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

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000
FXUS64 KFWD 241805 AAB
AFDFWD

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE FORT WORTH TX
105 PM CDT TUE MAR 24 2015

.AVIATION...
/18Z TAFS/

VFR CONDITIONS WILL OCCUR THROUGH MIDNIGHT AS A WEAK COLD FRONT
AND DRYLINE APPROACH THE DFW METRO AIRPORTS. THESE FEATURES WILL
NOT AFFECT THE PREVAILING SOUTHERLY LOW LEVEL FLOW OF AROUND 10
KTS. THESE FEATURES DO RETROGRADE BACK WEST BY LATE EVENING IN
RESPONSE TO NEW HEIGHT FALLS ASSOCIATED WITH ANOTHER SHORTWAVE
ROTATING ESE ACROSS THE CENTRAL HIGH PLAINS. THERE IS A VERY LOW
CONDITIONAL RISK FOR AN ISOLATED STRONG TO SEVERE STORM NORTH OF
THE DFW METRO AIRPORTS THIS EVENING...THOUGH CONFIDENCE IS
CERTAINLY TOO LOW FOR MENTION IN THE CURRENT TAF SET. WACO
REGIONAL WILL REMAIN VFR UNTIL JUST BEFORE MIDNIGHT...WHEN AN
INCREASING NOCTURNAL LLJ HELPS BRING IN LOW MVFR CIGS.

OVERNIGHT AND THROUGH LATE MORNING WEDNESDAY...CIGS WILL BE A
CHALLENGE AS MOISTURE SATURATION OCCURS ON EITHER SIDE OF 1 KFT.
WE BELIEVE INITIALLY THE CIGS WILL START OFF IFR AT DFW SITES FOR
A FEW HOURS AFTER 09Z...BEFORE APPROACHING LIFT AND A WEAKENING
LLJ BY SUNRISE ALLOW FOR CIGS TO RISE INTO LOW MVFR. WARMING AND
MIXING OF THE BOUNDARY LAYER BY LATE MORNING SHOULD BRING A RETURN
TO GUSTY SOUTH WINDS 15-20 KTS AND VFR CONDITIONS. NO 24-30 HR
FORECAST GROUP WAS ADDED TO DFW AIRPORTS WITH CONVECTION LATE
WEDNESDAY EXPECTED AFTER 00Z THURS. WACO WILL SEE MVFR CIGS LOWER
TO IFR BY 08Z...THEN BACK TO MVFR BY MID MORNING AS THEY MIX AND
WARM AS WELL.

BEST CONVECTIVE CHANCES WITH OUR SECOND UPPER SHORTWAVE WILL
OCCUR BETWEEN 02Z-05Z THURS FOR DFW AIRPORTS...THEN AFTER MIDNIGHT
THURS FOR WACO. A STRONG FROPA WILL MOVE ACROSS ALL AIRPORTS
BETWEEN MIDNIGHT AND SUNRISE THURSDAY MORNING WITH GUSTY NORTH
WINDS AROUND 20 KTS.

05/

&&

.UPDATE...
A QUICK FORECAST UPDATE WAS DONE TO BUMP UP THE HIGH TEMPERATURES
ACROSS THE NORTHEAST COUNTIES BY A COUPLE OF DEGREES WHERE
READINGS HAVE BEEN RUNNING 3 TO 5 DEGREES ABOVE FORECAST FOR THE
PAST FEW HOURS. TEMPERATURES ACROSS THE REST OF THE REGION ARE
LOOKING GOOD WITH HIGHS GENERALLY IN THE 80S EXPECTED THIS
AFTERNOON. AREAS OF STRATUS OCCURRING ACROSS THE SOUTHEAST
COUNTIES AND IN THE METROPLEX SHOULD SCATTER OUT OVER THE NEXT FEW
HOURS.

OTHERWISE ...ISOLATED STORMS ARE STILL EXPECTED NEAR THE RED
RIVER THIS EVENING...WITH HIGHER CHANCES OF STORMS ON TRACK FOR
TOMORROW EVENING. MORE DETAILS TO COME IN THE AFTERNOON PACKAGE.

30

&&

.PREV DISCUSSION... /ISSUED 418 AM CDT TUE MAR 24 2015/
AT 3 AM SURFACE ANALYSIS INDICATED A SURFACE LOW WAS LOCATED NEAR
DODGE CITY AND WAS MOVING FAIRLY QUICKLY OFF TO THE EAST. OVER
NORTH TEXAS...SOUTHERLY WINDS HAVE INCREASED IN RESPONSE TO THE
FALLING PRESSURES IN THE HIGH PLAINS. ONCE MIXING ENSUES THIS
MORNING...BREEZY AND OCCASIONALLY GUSTY SOUTH WINDS WILL OCCUR
UNTIL EARLY AFTERNOON WHEN WINDS BEGIN TO VEER TO THE SOUTHWEST
AND RELAX AHEAD OF A WEAK COLD FRONT THAT MOVES INTO THE NORTHWEST
ZONES. WHILE TRYING TO CLASSIFY THESE NEBULOUS SURFACE FEATURES IN
THE SPRING CAN BE TRICKY...THE NORTHWEST WINDS...RISING PRESSURES
AND WEAK COLD ADVECTION BEHIND THE BOUNDARY WOULD DEFINITELY ARGUE
A COLD FRONT RATHER THAN A DRY LINE WILL BE THE PRIMARY SURFACE
FEATURE THAT ARRIVES INTO THE AREA THIS AFTERNOON. WITH GENERALLY
SUNNY SKIES AND VEERING SURFACE WINDS...HAVE INCREASED HIGH TEMPS
TO THE LOW 90S IN THE WESTERN ZONES...AND MID-UPPER 80S ACROSS THE
I-35 CORRIDOR DUE TO ANTICIPATED PRE-FRONTAL SUBSIDENCE WARMING.

THE MAIN CHALLENGE IN THE FORECAST TODAY IS WHETHER CONVECTION CAN
INITIATE ALONG THE FRONTAL BOUNDARY LATE THIS AFTERNOON AND EARLY
EVENING. THE PRIMARY SHORTWAVE AND SURFACE LOW WILL TRACK MUCH TOO
FAR NORTH TO PROVIDE ANY DIRECT FORCING OVER THE REGION. THE CAP
WILL BE QUITE STRONG OVER THE REGION TODAY...BUT ALL GUIDANCE
SHOWS THE CAP LIFTING AND WEAKENING DURING THE COURSE OF THE DAY.
MOST OF THIS DYNAMIC LIFT TODAY IS A RESULT OF DIFFERENTIAL WARM
ADVECTION WHICH IS JUST AS IMPORTANT TO FINDING AREAS OF LIFT AS
THE MORE POPULAR CYCLONIC VORTICITY ADVECTION IS. USING MATH WE
CAN FIND AREAS OF DIFFERENTIAL THERMAL ADVECTION BY USING THE
LAPLACE OPERATOR TAUGHT IN A STANDARD DIFFERENTIAL EQUATIONS
COURSE. OF COURSE DOING THAT WOULD PROBABLY GIVE ME PTSD...SO THE
EASY WAY IS JUST TO LOOK FOR THE THERMAL ADVECTION THAT OCCURS
WITHIN A LOW LEVEL JET...SUCH THAT THE WARM ADVECTION FIELDS SHOW
A NOSE OR BULGE NORTHWARD. THE END RESULT IS THAT CINH BECOMES LOW
ENOUGH NORTH OF I-20 THAT GIVEN A SUFFICIENT MECHANICAL
PERTURBATION...CONVECTION WOULD DEVELOP. NEAR THE RED RIVER...CINH
IS EXPECTED TO BECOME ALMOST ZERO...AND THUS CONVECTIVE INITIATION
BECOMES MORE LIKELY FARTHER NORTH INTO OKLAHOMA.

GIVEN THE VEERING FLOW AHEAD OF THE FRONT...CONVERGENCE ALONG THE
BOUNDARY WILL NOT BE PARTICULARLY IMPRESSIVE. THERE IS VIRTUALLY
NO GUIDANCE...HIGH-RESOLUTION CONVECTION RESOLVING OR LOW-
RESOLUTION CONVECTION PARAMETERIZING...THAT FORECASTS INITIATION
TO OCCUR OVER OUR CWA TODAY. ALL OF THE GUIDANCE SHOWS US BEING
VERY CLOSE THOUGH...WITH INCREASING RH IN THE 800-900MB LAYER
ALONG THE FRONT. FURTHERMORE BECAUSE THIS BOUNDARY IS A FRONT
RATHER THAN A DRY LINE...THE FRONTOGENESIS LIFT ASSOCIATED WITH IT
IS ON THE WARM MOIST SIDE OF THE BOUNDARY. IN CONTRAST...THE
FRONTOGENESIS LIFT WITH A DRY LINE IS ON THE DRY AND WARMER
WESTERN SIDE...WHICH CAN BE A SIGNIFICANT IMPEDANCE TO CONVECTIVE
INITIATION. BECAUSE OF THIS WE ARE MORE INCLINED TO CONTINUE TO
KEEP POPS IN THE 10-20 PERCENT RANGE EAST OF A LINE FROM
GAINESVILLE TO WEATHERFORD LATE THIS AFTERNOON AND EVENING. WE
WILL LIKELY SEE CUMULUS CONGESTUS AND TOWERING CUMULUS ALONG THE
FRONT THIS AFTERNOON...AND IT IS REALLY UP TO A RANDOM CHANCE
EVENT THAT A STORM CAN FORM WHERE MECHANICAL FORCING IS STRONG
ENOUGH TO OVERCOME THE WEAK THERMODYNAMIC STABILITY. SHOULD A
STORM FORM AND GET GOING BEFORE TOO LONG AFTER SUNSET...IT WOULD
BECOME SUPERCELLULAR AND THE STEEP LAPSE RATES AND VERY COLD AIR
ALOFT WILL ALLOW FOR A POTENTIAL FOR VERY LARGE HAIL. FLOW IN THE
LOWER LEVELS LOOKS TOO WEAK TO BE CONCERNED ABOUT A TORNADO
THREAT...BUT OBVIOUSLY THIS THREAT IS NON-ZERO WHEN SURFACE BASED
SUPERCELLS ARE IN PLAY.

ON WEDNESDAY ANOTHER SHORTWAVE TROUGH WILL BE APPROACHING OUR
REGION ON A MORE SOUTHERLY TRACK THAN TODAYS SYSTEM. THIS WILL
CAUSE THE SURFACE LOW TO DEVELOP NEAR WICHITA FALLS...WITH AN
ATTENDANT DRYLINE S/SW OF THERE. THE GFS/ECMWF APPEAR TO BE MUCH
TOO FAR EAST WITH THE POSITION OF THE DRY LINE...AND PREFER THE
NAM/WRF MODELS WHICH HAVE THE DRYLINE JUST BEYOND OUR CWA DURING
THE AFTERNOON HOURS. MOST OF NORTH TEXAS WILL BE STRONGLY CAPPED
DURING THE DAYLIGHT HOURS...WITH ONLY THE CAP BECOMING BREAKABLE
WEST OF A COMANCHE TO MINERAL WELLS TO GAINESVILLE LINE BEFORE
SUNSET. ACROSS THE NW ZONES...SBCAPE WILL REACH 1500-2000 J/KG
AND LOW LEVEL WIND FIELDS WILL BE MORE STRONGLY SHEARED THAN THEY
ARE TODAY. THUS...ANY SUPERCELLS THAT FORM ON THE DRYLINE WILL BE
CAPABLE OF TORNADOES...IN ADDITION TO VERY LARGE HAIL AND DAMAGING
WINDS. WE DONT EXPECT THE STORMS TO DISSIPATE WHEN THEY REACH THE
MORE CAPPED AREAS ACROSS THE CENTRAL AND EASTERN ZONES WEDNESDAY
EVENING. INSTEAD THEY WILL KEEP TRACKING EAST...BUT JUST BECOME
ELEVATED ABOVE THE CAP WHERE VERY STEEP LAPSE RATES WILL STILL
YIELD 1000-1500 J/KG OF CAPE FOR THESE STORMS TO UTILIZE. SO WHILE
THE TORNADO THREAT WILL DROP OFF AS THEY REACH THE I-35
CORRIDOR...A HAIL AND WIND THREAT WILL CONTINUE TO EXIST...BUT THE
SEVERE THREAT WILL NOT BE AS SIGNIFICANT IN THIS REGION DUE TO THE
MORE LIMITED INSTABILITY.

THE COLD FRONT WILL PUSH THROUGH THE CWA RAPIDLY WEDNESDAY NIGHT
WITH PERHAPS MORE SCATTERED NON-SEVERE CONVECTION BEHIND THE
FRONT. ALL OF THIS ACTIVITY WILL PUSH SOUTHEAST AND OUT OF THE CWA
BY MIDDAY THURSDAY. MUCH COOLER TEMPERATURES ARE EXPECTED THURSDAY
WITH HIGHS NEAR 60. SKIES WILL CLEAR DURING THE DAY WITH A COUPLE
OF COOL NIGHTS THURSDAY NIGHT AND FRIDAY NIGHT. SOME PATCHY FROST
MAY BE POSSIBLE IN OUTLYING LOCATIONS THURSDAY NIGHT. OTHERWISE
THE WEEKEND LOOKS PRETTY PLEASANT WITH TEMPERATURES NEAR NORMAL
AND CLEAR SKIES. THE NEXT SYSTEM WILL ARRIVE EARLY NEXT WEEK...BUT
WILL KEEP POPS LOW ON MONDAY FOR NOW.

TR.92



&&


.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX  83  61  82  51  61 /  10  10   5  50  10
WACO, TX              83  61  80  55  63 /   0   5   5  50  20
PARIS, TX             80  59  80  52  59 /  10  20   5  70  30
DENTON, TX            84  58  83  49  61 /  10  10  10  50  10
MCKINNEY, TX          82  59  80  51  60 /  10  10   5  60  10
DALLAS, TX            84  62  81  53  61 /  10  10   5  50  10
TERRELL, TX           82  61  80  54  61 /   5  10   5  60  20
CORSICANA, TX         81  61  80  56  62 /   0   5   5  50  30
TEMPLE, TX            82  60  80  56  64 /   0   5   5  40  20
MINERAL WELLS, TX     89  57  84  49  62 /   5   5  20  30  10

&&

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

&&

$$

05/30


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