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

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000 FXUS64 KFWD 021751 AAC AFDFWD AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE FORT WORTH TX 1251 PM CDT TUE SEP 2 2014 .UPDATE... HAVE DECIDED TO ADD 20 POPS FROM ATHENS NORTHWARD INTO THE SHERMAN TO PARIS AREAS FOR THE AFTERNOON. CONVECTION IS STILL PROGRESSING SOUTH-SOUTHWESTWARD AT MIDDAY AND SHOULD HANG TOGETHER LONG ENOUGH TO MOVE SOUTH OF THE RED RIVER OVER BOTH LAMAR AND FANNIN COUNTIES. 75 && .AVIATION... /ISSUED 1240 PM CDT TUE SEP 2 2014/ 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 && .PREV UPDATE... .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 / 10 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 / 10 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 / 10 5 5 0 0 && .FWD WATCHES/WARNINGS/ADVISORIES... NONE. && $$ /75

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