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

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000
FXUS64 KFWD 021740
AFDFWD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
1240 PM CDT TUE SEP 2 2014

.AVIATION...
TAF FORECAST IS ONE OF PERSISTENCE AS VFR WILL PREVAIL THROUGH
TONIGHT BEFORE ANOTHER ROUND OF MVFR STRATUS IMPACTS KDAL/KACT
AIRPORTS BETWEEN 11-16Z. KDFW/KGKY ARE FORECAST TO BE RIGHT ON THE
EDGE OF THE STRATUS DECK AND WILL SHOW ONLY A TEMPO FROM 13-15Z
DUE TO LOWER CONFIDENCE. OTHERWISE SOUTH WINDS WILL PREVAIL AT
10-15KT THROUGH THE PERIOD.

SOME CONVECTION IS EXPECTED NORTHEAST OF THE METROPLEX...AND JUST
SOUTHEAST OF KACT THIS AFTERNOON. ACTIVITY WILL LIKELY BE JUST
SHOWERS AND TOO FAR REMOVED FROM METROPLEX SITES FOR ANY MENTION
OF VCSH. LIKEWISE...CONVECTION SHOULD STAY SHOWERS NEAR WACO...BUT
PROBABILITY IS TOO LOW TO INCLUDE IN TAF AT THIS TIME.

TR.92

&&

.UPDATE...
WE WILL LET THE CURRENT FORECAST RIDE THE REST OF THE AFTERNOON.
CONVECTION ACROSS SOUTHEAST OKLAHOMA IS MOVING SOUTH BUT SHOWING
SIGNS OF WEAKENING. DO EXPECT SOME ACTIVITY TO MAKE IT INTO THE
RED RIVER VALLEY NEAR PARIS BY 1 PM BEFORE DYING OFF. THE ACTIVITY
DEVELOPING OVER THE SOUTHEAST COUNTIES IS VERY SPOTTY AT THE
MOMENT BUT SHOULD INCREASE IN COVERAGE AND SPREAD FARTHER NORTH
DURING THE AFTERNOON. LATE MORNING TEMPS LOOK GOOD BUT WILL UPDATE
THE HOURLY GRIDS TO BETTER MATCH CURRENT WARMING TRENDS. 75

&&

.PREV DISCUSSION... /ISSUED 401 AM CDT TUE SEP 2 2014/

08Z/3AM REGIONAL RADAR DERIVED WINDS (VAD WINDS) INDICATED A 35 KT
LOW LEVEL JET IN PLACE EXTENDING FROM CENTRAL TEXAS NORTH TO THE
OK/KS BORDER. A FRONTAL BOUNDARY WAS IN PLACE ALONG THE KS/OK
BORDER AS INDICATED BY SURFACE OBSERVATIONS...AND NUMEROUS
THUNDERSTORMS WERE ACTIVE ALONG THE FRONT AT THE TIME OF THIS
DISCUSSION PER REGIONAL RADAR IMAGERY. 00Z UPPER AIR ANALYSIS
CONTINUED TO SHOW UPPER LEVEL RIDGING OVER MUCH OF TEXAS AT THE
500 MB LEVEL...AND THE 00Z FWD RAOB SHOWED A STOUT MID-LEVEL CAP
IN PLACE OVER THE CWA AS A RESULT OF PERSISTENT SUBSIDENCE
ASSOCIATED WITH THIS UPPER LEVEL RIDGE. INFRARED AND WATER VAPOR
SATELLITE IMAGERY CONTINUED TO TRACK AN AREA OF ORGANIZED
THUNDERSTORM ACTIVITY OVER THE BAY OF CAMPECHE. OVERNIGHT THE
NATIONAL HURRICANE CENTER UPGRADED THIS ACTIVITY TO TROPICAL STORM
STRENGTH...SO WE OFFICIALLY HAVE TROPICAL STORM DOLLY...WHICH WAS
MOVING TO THE NORTHWEST EARLY THIS MORNING.

TODAY...THERE ARE A COUPLE OF FEATURES TO WATCH TODAY THAT MAY
BRING THUNDERSTORMS ACROSS PARTS OF NORTH AND CENTRAL TEXAS. THE
FIRST IS THE THUNDERSTORM ACTIVITY ONGOING ALONG THE OK/KS BORDER
THIS MORNING...AND THE SECOND IS A SURGE OF MOISTURE ASSOCIATED
WITH DOLLY MOVING NORTHWEST LATER TODAY.

FOR THIS MORNING...HIGH RESOLUTION MODELS ARE INDICATING THAT THE
THUNDERSTORM ACTIVITY ALONG THE OK/KS BORDER WILL START TO BECOME
STRONGLY INFLUENCED BY PROPAGATION AND MOVE SOUTH RIGHT AROUND
SUNRISE. THIS IS ASSUMING THAT THIS THUNDERSTORM COMPLEX CAN
BECOME ORGANIZED ENOUGH FOR ITS COLD POOL TO MOVE THIS LINE OF
STORMS IN A NEW DIRECTION THIS MORNING.

...THIS NEXT PARAGRAPH IS AN EXPLANATION OF THOSE FACTORS THAT
DICTATE STORM MOTION AND REALLY DOES NOT CONTRIBUTE TO THE
FORECAST...IT IS INCLUDED TO HELP PROVIDE INSIGHT/UNDERSTANDING
FOR THOSE INTERESTED. YOU CAN SKIP THIS NEXT PARAGRAPH TO
CONTINUE ON WITH THE FORECAST DISCUSSION...

IN A BASIC SENSE...THE MOVEMENT OF THUNDERSTORM SYSTEMS IS
CONTROLLED BY THE AVERAGE OF THE WINDS ALOFT...OFTEN REFERRED TO
AS THE STEERING WINDS. IN MOST CASES...THUNDERSTORMS WILL SIMPLY
MOVE IN THE DIRECTION IN WHICH THE WINDS ALOFT ARE BLOWING.
HOWEVER THE SECOND COMPONENT TO CONSIDER IS OFTEN REFERRED TO AS
THE PROPAGATION COMPONENT OF STORM MOTION. PROPAGATION INFLUENCES
STORM MOTION BY CHANGING THE DIRECTION OF MOTION OF A THUNDERSTORM
SYSTEM IN THE DIRECTION THAT NEW THUNDERSTORMS DEVELOP. THIS IS
THE MORE COMPLICATED FACTOR TO UNDERSTAND...BUT IN GENERAL...NEW
THUNDERSTORMS TEND TO DEVELOP IN THE OPPOSITE DIRECTION OF THE LOW
LEVEL JET. ON A DAY LIKE TODAY...WHERE THE STEERING WINDS ARE
SOMEWHAT LIGHT DUE TO UPPER LEVEL RIDGING OVER TEXAS...BUT THE
LOW-LEVEL JET IS RELATIVELY STRONG...THE PROPAGATION COMPONENT CAN
DOMINATE THE DIRECTION IN WHICH THE THUNDERSTORM SYSTEM MOVES. FOR
TODAY...THE STEERING WINDS ARE SOMEWHAT LIGHT AND WOULD INDICATE
AN EASTERLY STORM MOTION. THIS IS WHY THE STORMS ARE JUST SORT OF
SITTING THERE ALONG THE FRONT AS OF 3 AM. HOWEVER IF THIS RESULTS
IN A STRONG ENOUGH COLD POOL (A COLLECTION OF RAIN COOLED AIR)
THIS COLD POOL COULD START TO SURGE SOUTH...CAUSING NEW STORMS TO
DEVELOP IN THE OPPOSITE DIRECTION OF THE LOW-LEVEL JET. SINCE THE
LOW-LEVEL JET EXTENDS FROM OUR CWA TO THE FRONT...THE WHOLE
COMPLEX OF STORMS COULD START TO MOVE SOUTH DIRECTLY TOWARDS THE
RED RIVER...BUT WILL STILL MOVE AT LEAST SLIGHTLY TO THE EAST DUE
TO THE STEERING WINDS ALOFT. THIS IS A DRAMATIC SHIFT IN DIRECTION
FROM WHAT STORMS HAVE BEEN DOING OVERNIGHT...BUT IT MAKES SENSE IN
THE CONTEXT OF WHAT WAS DESCRIBED ABOVE.

THE MAIN POINT OF UNCERTAINTY THIS MORNING IS: WILL
THUNDERSTORMS BECOME ORGANIZED ENOUGH TO MOVE AS A SYSTEM?

THAT IS LARGELY UNKNOWN BECAUSE JUST LOOKING AT THE STORMS ON
RADAR IS NOT ENOUGH TO DETERMINE HOW STRONG THE COLD POOL WILL
GET...BUT THE FACT THAT THE HRRR AND THE TEXAS TECH WRF BOTH
ADVERTISE A DRAMATIC SHIFT TO THE SOUTH OF THUNDERSTORMS TOWARDS
THE RED RIVER AROUND SUNRISE GIVES CONFIDENCE IN THIS SOLUTION.
WENT AHEAD AND PLACED A VERY SMALL AREA OF 20 POPS IN THE FORECAST
FROM JUST NORTH OF SHERMAN EXTENDING TO THE SOUTHEAST INCLUDING
MUCH OF LAMAR COUNTY. IF THE STORMS DO MOVE TO THE SOUTH AS THESE
HIGH RESOLUTION MODELS INDICATE...THEY WILL BE IN THEIR
DISSIPATING STAGES BY THE TIME THEY CROSS THE RED RIVER WELL
AFTER SUNRISE THIS MORNING...SO NO STRONG OR SEVERE WEATHER IS
EXPECTED AT THIS TIME.

THIS AFTERNOON...MODELS CONTINUE TO CONSISTENTLY SHOW A SURGE OF
TROPICAL MOISTURE TO THE NORTHWEST FROM THE TX GULF COAST THIS
AFTERNOON. THIS SURGE OF MOISTURE APPEARS TO BE ASSOCIATED WITH A
SUBTLE BUT IMPORTANT MID-LEVEL WIND SHIFT ASSOCIATED WITH DOLLY
MOVING NORTHWEST TOWARDS THE NORTHERN MEXICO GULF COAST. THIS
DEEPER TROPICAL MOISTURE IS EXPECTED TO REMAIN SOUTH OF THE
INTERSTATE 20 CORRIDOR THIS AFTERNOON...SO REORIENTED POPS A BIT
TO HIGHLIGHT THE SOUTHERN HALF OF THE CWA. IN GENERAL...THERE IS
STILL NO OBVIOUS LIFT...SO THE COVERAGE OF STORMS WILL PROBABLY BE
ISOLATED IN NATURE...AND LEFT POPS AT THE 20 PERCENT LEVEL FOR NOW.

WEDNESDAY THROUGH FRIDAY...DOLLY IS EXPECTED TO MAKE LANDFALL OVER
NORTHERN MEXICO LATE THIS EVENING...AND THEN CONTINUE OFF TO THE
WEST-NORTHWEST THROUGH THE END OF THE WEEK. MODELS SEEM TO SEND
THE DEEPER MID-LEVEL TROPICAL MOISTURE PLUME TO THE WEST WITH
DOLLY...SO WENT AHEAD AND REMOVED POPS FROM THE FORECAST ON
WEDNESDAY AFTERNOON ACROSS THE SOUTHERN CWA AND LEFT THE REMAINDER
OF THE FORECAST DRY. WEAK UPPER LEVEL RIDGING IS THE DOMINANT
FEATURE DURING THIS TIME FRAME...SO EXPECT SUBSIDENCE TO WIN OUT
IN KEEPING THINGS DRY ACROSS NORTH AND CENTRAL TEXAS.

THIS WEEKEND...MODELS CONTINUE TO HINT AT A COLD FRONT MOVING
SOUTH OF THE RED RIVER SOMETIME SATURDAY AFTERNOON THROUGH SUNDAY
MORNING. MODELS STILL SEEM TO INDICATE THAT THE PRIMARY REASON
THAT THE FRONT MAKES IT SOUTH OF THE RED RIVER IS DUE TO
PERSISTENT THUNDERSTORM ACTIVITY ALONG THE FRONT LATE THIS WEEK.
IF THE FRONTAL MOTION IS REALLY DEPENDENT UPON PERSISTENT
THUNDERSTORM ACTIVITY...CONFIDENCE IN THE TIMING AND PLACEMENT OF
THE FRONT IS GOING TO REMAIN LOW UNTIL LATE THIS WEEK.

THE BIGGEST REASON FOR OPTIMISM IN THE FRONT MAKING IT THIS FAR
SOUTH IS OBSERVING WHAT HAPPENS TODAY. IF MCS ACTIVITY FROM THE
OK/KS BORDER ACTUALLY SURGES SOUTH THIS MORNING...IT BECOMES EASY
TO SEE HOW PERSISTENT STORMS TO OUR NORTH CAN SEND A STRONG
OUTFLOW BOUNDARY/FRONT ACROSS NORTH TEXAS UNDER WEAK RIDGING
ALOFT. THE FRONT IS MOST LIKELY TO BE IN PLACE OVER THE CWA ON
SUNDAY...SO LEFT POPS MAINLY ALONG AND NORTH OF INTERSTATE 20 ON
SATURDAY...AND KEPT THEM BROAD BRUSHED OVER THE ENTIRE CWA ON
SUNDAY.

EARLY NEXT WEEK...THE FRONT...ASSUMING IT MAKES IT HERE THIS
WEEKEND...WILL PROBABLY DISSIPATE BY MONDAY. BECAUSE THE FRONT
DOES NOT REPRESENT A TRUE AIRMASS REPLACEMENT...THAT IS...THERE IS
NO CANADIAN/OR SIGNIFICANTLY COOL AIR TO THE NORTH OF THIS
FRONT...IT WILL UNDERGO FRONTOLYSIS AND LOSE DEFINITION QUICKLY
UNDER RIDGING ALOFT. LEFT THE FORECAST FOR EARLY NEXT WEEK DRY AS
A RESULT.

CAVANAUGH



&&


.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX  97  77  96  77  96 /   5   5   5   5   0
WACO, TX              98  75  97  74  97 /  20  20  10   5   5
PARIS, TX             92  72  91  72  92 /  20  10   5   5   0
DENTON, TX            96  75  95  74  95 /  10   5   5   0   0
MCKINNEY, TX          95  74  94  74  94 /  10   5   5   5   0
DALLAS, TX            97  78  96  78  96 /   5   5   5   5   0
TERRELL, TX           96  76  96  75  96 /  10  10   5   5   0
CORSICANA, TX         97  76  96  75  96 /  20  20  10   5   5
TEMPLE, TX            98  72  97  73  97 /  20  20  10   5   5
MINERAL WELLS, TX     97  73  96  72  96 /   5   5   5   0   0

&&

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

&&

$$

 /






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