MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 144 AM EST FRI DEC 9 2016 VALID DEC 9/0000 UTC THRU DEC 12/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM/GFS MODEL EVALUATION ALONG WITH PREFERENCES AND CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ***00Z NAM INITIALIZED 850MB TEMPERATURES 3-4 DEGREES C TOO COLD OVER PARTS OF THE PACIFIC NORTHWEST*** DEEP UPPER TROUGH SWINGING THROUGH THE NORTHEASTERN U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE LARGE SYNOPTIC SCALE TROUGH OVER THE NORTHEAST U.S. AT THE BEGINNING OF THE PERIOD IS PROGGED TO MOVE OVER THE CANADIAN MARITIMES BY FRIDAY. GOOD OVERALL MODEL AGREEMENT EXISTS TO SUPPORT A GENERAL MODEL COMPROMISE HERE. LOW AMPLITUDE SHORTWAVE CROSSING THE GREAT LAKES AND NEW ENGLAND THROUGH SATURDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~ PREFERENCE: 00Z NAM/00Z UKMET/00Z ECMWF COMPROMISE CONFIDENCE: SLIGHTLY ABOVE AVERAGE A COUPLE OF WEAK SHORTWAVES CURRENTLY OVER SOUTH-CENTRAL CANADA SHOULD MIGRATE EASTWARD AND CONSOLIDATE INTO A LOW-AMPLITUDE LONGWAVE TROUGH WHICH WILL MOVE ACROSS THE GREAT LAKES BY FRIDAY NIGHT AND INTO SATURDAY. THE 00Z CMC HAS TRENDED FASTER TOWARDS THE MODEL CONSENSUS, WITH THE 00Z GFS NOW ONLY SLIGHTLY MORE AMPLIFIED COMPARED TO ITS EARLIER RUN. GIVEN THIS IMPROVED MODEL AGREEMENT, A GENERAL MODEL COMPROMISE CAN ALSO BE ADVISED HERE. PROGRESSIVE SHORTWAVE AND SURFACE LOW REACHING THE MIDWEST BY MONDAY MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~ PREFERENCE: 12Z ECMWF/00Z ECMWF/00Z CMC COMPROMISE CONFIDENCE: SLIGHTLY BELOW AVERAGE A SURFACE LOW TRACKING FROM THE LEE OF THE ROCKIES SATURDAY AFTERNOON TO THE OHIO VALLEY BY MONDAY MORNING WILL BE SUPPORTED BY A BROAD MID-LEVEL TROUGH ORIGINATING FROM THE PACIFIC NORTHWEST. BY THE END OF THE FORECAST PERIOD ON MONDAY, THE 00Z ECMWF/UKMET HAVE TRENDED NORTHWARD CLOSER TO THE 00Z GFS, AND THE NAM AND CMC FARTHER TO THE SOUTHWEST WITH THE SURFACE LOW. THE NAM IS AN OUTLIER WITH HAVING AN OVER-AMPLIFIED TROUGH OVER THE MIDWEST, AND THE GFS IS SLIGHTLY STRONGER THAN THE MODEL CONSENSUS. ALTHOUGH THE UKMET AND ECMWF TRENDED CLOSER TO THE GFS THIS CYCLE, WE WOULD LIKE TO SEE MORE MODEL CONTINUITY BEFORE MAKING ANY MAJOR CHANGES IN THE MODEL PREFERENCE, SO THE PREVIOUS 12Z ECMWF IS PART OF THE BLEND. PACIFIC STORM SYSTEM AFFECTING THE PACIFIC NORTHWEST THIS WEEKEND ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 00Z GFS/00Z CMC/00Z GEFS MEAN CONFIDENCE: SLIGHTLY BELOW AVERAGE A STRONG PACIFIC STORM OFF THE PACIFIC NORTHWEST COAST ON FRIDAY IS PROGGED TO APPROACH THIS REGION ON SATURDAY, WITH THE SURFACE LOW EXPECTED TO REACH NORTHWESTERN WASHINGTON AROUND 00Z SUNDAY. BOTH THE 00Z ECMWF AND UKMET ARE INDICATING TWO SEPARATE LOWS PIVOTING AROUND EACH OTHER THROUGH THE FIRST 36 HOURS OF THE FORECAST, WHEREAS THE OTHER MODELS ARE ON BOARD WITH THE IDEA OF ONE MAIN SURFACE LOW. LOOKING ALOFT, THE NAM BECOMES MORE AMPLIFIED WITH THE SHORTWAVE AXIS BY 36 HOURS, AND THE 12Z EC MEAN IS A BIT SLOWER THAN THE MODEL CONSENSUS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... HAMRICK