MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1141 PM EST SUN JAN 25 2015 VALID JAN 26/0000 UTC THRU JAN 29/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. MID-LEVEL SHORTWAVE MOVING INTO BRITISH COLUMBIA MON NIGHT SUBSEQUENT MOVEMENT INTO THE N-CNTRL U.S. EARLY THU ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS...12Z ECMWF BLEND CONFIDENCE: AVERAGE THE 00Z GFS AND 12Z ECMWF REPRESENT THE MIDDLE OF THE LATEST DETERMINISTIC/ENSEMBLE SPREAD WITH A MID-LEVEL SHORTWAVE FORECAST TO CROSS INTO SWRN CANADA TUE MORNING. THE 00Z NAM AND 12Z CMC ARE FLATTER...WHILE THE 12Z UKMET IS ON THE STRONGER/DEEPER SIDE OF THE AVAILABLE GUIDANCE. WEAKENING CLOSED LOW MOVING INTO CALIFORNIA EARLY TUESDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE THROUGH 12Z/28 70% 12Z ECMWF / 30% GFS BLEND CONFIDENCE: AVERAGE THE GUIDANCE IS IN GOOD AGREEMENT HERE THROUGH 12Z/28 AT WHICH POINT THE 12Z ECMWF HOLDS MORE SHORTWAVE ENERGY BACK TO THE WEST ACROSS THE GREAT BASIN WHILE THE GFS FOCUSES MORE TOWARD THE FRONT END OF THE SHORTWAVE TROUGH PROGRESSING ACROSS THE WEST. THE ECMWF/NAM/CMC HAVE TRENDED TOWARD THE 12Z ECMWF IDEA COMPARED TO PREVIOUS CYCLES...BUT THE GFS HOLDS GOOD CONTINUITY FROM 00Z/25. THE ENSEMBLE MEANS ARE SPLIT ON THIS IDEA...BUT GIVEN THE TRENDS...WILL LEAN MORE TOWARD THE ECMWF. WEAK CLIPPER PASSING THROUGH THE UPPER MISS VALLEY MON/TUE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: AVERAGE THE GUIDANCE IS IN GOOD AGREEMENT HERE. CLIPPER-TYPE SYSTEM EVOLVING INTO A NOR'EASTER MON/TUE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z NAM / 12Z ECMWF COMPROMISE CONFIDENCE: AVERAGE THE MODELS HAVE CONVERGED TOWARD A COMMON SOLUTION BUT AS IS ALWAYS THE CASE WITH THESE BIG STORMS...SMALL DETAIL DIFFERENCES RESULT IN LARGE IMPACT DIFFERENCES...ESPECIALLY WITH PRECIPITATION. PREFERENCES LISTED HERE REFLECT MODEL POSITION AND MASS FIELDS...BUT REFER TO WPC WINTER WEATHER AND QPF DESK PRODUCTS FOR INFORMATION ON LIQUID EQUIVALENTS/SNOW. THROUGH 12Z/27...THE 00Z NAM...00Z GFS AND 12Z ECMWF SHOW FAIRLY GOOD AGREEMENT IN POSITION AND STRENGTH REGARDING THE SURFACE AND MID-LEVEL LOWS BUT THE GFS IS SLIGHTLY WEAKER BY TUE MORNING. ENSEMBLE TRENDS AND THE LATEST ENSEMBLE MEANS...INITIALIZED 12Z/25...SUPPORT THE NAM/GFS/ECMWF COMBO. BEYOND 12Z/27...A BLEND OF THE 00Z NAM AND 12Z ECMWF APPEARS BEST AS THE GFS LIFTS THE PRIMARY SURFACE LOW TO THE NORTH...QUICKER THAN PREFERRED. HOWEVER...THE 21Z SREF MEAN...12Z EC MEAN AND 00Z NAM ARE IN GOOD AGREEMENT AND SUPPORT A TRACK THAT IS FASTER TO DEPART THE PRIMARY SURFACE LOW COMPARED TO THE 12Z ECMWF. THEREFORE REGARDING POSITION/STRENGTH...A BLEND OF THE 00Z NAM AND 12Z ECMWF IS PREFERRED. BOTH THE 12Z UKMET/CMC APPEAR EITHER UNSUPPORTED IN POSITION OR STRENGTH. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO