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

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FXUS64 KFWD 202151 CCA
AFDFWD

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE FORT WORTH TX
339 PM CST THU NOV 20 2014

.DISCUSSION...

20Z/2PM SUBJECTIVE SURFACE ANALYSIS INDICATED A WARM FRONT WAS IN
PLACE NEAR THE RED RIVER. TO THE NORTH OF THE FRONT TEMPERATURES
WERE IN THE UPPER 50S TO LOW 60S WHILE SOUTH OF THE FRONT (ACROSS
MOST OF THE CWA) TEMPERATURES WERE IN THE LOW 70S FOR THE FIRST
TIME IN OVER A WEEK. DEW POINTS ACROSS CENTRAL TEXAS STARTED THE
DAY OFF IN THE LOW 40S...WHICH INCREASED INTO THE MID TO UPPER 50S
AT 20Z. LOW 60S DEW POINTS WERE OBSERVED ACROSS DEEP SOUTH
TEXAS...ADVECTING NORTH TOWARDS THE HILL COUNTRY AND ALONG THE
TEXAS GULF COAST. AFTERNOON WATER VAPOR SATELLITE IMAGERY SHOWED A
SHORTWAVE TROUGH OVER ARIZONA MOVING EAST...AND ANOTHER
SIGNIFICANTLY STRONGER UPPER LEVEL TROUGH JUST OFF THE CENTRAL
CALIFORNIA COAST...MOVING SOUTHEAST. THESE TWO UPPER TROUGHS ARE
EXPECTED TO BRING GOOD RAIN CHANCES ACROSS THE CWA FROM TOMORROW
THROUGH SATURDAY EVENING.

THROUGH TONIGHT...REGIONAL RADARS WERE ALREADY SHOWING SOME
ISOLATED RAIN SHOWERS EAST OF INTERSTATE 35 FROM WACO TO
TEMPLE...MOVING NORTHEAST AS OF 3 PM CDT. THIS WAS WELL CORRELATED
WITH A 850 MB JET OF 25 TO 30 KTS PER REGIONAL VAD WIND PROFILES
WITHIN THE CORRIDOR OF 50S DEW POINTS SURGING NORTH ACROSS CENTRAL
TEXAS. EXPECT THAT THIS ELEVATED RAIN SHOWER ACTIVITY WILL
PERSIST...BUT ALSO INCREASE IN COVERAGE OVERNIGHT AS THE LOW-LEVEL
JET STRENGTHENS SLIGHTLY WITH THE AID OF THE ARIZONA SHORTWAVE
TROUGH MOVING EAST ACROSS THE REGION. 12Z RAOB ANALYSIS INDICATED
A PLUME OF STEEPER LAPSE RATES IN THE 700 TO 500 MB LAYER OUT
AHEAD OF THE ARIZONA SHORTWAVE TROUGH. EXPECT THESE STEEPER LAPSE
RATES TO ADVECT EAST WITH THE TROUGH OVERNIGHT...INCREASING THE
POTENTIAL FOR THUNDERSTORMS TO BECOME EMBEDDED IN THE MORE
WIDESPREAD RAIN SHOWER ACTIVITY THROUGH SUNRISE. NO SEVERE WEATHER
IS EXPECTED TONIGHT AS ALL THUNDERSTORM ACTIVITY IS EXPECTED TO
REMAIN ELEVATED IN NATURE. THE STRENGTHENING LOW-LEVEL JET AND
PERSISTENT POSITIVE MOISTURE ADVECTION WILL KEEP TEMPERATURES MUCH
WARMER TONIGHT THAN THEY HAVE BEEN THE PAST SEVERAL NIGHTS. EXPECT
LOWS TO HOLD UP IN THE MID TO UPPER 50S FOR MOST LOCATIONS.

FRIDAY...THE ARIZONA SHORTWAVE TROUGH IS EXPECTED TO PUSH EAST OF
THE REGION BY FRIDAY MORNING...RESULTING IN SOME WEAK SHORTWAVE
RIDGING SETTING UP OVER THE REGION OUT AHEAD OF THE
APPROACHING...AND SIGNIFICANTLY STRONGER...CALIFORNIA UPPER
TROUGH. IN GENERAL...SHORTWAVE RIDGING DOES NOT BODE WELL FOR
PRECIPITATION CHANCES...AND IF WE WERE ONLY DEALING WITH SHORTWAVE
RIDING...A DRY FORECAST WOULD LIKELY BE SUPPORTED ON FRIDAY. THE
PROBLEM IS THAT THE APPROACHING CALIFORNIA UPPER TROUGH WILL BE
INDUCING STRONG LOW-LEVEL CYCLOGENESIS OVER THE SOUTHERN HIGH
PLAINS AT THE SAME TIME. THIS LOW-LEVEL CYCLOGENESIS WILL RESULT
IN STRONG LOW-LEVEL WARM AIR AND POSITIVE MOISTURE
ADVECTION...WHICH ARE BOTH CATALYSTS FOR PRECIPITATION. ALSO...AS
THE ARIZONA UPPER TROUGH MOVES OVER THE REGION OVERNIGHT...THE
STRONGEST FORCING FOR SUBSIDENCE IN ITS WAKE REALLY MOVES EAST OF
THE AREA BY FRIDAY AFTERNOON. THE LACK OF SUBSIDENCE ALOFT DOES
NOT EQUATE TO LIFT...BUT IT WILL NOT WORK AS STRONGLY AGAINST THE
PERSISTENT LOW-LEVEL LIFT THAT IS EXPECTED TO BE PRESENT ALL DAY
FRIDAY. AS A RESULT...THINK THAT THE PERSISTENT LOW-LEVEL LIFT
EVENTUALLY WINS OUT...AND BUMPED POPS UP INTO THE LIKELY CATEGORY
(AROUND 60 PERCENT) FOR LOCATIONS EAST OF INTERSTATE 35 FRIDAY
AFTERNOON AS A RESULT.

SEVERE WEATHER CHANCES ON FRIDAY ARE GENERALLY LOW FOR MOST
LOCATIONS...HOWEVER THE NAM DOES INDICATE A CONDITIONAL WINDOW OF
OPPORTUNITY FOR SOME SURFACE BASED SEVERE STORMS WEST OF
INTERSTATE 35 DURING THE PEAK HEATING HOURS OF THE DAY. NAM
FORECAST SOUNDINGS FOR STEPHENVILLE INDICATE THE POTENTIAL FOR
AROUND 1500 J/KG OF CAPE WITH 0-6 KM BULK SHEAR MAGNITUDES AROUND
40 KTS. FROM A PARAMETER STAND POINT ALONE...THIS IS SUFFICIENT TO
SUPPORT SUPERCELL THUNDERSTORMS WHICH WOULD BE CAPABLE OF
PRODUCING ALL TYPES OF SEVERE WEATHER. HOWEVER...THERE ARE SOME
STRONG CAVEATS THAT LIMIT CONFIDENCE IN THIS SOLUTION AT THIS
TIME.

THE FIRST LIMITING FACTOR IS THAT THERE IS NO STRONG LIFTING
MECHANISM FOR STORMS WEST OF INTERSTATE 35 FRIDAY AFTERNOON. IF
THERE ARE NO STORMS...THERE IS OBVIOUSLY NO SEVERE WEATHER
THREAT...SO THAT REPRESENTS A FAIRLY BIG LIMITING FACTOR AT THIS
TIME. THE SECOND LIMITING FACTOR IS THAT THE NAM SEEMS TO
REPRESENT THE WORST CASE SCENARIO WHEN COMPARED TO OTHER MODEL
GUIDANCE. IT IS POSSIBLE THAT THE NAM IS SIMPLY OVER-DOING THE
STRONG MOISTURE RETURN...AND OVERESTIMATING THE POTENTIAL FOR
AFTERNOON HEATING. SO...WHILE IT LOOKS VERY UNLIKELY AT THIS
TIME...IF THERE IS GOING TO BE AN ENHANCED SEVERE WEATHER THREAT
TOMORROW AFTERNOON...WE WILL NEED SOME SUNSHINE WHICH MAY BE HARD
TO COME BY...AND DEW POINTS WILL NEED TO SURGE UP TO AROUND 65
DEGREES WEST OF INTERSTATE 35. AT THIS TIME 65 DEGREE DEW POINTS
ONLY EXIST AROUND CORPUS CRISTI...SO WE WILL CONTINUE TO ADVERTISE
A LOW SEVERE WEATHER THREAT FOR FRIDAY...WHILE WATCHING THE ABOVE
MENTIONED FEATURES THROUGHOUT THE DAY FOR ANY CHANGES TO THIS
THINKING.

FRIDAY NIGHT...THE CALIFORNIA UPPER TROUGH IS EXPECTED TO MOVE
OVER FAR WEST TEXAS...CAUSING STRONG FRONTOGENESIS AND LOW-LEVEL
CONVERGENCE TO DEVELOP FROM OKLAHOMA CITY...SOUTH-SOUTHWEST ACROSS
WEST CENTRAL TEXAS TOWARDS ABILENE. THIS WILL CHANGE THE FOCUS FOR
PRECIPITATION FROM LOCATIONS EAST OF INTERSTATE 35 TO LOCATIONS
WEST OF INTERSTATE 35 OVERNIGHT. THE BEST CHANCES FOR ELEVATED
SEVERE STORMS APPEAR TO REMAIN JUST WEST OF THE CWA
OVERNIGHT...HOWEVER IF ORGANIZED/SEVERE STORMS MATERIALIZE OVER
THE WESTERN CWA...LARGE HAIL APPEARS TO BE THE PRIMARY THREAT.
HEAVY RAINFALL IS ALSO POSSIBLE FRIDAY NIGHT...HOWEVER THIS THREAT
ALSO LOOKS MAXIMIZED NEAR THE STRONGEST ZONE OF CONVERGENCE WEST
OF THE CWA AT THIS TIME.

SATURDAY...THE UPPER TROUGH IS EXPECTED TO SWING OUT TO THE EAST
OVER THE REMAINDER OF TEXAS ON SATURDAY...SPREADING STRONG LARGE
SCALE FORCING FOR ASCENT OVER THE CWA FROM WEST TO EAST AS IT
MOVES BY. SATURDAY STILL REPRESENTS THE OVERALL BEST CHANCES FOR
THUNDERSTORMS...LOCALLY HEAVY RAINFALL...AND SEVERE WEATHER ACROSS
NORTH AND CENTRAL TEXAS. THE TROUGH IS EXPECTED TO MOVE OVER THE
AREA AND AT LEAST BE NEUTRALLY TILTED...POSSIBLY BECOMING
NEGATIVELY TILTED BY LATE SATURDAY AFTERNOON AS IT HEADS ALMOST
DIRECTLY OVER CENTRAL TEXAS. THE TILT OF A TROUGH RELATES TO HOW
ITS BASE IS ORIENTED WITH RESPECT TO THE REST OF THE TROUGH. IF
THE TROUGH IS MOVING EAST...AND ITS BASE IS ORIENTED DUE
SOUTH...THIS IS NEUTRALLY TILTED. IF THE BASE OF THE TROUGH TILTS
TOWARDS THE SOUTHEAST IN THIS CASE...IT BECOMES NEGATIVELY TILTED.
THE REASON A TROUGH`S TILT IS IMPORTANT IS BECAUSE AN UPPER LEVEL
TROUGH TYPICALLY CONTAINS COLD AIR IN ITS BASE. A NEGATIVELY
TILTED TROUGH ALLOWS COLD AIR ALOFT TO MOVE OVER WARM AIR NEAR THE
SURFACE...INCREASING INSTABILITY DOWNSTREAM.

ON SATURDAY...TO ASSESS THE SEVERE WEATHER POTENTIAL...ONE OF THE
THINGS WE WILL BE WATCHING FOR IS THE UPPER TROUGH`S TILT. IF IT
BECOME NEGATIVELY TILTED...THE RISK OF SEVERE STORMS WILL BE MORE
LIKELY TO SURGE NORTH ACROSS THE CWA. IF IT REMAINS NEUTRALLY
TILTED...THE STRONGEST SEVERE STORMS WILL TEND TO REMAIN
SOUTH...EITHER IN CENTRAL TEXAS OR FARTHER SOUTH TOWARDS THE GULF
COAST. ASIDE FROM THE TILT...WE WILL ALSO HAVE TO ASSESS THE
STRENGTH AND QUALITY OF LOW-LEVEL MOISTURE RETURN ON SATURDAY.
MODELS ARE FORECASTING A 50 KT LOW-LEVEL JET (SPRING TIME SEVERE
WEATHER STRENGTH) WHICH CERTAINLY HAS THE POTENTIAL TO BUMP UP THE
INSTABILITY AND POTENTIAL FOR SEVERE STORMS ACROSS THE CWA. THE
BIGGEST LIMITING FACTOR IS GOING TO BE HEATING. EVERY MODEL SHOWS
THICK CLOUD COVER OVER THE ENTIRE CWA ON SATURDAY...SO SIGNIFICANT
HEATING JUST DOES NOT LOOK LIKE IT`S GOING TO HAPPEN. AS A
RESULT...OUR SEVERE WEATHER THREAT ON SATURDAY IS ALSO
CONDITIONAL...AND WE WILL HAVE TO WAIT AND SEE HOW STRONG MOISTURE
RETURN IS FRIDAY NIGHT...AND MONITOR THE TILT OF THE TROUGH ON
SATURDAY TO TRULY ASSESS OUR SEVERE WEATHER THREAT LOCALLY.

NO MATTER WHAT...THERE WILL BE AT LEAST A LOW CHANCE FOR SEVERE
STORMS ACROSS MOST OF THE CWA ON SATURDAY. THE BEST CHANCE FOR
STORMS ALONG THE INTERSTATE 35 CORRIDOR APPEARS TO BE IN THE
MIDDLE OF SATURDAY AFTERNOON. PARAMETERS INDICATE THAT THIS IS A
GOOD SET UP FOR SEVERE WEATHER IN A SET UP THAT HAS BEEN
CLASSIFIED AS "LOW-CAPE/HIGH-SHEAR". THERE IS A COMPOSITE
PARAMETER THAT WAS DEVELOPED RECENTLY CALLED THE SHERB THAT
ASSESSES THIS TYPE OF SEVERE WEATHER POTENTIAL. THIS PARAMETER`S
IDEAL VALUE...WHICH IS ANYTHING CLOSE TO 1.0...OCCURS ALONG THE
INTERSTATE 35 CORRIDOR SATURDAY AFTERNOON. SO NO MATTER
WHAT...THERE APPEARS TO BE A LOW-END THREAT FOR HAIL AND DAMAGING
WINDS ACROSS THE AREA SATURDAY...WITH TORNADOES AND HIGHER END
SEVERE WEATHER CONTINGENT ON OTHER FACTORS DISCUSSED ABOVE COMING
TOGETHER.

THERE IS ALSO A THREAT FOR HEAVY RAINFALL ANYWHERE ACROSS THE CWA
ON SATURDAY. DO NOT THINK WIDESPREAD FLOODING IS LIKELY AT THIS
TIME AS MOST OF THE AREA REMAINS ENTRENCHED IN A SIGNIFICANT
DROUGHT. BECAUSE OF RECENT HARD FREEZES...MOST AREA VEGETATION IS
DORMANT. THIS WILL INCREASE RUNOFF...HOWEVER...AREA
LAKES..RESERVOIRS AND RIVERS ARE SO LOW THAT THERE IS AN
INCREDIBLE AMOUNT OF CAPACITY FOR RUNOFF. THE WEST GULF RIVER
FORECAST CENTER RAN A CONTINGENCY FORECAST FOR WIDESPREAD 4 INCHES
OF RAIN AND NOTED NO HIGH END RIVER FLOODING IN THEIR MODELS.
WIDESPREAD 4 INCH RAINFALL IS WELL BEYOND ANYTHING IN THE
FORECAST...BUT WAS DONE SIMPLY TO ILLUSTRATE THE IMMENSE CAPACITY
FOR RUNOFF THAT CURRENT HYDROLOGIC CONDITIONS CAN TAKE. HEAVY
RAINFALL OVER ANY URBAN AREA MAY RESULT IN FLASH FLOODING...BUT
THIS IS EXPECTED TO REMAIN LOCALIZED...SO NO FLOOD WATCH IS
PLANNED AT THIS TIME.

BEHIND THE UPPER TROUGH ON SUNDAY...STRONG FORCING FOR SUBSIDENCE
WILL BRING ABOUT AN ABRUPT END TO PRECIPITATION ACROSS THE REGION
BY SUNDAY MORNING...LEAVING MOSTLY SUNNY SKIES AND DRY WEATHER FOR
ALL DAY ON SUNDAY. MODELS ARE INDICATING THAT STRONG WESTERLY
WINDS MAY BUILD ACROSS THE AREA ON SUNDAY. AT THIS TIME MODEL
SURFACE WINDS ARE ONLY ADVERTISING 15-25 MPH WINDS...HOWEVER MODEL
850 MB WINDS (AROUND 5000 FEET ABOVE GROUND LEVEL) ARE BEING
ADVERTISED IN THE 40-50 KT RANGE. IF ANY OF THIS STRONG WIND ALOFT
MIXES DOWN TO THE SURFACE...A WIND ADVISORY MAY BE NEEDED...AND
SIGNIFICANT CROSSWIND IMPACTS COULD OCCUR AT REGIONAL AIRPORTS. AT
THIS TIME THESE STRONG WINDS ALOFT ARE NOT EXPECTED TO MIX
DOWN...BUT THIS IS SOMETHING WE WILL BE WATCHING CLOSELY OVER THE
NEXT COUPLE OF DAYS.

REMAINDER OF THE FORECAST...RELATIVELY COOL AND DRY CONDITIONS ARE
EXPECTED BEHIND SATURDAY`S BIG UPPER TROUGH. A FRONT WILL MOVE
ACROSS THE AREA SUNDAY NIGHT...BUT THIS IS NOT A STRONG ARCTIC
COLD FRONT...AND TEMPERATURES ARE ONLY EXPECTED TO FALL SLIGHTLY
BELOW NORMAL FOR EARLY NEXT WEEK. MODELS CONTINUE TO STRUGGLE WITH
THE LARGE SCALE FLOW PATTERN FOR LATE NEXT WEEK. THE ECMWF
CONTINUES TO ADVERTISE A STRONG COLD FRONT MOVING ACROSS THE
REGION ON THANKSGIVING DAY...WHILE THE GFS KEEPS THIS FRONT OVER
THE EASTERN CONUS...MAKING FOR MUCH MILDER WEATHER FOR
THANKSGIVING WEEKEND. THE CURRENT FORECAST IS MORE IN LINE WITH
THE GFS SOLUTION AT THIS TIME.

CAVANAUGH

&&

.AVIATION...
/ISSUED 1133 AM CST THU NOV 20 2014/
/18Z TAFS/

CONCERNS...VFR CONDITIONS WILL DETERIORATE INTO LIFR/IFR CATEGORY
THIS EVENING AND OVERNIGHT. SCATTERED SHOWERS WILL BE POSSIBLE
THIS EVENING AND OVERNIGHT.

VFR CONDITIONS WILL PREVAIL THIS AFTERNOON WITH SOUTH WINDS
GENERALLY BELOW 12 KTS. BKN VFR CIGS BETWEEN 3-5 KFT WILL SPREAD
NORTH ACROSS THE REGION THIS AFTERNOON AND THEN CIGS WILL START TO
LOWER THIS EVENING AS ADDITIONAL GULF MOISTURE SPREADS ACROSS THE
REGION. EXPECT IFR CIGS AND MVFR VISBY AT THE DFW TAF SITES AND LIFR
CIGS AND MVFR VISBY AT KACT BY MIDNIGHT /05-06Z/. IN
ADDITION...SCATTERED AREAS OF LIGHT RAIN AND/OR SHOWERS ARE
EXPECTED TO DEVELOP OVERNIGHT BUT MOST OF THE RAIN ACTIVITY WILL
REMAIN EAST OF THE AIRPORTS. WILL KEEP A VCSH MENTION OVERNIGHT.
THE PRECIPITATION FORECAST BEYOND 21/12Z IS A LITTLE UNCERTAIN
WITH SEVERAL DIFFERENT SOLUTIONS SUGGESTED BY THE VARIOUS MODELS.
THE HI-RES MODELS SUGGEST A BREAK IN THE PRECIPITATION AS WEAK
RIDGING MOVES OVER THE REGION DURING THE DAY FRIDAY. WILL SIDE
WITH THE HI-RES MODELS AND KEEP THE TAF DRY DURING THE DAY ON
FRIDAY. HOWEVER...BY LATE FRIDAY AFTERNOON...MAY HAVE TO INCLUDE A
VCTS MENTION. IFR AND LIFR CIGS MAY LIFT INTO MVFR CATEGORY BY
FRIDAY AFTERNOON WITH THE FOG DISSIPATING AS WELL. HOWEVER...WITH
WARM AIR ADVECTION AND SOUTH WINDS CONTINUING TO ADVECT GULF
MOISTURE INTO THE REGION...MAY HAVE TO HOLD ONTO IFR CONDITIONS
INTO THE FRIDAY AFTERNOON HOURS.

82/JLD


&&

.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX  58  71  61  68  55 /  30  40  50 100  60
WACO, TX              60  72  62  70  53 /  30  60  50 100  40
PARIS, TX             52  65  57  66  57 /  40  60  70  90 100
DENTON, TX            57  70  61  66  53 /  30  40  70 100  60
MCKINNEY, TX          57  68  60  67  55 /  30  50  50 100  70
DALLAS, TX            59  70  61  67  55 /  30  50  50 100  70
TERRELL, TX           58  69  59  69  56 /  40  60  50 100  80
CORSICANA, TX         59  71  60  70  56 /  40  60  40 100  70
TEMPLE, TX            60  73  63  71  53 /  30  60  50 100  30
MINERAL WELLS, TX     56  70  61  68  50 /  20  30  80 100  30

&&

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

&&

$$

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