MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 254 PM EDT FRI JUL 24 2015 VALID JUL 24/1200 UTC THRU JUL 28/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION...INCLUDING THE NAM/GFS/UKMET/CMC AND ECMWF ...INITIAL UPPER TROUGH OVER THE UPPER MIDWEST... ...COLD FRONT CROSSING THE GREAT LAKES... PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF CONFIDENCE: ABOVE AVERAGE THE MODELS ARE IN PRETTY GOOD AGREEMENT IN TAKING THE UPPER TROUGH OVER THE UPPER MIDWEST AND WESTERN ONTARIO OFF TO THE EAST THE NEXT COUPLE OF DAYS WHICH WILL DRIVE A COLD FRONT EAST ACROSS THE GREAT LAKES REGION. BY LATE SAT AND SUN...THE 12Z CMC AND 12Z UKMET TEND TO HANG ON TO A STRONGER TROUGH THAT ATTEMPTS TO DIG TOWARD THE NORTHEAST...BUT THE 12Z NAM/12Z GFS AND 12Z ECMWF ARE WEAKER WHICH IS BETTER SUPPORTED BY THE ENSEMBLE GUIDANCE. WILL FAVOR A BLEND OF THE GFS AND ECMWF BASED ON STRONGER RUN TO RUN CONTINUITY. ...UPPER LOW/TROUGH DIGGING INTO WESTERN BRITISH COLUMBIA... ...TROUGH RELOADING IN THE WEST BY SAT AND SUN... ...CYCLOGENESIS OVER THE NORTHERN HIGH PLAINS... PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE AN UPPER LOW AND ASSOCIATED TROUGH DIGGING SOUTHEAST OUT OF THE GULF OF AK WILL DROP DOWN ACROSS BRITISH COLUMBIA THROUGH SAT AND THEN INTO NORTHWEST U.S. SUN AND MON. A LARGER SCALE TROUGH ASSOCIATED WITH THE UPPER LOW WILL RELOAD THROUGHOUT THE INTERMOUNTAIN WEST. MEANWHILE...LEE-SIDE CYCLOGENESIS OVER THE NORTHERN HIGH PLAINS WILL OCCUR BY MON. THE 12Z UKMET IS FASTER THEN THE 12Z NAM/12Z GFS AND 12Z ECMWF IN EJECTING THESE HEIGHT FALLS EAST ACROSS THE INTERMOUNTAIN REGION AND TOWARD THE NORTHERN HIGH PLAINS ON MON. THE 12Z CMC TRENDED A TAD SLOWER AND IS NOW IN LINE WITH THE NON-UKMET CONSENSUS. THE LATEST SREF MEAN...GEFS MEAN AND ECENS MEAN ARE ALL A BIT SLOWER THAN THE UKMET AS WELL. THERE IS SLIGHTLY STRONGER MODEL CLUSTERING BETWEEN THE GFS AND ECMWF...AND SO A BLEND OF THESE SOLUTIONS WILL BE PREFERRED. ...UPPER TROUGH SWINGING THROUGH THE NORTHEAST THROUGH SAT... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE MODELS SHOW VERY GOOD AGREEMENT IN TAKING THE CURRENT TROUGH DIGGING INTO THE NORTHEAST GRADUALLY EAST AND THEN UP ACROSS THE CANADIAN MARITIMES THROUGH SAT. A GENERAL MODEL COMPROMISE WILL BE PREFERRED. ...MID LEVEL TROUGH IMPACTING THE SOUTHEAST/FL PENINSULA... PREFERENCE: NON-NAM CONSENSUS CONFIDENCE: AVERAGE THE MODELS INDICATE THE DEVELOPMENT OF A SW/NE ORIENTED MID LEVEL TROUGH AXIS THIS WEEKEND EXTENDING FROM THE EASTERN GULF OF MEXICO TO THE SOUTHWEST ATLANTIC BASIN. A FRONTAL ZONE WILL BE DRAPED ACROSS THE SAME AREA AND THE MODELS INDICATE THE DEVELOPMENT OF MULTIPLE WAVES OF LOW PRESSURE. THE 12Z NAM AND 12Z ECMWF OVERALL ARE THE STRONGER MODELS ALOFT COMPARED TO THE 12Z GFS/12Z CMC AND 12Z UKMET. AT THE SURFACE...THE NAM HAS A STRONGER SURFACE WAVE EJECTING ALONG THE FRONT AND WELL OFFSHORE THE SOUTHEAST COAST SAT AND SUN. THE NAM ALSO HAS A RELATIVE LACK OF LOW PRESSURE NEAR THE FL PENINSULA SAT AND SUN WHICH THE GLOBAL MODELS FAVOR. WHILE THE ECMWF MAY BE A TAD TOO STRONG ALOFT...IT DOES APPEAR REASONABLE AT THE SURFACE IN CONJUNCTION WITH THE OTHER GLOBAL MODELS. AT THIS POINT...A CONSENSUS APPROACH AWAY FROM THE NAM APPEARS REASONABLE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON