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

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000 FXUS64 KFWD 211745 AFDFWD AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE FORT WORTH TX 1245 PM CDT THU AUG 21 2014 .AVIATION... THE LAST BATCH OF STRAOCU WILL CONTINUE TO LIFT ABOVE 4000 FT AS IT MOVES NORTH OF THE METROPLEX TAF SITES. WE EXPECT FEW TO SCATTERED CU TO LINGER THROUGH THE AFTERNOON AND DISSIPATE WITH THE LOSS OF SURFACE HEATING. A 25 TO 30 KNOT LOW LEVEL JET WILL DEVELOP LATE THIS EVENING AND WILL BRING ANOTHER ROUND OF STRATUS TO THE HILL COUNTRY AND PORTIONS OF NORTH TEXAS. IT LOOKS LIKE THE LOW LEVEL JET WILL BE A BIT MORE SOUTHWESTERLY FRIDAY MORNING THAN IT WAS THIS MORNING AND THIS SHOULD KEEP MOST OF THE LOW CLOUDS EAST/SOUTHEAST OF THE METROPLEX TAF SITES. WE WILL STILL CARRY SCATTERED LOW CLOUDS AT THE METRO TERMINALS FROM 14 TO 17Z. WACO WILL HAVE A BETTER CHANCE AT SEEING MVFR CEILINGS BETWEEN 11 AND 17Z. A SOUTHERLY WIND WILL PREVAIL THROUGH FRIDAY MORNING AT SPEEDS BETWEEN 12 AND 17 KNOTS THIS AFTERNOON AND BETWEEN 10 AND 15 KNOTS TONIGHT/FRIDAY MORNING. 79 && .UPDATE... LOW CLOUDS WILL CONTINUE TO SCATTER OUT ACROSS THE REGION AS DRIER AIR MIXES DOWN THROUGH THE BOUNDARY LAYER. A PARTLY CLOUDY AND HOT AFTERNOON IS STILL EXPECTED WITH AFTERNOON HIGHS FROM THE UPPER 90S TO AROUND 101. THE CURRENT FORECAST IS IN GOOD SHAPE SO NO UPDATE IS NEEDED AT THIS TIME. 79 && .PREV DISCUSSION... /ISSUED 542 AM CDT THU AUG 21 2014/ REMARKABLY STOUT LLJ FOR THIS TIME OF YEAR (35-40KTS) HAS RESULTED IN WIDESPREAD (ALBEIT THIN) STRATUS ALONG THE BALCONES ESCARPMENT. A FIBROUS DECK HAS INVADED SOUTHERN PORTIONS OF THE CWA EARLY THIS MORNING...AND A FEW FRAGMENTS WILL LIKELY REACH THE I-20 CORRIDOR AFTER DAYBREAK. AS THESE STRONG WINDS MIX WITH THE SURFACE LAYER LATER THIS MORNING...WIND GUSTS WILL PICK UP AGAIN. SUNNY SKIES WILL PUSH TEMPERATURES BACK UP INTO THE UPPER 90S TO NEAR 100 DEGREES...BUT THE WIND WILL HELP TAKE AN EDGE OFF THE HEAT. WITH THE BEST MOISTURE FLUX INTO LOUISIANA TODAY...EXPECT THE WESTERN EXTENT OF THE SEA BREEZE ACTIVITY THIS AFTERNOON WILL BE IN FAR SOUTHEAST TEXAS. THE TROUGHING IN THE WESTERN STATES IS PROGGED TO BE A BIT WEAKER WITH THE MAIN UPPER LOW TAKING A SHARP LEFT TURN INTO THE PRAIRIE PROVINCES LATE IN THE WEEKEND. AS A RESULT...THE MID-LEVEL RIDGE IN THE SOUTHEAST WILL BE ABLE TO BUILD FARTHER WEST THE PREVIOUSLY PROGGED. THE RIDGE WILL BE NEATLY STACKED VERTICALLY ABOVE THE BOUNDARY LAYER...FROM 10KFT ABOVE MSL TO AROUND 35KFT...WHICH WILL ASSURE SUBSIDENCE WILL DOMINATE INTO NEXT WEEK. HOWEVER...ITS INTENSITY IS STILL RATHER ORDINARY FOR AUGUST...AND ITS PLACEMENT EAST OF TEXAS SHOULD PREVENT TEMPERATURES FROM SOARING INTO THE TRIPLE DIGITS. IN ADDITION...BREEZY CONDITIONS WILL CONTINUE THE REMAINDER OF THE WEEK...WHICH WILL PREVENT OPTIMAL HEATING OF THE SURFACE LAYER. THIS WILL REDUCE HIGH TEMPERATURES 1-2 DEGREES FROM WHAT WOULD OTHERWISE BE EXPECTED...MEANING THAT ACHIEVING TRIPLE- DIGIT HIGHS WILL BE A LITTLE MORE DIFFICULT. A NIGHTLY LLJ WILL MEAN REPEATED STRATUS INTRUSIONS...PRIMARILY INTO CENTRAL TEXAS. THESE MORNING CLOUDS WILL BE SHORT-LIVED AND WILL DO LITTLE TO PREVENT HOT AFTERNOONS. HEAT INDEX VALUES WILL EASILY TOP 100 BUT SHOULD REMAIN BELOW 105. A PIECE OF UPPER VORTICITY IS STILL PROGGED TO EJECT FROM THE TUTT SOUTH OF BROWNSVILLE...AND THE SOUTHERLY FLOW BENEATH IT WILL GUIDE IT NORTHWARD OVER THE LONE STAR STATE. THE POLAR JET WILL EFFECTIVELY SHEAR IT...BUT THE TROUGHINESS IN THE UPPER REACHES OF THE TROPOSPHERE WILL LINGER THROUGH THE WEEKEND. EVEN SO...THE FEATURE WILL QUICKLY BECOME AN OPEN WAVE AND SHOULD BE UNABLE TO DISRUPT THE DEEP SUBSIDENCE BENEATH IT. AS THE UPPER LOW ENTERS CANADA...THE FLOW ALOFT INTO THE CENTRAL PLAINS WILL DIMINISH CONSIDERABLY. A CORRESPONDING WEAKENING OF THE PERSISTENT LEE TROUGH WILL MEAN LIGHTER SURFACE WINDS ACROSS NORTH AND CENTRAL TEXAS. THIS WILL BRING AN END TO THE MORNING STRATUS AND WILL MAKE THE HEAT FEEL A LITTLE MORE OPPRESSIVE... BUT IT MAY ALSO ALLOW THE SEA BREEZE TO REAWAKEN. THE GFS AND ECMWF SOLUTIONS DIVERGE NEXT WEEK...WITH THE ECMWF DEVELOPING A CUT-OFF LOW AND THE GFS FAR MORE PROGRESSIVE. THE CANADIAN IS A COMPROMISE BETWEEN THE TWO...BUT LEANS TOWARD THE GFS IN THAT IT KEEPS THE FLOW UNIMPEDED. DESPITE CONSIDERABLE SPREAD AMONG THE GFS ENSEMBLE MEMBERS...THE CONSENSUS FAVORS A FRONTAL PASSAGE LATE NEXT WEEK. HAVE INTRODUCED NORTH WINDS AND SLIGHT PRECIP CHANCES ON THURSDAY NEXT WEEK...BUT THESE WILL NOT APPEAR IN THE PUBLIC FORECAST UNTIL THE AFTERNOON PACKAGE TODAY. 25 && .FIRE WEATHER... HOT AND RAIN-FREE CONDITIONS WILL PERSIST THROUGH THE WEEKEND. A BROAD UPPER HIGH WILL BE CENTERED ACROSS THE WESTERN GULF STATES AND WILL RESULT IN HIGHS BETWEEN THE MID 90S AND 102 DEGREES ACROSS THE AREA. HOTTEST HIGH TEMPERATURES WILL BE ACROSS THE FAR WESTERN COUNTIES WHERE DEEPER MIXING WILL RESULT IN LOWER AFTERNOON HUMIDITY VALUES EACH DAY BETWEEN 20 AND 30 PERCENT. HOWEVER...20 FOOT WINDS WILL REMAIN SUSTAINED BETWEEN 10 TO 15 MPH WITH OCCASIONAL GUSTS EXCEEDING 20 MPH. A WEAK SURFACE LOW NEAR THE WESTERN HALF OF NORTH TEXAS SHOULD KEEP WINDS FROM BECOMING TOO STRONG. THIS AREA WILL NEED TO BE WATCHED CLOSELY IN THE COMING DAYS FOR A HIGH FIRE DANGER...PARTICULARLY THOSE AREAS NORTHWEST OF A GAINESVILLE...DECATUR...COMANCHE LINE. FUEL MOISTURE LEVELS AT BOTH POSSUM KINGDOM RESERVOIR AND MILLER/S CREEK RAWS OBSERVATIONS WERE ALREADY BELOW 10...INDICATING SOME DRYING OF FINE FUELS ACROSS THE AREA. OTHERWISE...AREAS FURTHER TO THE EAST MAY SEE OCCASIONAL HIGHER GUSTS BUT WILL ALSO SEE RICHER GULF MOISTURE AND AFTERNOON HUMIDITY VALUES REMAINING ABOVE CRITICAL LEVELS. THE HIGHER HUMIDITY ACROSS THE EASTERN AREAS SHOULD HOLD HIGH TEMPERATURES INTO MID TO UPPER 90S. THE FIRE DANGER SHOULD REMAIN LOW INTO EARLY NEXT WEEK...AS WIND SPEEDS REMAIN BELOW 15 MPH. 05 && .CLIMATE... LATE AUGUST FRONTAL PASSAGES ARE REMARKABLY COMMON. ALTHOUGH NORMAL HIGH TEMPERATURES (BASED ON DFW DATA 1981-2010) GRADUALLY DECREASE AFTER AUGUST 17 AT A STEADY RATE...THE AVERAGE TEMPERATURES TELL A DIFFERENT STORY. DAILY NORMALS ARE CREATED USING A HARMONIC FIT...A METHOD EMPLOYED TO DAMPEN OUTLIERS. THE RESULT ASSURES A SMOOTH TRANSITION FROM ONE DAY TO THE NEXT...BUT THIS SMOOTHING REMOVES INTRICACIES IN THE DATA THAT CAN REVEAL MORE ABRUPT SEASONAL TRANSITIONS. FOR EXAMPLE...MUCH OF THE DECREASE IN HIGH TEMPERATURES DURING LATE AUGUST OCCURS IN A 2-DAY SPAN BETWEEN AUGUST 26 AND 28. THE DATA BELOW ARE BASED ON THE DALLAS/FORT WORTH CLIMATE RECORD 1981-2010. AVERAGE NORMAL HIGH / LOW HIGH / LOW AUGUST 26 97.4 / 75.4 95 / 74 AUGUST 28 93.5 / 73.4 94 / 74 THE AVERAGE HIGH TEMPERATURE (1981-2010) ACTUALLY INCREASES BETWEEN AUGUST 17 AND 26. THE SUDDEN 3.9-DEGREE DROP IN JUST 2 DAYS (AUGUST 26-28) IS THUS VERY SIGNIFICANT. THESE ARE NOT SIMPLY ARTIFACTS OF A 30-YEAR DATA SET. USING THE ENTIRE CLIMATE RECORD (WHICH BEGAN IN SEPTEMBER 1898) YIELDS A DECREASE IN THE AVERAGE HIGH TEMPERATURE BETWEEN AUGUST 17 AND 26 (1.2 DEGREES) THAT IS STILL LESS THAN THE 2-DAY SPAN AUGUST 26-28 (1.4 DEGREES). AND YES...WHEN INCORPORATING THE ENTIRE CLIMATE RECORD OF MORE THAN A CENTURY OF DATA...THE TIME FRAME OF THE SIGNIFICANT DROP REMAINS AUGUST 26-28. WHAT DOES THIS MEAN? IT MEANS THAT HISTORICAL FRONTAL PASSAGES CLUSTER AROUND THESE DATES...SHOWING A TENDENCY FOR THE FIRST SIGNIFICANT LATE SUMMER FRONT TO OCCUR AT THIS TIME. IT LOOKS LIKE 2014 MAY FOLLOW SUIT. THE GFS PROJECTS A FRONTAL PASSAGE NEXT WEEK ON AUGUST 28. DOES THIS MEAN FALL HAS ARRIVED? NOT QUITE YET...AS HIGH TEMPERATURES WILL LIKELY BE IN THE 90S EVEN IF THE COLD FRONT ARRIVES. NORMAL (AND AVERAGE) HIGH TEMPERATURES ARE STILL IN THE 90S IN EARLY SEPTEMBER. ANOTHER SIGNIFICANT DROP IN AVERAGE TEMPERATURES OCCURS AROUND THE AUTUMNAL EQUINOX...WHICH IS ONLY A MONTH AWAY. (THE BELOW ARE BASED ON DFW DATA 1981-2010.) AVERAGE NORMAL HIGH / LOW HIGH / LOW SEPTEMBER 20 88.1 / 65.8 87 / 66 SEPTEMBER 24 83.1 / 62.6 85 / 64 PERHAPS THERE IS SOMETHING TO THE FIRST DAY OF FALL. && .PRELIMINARY POINT TEMPS/POPS... DALLAS-FT. WORTH, TX 99 78 99 78 100 / 0 0 0 0 0 WACO, TX 100 76 100 76 100 / 0 0 0 0 0 PARIS, TX 97 74 97 74 98 / 0 0 0 0 0 DENTON, TX 99 77 99 75 100 / 0 0 0 0 0 MCKINNEY, TX 97 75 98 74 99 / 0 0 0 0 0 DALLAS, TX 99 78 99 79 99 / 0 0 0 0 0 TERRELL, TX 97 75 98 75 98 / 0 0 0 0 0 CORSICANA, TX 98 75 98 75 98 / 0 0 0 0 0 TEMPLE, TX 99 76 98 74 98 / 0 0 0 0 0 MINERAL WELLS, TX 99 73 99 73 101 / 0 0 0 0 0 && .FWD WATCHES/WARNINGS/ADVISORIES... NONE. && $$ 79/79

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