000 FXUS64 KFWD 041120 AAA AFDFWD AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE FORT WORTH TX 620 AM CDT SAT JUL 4 2009 .AVIATION... A COLD FRONT WILL MOVE INTO NORTH TEXAS LATE TONIGHT WITH THUNDERSTORMS. THE STORMS WILL PUSH INTO THE KDFW TRACON SOMETIME AROUND 09 UTC (4 AM) WITH THE FRONT ARRIVING SHORTLY AFTERWARD WITH WINDS GOING NORTHERLY. HIGH ATMOSPHERIC MOISTURE CONTENT WILL MEAN VERY HEAVY DOWNPOURS ARE POSSIBLE FROM THE STRONGER CELLS...AND COULD RESULT IN A BRIEF PERIOD MVFR VISIBILITY AND A POSSIBLE AIRPORT WEATHER WARNING FOR LIGHTNING AT KDFW. KACT WILL NOT SEE THIS ACTIVITY UNTIL AFTER THE TAF ENDS. OTHERWISE...TODAY AND TONIGHT WILL BE VFR WITH SOME HIGH CIRRUS AND SOUTHERLY WINDS 8-14KT. 75 && .PREV DISCUSSION... /ISSUED 420 AM CDT SAT JUL 4 2009/ PRIMARY FORECAST CONCERN IS TSTM CHANCES TONIGHT THROUGH SUNDAY ASSOCIATED WITH COLD FRONT DROPPING SOUTH THROUGH THE CENTRAL PLAINS AT FORECAST TIME. 00Z UPPER AIR ANALYSIS INDICATED UPPER LVL RIDGE OVER THE SOUTHERN PLAINS WITH A SHORTWAVE TROUGH TRANSLATING EAST ACRS THE CENTRAL PLAINS AND A COLD FRONT PUSHING SOUTH IN RESPONSE TO THE COMBINATION OF UPPER LVL FORCING AND A NEARLY SOLID LINE OF CONVECTION ALONG AND JUST BEHIND THE FRONTAL BOUNDARY. H850 ANALYSIS INDICATED DEEP LOW LVL MOISTURE POOLED UP AHEAD OF THE COLD FRONTAL BOUNDARY WITH DEW POINT VALUES OF 16-17 DEG C IN THE CENTRAL PLAINS. MID LEVEL ANALYSIS INDICATED WEAK MID LVL LAPSE RATES AND A FAIRLY WEAK PRESENCE OF WARM AIR ALOFT WITH H700 TEMPS OF 10-11 DEG C NEAR THE RED RIVER. H500 ANALYSIS INDICATED GENERAL HEIGHT RISES OVER THE WESTERN CONUS WITH NEUTRAL OR WEAK HEIGHT FALLS ACRS THE CENTRAL PORTION OF THE COUNTRY. A COMPLEX FORECAST FOR THE OVERNIGHT HRS...HOWEVER DURING THE DAY TODAY GUIDANCE INDICATES THAT HIGH PRESSURE WILL HOLD OVER NORTH TX ALLOWING FOR MOSTLY SUNNY SKIES AND ANOTHER HOT DAY FOR MOST LOCATIONS WITH TEMPS ONCE AGAIN LOOKING TO TOP THE CENTURY MARK. TOWARDS THE RED RIVER TEMPS MAY NOT BE QUITE AS HIGH AS DEBRIS CLOUDS FROM EXPECTED CONVECTION TO THE NORTH MAY BRING SOME SCATTERED TO BROKEN HIGH CLOUD COVER ALOFT DURING THE AFTERNOON HRS KEEPING HIGHS A COUPLE OF DEGREES LOWER THAN POINT SOUTH. HEAT INDICES LOOK TO APPROACH 105 DEGREES THIS AFTERNOON...HOWEVER WITH OVERNIGHT LOWS EXPECTED TO FALL TOWARDS THE MID 70S WITH COLD FRONT MOVING INTO THE AREA...HAVE DECIDED NOT TO HOIST A HEAT ADVISORY ATM. ANYONE OUT ENJOYING INDEPENDENCE DAY ACTIVITIES SHOULD STILL TAKE PRECAUTIONS IF REMAINING OUT IN THE HEAT FOR A SIGNIFICANT PORTION OF THE DAY. TONIGHT...GFS/NAM/ECMWF ALL INDICATE THE STRONGER SHORTWAVE TROUGH OVER THE CENTRAL CONUS WILL TRANSLATE EAST DURING THE DAY TODAY. THE COLD FRONT IS EXPECTED TO SLOWLY CONTINUE SOUTH TODAY...BUT FEELING IS THAT WITH THE LOSS OF UPPER LVL SUPPORT...COLD FRONT WILL TEND TO SLOW DOWN AND CONVERGENCE ALONG THE LEADING EDGE OF THE FRONT WILL TEND TO WEAKEN DURING THE AFTERNOON AND EVENING HRS. THE PRIMARY CAVEAT HERE IS THE AMOUNT OF CONVECTION THAT IS ABLE TO SUSTAIN ITSELF ALONG THE FRONT UPSTREAM THIS AFTERNOON. IF CONVECTION IS VIGOROUS THIS AFTERNOON...WELL ORGANIZED COLD POOL STRUCTURES COULD SEND THE FRONTAL BOUNDARY SOUTH MUCH FASTER THAN THIS FORECAST INDICATES WILL HAPPEN. IF THAT OCCURS TSTMS MAY BE POSSIBLE ALONG AND BEHIND THE FRONTAL BOUNDARY LATE THIS AFTERNOON AND INTO THE EVENING HRS. IN THE ABSENCE OF VIGOROUS/PERSISTENT CONVECTION UPSTREAM THIS AFTERNOON...FEELING IS THAT FRONTAL PASSAGE WILL TEND TO FAVOR LATE EVENING/AFTER MIDNIGHT ACROSS MUCH OF NORTH TX. GFS INDICATES THE PASSAGE OF A SUBTLE SHORTWAVE TROUGH...ANALYZED AS A WEAK PRESSURE MAXIMA ON THE 1.5 PVU SFC AROUND 06Z TONIGHT. IF THIS OCCURS WOULD BE MORE CONFIDENT IN TSTMS ALONG AND NORTH OF INTERSTATE 20 BEFORE 06Z (1AM) TONIGHT. OTHERWISE FEEL THAT WITH FRONT EXPECTED TO SLOW DOWN...WILL HAVE TO WAIT FOR DEEPER SURGE OF COOL AIR MOVING SOUTH THRU THE PLAINS TO INCREASE FORCING ALONG THE FRONTAL BOUNDARY FOR STORMS TO DEVELOP ALONG THE RED RIVER AND COUNTIES SOUTH CLOSER TO 12Z EARLY SUNDAY MORNING. FEEL THAT IN THE ABSENCE OF SIGNIFICANT LARGE SCALE FORCING ALOFT...THE SLOWER FRONTAL PASSAGE IS MORE REALISTIC AND CURRENT FORECAST REFLECTS THIS THINKING. FEEL THAT STORMS WILL EVENTUALLY DEVELOP ALONG THE FRONT...BUT FEEL THAT BEST CHANCE IS LATE SATURDAY NIGHT INTO SUNDAY MORNING. WHENEVER STORMS DO DEVELOP ALONG THE FRONT...MODELS INDICATE THAT THERE IS A GOOD CHANCE THAT STORMS WILL PRODUCE COPIOUS AMTS OF RAINFALL. THIS IS GOOD NEWS FOR MOST LOCATIONS ACRS NORTH TX...HOWEVER WITH EXPECTED SLOW MOVEMENT OF THE COLD FRONT...DEEP LOW LVL MOISTURE POOLED UP ALONG AND BEHIND THE SFC COLD FRONT...AND WEAK MID TO UPR LVL FLOW ALOFT...TRAINING OF STORMS IS LIKELY. WEAK MID LVL LAPSE RATES AND GUIDANCE SUPPORTING PWATS IN THE 2 TO 2.25 INCH RANGE ALONG AND NORTH OF INTERSTATE 20 ALL POINT TO POTENTIAL LOCALIZED FLOODING WHEREVER STORMS DEVELOP. WITH WEAK FORCING NOT CONFIDENT ENOUGH TO GO WITH A FLOOD WATCH AS AERIAL EXTENT MAY BE SOMEWHAT LIMITED...BUT FLOODING CERTAINLY A SHORT TERM FORECAST CONCERN ONCE THE PLACEMENT AND MOVEMENT OF STORMS IS BETTER RESOLVED. STORMS CAPABLE OF PRODUCING 2-3 INCH/HR RAINFALL RATES ARE POSSIBLE...WITH STRONGEST CELLS. EXTENDED...GFS/NAM BOTH POINT TO FAIRLY STOUT SHORTWAVE TROUGH PUSHING SOUTHEAST THROUGH THE PLAINS AND INTO NORTH TX LATE MONDAY AFTERNOON AND THRU THE OVERNIGHT HRS. DEEP MOISTURE SOMEWHAT LIMITED...HOWEVER COULD NOT IGNORE GOOD LARGE SCALE FORCING FOR ASCENT...AND UPPED POPS TO COINCIDE WITH BEST MODEL ESTIMATE ON THE PASSAGE OF THIS FEATURE (00-06Z MONDAY NIGHT). ALSO MENTIONED SOME SLIGHT CHANCE POPS FOR LATE TUESDAY AFTERNOON THRU THE OVERNIGHT HRS WITH GFS INDICATING THE PASSAGE OF ANOTHER SHORTWAVE TROUGH. THIS FEATURE IS NOT ANALYZED AS STRONG AS THE MONDAY NIGHT FEATURE SO KEPT POPS AROUND 20 PERCENT. STARTING WEDNESDAY UPPER LVL RIDGE BUILDS BACK EAST INTO THE SOUTHERN PLAINS...AND HAVE GONE WITH AROUND 10 POPS THRU THE REST OF THE PERIOD BUT NO MENTION OF WX AS FORCING MECHANISMS FOR TSTMS LIKELY TO BE MESOSCALE IN NATURE. NO OTHER SIGNIFICANT CHANGES MADE TO THE PREVIOUS FORECAST PACKAGE. CAVANAUGH && .PRELIMINARY POINT TEMPS/POPS... DALLAS-FT. WORTH, TX 101 76 92 74 91 / 5 30 50 30 30 WACO, TX 101 79 97 75 94 / 5 10 40 40 30 PARIS, TX 98 73 90 73 89 / 5 40 50 20 30 DENTON, TX 101 75 91 72 90 / 10 40 50 20 30 MCKINNEY, TX 101 74 92 73 90 / 5 40 50 30 30 DALLAS, TX 101 77 93 74 91 / 5 30 50 30 30 TERRELL, TX 101 77 94 74 91 / 5 20 50 30 30 CORSICANA, TX 101 76 96 74 93 / 5 20 40 40 30 TEMPLE, TX 101 76 97 73 95 / 5 10 20 40 30 && .FWD WATCHES/WARNINGS/ADVISORIES... NONE. && $$ 75/