232 FXUS64 KFWD 252331 AFDFWD AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE FORT WORTH TX 631 PM CDT SAT MAY 25 2013 .AVIATION... SHOWERS AND THUNDERSTORMS BETWEEN KAFW AND KCRS WILL CONTINUE TO MOVE NORTHEAST THIS EVENING. WILL LEAVE A TEMPO 6SM -SHRA IN BETWEEN 00Z AND 01Z AT KDAL. VFR CONDITIONS ARE EXPECTED AT THE AREA AIRPORTS FOR MOST OF THE OVERNIGHT PERIOD. SOME MVFR STRATUS WILL SPREAD NORTH INTO THE WACO AREA AROUND 09Z...AND INTO THE METROPLEX AROUND 11Z. THE LOW CLOUDS WILL SCATTER OUT AFTER 16Z SUNDAY. SOUTH WINDS AROUND 10 KNOTS WILL INCREASE TO AROUND 15 KNOTS BY 16Z SUNDAY AND SOME GUSTS OVER 20 KNOTS ARE LIKELY SUNDAY AFTERNOON. 58 && .PREV DISCUSSION... /ISSUED 414 PM CDT SAT MAY 25 2013/ THROUGH TONIGHT...LEFT THE EARLY AFTERNOON UPDATE FORECAST DISCUSSION ATTACHED BELOW FOR REFERENCE AND MORE DETAILS ON THE SHORT TERM FORECAST CONCERNS. CHANGES FROM EARLIER DISCUSSION...THE MCV THAT WAS EXPECTED TO DEVELOP NEAR SAN ANTONIO WAS APPARENT IN REGIONAL RADAR RETURNS NEAR AUSTIN AND GONZALEZ AT THE TIME OF THIS DISCUSSION. ASSUMING THAT THIS IS THE PRIMARY MID-LEVEL LOW/MCV PRODUCED BY THE PERSISTENT SAN ANTONIO AREA CONVECTION THIS MORNING...ADJUSTED RAIN CHANCES THIS EVENING AND OVERNIGHT IN LINE WITH ITS EXPECTED TRAJECTORY. THE 19Z RUN OF THE RAP SEEMS TO HAVE A GOOD HANDLE ON THE POSITION OF THIS MCV...SO GENERALLY USED THIS MODEL FOR GUIDANCE OVER THE NEXT 12 TO 18 HRS. THE MCV IS EXPECTED TO MOVE GENERALLY IN A NORTHEASTERLY DIRECTION THROUGH TONIGHT...TAKING IT FROM ITS CURRENT LOCATION TO JUST NORTHEAST OF TYLER BY SUNRISE SUNDAY. THE GFS INDICATES THAT THE UPPER TROUGH THAT WAS ANALYZED IN THE 12Z RAOB ANALYSIS TO THE WEST OF THE CWA WILL INTERACT WITH THIS MCV FAVORABLY AND RESULT IN WIDESPREAD THUNDERSTORM ACTIVITY GENERALLY EAST OF I-35 AND SOUTH OF I-20 AFTER MIDNIGHT...SPREADING NORTHEAST INTO THE ARKLATEX AREA JUST AFTER SUNRISE. BOTH OF THESE FEATURES EXIST...SO THIS SOLUTION IS VIABLE...HOWEVER THE FORCING FOR ASCENT ADVERTISED BY THE GFS IS GREATLY ENHANCED BY CONVECTIVE FEEDBACK. THAT IS...MODEL GENERATED STORMS COOL OFF LOCATIONS DOWNSTREAM /NORTHEAST/ ALLOWING WARM AIR ADVECTION TO ARTIFICIALLY RAMP UP RESULTING IN THE GENERATION OF MORE STORMS. IN SHORT...A MODEL GENERATED FEEDBACK LOOP. THIS LOOP MAY VERIFY AND RESULT IN A HEAVY RAINFALL EVENT EAST OF I-35 TO THE ARKLATEX AREA TONIGHT THROUGH SUNDAY MORNING. HOWEVER THERE IS NOT REALLY ANY HIGH RESOLUTION MODEL OUTPUT SUPPORT FOR THIS SOLUTION AT THIS TIME...THEREFORE CONFIDENCE IS SOMEWHAT LOW IN A WIDESPREAD HEAVY RAIN EVENT. THAT SAID...MANY FACTORS ARE IN PLACE TO SUPPORT A LOCALIZED HEAVY RAINFALL EVENT ANYWHERE STORMS EXIST OVER THE NEXT 12 TO 18 HRS. PRECIPITABLE WATER VALUES ARE ABOVE THE 75TH PERCENTILE OF HISTORICAL PRECIPITABLE WATER VALUES FOR THIS REGION IN LATE MAY. MID-LEVEL LAPSE RATES ARE POOR BUT THE ENVIRONMENT IS UNCAPPED...IN SHORT A FAVORABLE ENVIRONMENT FOR VERY TALL RAIN SHOWERS WITH LITTLE LIGHTNING ACTIVITY AND ONLY WEAK GENERATION OF OUTFLOW BOUNDARIES. WEAK OUTFLOW MEANS THAT STORMS CAN REMAIN IN ONE PLACE FOR A LONGER PERIOD OF TIME INCREASING THE CHANCES FOR TRAINING OF STORMS AND A LOCALIZED FLOODING THREAT. AT THIS TIME WENT WITH A MENTION OF LOCALIZED HEAVY RAIN AND FLOODING IN THE HAZARDOUS WEATHER OUTLOOK AND WORDED FORECAST. WITH WEAK WIND SHEAR IN THIS THERMODYNAMIC ENVIRONMENT STORMS ARE EXPECTED TO BEHAVE IN A NEARLY TROPICAL NATURE WITH EFFICIENT RAINFALL PRODUCTION. THEREFORE CHANCES OF SEVERE WEATHER APPEAR TO BE VERY SMALL TONIGHT. WE WILL HAVE TO KEEP A CLOSE EYE ON THE EVOLUTION OF A LOCALIZED FLOODING EVENT...ESPECIALLY WITH MANY PEOPLE LIKELY CAMPING OUTDOORS IN FLOOD PRONE AREAS THROUGH TONIGHT. SUNDAY...SUNDAY MORNING WE WILL LIKELY HAVE SOME REMNANT POCKETS OF HEAVY RAIN ALONG A SULPHUR SPRINGS TO PALESTINE LINE...LIKELY MOVING NORTHEAST TOWARDS THE ARKLATEX REGION THROUGHOUT THE MORNING HOURS. FROM THE WEST...THE HRRR HAS CONSISTENTLY INDICATED THAT A SQUALL LINE WILL ORGANIZE OVER THE SOUTHERN HIGH PLAINS/TX PANHANDLE TONIGHT AND MOVE EAST TOWARDS OUR WESTERN CWA EARLY SUNDAY MORNING. WE WILL HAVE TO KEEP AN EYE ON THIS...NOT SO MUCH FROM A SEVERE WEATHER STAND POINT BUT FROM ANOTHER POTENTIAL SOURCE FOR MCV PRODUCTION. WITH THE SAN ANTONIO AREA MCV AND LARGER UPPER TROUGH MOVING EAST...SUBSIDENCE WILL LIKELY DOMINATE ANY MCV MOVING OFF THE HIGH PLAINS AND THRU NORTH TX TOMORROW. HOWEVER UNTIL WE GET SOME DRIER AIR IN OVER THE REGION CAPPING OFF THE ATMOSPHERE FOR THUNDERSTORM DEVELOPMENT...WILL HOLD ON TO A BROAD BRUSHED MENTION OF SHOWERS AND THUNDERSTORMS IN THE FORECAST ACROSS ALL OF NORTH TX THROUGH SUNDAY. NEXT WEEK...BEGINNING MONDAY A WESTERN CONUS TROUGH IS EXPECTED TO ORGANIZE SENDING THE WEAK UPPER LEVEL RIDGE AND ENTRAPPED MCV FEATURES OFF TO THE EAST OF THE REGION. THIS IS EXPECTED TO RESULT IN SOUTHWEST FLOW ALOFT OVER NORTH TX ON MONDAY WHICH SHOULD HELP TO ADVECT A RELATIVELY STOUT CAP IN PLACE OVER THE REGION BY MONDAY AFTERNOON. THIS CAP IS EXPECTED TO HOLD IN PLACE THROUGH THE WEEK UNLESS THE DRYLINE OR A STRONG SHORTWAVE TROUGH CAN LIFT THE CAP AND RESULT IN THUNDERSTORM INITIATION DURING THE WEEK AHEAD. WE ARE EXPECTED TO HAVE RELATIVELY PERSISTENT...BREEZY SOUTH WINDS IN PLACE BELOW THE CAP THROUGH THE WEEK. THIS WILL HELP KEEP GOOD GULF MOISTURE IN PLACE UNDER THE CAP PROVIDING PLENTY OF POSITIVE CAPE FOR THUNDERSTORM DEVELOPMENT IF ANYTHING CAN REMOVE THE CAP. WITHOUT STORMS...WE WILL LIKELY SEE HIGHS HOLD IN THE UPPER 80S WITH LOWS IN THE LOWER TO MID 70S EACH DAY. THE GFS AND ECMWF BOTH INDICATE THAT A STRONG SHORTWAVE TROUGH WILL MOVE OVER THE SOUTH PLAINS WEDNESDAY THROUGH WEDNESDAY EVENING. THE ECMWF REMAINS FURTHER SOUTH WITH THIS TROUGH WHICH IS WHAT WE WILL NEED TO LIFT THE CAP AND RESULT IN STORMS ACROSS THE CWA WEDNESDAY AFTERNOON AND EVENING. THE GFS INDICATES THE BEST FORCING STAYS NORTH OF THE CWA. WENT AHEAD WITH 20 TO 30 POPS WEST OF INTERSTATE 35...CLOSEST TO THE UPPER TROUGH WEDNESDAY AFTERNOON THROUGH WEDNESDAY NIGHT AS RESULT. REMOVED POPS THEREAFTER WITH ALL GUIDANCE INDICATING SUBSIDENCE BEHIND THIS UPPER TROUGH ON THURSDAY. CAVANAUGH && .PRELIMINARY POINT TEMPS/POPS... DALLAS-FT. WORTH, TX 69 84 67 86 69 / 30 20 10 0 0 WACO, TX 68 86 67 88 69 / 40 20 10 0 0 PARIS, TX 68 82 65 84 67 / 30 30 10 0 0 DENTON, TX 67 83 66 85 68 / 30 20 10 0 0 MCKINNEY, TX 68 82 66 86 68 / 30 20 10 0 0 DALLAS, TX 71 83 70 88 72 / 30 20 10 0 0 TERRELL, TX 70 82 67 87 69 / 40 30 10 0 0 CORSICANA, TX 69 83 68 88 69 / 40 20 10 0 0 TEMPLE, TX 68 85 67 87 69 / 40 20 10 0 0 MINERAL WELLS, TX 67 86 66 87 68 / 20 20 10 0 5 && .FWD WATCHES/WARNINGS/ADVISORIES... NONE. && $$ 58/85