000
FXUS64 KFWD 180448
AFDFWD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
1148 PM CDT FRI MAY 17 2013

.UPDATE...

SENT OUT A QUICK FORECAST UPDATE TO BUMP UP POPS A BIT FOR AREAS
ALONG AND WEST OF A LINE FROM BOWIE TO LAMPASAS. THE PRIMARY
REASON FOR THIS IS THAT AFTERNOON HIGH RESOLUTION MODEL GUIDANCE
IS MORE AGGRESSIVE WITH ISOLATED THUNDERSTORM INITIATION EAST OF
THE DRYLINE NEAR OUR FAR WESTERN CWA LATE TOMORROW AFTERNOON. THIS
ISOLATED CONVECTION IS INITIATED IN A MODELED ENVIRONMENT
CHARACTERIZED BY 3000 TO 3500 J/KG OF CAPE AND WEAK TO MODERATE
VALUES OF DEEP LAYER BULK SHEAR. THE COMBINATION OF POTENTIAL
ENERGY FOR CONVECTION AND DEEP LAYER SHEAR SHOULD SUPPORT
SUPERCELL THUNDERSTORMS ASSUMING CONVECTION INITIATES AS HIGH
RESOLUTION MODELS ADVERTISE. THERE WILL BE A CAP IN PLACE OVER
MUCH OF NORTH TEXAS...SO ONCE AGAIN THINK THUNDERSTORMS WILL
STRUGGLE TO MOVE EAST OF THIS LINE FROM BOWIE TO LAMPASAS TOMORROW
AFTERNOON OR EVENING. LARGE HAIL AND DAMAGING WINDS WOULD BE THE
PRIMARY HAZARDS...HOWEVER A TORNADO THREAT CANNOT BE RULED OUT.

BACK TO THE CAP...THE 00Z FWD SOUNDING THIS EVENING SHOWED A STOUT
CAP WITH A DEEP DRY ADIABATIC LAYER EXTENDING ABOVE THE CAP FROM
850 MB UP PAST 600 MB. THIS LAYER HAS LAPSE RATES AS STEEP AS OUR
ATMOSPHERE WILL ALLOW AWAY FROM GROUND LEVEL. ANY PRECIPITATION
INTO THIS LAYER OF STEEP LAPSE RATES AND LOW RELATIVE HUMIDITY
WILL ACCELERATE AIR DOWNWARD QUICKLY AS THIS REPRESENTS THE IDEAL
ENVIRONMENT FOR RAIN DROPS TO EVAPORATE...ADDING NEGATIVE
BUOYANCY TO AIR THAT IS ALREADY HEADED TOWARDS THE EARTH. THIS
WILL LIKELY SUPPORT HEAT BURSTS THROUGHOUT THE OVERNIGHT HOURS
WHICH IS WHAT WAS HAPPENED IN COMANCHE EARLIER THIS EVENING. A
LIGHT TO MODERATE ELEVATED RAIN SHOWER MOVED OVER COMANCHE AND
CAUSE THE TEMPERATURE TO CLIMB 4 DEGREES WHILE THE DEW POINT
DROPPED 24 DEGREES AND WINDS GUSTED TO 57 MPH. GRANTED...WE DO NOT
EXPECT MUCH IN THE WAY OF RAIN SHOWER ACTIVITY ACROSS NORTH TX
TONIGHT...BUT THERE IS A WEAK SHORTWAVE TROUGH UPSTREAM...AND IT
WOULD NOT TAKE MUCH OF A RAIN SHOWER TO INITIATE A HEAT BURST. THIS
IS SOMETHING WE WILL BE KEEPING A CLOSE EYE ON THROUGHOUT THE
OVERNIGHT HOURS. NO OTHER SIGNIFICANT CHANGES WERE MADE TO THE
FORECAST.

CAVANAUGH

&&

.AVIATION...

AN UPDATE FROM THE 00Z TAFS...LIGHT RAIN...MOSTLY EVAPORATING
BEFORE REACHING THE GROUND. THIS LIGHT RAIN WAS CAUSING WINDS TO
GUST UP TO 35 TO 40 MPH TO THE NORTHWEST OF THE METROPLEX...AND
WAS PRODUCING ISOLATED CLOUD TO GROUND LIGHTNING STRIKES OVER THE
SAME AREAS. AT THIS TIME IT LOOKS LIKE THE CORE OF THIS LIGHT
ANVIL CLOUD PRECIP WILL REMAIN NORTHWEST OF DFW AIRPORT...BUT WILL
BE WATCHING LOCAL AREA OBS CLOSELY FOR ANY DEVIATION FROM THIS
THINKING. WENT AHEAD AND AMENDED KAFW FOR VCTS AND GUSTY WINDS
FROM 02 TO 03Z DUE TO A RECORDED LIGHTNING STRIKE AROUND HASLET.
THE STORMS OUT WEST ARE BEGINNING TO DISSIPATE...SO THE THREAT FOR
GUSTY WINDS AND ANVIL CLOUD LIGHTNING STRIKES IS EXPECTED TO
DIMINISH THROUGH 04Z AS WELL.

CAVANAUGH

.../PREVIOUS AVIATION DISCUSSION/...

FOR THE 00Z TAFS...TIMING THE ONSET OF MVFR CIGS AND WATCHING FOR
ANY IMPACT TO TAF SITES FROM STORMS OUT WEST ARE THE PRIMARY
FORECAST CONCERNS.

AT THIS TIME...THE CAP ALOFT OVER AREA TAF SITES LOOKS TOO STRONG
TO ALLOW STORMS ONGOING NEAR SAN SABA AND GRAHAM TO MOVE EAST AND
DIRECTLY IMPACT THE INTERSTATE 35 CORRIDOR. STORMS WOULD LIKELY
DISSIPATE BEFORE MINERAL WELLS IF THEY STARTED TO MOVE EAST THIS
EVENING. WILL CONTINUE TO MONITOR THE IMPACT OF THESE STORMS ON
AREA TAF SITES HOWEVER AS ANVIL CLOUDS ARE THICK AND HAVE PRODUCED
LIGHTNING STRIKES AS FAR EAST AS DECATUR THIS EVENING. IF
LIGHTNING LOOKS TO IMPACT LOCAL AREA TAFS THIS EVENING MAY HAVE TO
ISSUE AN AIRPORT WEATHER WARNING FOR DFW AND AMEND TAFS TO MENTION
A THUNDERSTORM WITH NO RAIN. AT THIS TIME...THE PRESENCE OF SOME
HIGHER MID-LEVEL RH PRECLUDES A LARGER THREAT FOR HEAT BURSTS
ASSOCIATED WITH ANVIL CLOUD LIGHT PRECIPITATION.

DID NOT CHANGE THE TIMING OF THE ONSET OF MVFR STRATUS OVER AREA
TAF SITES AT THIS TIME. THE LAMP GUIDANCE IS THE MOST AGGRESSIVE
WITH THIS WITH LESS SUPPORT FROM RAP AND NAM FORECAST SOUNDINGS.
WILL MONITOR UPSTREAM STRATUS DEVELOPMENT TONIGHT AND MAY PULL
STRATUS FROM THE FORECAST BY 06Z IF THERE IS LITTLE UPSTREAM
DEVELOPMENT.

CAVANAUGH




&&




.SHORT TERM...
DRYLINE IS SHARPENING AND IS LOCATED FROM OLNEY TO BRECKENRIDGE
TO BRADY. THE DRYLINE HAS LIKELY REACHED ITS EASTERN MOST
LOCATION...AS A SURFACE LOW INDUCED BY VERY HOT TEMPERATURES IS
DEEPENING NORTH OF ABILENE. THIS HAS CAUSED SURFACE WINDS TO BEGIN
TO BACK TO THE SOUTHEAST ACROSS THE NW CWA...WHICH WILL PULL RICH
LOW LEVEL MOISTURE CHARACTERIZED BY DEWPOINTS NEAR 70 DEGREES BACK
TO THE WEST. THE COMBINATION OF TEMPS NEAR 100 WITH THESE DEWPOINTS
AND NEARLY DRY ADIABATIC LAPSE RATES FROM 500MB TO 850MB HAS
PRODUCED AN EXTREMELY UNSTABLE AIRMASS ACROSS OUR WESTERN ZONES
THIS AFTERNOON. LOCAL OBJECTIVE ANALYSIS IS DEPICTING SBCAPE
AROUND 3500 J/KG...AND POCKETS OF CAPE OVER 4000 J/KG WILL BE
POSSIBLE THROUGH EARLY EVENING. THE STRONG CAP THAT WAS EVIDENT ON
THE MORNING SOUNDING IS CLOSE TO BEING ERODED OVER THE WESTERN
ZONES...OR THE WESTERN 2 COLUMNS OF COUNTIES OF THE CWA. ALONG AND
EAST OF A BOWIE TO GRANBURY TO TEMPLE LINE...OBJECTIVE ANALYSIS
SHOWS CIN WELL ABOVE 200 J/KG AND VIS SATELLITE CONFIRMS THE
PRESENCE OF STRONG CAPPING IN CUMULUS FIELD. WITHOUT UPPER LEVEL
FORCING THIS CAP SHOULD REMAIN...WITH HEATING NOT SUFFICIENT ALONE
TO WEAKEN IT.

CONVECTIVE INITIATION IS NOW OCCURRING SOUTHWEST OF BROWNWOOD AND
CUMULUS IS ORGANIZING TO THE WEST OF BRECKENRIDGE. THIS IS TO
THE WEST OF THE DRY LINE...BUT THIS IS ACTUALLY THE FAVORED
LOCATION FOR UPWARD MESOSCALE FORCING ASSOCIATED WITH DRYLINES.
OFTEN THE LOW MOISTURE CONTENT BEHIND THE DRY LINE IS NOT
SUFFICIENT TO PRODUCE CUMULUS OR PRECIPITATION SO WE CANT SEE THE
LIFT...BUT THIS DRY LINE SEEMS TO HAVE MORE MOISTURE TO WORK WITH.
ONCE THE INFANT UPDRAFTS ARE ADVECTED TO THE MOIST SIDE OF THE DRY
LINE...THEY TAP INTO RICHER MOISTURE AND OFTEN GROW INTO CELLS
THAT RADAR CAN SEE. NEEDLESS TO SAY...CONVECTIVE INITIATION IS A
CERTAINTY AT THIS POINT...BUT COVERAGE OF STORMS WILL BE FAIRLY
LOW DUE TO WEAK UPPER LEVEL FORCING AND THE STRONG CAP. POPS WILL
RANGE FROM 20-40 PERCENT ACROSS THE WESTERN THIRD OF THE CWA.

DEEP LAYER SHEAR IS ON THE LOW SIDE OF WHAT IS TYPICALLY FOUND IN
SUPERCELL ENVIRONMENTS...BUT EXTREME INSTABILITY WILL LIKELY
COMPENSATE. STORM MOTION WILL START OUT EAST BUT AS SUPERCELLS
ORGANIZE AND MATURE THEY WILL LIKELY TURN TO THE SOUTH. THIS
SOUTHWARD MOVEMENT WILL ENHANCE LOW LEVEL STORM RELATIVE
HELICITY...WHICH MAY REACH 150-200 MS/S2 ACROSS THE NW ZONES WHERE
AN ISOLATED TORNADO THREAT IS GREATEST. HOWEVER THE MAIN THREAT
WILL BE GIANT HAIL AND DAMAGING WINDS GIVEN THE EXTREME INSTABILITY
AND LARGE DEWPOINT SPREADS. SPC HAS JUST ISSUED A SEVERE WATCH FOR
THE WESTERN ZONES...AND AGAIN DUE TO THE STRONG CAP AND SOUTHERLY
STORM MOTION BELIEVE ALL SEVERE ACTIVITY WILL REMAIN WEST OF THE
I-35 CORRIDOR. SOME LINGERING AND ELEVATED ACTIVITY MAY IMPACT THE
CENTRAL ZONES LATE TONIGHT...BUT THIS REMAINS A LOW PROBABILITY
AND KEPT POPS OUT OF THE FORECAST.

TR.92

&&

.LONG TERM...
A STRONG CAP WILL REMAIN IN PLACE ACROSS NORTH TEXAS THROUGH
MONDAY...SO THE CONVECTIVE FORECAST WILL HINGE ON WHETHER FORCING
FROM THE DRY LINE OR UPPER LEVEL SHORTWAVES WILL BE PRESENT. THE
DRYLINE WILL HEAD FARTHER WEST SATURDAY...AND ALTHOUGH A WELL
DEFINED SHORTWAVE MOVES ACROSS THE REGION...BELIEVE STORM
INITIATION WILL BE WELL NW OF THE CWA. A FEW OF THESE CELLS MAY
TRACK INTO THE NORTHWESTERN PARTS OF THE CWA SATURDAY
EVENING...BUT WILL KEEP POPS LOW AND AT 20 PERCENT. ON SUNDAY THE
DRY LINE WILL MIX EAST AGAIN AND FLIRT WITH THE NW CWA...AND HAVE
POPS A LITTLE HIGHER...BUT STILL PRIMARILY OVER THE NW ZONES IN
THE AFTERNOON. SINCE THE TAIL END OF THE PLAINS TROUGH WILL PASS
THROUGH THE NORTHERN ZONES SUNDAY NIGHT...CONVECTION MAY SURVIVE
PAST SUNSET AND TRACK ACROSS THE AREA NORTH OF I-20. EXPECT THE
SAME PATTERN ON MONDAY AND POPS ARE SIMILAR TO SUNDAYS. GIVEN THE
INSTABILITY AND SHEAR PROFILES SEVERE STORMS ARE POSSIBLE WITH ANY
ACTIVITY SATURDAY THROUGH MONDAY. FOR TEMPERATURES...SATURDAY WILL
BE THE WARMEST DAY WITH HIGHS IN THE 90S MOST AREAS...BUT WINDS
WILL INCREASE A BIT SUNDAY AND MONDAY WHICH SHOULD SHAVE A COUPLE
DEGREES...WITH HIGHS IN THE UPPER 80S EAST TO MID 90S WEST. LOWS
WILL REMAIN MUGGY AND IN THE LOW-MID 70S...WITH TONIGHT THE
COOLEST DUE TO FEWER CLOUDS AND LIGHTER WINDS.

ON TUESDAY ANOTHER LOBE OF ENERGY WILL ROTATE AROUND THE PLAINS
TROUGH AND HELP PROPEL A WEAK COLD FRONT SOUTH INTO THE AREA. THE
FRONT/DRYLINE COMBINATION WILL REACH THE NW CWA AND BECOME A FOCUS
FOR CONVECTION BY TUESDAY AFTERNOON. STRONG FORCING ASSOCIATED
WITH THE UPPER SHORTWAVE TROUGH WILL ENHANCE LIFT...AND EXPECT
SCATTERED CONVECTION TO OCCUR TUESDAY AFTERNOON AND WORK
SOUTHEAST ACROSS THE AREA. HAVE BUMPED POPS UP TO CHANCE AS THIS
WILL BE THE BEST DAY FOR RAIN CHANCES. AGAIN...THERE IS A SEVERE
WEATHER THREAT WITH THIS CONVECTION AS WELL.

THE FRONT WILL NOT BE VERY STRONG...AND WINDS MAY NOT SPEND MUCH
OR ANY TIME FROM THE NORTH...BUT THE AXIS OF BEST MOISTURE AND
INSTABILITY SHOULD GET PUSHED SOUTHEAST OF THE AREA. WILL KEEP A
SLIGHT CHANCE OF CONVECTION WEDNESDAY...BUT THIS ACTIVITY IS NOT
EXPECTED TO BE VERY SIGNIFICANT. TEMPS WILL BE A LITTLE COOLER AS
HEIGHTS LOWER...AND THE SLIGHTLY DRIER AIR WILL HELP LOWS FALL TO
NEAR NORMAL. HAVE KEPT THE REMAINDER OF THE FORECAST DRY AS UPPER
LEVEL RIDGING BUILDS INTO THE AREA...WHICH IS WELL AGREED UPON BY
EXTENDED GUIDANCE.

TR.92

&&


.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX  71  92  72  90  72 /  10   5   5  10  20
WACO, TX              70  92  72  91  73 /  10   5   5  10  10
PARIS, TX             69  88  70  87  68 /  10  10   5   5  20
DENTON, TX            70  93  72  90  72 /  10  10  10  10  30
MCKINNEY, TX          69  90  71  89  71 /  10   5   5   5  20
DALLAS, TX            73  93  74  91  74 /  10   5   5  10  20
TERRELL, TX           69  90  70  91  71 /  10   5   5   5  10
CORSICANA, TX         70  90  70  89  73 /  10   5   5   5  10
TEMPLE, TX            69  92  71  91  72 /  20  10   5  10  10
MINERAL WELLS, TX     71  96  69  94  70 /  20  10  20  20  20

&&

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

&&

$$

 /