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

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000
FXUS64 KFWD 210442 AAC
AFDFWD

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE FORT WORTH TX
1142 PM CDT SUN JUL 20 2014

.AVIATION...
LOW CLOUDS ARE STARTING TO DEVELOP ACROSS SOUTH TEXAS. WITH SOUTH
SOUTHWEST WINDS JUST ABOVE THE SURFACE...SOME MVFR CEILINGS ARE
EXPECTED TO MOVE INTO THE WACO AREA 10-11Z MONDAY. THUS HAVE
INDICATED BKN020 FOR THE 10-16Z PERIOD...WITH A TEMPO 5SM BR
BKN012 FOR THE 11-14Z PERIOD. THERE IS A LOWER CHANCE THAT SOME
MVFR CEILINGS WILL MAKE IT INTO THE METROPLEX TAF SITES BETWEEN
12-13Z...THE CHANCES ARE TOO LOW TO INCLUDE A CEILING...BUT WILL
PLACE A SCT020 STARTING AT 12Z. IF THE MVFR CEILINGS MOVE INTO
THE METROPLEX...THEY SHOULD LIFT AND START TO SCATTER AROUND 16Z.
SOUTHEAST WINDS AT 10 KNOTS OR LESS TONIGHT WILL BECOME SOUTHERLY
BY 12Z MONDAY. WINDS WILL BACK AROUND TO THE SOUTHEAST BY 00Z
TUESDAY.

58

&&

.UPDATE...
OTHER THAN UPDATING THE HOURLY GRIDS SLIGHTLY FOR THE OVERNIGHT
PERIOD THERE IS LITTLE NEED TO TWEAK THE REST OF THE FORECAST
PERIODS.

SOME HIGH CLOUDS WILL LIKELY SPREAD ACROSS THE WESTERN CWA LATER
TONIGHT. LOW CLOUDS ARE EXPECTED TO FORM ACROSS SOUTH-CENTRAL
TEXAS AND SPREAD INTO THE SOUTHERN COUNTIES AND WACO AREA AROUND
DAYBREAK. OTHERWISE...DRY WEATHER AND WARMER TEMPERATURES WILL BE
THE RULE UNTIL MID WEEK. THERE WILL BE A LOW CHANCE OF
SHOWERS/THUNDERSTORMS OVER THE CENTRAL AND EASTERN CWA WEDNESDAY
AND THURSDAY AS A WEAK FRONT ARRIVES.   75

&&

.PREV DISCUSSION... /ISSUED 332 PM CDT SUN JUL 20 2014/

EARLY AFTERNOON SURFACE OBSERVATIONS SHOWED A PLUME OF LOWER 70S
DEW POINTS IN PLACE FOR LOCATIONS ALONG AND WEST OF INTERSTATE 35
OR SOUTH OF INTERSTATE 20. THIS AREA OF 70S AND GREATER DEW POINTS
WERE ACCOMPANIED BY A LOW STRATUS DECK THIS MORNING...WHICH HAS
SINCE SCATTERED OUT ALLOWING PLENTY OF SUNSHINE TO REACH THE
GROUND ACROSS THE AREA FOR THE FIRST TIME IN A FEW DAYS. SUNSHINE
BROUGHT TEMPERATURES UP INTO THE MID TO UPPER 80S ACROSS THE
REGION AS OF 2 PM CDT WHICH IS THE WARMEST WE HAVE BEEN SINCE
WEDNESDAY OF LAST WEEK. EVEN THOUGH WE ARE MUCH WARMER THAN WE
HAVE BEEN IN A FEW DAYS...2 PM TEMPERATURES WERE STILL RUNNING
ABOUT 10 DEGREES BELOW NORMAL FOR MID TO LATE JULY ACROSS NORTH
AND CENTRAL TEXAS. HOWEVER WITH THE MOISTURE IN PLACE MOST AREA
HEAT INDICES WERE IN THE MID TO UPPER 90S...MAKING IT FEEL LIKE A
TYPICAL SUMMER DAY.

ANYTIME WE HOLD ON TO A 70 DEG F DEW POINT IN THE SUMMER DURING
THE PEAK HEATING HRS OF THE DAY...ISOLATED THUNDERSTORMS ARE
USUALLY A CONCERN. HOWEVER FOR TODAY...DESPITE THE FACT THAT IT
FEELS WARM AND HUMID OUTSIDE...OUR THUNDERSTORM CHANCES FOR THIS
AFTERNOON REMAIN VERY CLOSE TO ZERO. THE LATEST AIRCRAFT SOUNDING
FROM THE DFW AREA SHOWS POOR MID-LEVEL LAPSE RATES WITH A VERY DRY
AIR MASS LOCATED ON TOP OF OUR NEAR SURFACE MOIST LAYER. EVEN IF
WE WERE TO LIFT THE WARM MOIST AIR NEAR THE SURFACE...THERE IS
VERY LITTLE CAPE AVAILABLE FOR BUOYANT ASCENT. ALSO...THERE IS A
VERY STRONG CAP IN PLACE THAT WOULD REQUIRE TEMPERATURES TO CLIMB
TO AROUND 105 DEGREES TO OVERCOME WITHOUT COOLING THE CAP ITSELF.
AS A RESULT...LEFT THE FORECAST DRY OVER THE NEXT 24 HRS WITH
LITTLE CHANGE IN THE THERMODYNAMIC ENVIRONMENT EXPECTED.

IN THE LARGE SCALE PATTERN...12Z UPPER AIR ANALYSIS AND EARLY
AFTERNOON WATER VAPOR IMAGERY SHOW AN UPPER LEVEL RIDGE BUILDING
OVER THE MEXICO/NEW MEXICO BORDER WITH FAIRLY WELL DEFINED
SHORTWAVE TROUGHS ON ITS OUTER PERIPHERY. ONE OF THESE TROUGHS WAS
LOCATED ALONG THE NV/UT BORDER MOVING TO THE NORTH WHILE THE OTHER
WAS LOCATED OVER THE OK/AR BORDER MOVING TO THE SOUTHEAST. THESE
UPPER TROUGHS...COMBINED WITH A STRONG UPPER LOW EXPECTED TO MOVE
OVER THE CONUS/CANADIAN BORDER BY THE END OF THE WEEK ARE THE
MAIN PLAYERS IN OUR WEATHER PATTERN OVER THE NEXT 7 DAYS.

FOR TOMORROW AND TUESDAY...IN GENERAL UPPER LEVEL RIDGING IS
EXPECTED TO DOMINATE THE LARGE SCALE WEATHER PATTERN. THE UPPER
LEVEL RIDGE IS ACTUALLY EXPECTED TO STRENGTHEN AND MOVE WEST A BIT
DURING THIS TIME PERIOD...SO IT IS NOT EXPECTED TO BE DIRECTLY
OVER THE CWA. REGARDLESS...WITH THE RIDGE PROGGED TO GET
STRONGER...WE ARE EXPECTED TO REMAIN UNDER SUBSIDENCE ALOFT WHICH
SHOULD ONLY REINFORCE THE THERMODYNAMIC ENVIRONMENT ALREADY IN
PLACE. AS A RESULT...KEPT THE FORECAST DRY FOR THE MOST PART
THROUGH TUESDAY NIGHT. LEFT IN THE 10 PERCENT CHANCE OF STORMS FOR
LOCATIONS GENERALLY SOUTHEAST OF CORSICANA TUESDAY AFTERNOON AS
THE SEA-BREEZE BOUNDARY COULD BE RESPONSIBLE FOR SETTING OFF A
STORM OR TWO LATE TUESDAY AFTERNOON. TEMPERATURES WILL RETURN TO
SEASONAL NORMALS WITH HIGHS IN THE MID TO UPPER 90S AND HEAT
INDICES HOLDING BETWEEN 100 AND 105 DURING THE AFTERNOON HRS OF
THE DAY.

WEDNESDAY AND THURSDAY...FOR MOST OF THE DAY ON WEDNESDAY...WE ARE
EXPECTED TO REMAIN HOT AND DRY...VERY SIMILAR TO MONDAY AND
TUESDAY. HOWEVER THUNDERSTORMS ENTER THE FORECAST FROM THE EAST
WEDNESDAY AFTERNOON...AND SPREAD WESTWARD WEDNESDAY NIGHT. THE
PRIMARY REASON FOR THIS IS THAT MODELS INDICATE THAT THE OK/AR
SHORTWAVE TROUGH WILL STALL OUT OVER THE AL/MS GULF COAST BY
TUESDAY MORNING...HOLDING IN PLACE THROUGH WEDNESDAY MORNING. BY
WEDNESDAY MORNING...THE NV/UT SHORTWAVE TROUGH...OR SOME REMNANTS
OF IT AT LEAST...MERGE WITH THE STALLED OUT TROUGH OVER THE GULF
COAST AND BEGIN TO RETROGRADE TO THE WEST TOWARDS NORTH TX.

THIS TROUGH EVOLUTION/MERGER WAS ANALYZED BY FOLLOWING THESE
UPPER LEVEL TROUGHS ON A DYNAMIC TROPOPAUSE MAP. THE UPPER LEVEL
POTENTIAL VORTICITY (PV) RESERVOIRS IN EACH OF THESE TROUGHS ARE
CORRELATED WITH DIPS OR VALLEYS ON THE DYNAMIC TROPOPAUSE. THAT
MEANS THAT WHEREVER THESE DIPS ON THE TROPOPAUSE ARE...DIRECTLY
UNDERNEATH THEM THE ATMOSPHERE IS RELATIVELY COOLER THAN IN THE
SURROUNDING AREAS. THIS IS BECAUSE THE TROPOSPHERE UNDER THESE
UPPER LEVEL TROUGHS HAS LESS THICKNESS THAN IN THE SURROUNDING
AREAS. WITH THE RELATIVELY WARMER AIR TO THE WEST...FRONTOGENETIC
FORCING AND LARGE SCALE FORCING FOR ASCENT WILL OCCUR TO THE WEST
OF THE TROUGH AS OPPOSED TO THE EAST/SOUTHEAST. I JUST WANTED TO
POINT THIS OUT BECAUSE THIS IS BASICALLY THE OPPOSITE BEHAVIOR
FROM WHAT TYPICALLY OCCURS WHEN FOLLOWING UPPER TROUGHS ON WEATHER
MAPS/FORECAST MODELS.

SO IN OUR CASE...WITH AN UPPER LEVEL PV BLOB APPROACHING NORTH
TEXAS FROM THE EAST LARGE SCALE FORCING FOR ASCENT ASSOCIATED WITH
THIS TROUGH/BLOB SHOULD MOVE OVER THE AREA FROM THE NORTHEAST OR
EAST TOWARDS THE SOUTHWEST LATE ON WEDNESDAY THROUGH WEDNESDAY
NIGHT. ASSUMING THE FORCING FOR ASCENT WITH THE WESTWARD MOVING
TROUGH IS SUFFICIENT TO LIFT AND COOL THE CAP IN PLACE...WE
SHOULD SEE THUNDERSTORMS DEVELOP OFF TO OUR NORTHEAST WEDNESDAY
AFTERNOON...AND MOVE SOUTHWEST TOWARDS NORTH TEXAS THAT EVENING
AND POSSIBLY OVERNIGHT. THE 20/12Z GFS AND CANADIAN MODEL RUNS
BOTH INDICATE THAT THIS RETROGRADING PATTERN OCCURS IN CONCERT
WITH THE PASSAGE OF A STRONG NORTHERN STREAM SHORTWAVE TROUGH OVER
THE GREAT LAKES REGION. IF THIS OCCURS...THE RETROGRADING UPPER
TROUGH COULD HELP DRAG SOME OF THE RELATIVELY COOLER LOW-LEVEL
AIR TO OUR NORTHEAST ACROSS THE CWA LATE ON WEDNESDAY IN THE FORM
OF A "BACK DOOR" COLD FRONT.

IF A COLD FRONT DOES PUSH SOUTHWEST INTO THE CWA WITH THE
RETROGRADING TROUGH...WE MAY NEED TO INCREASE POPS IN LATER
FORECASTS FOR WEDNESDAY EVENING AND OVERNIGHT. AT THIS TIME THE
20/12Z ECMWF IS MUCH LESS ROBUST WITH THIS FRONT...WHICH IS MORE
IN LINE WITH PREVIOUS RUNS OF THE GFS. WITHOUT A FRONT TO HELP
ORGANIZE CONVECTION...THINK THAT THE COVERAGE OF STORMS WILL TEND
TO BE ISOLATED TO SCATTERED AT BEST...SO KEPT POPS IN THE 20
PERCENT RANGE FOR NOW...BUT DID EXPAND THE COVERAGE OF 20 POPS
WEST TO COVER MOST OF THE CWA THROUGH WEDNESDAY NIGHT.

SEVERE WEATHER IS NOT LIKELY...HOWEVER IT IS NOT AS FAR FETCHED
AS YOU WOULD EXPECT AT THIS TIME OF YEAR. IF THE THERMODYNAMIC
ENVIRONMENT WERE SUPPORTIVE OF HIGHER CAPE VALUES...ORGANIZED
SEVERE STORMS COULD BE POSSIBLE WITH MOST MODELS SHOWING 500 MB
FLOW OUT OF THE NORTH-NORTHEAST AT 35 KTS. THAT IS PRETTY
IMPRESSIVE FOR THIS TIME OF YEAR AND RESULTS IN BULK SHEAR
MAGNITUDES OF 35 TO 40 KTS WHICH IS BORDERLINE STRONG ENOUGH FOR
SUPERCELLS. HOWEVER...CAPE VALUES ARE EXPECTED TO BE LIMITED BY
MEAGER MID-LEVEL LAPSE RATES...SO MULTI-CELL AND ELEVATED STORMS
ARE MOST LIKELY...ASSUMING THE BEST CHANCE FOR STORMS FOR THE CWA
OCCURS AFTER SUNSET ON WEDNESDAY.

LEFT 20 POPS IN ACROSS THE CWA ON THURSDAY AS CONFIDENCE IS HIGHER
IN STORMS MOVING INTO THE CWA FROM THE NORTHEAST THAN IS HAS BEEN
LOOKING AT MODELS OVER THE PAST FEW DAYS. ASSUMING STORMS PAN
OUT WEDNESDAY/WEDNESDAY NIGHT...THERE WILL LIKELY BE SOME REMNANT
OUTFLOW BOUNDARIES...IF NOT A STALLED OUT WEAK FRONTAL
BOUNDARY...OVER THE CWA THAT MAY SET OFF ISOLATED STORMS DURING
THE DAY ON THURSDAY. OF COURSE IF STORMS DO NOT PAN OUT AT ALL
FROM WEDNESDAY AFTERNOON THROUGH THURSDAY MORNING...OUR CHANCES OF
STORMS ON THURSDAY WILL PROBABLY BE LOW. LOWERED HIGHS A FEW
DEGREES ON THURSDAY ASSUMING WE WOULD AT LEAST HAVE SOME HIGH
LEVEL CLOUDS LEFT OVER FROM WEDNESDAY NIGHT STORMS THAT WILL SLOW
DOWN HEATING A BIT...IF ONLY FOR A DAY.

FRIDAY THROUGH SATURDAY...MOST GUIDANCE AGREES THAT A STRONG
UPPER LEVEL LOW PRESSURE SYSTEM WILL MOVE OVER THE PACIFIC
NORTHWEST AND THEN PUSH EAST ALONG THE CONUS/CANADIAN BORDER LATE
THIS WEEK INTO THE WEEKEND. THIS SHOULD HELP DE-AMPLIFY THE UPPER
RIDGE IN PLACE OVER THE SOUTHERN CONUS ROCKIES...AND AT LEAST
TEMPORARILY REORIENT THE RIDGE AXIS OVER THE SOUTH PLAINS FOR
FRIDAY AND SATURDAY. ASSUMING A WEAK RIDGE IS IN PLACE OVER THE
CWA FRIDAY AND SATURDAY...THESE SHOULD BE OUR HOTTEST DAYS IN THE
7 DAY FORECAST AND CONTINUED TO ADVERTISE HIGHS IN THE 100 TO 103
DEGREE RANGE AS A RESULT.

THE HEAT WILL LIKELY CONTINUE ON SUNDAY INTO EARLY NEXT
WEEK...BUT CONFIDENCE IS LOWER IN THAT VERIFYING AS SOME OF THE
12Z MODEL RUNS ADVERTISE A COLD FRONT PUSHING TOWARDS THE CWA ON
SUNDAY BECAUSE OF THE PASSAGE OF THE STRONG NORTHERN STREAM UPPER
LOW WELL OFF TO OUR NORTH. BECAUSE THE UPPER LEVEL ENERGY IS SO
FAR REMOVED FROM THE CWA...THE FRONT PROBABLY WILL NOT MAKE IT
HERE...SO JUST MAINTAINED A HOT AND DRY FORECAST AT THIS TIME.
HOWEVER IF THE UPPER LOW DIGS SOUTH AND MOVES DIRECTLY OVER THE
GREAT LAKES STATES ON MONDAY...IT COULD PUSH THE UPPER LEVEL RIDGE
FAR ENOUGH WEST TO MAKE IT EASIER FOR COOLER AIR TO INVADE THE
REGION. WILL CONTINUE TO CLOSELY WATCH FUTURE MODEL RUNS TO SEE
HOW THIS STRONG UPPER LOW WILL EVOLVE OVER THE CONUS HEADED INTO
EARLY NEXT WEEK.

CAVANAUGH



&&


.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX  73  96  75  98  76 /   0   0   0   5   5
WACO, TX              74  95  74  96  74 /   0   0   0   5   5
PARIS, TX             67  91  71  93  73 /   0   0   0   5   5
DENTON, TX            70  95  72  96  73 /   0   0   0   5   5
MCKINNEY, TX          69  95  72  97  73 /   0   0   0   5   5
DALLAS, TX            74  96  77  97  78 /   0   0   0   5   5
TERRELL, TX           72  97  75  99  75 /   0   0   0   5   5
CORSICANA, TX         73  95  74  98  74 /   0   0   0  10  10
TEMPLE, TX            73  94  72  95  73 /   0   0   0   5   5
MINERAL WELLS, TX     71  95  72  97  72 /   0   0   0   5   5

&&

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

&&

$$

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