Prognostic Meteorological Discussion
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000 FXUS10 KWNH 300644 PMDHMD MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 244 AM EDT FRI SEP 30 2016 VALID SEP 30/0000 UTC THRU OCT 03/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...INCLUDING THE NAM/GFS/UKMET AND ECMWF ...UPPER LOW CROSSING BACK TO THE LOWER GREAT LAKES... ...ADVANCING EAST INTO THE NORTHEAST THIS WEEKEND... PREFERENCE: BLEND OF THE 00Z GFS/UKMET/ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE MODELS TAKE THE UPPER LOW OVER THE OH VALLEY GRADUALLY BACK NORTH INTO THE LOWER GREAT LAKES REGION BY SATURDAY...AND THEN EAST INTO THE NORTHEAST ON SUNDAY. THE UKMET AND TO SOME EXTENT THE ECMWF HAVE TRENDED TOWARD THE FASTER GFS BY THE END OF THE PERIOD WITH THE HEIGHT FALLS MOVING INTO THE NORTHEAST. THE CMC AND ESPECIALLY THE NAM ARE ON THE SLOWER SIDE OF THE GUIDANCE AT THIS POINT. SINCE THE LATEST GEFS MEAN HAS TRENDED TOWARD THE MORE PROGRESSIVE CAMP...WILL OPT TO LEAN TOWARD A GFS/UKMET/ECMWF BLEND. ...WEAK UPPER TROUGH DEVELOPING OVER THE GULF COAST STATES... PREFERENCE: BLEND OF THE 00Z GFS/UKMET/ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE IN THE WAKE OF THE UPPER LOW OVER THE OH VALLEY LIFTING OFF TO THE NORTH AND NORTHEAST...THE GUIDANCE ALLOWS FOR A BROAD WEAKNESS/UPPER TROUGH TO DEVELOP OVER THE GULF COAST STATES BY SUNDAY AND MONDAY. THE NAM AND CMC APPEAR TO BOTH BE TOO DEEP WITH THIS SYSTEM. THE GFS/UKMET AND ECMWF ARE ALL A LITTLE WEAKER AND HAVE STRONGER MODEL CLUSTERING AND ENSEMBLE SUPPORT. WILL LEAN TOWARD THE GFS/UKMET/ECMWF CAMP FOR NOW. ...SHORTWAVE SHEARING FROM THE GREAT BASIN TO THE NORTHERN PLAINS... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE A SHEARING MID-LEVEL PERTURBATION WILL EJECT ACROSS THE GREAT BASIN AND ACROSS THE NORTHERN PLAINS THROUGH FRIDAY. DIFFERENCES AMONG THE MODELS ARE MINOR WITH THIS SYSTEM...AND A GENERAL MODEL COMPROMISE SHOULD SUFFICE TO RESOLVE THIS AT THIS POINT. ...DEEP UPPER TROUGH/CLOSED LOW MOVING INTO THE WEST... ...LEAD SHORTWAVE CROSSING THE PACIFIC NORTHWEST... PREFERENCE: BLEND OF THE 00Z NAM/GFS/ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE AN ACTIVE SYNOPTIC PATTERN IS IN PLACE OVER THE EASTERN PACIFIC WITH A PAIR OF SYSTEMS EXPECTED TO AFFECT THE WESTERN U.S. THIS WEEKEND. INITIALLY...AN UPPER TROUGH JUST OFFSHORE THE PACIFIC NORTHWEST WILL PIVOT INLAND ACROSS THE PACIFIC NORTHWEST BY SATURDAY BEFORE LIFTING NORTHEAST INTO SOUTHWEST AND THEN SOUTH-CENTRAL CANADA THROUGH SUNDAY. THE MODELS SHOW GOOD AGREEMENT WITH THE EVOLUTION OF THIS SYSTEM. MEANWHILE...MUCH STRONGER HEIGHT FALLS ASSOCIATED WITH AN UPPER LOW WILL DIG SOUTH OFF THE WEST COAST AND THEN INLAND ACROSS THE GREAT BASIN SUNDAY AND MONDAY. THE CMC IS LIKELY TOO SLOW WITH THIS SYSTEM...AS THE OTHER MODELS CLUSTERED ON A SOMEWHAT MORE PROGRESSIVE EVOLUTION THAT FEATURES A CLOSED LOW OVER THE GREAT BASIN BY EARLY MONDAY. HOWEVER...THE UKMET MAY BE JUST A TAD TOO PROGRESSIVE BY THAT TIME. STRONGER MODEL CLUSTERING WOULD FAVOR A BLEND OF THE NAM/GFS AND ECMWF...AND THIS WILL BE THE LATEST PREFERENCE. ...MODEL TREND GRAPHICS AT www.wpc.ncep.noaa.gov/html/model2.shtml... ...500 MB FORECASTS AT www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON $$

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