MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 150 PM EST SAT DEC 19 2015 VALID DEC 19/1200 UTC THRU DEC 23/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION...INCLUDING THE NAM/GFS/UKMET/CMC AND ECMWF ...SHORTWAVE TROUGH CROSSING NORTHERN NEW ENGLAND TONIGHT AND EARLY SUN... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE A NORTHERN STREAM SHORTWAVE TROUGH DIGGING SOUTHEAST FROM SOUTHERN QUEBEC WILL CROSS NORTHERN NEW ENGLAND LATER TONIGHT AND EARLY SUN. THE MODELS ARE IN VERY GOOD AGREEMENT WITH THIS SYSTEM...THUS A GENERAL MODEL COMPROMISE WILL BE PREFERRED. ...SPLIT-FLOW TROUGH MOVING FROM THE WEST COAST THROUGH THE MIDWEST THIS WEEKEND... ...SURFACE LOW PRESSURE DEVELOPING AND CROSSING THE PLAINS/MIDWEST/GREAT LAKES... PREFERENCE: BLEND OF THE 12Z GFS/12Z ECMWF AND 12Z UKMET CONFIDENCE: AVERAGE ALL MODELS AGREE IN ALLOWING A SPLIT-FLOW TROUGH TO PROGRESSIVELY CROSS THE WEST TODAY AND THEN EJECT OUT INTO THE PLAINS ON SUN. MEANWHILE...SURFACE LOW PRESSURE WILL DEVELOP IN THE LEE OF THE ROCKIES OVER THE CENTRAL HIGH PLAINS AND EJECT THROUGH THE MIDWEST AND UPPER GREAT LAKES THROUGH EARLY MON. HOWEVER...IT AGAIN APPEARS AS THOUGH THERE WILL BE SUFFICIENT STREAM SEPARATION FOR DISTINCT LOW CENTERS IN BOTH THE NORTHERN AND SOUTHERN STREAMS. THE 12Z UKMET AND 12Z CMC HAVE TRENDED A BIT MORE PROGRESSIVE WITH THE SOUTHERN STREAM ENERGY AND ASSOCIATED LOW CENTER...AND ARE CLUSTERING CLOSER TO THE 12Z GFS SOLUTION WHICH HAD SLOWED DOWN SOMEWHAT. THE 12Z ECMWF ALSO HAS TRENDED A LITTLE MORE PROGRESSIVE...BUT DOES LAG THE CONSENSUS JUST A BIT AFTER ABOUT 48 HOURS. ALL OF THE MODELS HAVE A SEPARATE NORTHERN STREAM LOW...AND THERE IS BETTER AGREEMENT NOW WITH TIMING OF THIS FEATURE BETWEEN THE NCEP AND NON-NCEP SOLUTIONS AS THIS ENERGY LIFTS INTO SOUTHEAST CANADA. BASED ON STRONGER MODEL CLUSTERING AND TRENDS...WILL PREFER A MULTI-MODEL BLEND WEIGHTED TOWARD THE 12Z GFS/12Z ECMWF AND 12Z UKMET. ...SHORTWAVE/COLD FRONT ARRIVING IN THE PACIFIC NORTHWEST EARLY SUN... ...WEAK SURFACE LOW IMPACTING NORTHWEST CALIFORNIA ON SUN... ...ENERGY SHEARING THROUGH THE PLAINS THROUGH BY TUES... PREFERENCE: NON-GFS CONSENSUS...THROUGH 48 HOURS NON-NAM CONSENSUS...AFTER 48 HOURS CONFIDENCE: ABOVE AVERAGE A PACIFIC SHORTWAVE TROUGH DIVING SOUTHEAST FROM THE GULF OF AK WILL CROSS THE COASTAL RANGES OF WA/OR EARLY SUN AND THEN CROSS THE INTERMOUNTAIN WEST THROUGH MON. THIS WILL ALSO BRING A WEAK SURFACE SURFACE LOW TOWARD NORTHWEST CA THROUGH SUN. THE 12Z GFS IS SOMEWHAT OF A SLOW OUTLIER WITH THE INITIAL ENERGY THAT COMES INTO THE NORTHWEST ON SUN...AND THIS REFLECTS AT THE SURFACE WITH A SLOWER LOW CENTER APPROACHING NORTHWEST CA. THE REMAINING MODELS ARE WELL CLUSTERED WITH THE INITIAL ARRIVAL OF THE ENERGY. DOWNSTREAM AND AFTER 48 HOURS...THE 12Z NAM BEGINS TO SUGGEST A SOMEWHAT SHARPER MID LEVEL REFLECTION OF THE ENERGY AS IT SHEARS OUT ACROSS THE PLAINS. A NON-GFS CONSENSUS WILL BE PREFERRED THROUGH 48 HOURS...FOLLOWED BY A NON-NAM CONSENSUS THEREAFTER. ...SHORTWAVE/COLD FRONT/LOW CENTER CROSSING THE PACIFIC NORTHWEST ON MON... ...ENERGY EJECTING OUT INTO THE NORTHERN PLAINS BY TUES... PREFERENCE: 12Z ECMWF CONFIDENCE: AVERAGE ANOTHER FAST-MOVING SHORTWAVE AND ASSOCIATED COLD FRONT WILL ARRIVE ACROSS THE PACIFIC NORTHWEST ON MON...WITH A COMPACT LOW CENTER THAT WILL LIKELY MOVE IN ACROSS SOUTHWEST WA/NORTHWEST OR BY MIDDAY. THE 12Z NAM IS GENERALLY FLATTER WITH THE SHORTWAVE AND NOTABLY WEAK WITH ITS SURFACE WAVE REFLECTION AS IT APPROACHES THE NORTHWEST. THE 12Z GFS AND 12Z GEFS MEAN HAVE TRENDED STRONGER AND TOWARD THE NON-NCEP MODELS WHICH COLLECTIVELY ARE CONSIDERABLY STRONGER THAN THE NAM...AND ESPECIALLY THE 12Z UKMET WHICH IS THE STRONGEST ALOFT AND HAS A STRONG SURFACE LOW MOVING IN ALONG THE WA/OR BORDER ON MON. THE 12Z ECMWF IS A LITTLE WEAKER THAN THE UKMET...BUT THE ECMWF AGREES WITH THE TIMING OF THE UKMET. THE 12Z CMC IS A LITTLE SLOWER AND WEAKER THAN THE ECMWF. THE 00Z ECENS MEAN FAVORS A SOLUTION TOWARD THE OPERATIONAL ECMWF...WITH A LOW TRACK JUST A TAD FARTHER NORTH. ALTHOUGH THE GFS HAS TRENDED STRONGER...IT MAY STILL BE A TAD TOO WEAK. GIVEN THE NON-NCEP CLUSTERING OF AT LEAST A WELL-DEFINED AND STRONGER SURFACE LOW...AND WITH THE 00Z ECENS MEAN TRENDING IN THIS DIRECTION COMPARED TO YESTERDAY...WITH LEAN AWAY FROM THE NCEP MODELS AND LEAN SPECIFICALLY TOWARD THE 12Z ECMWF. ON TUES...THIS ENERGY WILL HAVE QUICKLY CROSSED THE NORTHERN ROCKIES AND WILL BE EJECTING OUT INTO THE PLAINS. THE NAM AND GFS ARE GENERALLY WEAKER WITH THE VORT ENERGY EVOLUTION AND SHOW LESS-DEFINED AREAS OF LOW PRESSURE IN THE LEE OF THE ROCKIES. THE NON-NCEP MODELS ARE STRONGER WITH THEIR LEE-SIDE CYCLOGENESIS...BUT THE CMC AND ESPECIALLY THE UKMET MAY BOTH BE A BIT TOO STRONG. WILL LEAN AGAIN TOWARD THE 12Z ECMWF WITH THIS EVOLUTION. ...SHORTWAVE TROUGH CROSSING THE PACIFIC NORTHWEST BY LATE TUES... PREFERENCE: 12Z ECMWF CONFIDENCE: BELOW AVERAGE THE MODELS SHOW ADDITIONAL ENERGY DROPPING EAST-SOUTHEAST IN OFF THE PACIFIC OCEAN AND INTO THE PACIFIC NORTHWEST BY LATE TUES. THE 12Z NAM AND 12Z GFS APPEAR TO PERHAPS BE TOO PROGRESSIVE...WITH THE 12Z ECMWF AND 12Z UKMET A LITTLE SLOWER. THE 12Z UKMET IS SUGGESTING A SURFACE WAVE THOUGH FARTHER SOUTH OFF THE OR COAST ON TUES WHICH IS NOT SUPPORTED BY ANY MODELS. WILL LEAN TOWARD THE 12Z ECMWF AT THIS POINT. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON