MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 147 AM EST SUN DEC 13 2015 VALID DEC 13/0000 UTC THRU DEC 16/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...INCLUDING THE NAM/GFS/UKMET/CMC/ECMWF ...UPPER-LEVEL TROUGH/CLOSED LOW EJECTING OUT INTO THE SOUTHERN PLAINS BY SUN... ...SURFACE LOW DEEPENING ACROSS THE CENTRAL U.S. ON SUNDAY... ...SURFACE LOW DEVELOPING OFF THE NEW ENGLAND COAST EARLY TUES... PRELIMINARY PREFERENCE: GFS/ECMWF BLEND CONFIDENCE: ABOVE AVERAGE THE GFS SOLUTION IS IN LINE WITH THE ECMWF/12Z ECMWF ENS MEAN/00Z GEFS MEAN WITH RESPECT TO THE UPPER-LEVEL LOW TRACKING ACROSS THE CENTRAL PLAINS THROUGH 12Z MONDAY. THE NAM IS NOT AS DEEP WITH THE UPPER LOW AND THIS BIAS PERSISTS EVEN AS THE SYSTEM REACHES THE NORTHEASTERN U.S. ON TUESDAY. BY EARLY TUESDAY THE UPPER LOW IN THE NAM ALSO BEGINS TO LAG BEHIND THE MODEL CONSENSUS. THE UKMET HAS JOINED THE NAM IN SHOWING A SLIGHTLY FARTHER WEST UPPER LOW BY MONDAY. THIS SLOWER MOTION IN THE NAM/UKMET APPLIES TO THE SURFACE LOW AS WELL AS IT CROSSES THE GREAT LAKES AND MOVES INTO ONTARIO/QUEBEC. BY TUESDAY MORNING CYCLOGENESIS IS FORECAST TO OCCUR ALONG THE NEW ENGLAND COAST BY ALL MODELS. THE GFS IS VERY CLOSE TO THE ECMWF WITH RESPECT TO THE TIMING AND INTENSITY OF THIS LOW. THE CMC IS VERY CLOSE TO CONSENSUS AS WELL...AND DEPICTS A SURFACE LOW POSITION OFF THE NEW ENGLAND COAST ON TUESDAY IN LINE WITH THE GFS/ECMWF. THE CMC APPEARS A LITTLE WEAKER WITH THE UPPER-LEVEL LOW...HOWEVER...WHICH COULD HAVE SOME IMPACTS ON ITS PRECIPITATION FORECAST ACROSS THE NORTHEAST. AT THIS POINT...A BLEND OF THE GFS AND ECMWF APPEARS TO REPRESENT A CONSENSUS SOLUTION. ...PACIFIC STORM SYSTEM AFFECTING THE NORTHWEST TONIGHT THROUGH SUN... PRELIMINARY PREFERENCE: GFS/ECMWF BLEND CONFIDENCE: ABOVE AVERAGE THE UPPER-LEVEL ENERGY ASSOCIATED WITH THE STRONG SURFACE LOW MOVING INTO BRITISH COLUMBIA TONIGHT IS FORECAST TO MOVE INLAND AND SHEAR OUT. MODEL AGREEMENT WITH RESPECT TO THIS SURFACE LOW AS IT MOVES INLAND IS RELATIVELY GOOD. SPREAD AMONG THE GFS/ECMWF/UKMET IS RELATIVELY LOW. THE NAM SEEMS A SLIGHT BIT FAST WITH THE UPPER-LEVEL WAVE AS IT BEGINS TO OPEN UP AND SHEAR INTO A BROADER TROUGH...WHILE THE CMC SEEMS SLIGHTLY TOO SLOW TO SHEAR THE TROUGH OUT. WILL RECOMMEND A GFS/ECMWF BLEND AT THIS TIME. ...UPPER-LEVEL TROUGH MOVING ONSHORE IN CALIFORNIA ON SUNDAY AND CROSSING THE GREAT BASIN SUNDAY NIGHT... ...CLOSED LOW CROSSING THE ROCKIES/HIGH PLAINS MON AND TUES... ...SURFACE LOW DEVELOPING EAST OF THE ROCKIES ON MON... PRELIMINARY PREFERENCE: GFS/UKMET BLEND CONFIDENCE: ABOVE AVERAGE THE NAM AND GFS ARE IN GOOD AGREEMENT WITH THE ECMWF/UKMET AS AN AMPLIFYING SHORTWAVE MOVES ONSHORE IN NORTHERN CALIFORNIA ON SUNDAY AND THEN CROSSES THE GREAT BASIN SUNDAY NIGHT BEFORE CLOSING OFF INTO AN UPPER-LEVEL LOW EARLY MONDAY. THE NAM APPEARS TO BE TOO AMPLIFIED WITH AN ADDITIONAL SHORTWAVE ON THE SOUTHWESTERN PERIPHERY OF THE UPPER LOW ON TUESDAY. BY EARLY WEDNESDAY...THE ECMWF HAS SLOWED DOWN THE UPPER-LOW RELATIVE TO ITS PREVIOUS RUN...AND RELATIVE TO THE 12Z ECMWF ENS MEAN AND THE 00Z GEFS MEAN. THE UKMET IS A BIT SLOWER/FARTHER WEST THAN THE GFS AS WELL...BUT TO A LESSER DEGREE THAN THE ECMWF. GIVEN THE CLOSE PROXIMITY OF THE GFS TO THE 00Z GEFS MEAN AND THE 12Z ECMWF ENS MEAN...THINK THERE IS SOME SUPPORT THERE FOR THE GFS. WILL RECOMMEND A BLEND OF THE GFS AND THE UKMET...WHICH WOULD RESULT IN A SLIGHTLY FARTHER WEST SURFACE LOW AT 12Z WED AS COMPARED TO THE GFS...BUT NOT AS FAR AS WEST AS THE ECMWF. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RYAN