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

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000
FXUS64 KFWD 061148 AAA
AFDFWD

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE FORT WORTH TX
648 AM CDT WED MAY 6 2015

.AVIATION...
/12Z TAFS/

WIDESPREAD MVFR CIGS PREVAIL ACROSS NORTH TEXAS THIS MORNING WITH
AREAS OF RAIN AND THUNDERSTORMS NOW MOVING EAST OF THE INTERSTATE
35 CORRIDOR. THE MAIN CLUSTER OF PRECIPITATION IS SOUTHEAST OF
WACO THIS MORNING AND IT CONTINUES TO DRIFT TO THE EAST SLOWLY.
ADDITIONAL LIGHT SHOWERS HAVE DEVELOPED FARTHER WEST OVER THE LAST
HOUR BUT A GENERAL DOWNWARD TREND IN COVERAGE IS EXPECTED THROUGH
LATE MORNING. FARTHER NORTH...MOST OF THE RAIN HAS MOVED AWAY FROM
THE LARGER AIRPORTS.

THE MAIN UPPER DISTURBANCE PROVIDING LIFT FOR THIS PRECIPITATION
IS MOVING AWAY AND SHOULD LEAVE NORTH TEXAS UNDER THE INFLUENCE OF
WEAK SUBSIDENCE THROUGH LATE THIS AFTERNOON. THIS SHOULD RESULT IN
MAINLY PRECIPITATION FREE CONDITIONS...HOWEVER WE WILL REMAIN
UNSTABLE AND UNCAPPED FOR MUCH OF THE AFTERNOON...SO ANY WEAK
ASCENT COULD RESULT IN SHOWER AND THUNDERSTORM DEVELOPMENT. AT
THIS TIME...WE WILL LEAVE PRECIPITATION OUT OF THE CURRENT TAFS
BUT THIS WILL NEED TO BE MONITORED CLOSELY THROUGH THE DAY.

IFR/MVFR CIGS WILL PREVAIL THROUGH MIDDAY BEFORE LIFTING TO VFR. A
QUICK RETURN TO MVFR CIGS IS EXPECTED TONIGHT THROUGH THE
REMAINDER OF THE TAF PERIOD.

DUNN

&&

.PREV DISCUSSION... /ISSUED 411 AM CDT WED MAY 6 2015/

THE 00Z FWD RAOB OBSERVED A THERMODYNAMIC PROFILE OF NORTH TEXAS
CHARACTERIZED BY DEEP MOISTURE AND LOW TO MID-LEVEL LAPSE RATES ON
THE ORDER OF 7 DEG C/KM. THIS RESULTED IN AN UNCAPPED SOUNDING
WITH RELATIVELY TALL AND SKINNY CAPE AND A VEERING WIND PROFILE
WITH HEIGHT. THE DEEP LAYER SHEAR WAS OBSERVED AT 39 KTS IN THE
0-6 KM LEVEL...HOWEVER THIS IS SOMEWHAT EXAGGERATED BY SOMEWHAT
LIGHT SURFACE WINDS INCREASING TO 30 KTS OF VEERED FLOW FAIRLY
QUICKLY TO THE 850 MB LEVEL AND MAINTAINING THAT WIND SPEED UP THE
300 MB LEVEL.

THE LACK OF ANY SIGNIFICANT SPEED SHEAR IN THE 850 MB TO 300 MB
LEVEL LIMITS THE POTENTIAL FOR STORMS TO SHED A SIGNIFICANT AMOUNT
OF HYDROMETEORS AWAY FROM UPDRAFTS AND AS A RESULT FAVORS MORE OF
A MULTI-CELLULAR STORM MODE VERSUS A SUPERCELLULAR ONE INDICATED
BY LOOKING AT BULK SHEAR MAGNITUDE ALONE. THINK THAT THE TALL AND
SKINNY CAPE PROFILE COMBINED WITH THE WIND SHEAR CONSIDERATIONS
MENTIONED ABOVE HELP TO EXPLAIN WHY THERE WAS REALLY NO ORGANIZED
CONVECTION THAT PRODUCED SEVERE WEATHER ACROSS NORTH TEXAS
YESTERDAY EVENING OR OVERNIGHT.

THE FWD RAOB DID OBSERVE A PWAT OF AROUND 1.6 INCHES WHICH RANKS
JUST BELOW 2 STANDARD DEVIATIONS ABOVE NORMAL FOR THIS TIME OF
YEAR. RADAR DERIVED VERTICAL WIND PROFILES ACROSS THE REGION
INDICATE THAT THE WINDS IN THE MIDDLE TROPOSPHERE HAVE NOT CHANGED
MUCH SINCE THE 00Z RAOB...HOWEVER THE WINDS AT THE 850 MB LEVEL
HAVE INCREASED 10 TO 15 KTS TO 40 TO 45 KTS OVER THE REGION. AS A
RESULT...THINK THAT ONGOING CONVECTION WILL CONTINUE TO MAINTAIN A
MULTI-CELLULAR STORM MODE THIS MORNING...WITH LOCALLY HEAVY
RAINFALL THAT MAY LEAD TO FLOODING POSING THE PRIMARY HAZARD. THE
INCREASE OF THE LOW-LEVEL JET WINDS WITHOUT A MATCHING INCREASE TO
THE UPPER LEVEL WINDS WILL ONLY RESULT IN VERY SLOW MOVING OR
BACKBUILDING STORM MOTIONS. THE LOW-LEVEL JET WILL LIKELY WEAKEN A
BIT AFTER SUNRISE...HOWEVER THIS MAY NOT OCCUR UNTIL AFTER 10 AM
OR SO. WILL NOT ISSUE A FLASH FLOOD WATCH FOR ANY PORTION OF THE
CWA AT THIS TIME...BUT WILL CONTINUE TO WATCH ONGOING THUNDERSTORM
ACTIVITY AND LOCAL AREA RAIN GAUGE NETWORKS FOR ANY SIGNS OF AN
INCREASED THREAT OF FLOODING THIS MORNING ACROSS NORTH AND CENTRAL
TEXAS.

OTHERWISE FOR THIS MORNING...KEPT POPS THE HIGHEST EAST OF THE
INTERSTATE 35/35E CORRIDOR. WATER VAPOR SATELLITE IMAGERY
INDICATES THAT THE SHORTWAVE TROUGH THAT PROVIDED THE IMPETUS FOR
WIDESPREAD CONVECTION YESTERDAY EVENING WILL MOVE NORTH OF THE
REGION. WHILE THERE ARE NO OBVIOUS SHORTWAVE TROUGHS IMMEDIATELY
UPSTREAM OF THE TROUGH EXITING THE SOUTHERN PLAINS...THERE IS NO
OBVIOUS STRONG FORCING FOR SUBSIDENCE OR RIDGING UPSTREAM EITHER.
INSTEAD...A FAIRLY BROAD UPPER TROUGH LOCATED OVER THE EASTERN
GULF OF MEXICO AND WESTERN FLORIDA HAS A BROAD UPPER LEVEL RIDGE
LOCATED TO THE NORTH OF IT OVER THE WESTERN GREAT LAKES REGION
THIS MORNING. THESE SOMEWHAT MERIDIONALLY STACKED FEATURES ARE
PROMOTING SPLIT FLOW IN THE UPPER LEVEL WIND FLOW OVER NORTH TEXAS
WHICH FAVORS PERSISTENT UPPER LEVEL DIFFLUENCE. WHILE THIS UPPER
LEVEL DIFFLUENCE DOES NOT REPRESENT ANY STRONG FORCING FOR
ASCENT...IT CAN CERTAINLY HELP ENHANCE ANY LIFT FROM BELOW.

WITH PERSISTENT THUNDERSTORMS MOVING EAST OF INTERSTATE 35 THIS
MORNING...THINK THAT THESE STORMS WILL LEAVE SOME RELATIVELY COOL
AIR IN PLACE FOR THIS AFTERNOON. THIS COOL AIR MAY SERVE TO
STEEPEN LOW-LEVEL ISENTROPIC SURFACES ALLOWING THE SOUTHERLY WINDS
ASSOCIATED WITH THE LOW-LEVEL JET TO PROVIDE MORE LIFT THAN NORMAL
OVER THESE AREAS TODAY. AS A RESULT...WENT AHEAD AND MAINTAINED
SCATTERED STORMS OVER THE EASTERN CWA THROUGH THIS AFTERNOON
DESPITE THE LACK OF ANY SYNOPTIC SCALE FORCING MECHANISM PRESENT
TO FOCUS LIFT. MODELS ALSO CONSISTENTLY SHOW CONVECTION INITIATION
NEAR WICHITA FALLS THIS AFTERNOON SO WENT AHEAD AND PLACED
SCATTERED THUNDERSTORMS IN THE FORECAST FOR AREAS NORTHWEST OF THE
METROPLEX AS WELL.

ALTHOUGH A FOCUSED FORCING MECHANISM IS DIFFICULT TO PICK OUT IN
THE MODEL MASS FIELDS AWAY FROM THE DRYLINE (WHICH IS EXPECTED TO
BE MUCH FARTHER WEST) THE CONSISTENCY OF CONVECTION INITIATION IN
THIS AREA WAS ENOUGH TO MENTION SCATTERED STORMS IN THE FORECAST
THIS AFTERNOON. WITH A NEARLY UNCAPPED ENVIRONMENT IT IS LIKELY
THE MODELS ARE PICKING UP ON SOME MESOSCALE FORCING THAT IS SIMPLY
NOT EASY TO IDENTIFY IN OBSERVATIONAL DATA AT THIS TIME. SEVERE
STORMS ARE GENERALLY NOT EXPECTED TODAY AS THE THERMODYNAMIC
PROFILE IS EXPECTED TO REMAIN SIMILAR TO WHAT IT WAS YESTERDAY
OVER THE REGION. LOCALLY HEAVY RAINFALL AND LOCALIZED FLOODING MAY
BE AN ISSUE IF ENOUGH THUNDERSTORM ACTIVITY CAN GET GOING THIS
AFTERNOON. SEVERE STORMS COULD BECOME MORE LIKELY IF WE RECEIVE A
SIGNIFICANT AMOUNT OF SUNSHINE OVER THE WESTERN CWA TODAY.

THURSDAY THROUGH SUNDAY...WATER VAPOR SATELLITE IMAGERY SHOWS
THREE UPSTREAM SHORTWAVE TROUGHS THAT ARE EXPECTED TO MOVE
NORTHEAST OVER THE PLAINS DURING THIS PERIOD. THE FIRST WAS
LOCATED OVER THE NORTHERN BAJA PENINSULA...THE SECOND WAS JUST
OFF THE SOUTHERN CALIFORNIA COAST...AND THE THIRD...AND MUCH
STRONGER TROUGH...WAS LOCATED OVER WASHINGTON AND OREGON MOVING
SOUTH ALONG THE PACIFIC COAST. THESE FEATURES ARE EXPECTED TO KEEP
SOUTHWESTERLY FLOW ALOFT IN PLACE OVER THE SOUTHERN PLAINS DURING
THIS PERIOD...WHICH AIDED BY THE UPPER TROUGH/RIDGE COUPLET TO THE
EAST...EFFECTIVELY LEAVES UPPER LEVEL DIFFLUENCE OVER THE REGION
THROUGH THE END OF THE WEEK.

THE SMALLEST OF THE SHORTWAVE TROUGHS OVER THE NORTHERN BAJA
PENINSULA MAY MOVE NORTHEAST OVER THE PLAINS ON THURSDAY...BUT IT
WILL PROBABLY REMAIN WELL NORTHWEST OF THE CWA. WITH LIFT DIRECTLY
MOVING OVER THE CWA FROM THIS FEATURE...THUNDERSTORM CHANCES ON
THURSDAY APPEAR DEPENDENT UPON STORMS MOVING INTO THE AREA FROM
THE NORTHWEST...CLOSER TO THE UPPER FORCING AND DRYLINE.
HOWEVER...AS MENTIONED ABOVE PERSISTENT UPPER LEVEL DIFFLUENCE AND
A LOW-LEVEL WARM AIR ADVECTION REGIME WILL KEEP SOME WEAK
BACKGROUND LIFT IN PLAY OVER THE REGION FOR THE NEXT 3 DAYS.
UNLESS SOME CAPPING INVERSION BUILDS OVER THE AREA...SCATTERED
THUNDERSTORMS ARE POSSIBLE EACH AFTERNOON IN A SEMI-UNORGANIZED
FASHION SIMILAR TO WHAT YOU MIGHT EXPECT TO DEVELOP DURING A
SUMMER AFTERNOON ALONG THE GULF COAST. THE MAIN DIFFERENCE IS THAT
THESE STORMS WILL HAVE FLOW TO WORK WITH...SO INSTEAD OF SINGLE
CELL POPCORN TYPE CONVECTION...AT LEAST A MULTI-CELLULAR STORM
MODE WOULD BE POSSIBLE. AS A RESULT...WENT AHEAD WITH BROAD
BRUSHED SCATTERED THUNDERSTORM CHANCES OVER THE ENTIRE CWA EACH
AFTERNOON THURSDAY THROUGH SATURDAY.

THURSDAY LIKELY REPRESENTS THE LOWEST CHANCES FOR STORMS AS SOME
MODELS INDICATE THAT AN ELEVATED MIXED LAYER MAKES A RUN AT OUR
SOUTHWESTERN CWA. IF THE EML MAKES IT OVER THE CWA... IT MAY SHUT
OFF THUNDERSTORM CHANCES FOR 24-36 HOURS. NOT ALL MODELS AGREE
THAT THIS WILL HAPPEN THOUGH...MOST NOTABLY THE ECMWF WHICH BRINGS
A COMPLEX OF STORMS OVER MOST OF THE CWA THURSDAY AFTERNOON AND
EVENING. THINK THE MAIN THREATS ON THURSDAY FROM STORMS WILL
CONTINUE TO BE HEAVY RAIN AND THE POTENTIAL FOR MARGINAL SEVERE
WEATHER.

ON FRIDAY...THE SECOND SHORTWAVE TROUGH IS EXPECTED TO MOVE OVER
THE SOUTHERN PLAINS...BUT ONCE AGAIN WELL NORTHWEST OF THE CWA.
HOWEVER THE STRONGER FORCING FOR ASCENT MAY HELP DRIVE THE DRYLINE
FARTHER EAST AND MAY CAUSE MORE CONVECTION TO DEVELOP IN GENERAL.
MAYBE MOST IMPORTANTLY...THE STRONGER SHORTWAVE TROUGH WILL BE
ASSOCIATED WITH STRONGER WINDS ALOFT INCREASING OUR DEEP LAYER
SHEAR OVER NORTH TEXAS BY 15 TO 20 KTS. ORGANIZED STORMS LOOK MORE
LIKELY ON FRIDAY...LIKELY LEADING TO AN ENHANCED THREAT FOR SEVERE
STORMS WEST OF INTERSTATE 35 FRIDAY AFTERNOON AND EVENING. THE
STORM MODE WILL DEPEND ON HOW MANY STORMS THERE ARE AND ON EXACTLY
HOW STRONG THE SHEAR IS FRIDAY AFTERNOON. AT LEAST A LINEAR STORM
MODE COULD BE SUPPORTED...WITH SUPERCELLS POSSIBLE AS WELL.

THE LARGE UPPER TROUGH IS EXPECTED TO SWING OVER THE PLAINS THIS
WEEKEND...SENDING ROUNDS OF WHAT WILL LIKELY BE ORGANIZED
THUNDERSTORMS ACROSS NORTH AND CENTRAL TEXAS ON SATURDAY AND
SUNDAY. ALL OF THE PARAMETERS ARE THERE TO SUPPORT AN ORGANIZED
STORM MODE OF EITHER A STRONG SQUALL LINE OR SUPERCELL
THUNDERSTORMS. THIS FAR OUT THE DETAILS OF SEVERE STORM EVOLUTION
ARE VERY DIFFICULT TO FORECAST CORRECTLY...ESPECIALLY WHEN
COMPLICATED BY THE POTENTIAL FOR ORGANIZED STORMS ON FRIDAY WHICH
MAY HAVE A BIG IMPACT ON THE MESOSCALE ENVIRONMENT FOR THE
WEEKEND. PWATS ARE ALSO EXPECTED TO REMAIN ABOVE NORMAL THROUGH
THIS WEEKEND...SO FLOODING WILL BE AN EVER-PRESENT THREAT WITH ANY
THUNDERSTORM ACTIVITY ACROSS THE REGION. CANNOT IDENTIFY ANY ONE
PERIOD WITH A SIGNIFICANTLY GREATER FLOODING THREAT THAN ANY OTHER
AT THIS TIME...SO NO FLASH FLOOD WATCH WILL BE ISSUED WITH THIS
FORECAST.

EARLY NEXT WEEK...MODELS INDICATE A COLD FRONT WILL MOVE SOUTH
ACROSS THE PLAINS SOMETIME EARLY NEXT WEEK...AND BEHIND THIS
FRONT...RAIN CHANCES SHOULD SHUT OFF FOR 36 TO 48 HOURS. HOWEVER
MOST MODEL GUIDANCE INDICATES THAT THIS FRONT WILL LIFT NORTH
SOMETIME DURING THE MIDDLE OF NEXT WEEK RESULTING IN MORE
THUNDERSTORM CHANCES ACROSS NORTH AND CENTRAL TEXAS.

CAVANAUGH

&&

.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX  80  68  82  69  81 /  20  30  30  30  40
WACO, TX              81  69  82  69  83 /  30  20  30  30  40
PARIS, TX             77  66  79  68  81 /  40  30  30  30  40
DENTON, TX            79  67  81  69  80 /  20  30  40  30  40
MCKINNEY, TX          78  67  80  69  80 /  30  30  30  30  40
DALLAS, TX            80  68  83  69  82 /  20  30  30  30  40
TERRELL, TX           79  68  82  68  82 /  40  30  30  30  40
CORSICANA, TX         80  68  82  69  83 /  40  20  30  30  40
TEMPLE, TX            82  70  83  69  83 /  30  20  30  30  40
MINERAL WELLS, TX     80  67  80  68  80 /  30  30  50  30  40

&&

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

&&

$$



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