVAIL.

WILL CONTINUE TO SEE PATCHY LIGHT DRIZZLE/FOG FROM THE I-35
CORRIDOR EASTWARD THROUGH ABOUT NOON OR SO BUT NO ACCUMULATING
PRECIP IS EXPECTED.

WILEY



&&

.AVIATION...
/ISSUED 529 AM CST THU DEC 18 2014/
NO BIG CHANGES FROM PREVIOUS TAF DISCUSSION. ALTHOUGH MID CLOUD
HAS ERODED...DEW POINTS WILL CONTINUE TO CLIMB A BIT HIGHER TODAY
KEEPING LOW LEVELS QUITE SOUPY. EXPECT A CIG/VIS LIFT TODAY...BUT
WITH SUN AT ITS LOWEST ANGLES OF THE YEAR IT WILL NOT BE MORE
THAN A CATEGORY OR TWO AND ALSO WILL NOT LAST LONG AFTER SUNSET.
THEN IT`S BACK TO IFR/LIFR. OF INTEREST IN THE 06Z NAM/GFS...THEY
BRING THE FRIDAY MORNING SHORT WAVE PRECIP A BIT FARTHER
NORTH...AND HAVE ADDED RAIN TO THE OUTLOOK PERIOD FOR KDFW. 84


&&



.PREV DISCUSSION... /ISSUED 356 AM CST THU DEC 18 2014/

EARLY MORNING WATER VAPOR IMAGERY SHOWS A SHEARED UPPER LEVEL
TROUGH EXTENDING FROM THE TEXAS PANHANDLE NORTHEAST OVER SOUTHWEST
MISSOURI. THIS TROUGH WAS MOVING NORTHEAST TOWARDS THE GREAT LAKES
REGION. ANOTHER UPPER TROUGH WAS EVIDENT OVER THE NORTHERN BAJA
PENINSULA...AND THIS TROUGH WAS MOVING ALMOST DUE EAST TOWARDS THE
ARIZONA AND MEXICO BORDER. REGIONAL RADARS SHOWED SOME VERY LIGHT
ISOLATED RAIN SHOWERS OVER THE SOUTHEASTERN PORTION OF THE CWA
EARLY THIS MORNING...MOVING NORTHEAST WITH THE UPPER TROUGH JUST
OFF TO THE NORTH. THE 00Z FWD RAOB WAS SATURATED FROM THE SURFACE
TO THE 600 MB LEVEL...HOWEVER THIS IS NOT LIKELY REPRESENTATIVE OF
THE ENVIRONMENT IN PLACE OVER NORTH TEXAS EARLY THIS MORNING. DRY
AIR ALOFT CAN BE SEEN ON WATER VAPOR SATELLITE IMAGERY FILTERING
OVER NORTH AND CENTRAL TEXAS EARLY THIS MORNING. HOWEVER...
INFRARED SATELLITE IMAGERY COMBINED WITH SURFACE OBSERVATIONS
INDICATE A LOW STRATUS DECK IN PLACE ACROSS THE ENTIRE CWA.

THINK THAT ISOLATED RAIN SHOWERS WILL ONLY REMAIN OVER THE FAR
SOUTHEASTERN CWA FOR A FEW HOURS THIS MORNING BEFORE ALL
PRECIPITATION MOVES EAST OR SOUTHEAST OF CENTRAL TEXAS AS DRIER
MID-LEVEL AIR CONTINUES TO BUILD OVER THE REGION. THE DEPTH OF
LOW-LEVEL MOISTURE IS MUCH MORE DIFFICULT TO ASSESS THIS
MORNING...AND UNFORTUNATELY THIS WILL PLAY A LARGE ROLE IN HIGH
TEMPERATURES TODAY. MODELS ARE CONSISTENT IN INDICATING THAT AS
THE UPPER TROUGH JUST NORTH OF NORTH TEXAS MOVES NORTHEAST
TODAY...850 MB WINDS WILL VEER AROUND TO THE WEST. THIS WILL
GENERALLY BRING WARMER AND DRIER AIR OVER THE CWA TODAY...BUT THIS
IS ONLY RELEVANT IF WE ARE ABLE TO GET RID OF THE LOW STRATUS
ALREADY IN PLACE.

IF THE LOW CLOUD COVER BREAKS UP THIS AFTERNOON...EVEN A FEW
HOURS OF HEATING SHOULD ALLOW TEMPERATURES TO CLIMB UP INTO THE
UPPER 50S TO LOWER 60S WITH THE WARM 850 MB TEMPERATURES IN PLACE.
HOWEVER...IF CLOUDS REMAIN IN PLACE...HIGHS MAY REMAIN IN THE
UPPER 40S TO LOWER 50S TODAY. CONFIDENCE IS HIGH THAT CLOUDS WILL
REMAIN IN PLACE THROUGH MIDDAY. AFTER THAT...HIGH RESOLUTION
GUIDANCE FAVORS CLOUDS REMAINING IN PLACE WHILE SOME OF THE
COARSER RESOLUTION MODELS FAVOR BREAKS IN THE STRATUS FOR A FEW
HOURS THIS AFTERNOON. WITH ALL MODELS SHOWING WESTERLY 850 MB
WINDS THROUGHOUT THE DAY TODAY...LEANED THE FORECAST IN FAVOR OF
THE WARMER SOLUTION. ALL GUIDANCE SHOWS THE STRATUS SLOWLY LIFTING
THROUGH THE MORNING HOURS OF THE DAY...SO THINK THAT THE
PERSISTENT 850 WESTERLY WINDS WILL EVENTUALLY HELP MIX ENOUGH DRY
AIR INTO THE RISING STRATUS DECK TO ALLOW FOR SOME BREAKS IN THE
CLOUDS BEFORE SUNSET. KEPT HIGHS 3-5 DEGREES BELOW MOS GUIDANCE
HOWEVER AS MOS SEEMS TO REPRESENT THE WARMEST WE COULD POSSIBLY
GET TODAY UNDER IDEAL CONDITIONS.

TONIGHT AND FRIDAY...THE BAJA UPPER TROUGH IS EXPECTED TO MOVE
EAST TOWARDS THE SOUTHERN PLAINS TONIGHT...CAUSING LOW-LEVEL
CYCLOGENESIS OVER SOUTH TEXAS. AT THE SAME TIME...THE DEPARTURE OF
THE NORTHERN UPPER TROUGH TO THE EAST IS EXPECTED TO SEND A COLD
FRONT SOUTH ACROSS MUCH OF NORTH AND CENTRAL TEXAS THIS EVENING.
WHERE THIS FRONT MEETS THE SOUTH TEXAS CYCLOGENESIS...A STRONG
BAROCLINIC ZONE/WARM FRONT TYPE FEATURE IS EXPECTED TO SET UP
SOMEWHERE ACROSS CENTRAL TEXAS. THIS BAROCLINIC ZONE SHOWS UP BEST
AT THE 850 MB LEVEL...AND THIS FEATURE IS LIKELY TO PLAY AN
IMPORTANT ROLE IN WHERE THE HEAVIEST RAINFALL WILL OCCUR WITH THIS
SECOND UPPER LEVEL STORM SYSTEM.

UNFORTUNATELY THE CONSENSUS OF GUIDANCE YESTERDAY EVENING (18/00Z
MODELS) KEEP THIS 850 FRONT FARTHER SOUTH THAN THEY WERE
ADVERTISING 24 HOURS AGO. AS A RESULT...CONFIDENCE IN HEAVY
RAINFALL OVER THE CWA DURING THIS EVENT HAS DIMINISHED. LOCATIONS
THAT MAY STILL SEE AN INCH OF RAINFALL ARE LIKELY RELEGATED TO
ALONG AND SOUTHEAST OF A LINE FROM TEMPLE TO PALESTINE...ASSUMING
MODELS ARE DOING A GOOD JOB WITH THE POSITION OF THE 850 MB FRONT.
A SHIFT TO THE SOUTH WILL KEEP THE HEAVIEST RAINS SOUTHEAST OF
COLLEGE STATION...WHILE A SHIFT TO THE NORTH COULD BRING THE
HEAVIER RAINFALL AXIS AS FAR NORTH AS WACO. THIS FORECAST SIDES
WITH A DRIER SOLUTION ON AVERAGE AS THE GFS AND ECMWF BOTH KEEP
THE 850 FRONT SOUTH OF THE CWA ENTIRELY.

LOCATIONS NORTH OF THIS FRONT...WHICH LIKELY INCLUDES MOST OF THE
CWA...ARE STILL LIKELY TO SEE MEASURABLE RAINFALL. MODEL MASS
FIELDS STILL INDICATE PERSISTENT ISENTROPIC LIFT FROM THE
INTERSTATE 20 CORRIDOR AND POINTS SOUTH. THESE LOCATIONS MAY PICK
UP ANYWHERE FROM ONE HALF TO ONE QUARTER OF AN INCH OF RAINFALL
FROM TONIGHT THROUGH FRIDAY MORNING. THE PROSPECTS OF PICKING UP
SUBSTANTIALLY HIGHER RAINFALL AMOUNTS ARE LOWER WITHOUT THE 850
MB FRONT IN PLACE. FOR LOCATIONS ALONG AND NORTH OF THE INTERSTATE
20 CORRIDOR...PRECIPITATION TOTALS ARE EXPECTED TO DROP OFF EVEN
FURTHER...WITH RAINFALL TOTALS LIKELY REMAINING AT OR BELOW ONE
TENTH OF AN INCH. FORCING FOR ASCENT NORTH OF INTERSTATE 20 IS
STILL PRESENT...HOWEVER IT IS NOT AS STRONG OR PROLONGED AS IT IS
FOR POINTS SOUTH. THE LACK OF STRONGER LIFT MEANS THAT THE 850 TO
700 MB DRY AIR ADVECTING OVER THE REGION EARLY THIS MORNING WILL
BE HARD TO OVERCOME. THIS LAYER OF DRY AIR ALOFT MAKES ANY
SUBSTANTIAL RAINFALL LOOK HARD TO COME BY.

RAINFALL IS STILL EXPECTED TO COME TO AN END FROM WEST TO EAST
FRIDAY AFTERNOON AS THE UPPER TROUGH MOVES EAST OF THE REGION.
HIGH RESOLUTION MODELS CONTINUE TO HINT AT SOME LIGHT
PRECIPITATION PERSISTING ALONG THE BACK SIDE OF THE UPPER
TROUGH...DUE TO RESIDUAL MOISTURE WRAPPED UP BEHIND THE TROUGH.
KEPT A MENTION OF LIGHT RAIN IN THE FORECAST GENERALLY ALONG AND
EAST OF THE INTERSTATE 35/35W CORRIDOR FRIDAY EVENING AND NIGHT AS
A RESULT. DO NOT EXPECT MUCH MORE THAN A COUPLE OF HUNDREDTHS OF
AN INCH OF RAINFALL IF THIS PANS OUT.

THIS WEEKEND...BEHIND FRIDAY`S UPPER TROUGH...MOST OF THE MOISTURE
FROM THE 850 MB LEVEL AND ABOVE IS EXPECTED TO MOVE EAST OR
SOUTHEAST AWAY FROM THE CWA. AN UPPER LEVEL RIDGE IS EXPECTED TO
AMPLIFY OVER THE PACIFIC OCEAN JUST OFF THE WEST COAST...AND LARGE
SCALE TROUGHING IS EXPECTED OVER THE MID-WEST CONUS...RESULTING
IN NORTHWEST FLOW ALOFT OVER THE SOUTHERN PLAINS. NORTHWEST FLOW
ALOFT IS TYPICALLY A DRY WEATHER PATTERN FOR THE REGION DURING THE
COOL SEASON...MAINLY BECAUSE THE BULK OF THE TRAJECTORIES OVER THE
REGION ARE FROM RELATIVELY DRY AND COOL PARTS OF THE CONTINENT
UPSTREAM. THIS PATTERN LOOKS FAIRLY TYPICAL OF A COOL SEASON
NORTHWEST FLOW REGIME...SO MAINTAINED A COOL AND DRY FORECAST AT
THIS TIME. MODELS DO CONTINUE TO BRING A RELATIVELY STRONG
SHORTWAVE TROUGH OVER THE CWA ON SUNDAY IN THE NORTHWEST FLOW
REGIME. HOWEVER...WITH DRY AIR ADVERTISED IN THE MID TO UPPER
TROPOSPHERE...DO NOT SEE MUCH EVIDENCE THAT THIS WILL RESULT IN
ANY RAIN FOR THE REGION AT THIS TIME. BUMPED UP CLOUD COVER A BIT
ON SUNDAY TO ACCOUNT FOR THIS FEATURE...AND WILL CONTINUE TO
MONITOR ITS STRENGTH AS IT GETS CLOSER TO THE SOUTH PLAINS.

MODELS CONTINUE TO ADVERTISE NORTHWEST FLOW OVER THE SOUTH PLAINS
FOR EARLY NEXT WEEK. THE ONLY CHANGE IS THAT GUIDANCE CONTINUES TO
INDICATE THAT A STRONG UPPER LEVEL SHORTWAVE TROUGH WILL DIG SOUTH
OUT OF CANADA AND SEND A STRONG COLD FRONT ACROSS THE CWA MONDAY
NIGHT INTO TUESDAY MORNING. THE UPPER TROUGH ITSELF IS EXPECTED TO
REMAIN WELL OFF TO THE NORTHEAST...SO THERE WILL BE LITTLE TO NO
UPPER LEVEL SUPPORT OR LIFT TO ACCOMPANY THE FRONT SOUTH ACROSS
THE PLAINS. WITHOUT UPPER LEVEL LIFT...THINK THAT THE STRONG LIFT
ALONG THE FRONT WILL NOT BE STRONG ENOUGH TO RESULT IN ANY
SIGNIFICANT RAIN CHANCES FOR MONDAY NIGHT INTO TUESDAY. MAINTAINED
A 20 PERCENT CHANCE OF RAIN OVER THE FAR EASTERN CWA WHERE LOW-
LEVEL MOISTURE MAY BE A BIT DEEPER...HOWEVER EVEN IF THIS PANS
OUT...EXPECT ANY RAINFALL TO BE VERY LIGHT AT THIS TIME. THINK
MOST OF THE CWA WILL REMAIN DRY EARLY NEXT WEEK.

TEMPERATURES WILL COOL DOWN A BIT BEHIND THE FRONT...BUT ALL
GUIDANCE INDICATES THAT THE STRONG CANADIAN AIRMASS BEHIND THE
FRONT WILL DEFLECT EAST OF THE REGION...MORE OR LESS IN LINE WITH
THE UPPER TROUGH THAT SENDS THIS FRONT SOUTH IN THE FIRST PLACE.
BECAUSE THE FRONT WILL SEND SOME VERY DRY LOW-LEVEL AIR ACROSS THE
AREA...HIGH TEMPERATURES MAY NOT BE ALL THAT DIFFERENT BEHIND THE
FRONT...MAYBE 5 DEGREES COOLER WITH A FULL DAY OF SUNSHINE BEHIND
THE FRONT ON TUESDAY. THE EFFECTS OF THE FRONT WILL BE MORE
APPARENT OVERNIGHT TUESDAY NIGHT AND WEDNESDAY NIGHT. OVERNIGHT
LOWS WILL LIKELY FALL INTO THE 30S WITH COOLER DRY AIR IN PLACE.

CHRISTMAS AND THE EXTENDED FORECAST...CHRISTMAS IS NOW 7 DAYS OUT
AND APPROACHING OUR VALID FORECAST COVERAGE. AT THIS TIME...THE
GFS AND ECMWF BOTH INDICATE NORTHWEST FLOW ALOFT TRANSITIONING TO
ZONAL FLOW ALOFT OVER THE SOUTHERN PLAINS BY CHRISTMAS DAY. IF
THIS OCCURS IT WILL GENERALLY RESULT IN WARMER WEATHER FOR THE
REGION. HOWEVER...THIS CHANGE IN FLOW ALOFT IS ONLY DUE TO BOTH
MODELS INDICATING THAT A POWERFUL UPPER LEVEL STORM SYSTEM WILL
NUDGE SOUTH OVER THE WESTERN CONUS. THIS SYSTEM LOOKS LIKE IT WILL
HOLD OFF ON REALLY IMPACTING THE SOUTHERN PLAINS UNTIL FRIDAY OR
SATURDAY AFTER CHRISTMAS. THERE ARE LARGE DIFFERENCES IN HOW THESE
MODELS HANDLE THE EVOLUTION OF THIS POWERFUL LOOKING STORM
SYSTEM...SO WILL NOT GET INTO THE DETAILS HERE. HOWEVER THE COMMON
THEME IN THESE MODELS IS THAT A STRONG ARCTIC FRONT WILL
EVENTUALLY MOVE SOUTH ACROSS THE PLAINS...LIKELY RESULTING IN
TEMPERATURES HOLDING WELL BELOW NORMAL THE WEEKEND AFTER
CHRISTMAS.

CAVANAUGH




&&


.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX  49  45  50  41  52 /  10  40  50  20   5
WACO, TX              52  48  51  42  54 /  10  70  70  10   5
PARIS, TX             45  43  48  40  51 /  10  30  50  30  10
DENTON, TX            47  43  49  39  52 /  10  30  40  20   5
MCKINNEY, TX          46  43  49  40  51 /  10  40  50  20   5
DALLAS, TX            49  46  50  42  53 /  10  40  50  20   5
TERRELL, TX           48  46  49  42  53 /  10  50  50  20   5
CORSICANA, TX         51  48  50  43  54 /  10  70  70  20  10
TEMPLE, TX            53  49  51  43  56 /  10  80  80  10   5
MINERAL WELLS, TX     50  43  49  37  52 /  10  40  50  10   5

&&

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

&&

$$

 /





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