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

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000
FXUS64 KFWD 140437
AFDFWD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
1137 PM CDT SUN JUL 13 2014

.AVIATION...

FOR THE 06Z TAFS...VFR CONDITIONS ARE EXPECTED THROUGH THE VALID
FORECAST PERIOD. THUNDERSTORMS TOMORROW AFTERNOON AND THE TIMING
OF A COLD FRONT INTO THE REGION ARE STILL THE PRIMARY AVIATION
WEATHER CONCERNS.

NOT MUCH HAS CHANGED WITH REGARDS TO THUNDERSTORM CHANCES FOR
TOMORROW AFTERNOON...SO THE PREVIOUS DISCUSSION HAS BEEN APPENDED
BELOW.

THE ONLY REAL CHANGE FROM THE 00Z TAFS WAS TO INCLUDE A LINE FOR
PERSISTENT SHOWERS AND EMBEDDED THUNDERSTORMS AT THE END OF THE
DFW TAF. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED
TO PRECEDE THE FRONTAL BOUNDARY INTO NORTH TEXAS TOMORROW NIGHT.
THE TIMING OF THE FRONT IS DIFFICULT TO PIN DOWN AS MODELS ARE ALL
OVER THE PLACE REGARDING THE EXACT PASSAGE OF THE FRONT ACROSS THE
METROPLEX. WENT WITH THE NAM 4KM FORECAST SOUNDINGS FOR NOW WHICH
BRING THE FRONT INTO THE METROPLEX JUST AFTER MIDNIGHT...BUT THIS
MAY BE REFINED IN LATER FORECASTS.

CAVANAUGH

.../PREVIOUS AVIATION DISCUSSION/...
/ISSUED 706 PM CDT SUN JUL 13 2014/

FOR THE 00Z TAFS...VFR CONDITIONS ARE EXPECTED THROUGH THE VALID
FORECAST PERIOD. THUNDERSTORMS TOMORROW AFTERNOON...AND THE TIMING
OF A COLD FRONT INTO THE AREA TOMORROW NIGHT ARE THE PRIMARY
FORECAST CONCERNS.

VFR CONDITIONS AND SOUTHERLY WINDS WILL HOLD OVER THE NEXT 24 HRS
AT ALL AREA AIRPORTS. THE PRIMARY AVIATION WEATHER CONCERN IS
THUNDERSTORMS NEAR THE DFW AREA TOMORROW AFTERNOON. FORECAST
SOUNDINGS INDICATE THAT SURFACE BASED AIR CAN BE LIFTED TO ITS
LEVEL OF FREE CONVECTION IF THE WELL-MIXED SURFACE LAYER CAN
ATTAIN AN ALTITUDE OF ABOUT 9000 FT AGL. THIS MEANS THAT WE
BASICALLY NEED SURFACE BASED THERMAL COLUMNS TO CLIMB TO THE 700
MB LEVEL FOR THUNDERSTORMS TO DEVELOP TOMORROW AFTERNOON. MOST
FORECAST SOUNDINGS SHOW THIS HAPPENING RIGHT AROUND THE PEAK
HEATING HRS OF THE DAY...OR AROUND 21Z. AS A RESULT...WENT AHEAD
AND BACKED UP THE MENTION OF VCTS AROUND THE DFW AREA TO 21Z FROM
19Z IN THE PREVIOUS SET OF TAFS.

ANY STORMS THAT MANAGE TO DEVELOP WILL PROBABLY BE SHORT
LIVED...BUT WILL BE CAPABLE OF PRODUCING SOME VERY STRONG
MICROBURST WINDS. A WELL-MIXED SURFACE LAYER 9000 FT DEEP IS A
CLASSIC ENVIRONMENT SUPPORTING STRONG DOWNDRAFTS/MICROBURSTS. THE
COVERAGE OF STORMS IS EXPECTED TO BE VERY SMALL TOMORROW... AROUND
10 TO 20 PERCENT. HOWEVER...ANY STORM WITHIN 15 MILES OF AN
AIRPORT MAY PRODUCE SUFFICIENTLY STRONG OUTFLOW TO SEND VERY
STRONG WINDS ACROSS AREA AIRPORTS TOMORROW. DID NOT WANT TO PUT
STRONG WINDS IN THE TAFS RIGHT NOW...MAINLY BECAUSE VRB 30G40KTS
IN A TAF WILL ALL BUT SHUT DOWN AREA AIRPORTS...BUT ALSO BECAUSE
CONFIDENCE IN THE PLACEMENT OF ANY INDIVIDUAL STORM TOMORROW IS
VERY LOW AT THIS TIME. WILL LIKELY NEED TO UPDATE TAFS FREQUENTLY
TOMORROW AFTERNOON BY WATCHING SHORT-TERM RADAR TRENDS.

IN TERMS OF THE COLD FRONT...MOST MODELS HAVE ITS LEADING EDGE
PASSING THE METROPLEX AREA AIRPORTS FROM 06-07Z TOMORROW NIGHT.
THIS IS RIGHT AT THE END OF THE DFW 30 HR TAF...SO WILL LEAVE THE
WIND SHIFT ASSOCIATED WITH THE FRONT OUT OF THE EXTENDED TAF AT
THIS TIME.

CAVANAUGH




&&

.UPDATE...
THUNDERSTORMS WILL REMAIN WELL NORTH OF THE RED RIVER OVERNIGHT
IN THE VICINITY OF A SLOW MOVING COLD FRONT. THE FRONT WILL PUSH
SOUTH DURING THE DAY MONDAY AS AN UPPER TROUGH DEEPENS OVER THE
GREAT LAKES REGION. IT STILL LOOKS LIKE SCATTERED STORMS WILL BE
POSSIBLE TOMORROW AFTERNOON AND EVENING ALONG AND AHEAD OF THE
FRONT...OVER AREAS MAINLY ALONG AND NORTH OF THE I-20 CORRIDOR. A
FEW OF THE STORMS COULD BECOME STRONG TO SEVERE WITH DAMAGING
WINDS THE PRIMARY THREAT.

OTHERWISE...MOSTLY CLEAR SKIES AND WARM CONDITIONS ARE EXPECTED
OVERNIGHT WITH LOWS IN THE 70S...FOLLOWED BY HIGHS APPROACHING
TRIPLE DIGITS ONE MORE TIME TOMORROW AFTERNOON AHEAD OF THE
FRONT. THE CURRENT FORECAST IS IN GOOD SHAPE WITH ONLY MINOR GRID
UPDATES NEEDED.

30

&&

.PREV DISCUSSION... /ISSUED 329 PM CDT SUN JUL 13 2014/
WATER VAPOR LOOP SHOWS THE TWO FEATURES OF PRIMARY INTEREST FOR
OUR REGION. THE FIRST FEATURE IS A LARGE UPPER LOW OVER MANITOBA
THAT WILL DROP SOUTHEAST AND SEND A COLD FRONT INTO OUR REGION
MONDAY NIGHT. THE SECOND FEATURE IS AN UPPER LOW OFF OF THE
PACIFIC NW COAST THAT WILL BECOME THE CATALYST FOR WHAT LOOKS LIKE
A WIDESPREAD RAIN EVENT FOR NORTH CENTRAL TEXAS MID TO LATE WEEK.

THERE ARE SIGNS THAT THE UPPER LEVEL HIGH CENTERED OVER OKLAHOMA
YESTERDAY IS ALREADY BEGINNING TO MOVE WESTWARD...AND NORTHERLY
MID LEVEL FLOW SHOULD BEGIN TO SET UP OVER THE REGION TOMORROW.
ALTHOUGH THE COLD FRONT WILL LIKELY NOT MAKE IT INTO THE CWA UNTIL
AFTER SUNSET MONDAY...THE MID LEVELS SHOULD BEGIN TO MOISTEN UP BY
THE AFTERNOON HOURS. WITH TEMPERATURES SET TO SOAR TO AROUND 100
AGAIN TOMORROW AFTERNOON...ISOLATED HIGH-BASED STORMS WILL DEVELOP
WITHIN THE ELEVATED MOISTURE PLUME GENERALLY NORTH OF I-20. MODEL
SOUNDINGS INDICATE THE CLASSIC INVERTED-V PROFILE CHARACTERISTIC
OF SEVERE MICROBURSTS. WHILE POPS WILL BE KEPT IN THE 10-20
PERCENT RANGE...IT IS WORTH STRESSING THAT THESE PROBABILITIES ARE
FOR MEASURABLE RAINFALL. MOS POPS INTERESTINGLY ENOUGH SHOW
PROBABILITY OF HEARING THUNDER AT 30-40 PERCENT IN THE AFTERNOON
AND EVENING SUGGESTING MANY MORE LOCATIONS MAY BE IMPACTED BY
GUSTY WINDS AND OUTFLOW BOUNDARIES FROM NEARBY STORMS WHILE SEEING
NO RAIN. THE CHANCE OF ACTUAL RAIN WILL INCREASE DURING THE
EVENING AND OVERNIGHT HOURS...BUT WITH THE ATMOSPHERE
COOLING...THIS ACTIVITY WILL BE ELEVATED AND FAIRLY WEAK...POSING
NO THREAT OF SEVERE WEATHER.

CONTINUE TO PREFER THE ECMWF/NAM FORECASTS OF DRYING THE REGION
OUT ON TUESDAY BEHIND THE FRONT...BUT WILL HOLD ONTO 20 POPS AREA
WIDE FOR ISOLATED MAINLY ELEVATED ACTIVITY AS THE LOW LEVEL
AIRMASS WILL FEATURE LITTLE INSTABILITY. THE FRONT WILL LIKELY
REACH THE SOUTHERN COUNTIES TUESDAY BUT COLD AIR WILL BE SLOW TO
FILTER INTO THE REGION AS IT UNDERGOES MODIFICATION IN THE INTENSE
JULY SUNSHINE AS IT TRAVELS THROUGH THE PLAINS. SO WHILE HIGH
TEMPS WILL BE 5 TO 10 DEGREES COOLER TUESDAY...THEY WILL STILL
BE IN THE 90S FOR MOST AREAS.

BY WEDNESDAY THE AFOREMENTIONED UPPER LEVEL LOW OFF THE PACIFIC NW
WILL BE APPROACHING THE REGION FROM THE NORTHWEST. THIS WILL CAUSE
THE COLD FRONT TO BECOME STATIONARY ROUGHLY ALONG A LINE FROM
ABILENE TO HILLSBORO TO PALESTINE. PERSISTENT MOISTURE CONVERGENCE
NEAR THE FRONTAL BOUNDARY WILL CAUSE PRECIPITABLE WATER VALUES TO
INCREASE TO 2 TO 2.25 INCHES CAUSING THE AIRMASS OVER THE REGION
TO BECOME CONDITIONALLY UNSTABLE. INCREASING LIFT AHEAD OF THIS
UPPER LEVEL ENERGY SHOULD RESULT IN CONVECTION BY LATE WEDNESDAY
AFTERNOON OVER THE NW ZONES...SPREADING EAST AND SOUTHEAST
WEDNESDAY EVENING. THE GFS AND THE OTHER MODELS TO A LESSER
DEGREE INDICATE AN ENVIRONMENT FAVORABLE FOR A MCS TO DEVELOP OVER
NW TEXAS AND SW OKLAHOMA WEDNESDAY AFTERNOON. SHOULD THIS MCS
DEVELOP...IT WILL MOVE SOUTHEASTWARD INTO OUR AREA WEDNESDAY
NIGHT. IT IS WORTH NOTING THAT THE GFS RUNS LATELY HAVE BEEN
SUFFERING FROM CONVECTIVE FEEDBACK...WITH CONTAMINATED MASS FIELD
AND OUTRAGEOUSLY HIGH QPF WEDNESDAY NIGHT AND THURSDAY MORNING.
WHILE THE ATMOSPHERE CAN UNDERGO A FEEDBACK LOOP OF ITS OWN AS A
RESULT OF WARM CORE VORTEX AMPLIFICATION...THIS IS UNLIKELY TO
OCCUR WHEN ANY LOW LEVEL BAROCLINICITY...IE A FRONT...IS IN THE
AREA. THUS IF A MCS WERE TO FORM IT WOULD TRACK FASTER TO THE
SOUTHEAST THAN THE GFS INDICATES...AND WOULD LIMIT THE POTENTIAL
FOR EXCESSIVE RAINFALL. STILL THIS WEDNESDAY NIGHT SYSTEM MAY DROP
AN EASY 1-2 INCHES ACROSS THE CWA...WITH THE NORTHERN HALF OF THE
AREA BEING MORE FAVORED. HIGHEST POPS OF 70 PERCENT WILL BE
FEATURED THERE WITH 40-50 PERCENT IN THE SOUTH.

IN THE WAKE OF THE PROBABLE WEDNESDAY NIGHT MCS...ADDITIONAL
ROUNDS OF CONVECTION WILL FIRE UP OVER THE REGION THURSDAY AND
INTO FRIDAY AS THE UPPER LOW LUMBERS EASTWARD OVER THE STATE. THE
FRONT DURING THIS TIME WILL ALSO ADVANCE SOUTHWESTWARD AIDED BY
COOL CONVECTIVE OUTFLOWS AND PERSISTENT ALBEIT WEAK COLD
ADVECTION FROM NORTHEASTERLY LOW LEVEL FLOW. ISENTROPIC LIFT OVER
THE INCREASINGLY FRONTOGENETIC FRONT SHOULD ENSURE SCATTERED TO
NUMEROUS SHOWERS AND STORMS THURSDAY AND INTO FRIDAY. THIS WEATHER
PATTERN IS A SET UP MORE TYPICAL OF LATE MAY OR EARLY JUNE...AND
THUS IS A REASON FOR THE HIGH CONFIDENCE OF RAINFALL IN OUR
TYPICALLY DRIEST MONTH.

AVERAGE RAIN TOTALS OF 2-3 INCHES ARE EXPECTED ALONG AND NORTH OF
I-20 WITH 1-2 INCHES SOUTH OF I-20. GIVEN THE HIGH PRECIPITABLE
WATER...FAIRLY WEAK WIND PROFILES AND SKINNY CAPE...THERE WILL BE
A THREAT FOR LOCALLY HEAVY RAINFALL AND FLASH FLOODING. WHETHER
FLASH FLOODING OCCURS IS GOING TO DEPEND ON MESOSCALE ATMOSPHERIC
INTERACTIONS AND THEREFORE WE WILL HAVE TO GET IN RANGE OF SOME OF
OUR HIGH-RES AND EXPLICIT CONVECTION RESOLVING MODELS BEFORE WE TRY
TO PINPOINT A FLOOD RISK REGION. AS FOR SEVERE WEATHER...THERE IS
SOME THREAT WEDNESDAY AFTERNOON AND EVENING AHEAD OF THE FIRST
ROUND OF WIDESPREAD CONVECTION WHEN THE ATMOSPHERE MAY CONTAIN
ENOUGH INSTABILITY FOR ROTATING UPDRAFTS. AGAIN IT IS TOO EARLY TO
GET A DEFINITE HANDLE ON THIS THREAT AS WELL.

HIGHS THURSDAY WILL BE IN THE 80S...AND POSSIBLY IN THE 70S FOR
NORTHERN AREAS AS CLOUDS AND RAIN LOOK LIKELY. TEMPS WILL NOT
REBOUND INTO THE 90S UNTIL SATURDAY WHEN THE UPPER TROUGH CLEARS
THE AREA AND THE SUN RETURNS. HAVE KEPT THE WEEKEND FORECAST
GENERALLY DRY FOR MOST AREAS IN FAVOR OF THE ECMWF FORECAST. IT IS
WORTH NOTING THAT THE GFS TRIES TO BRING ANOTHER NW FLOW MCS INTO
THE AREA THIS WEEKEND...BUT WILL NOT BITE OFF ON THIS YET. ALL
MODELS SHOW A RETURN TO A MORE TYPICAL JULY BY NEXT WEEK AS A
STRONG UPPER HIGH BUILDS TO OUR NORTHWEST.

TR.92



&&


.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX  78 100  75  92  72 /   0  10  30  20  10
WACO, TX              73  99  75  94  72 /   0   5  20  20  20
PARIS, TX             73  99  72  88  65 /   5  20  30  20  10
DENTON, TX            74 100  74  90  68 /   0  20  30  20  10
MCKINNEY, TX          74 100  73  91  69 /   0  20  30  20  10
DALLAS, TX            80 100  76  92  73 /   0  10  30  20  10
TERRELL, TX           76 100  74  92  72 /   0  10  30  20  10
CORSICANA, TX         74  98  74  92  71 /   5   5  20  20  20
TEMPLE, TX            72  99  75  97  72 /   0   5  10  20  20
MINERAL WELLS, TX     70 100  73  91  70 /   0  10  30  20  20

&&

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

&&

$$

 /




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