MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 139 PM EST FRI DEC 11 2015 VALID DEC 11/1200 UTC THRU DEC 15/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION - INCLUDING THE NAM/GFS/UKMET/CMC/ECMWF ANY MODEL INITIALIZATION ERRORS APPEAR NEGLIGIBLE WITH RESPECT TO THEIR FORECASTS ***TROUGH CROSSING NEW ENGLAND FRIDAY NIGHT*** PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE MODEL ARE NOW IN VERY GOOD AGREEMENT ON THE PROGRESSION OF A SURFACE LOW OVER QUEBEC AND ITS TROUGH AXIS OVER NEW ENGLAND. THEREFORE A GENERAL MODEL COMPROMISE IS RECOMMENDED. ***PACIFIC LOW MOVING ACROSS PACIFIC NORTHWEST FRIDAY AFTERNOON AND NIGHT*** PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE A RELATIVELY COMPACT SURFACE LOW AND TROUGH CROSSING THE PACIFIC NORTHWEST ON FRIDAY, ALONG WITH AN INITIALLY CLOSED OFF 500MB LOW, IS FORECAST TO GRADUALLY WEAKEN AS IT EVOLVES INTO AN OPEN WAVE AND BECOMES ABSORBED IN THE LARGE SCALE FLOW PATTERN NEAR THE CANADIAN BORDER. THE OVERALL MODEL AGREEMENT IS NOW VERY GOOD, WITH A RECOMMENDATION FOR A GENERAL MODEL COMPROMISES. ***LARGE SCALE TROUGH AND SHORTWAVE THAT EVOLVES INTO CLOSED UPPER LEVEL LOW AND STRONG SURFACE LOW OVER THE CENTRAL U.S. THIS WEEKEND*** PREFERENCE: GENERAL MODEL COMPROMISE THROUGH 00Z SUNDAY, 00Z EC MEAN/12Z ECMWF/12Z GFS AFTER 00Z SUNDAY CONFIDENCE: BELOW AVERAGE THROUGH THE FIRST 36 HOURS OF THE FORECAST PERIOD, THE MODELS ARE IN OVERALL GOOD AGREEMENT WITH THE DEEP TROUGH AND DEVELOPING CUT-OFF LOW AT 500MB. BEYOND THIS TIME, MORE SIGNIFICANT DIFFERENCES REMAIN WITH THE UPPER LEVEL LOW AND IT SURFACE LOW TRACKING ACROSS THE CENTRAL PLAINS TOWARDS THE GREAT LAKES LATE IN THE PERIOD. THE OPERATIONAL ECMWF REMAINS ON THE SOUTHWEST SIDE OF THE MODEL SPREAD BY 12Z MONDAY AND ALSO SOUTHWEST OF THE EC MEAN, WHILE THE NAM IS NORTHEAST OF THE MODEL CONSENSUS. THE NAM HAS ALSO SUFFERED FROM SOME RUN-TO-RUN CONTINUITY ISSUES OVER ITS PAST THREE RUNS. GIVEN THE AMOUNT OF SPREAD IN THE LATTER HALF OF THE PERIOD, A BLEND OF THE 00Z EC MEAN, 12Z GFS, AND 12Z ECMWF IS RECOMMENDED FOR THIS SYSTEM AFTER 12Z SUNDAY. ***PACIFIC STORM SYSTEM APPROACHING THE NORTHWEST BY SATURDAY NIGHT AND SUNDAY*** PREFERENCE: GFS/ECMWF COMPROMISE CONFIDENCE: AVERAGE ANOTHER STRONG AND OCCLUDED STORM SYSTEM FROM THE PACIFIC IS PROGGED TO REACH SOUTHERN BRITISH COLUMBIA BY SATURDAY NIGHT. THE TRAILING COLD FRONT FROM THIS DEEP SURFACE LOW WILL REACH SOUTHWARD TOWARDS NORTHERN CALIFORNIA AND HAVE AN ATMOSPHERIC RIVER OF MOISTURE ASSOCIATED WITH IT. WITH RESPECT TO MODEL PERFORMANCE, THE 12Z UKMET IS SOUTH OF THE MODEL CONSENSUS WITH THE SURFACE LOW. CONCERNING THE SURFACE COLD FRONT, THE 12 NAM IS NOTABLY SLOWER AND HAS A DEEPER SURFACE WAVE THAN THE OTHER GUIDANCE, AND ALSO APPARENT AT THE 500MB LEVEL. THE 12Z UKMET HAS TRENDED CLOSER TO THE MODEL CONSENSUS WITH THIS TROUGH AXIS. THE 12Z GFS REMAINS RELATIVELY CLOSE TO THE CONSENSUS, ALONG WITH THE 12Z ECMWF. THEREFORE, A BLEND OF THE GFS AND THE ECMWF SHOULD REPRESENT A GOOD CONSENSUS THROUGH MONDAY MORNING, AND THIS WAS THE SAME THINKING FROM THE OVERNIGHT MODEL RUNS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... HAMRICK