MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 124 PM EDT FRI SEP 30 2016 VALID SEP 30/1200 UTC THRU OCT 04/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 12Z NAM/GFS ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... ...PERSISTENT UPPER LOW SPINNING ACROSS THE OH VALLEY/GREAT LAKES REGION... PRELIMINARY PREFERENCE: NON-00Z CMC MODEL COMPROMISE FORECAST CONFIDENCE: AVERAGE WATER VAPOR IMAGERY AND 500-MB HEIGHT FIELDS SHOWED THE CONTINUED PRESENCE OF A CLOSED LOW SITTING OVER THE OH VALLEY. THIS SYSTEM REMAINS A FOCUS FOR AREAS OF MODERATE/HEAVY RAINFALL WITHIN THE COMMA-HEAD AS WELL AS ALONG AN ENHANCED MOISTURE CHANNEL ALONG THE EASTERN SEABOARD. MODELS CONTINUE TO SHOW THIS CIRCULATION LIFTING NORTHWARD REACHING THE LOWER GREAT LAKES BY 02/1200Z. DURING THIS PERIOD...THE 00Z CMC IS SLIGHTLY DISPLACED TO THE SOUTHWEST COMPARED TO THE BETTER CLUSTERING. THIS SLOW-MOVING UPPER LOW SHOULD EVENTUALLY MIGRATE EASTWARD TOWARD NEW ENGLAND AS IT FEELS THE EFFECTS OF AN UPPER TROUGH DIPPING THROUGH EASTERN CANADA. THERE ARE SOME DIFFERENCE WITH THE EVENTUAL POSITION OF THE UPPER TROUGH EARLY NEXT WEEK BUT A NON-00Z CMC SOLUTION APPEARS TO BE THE WAY TO GO. ...SHORTWAVE SHEARING ACROSS THE NORTHERN PLAINS EARLY IN THE PERIOD... PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: ABOVE AVERAGE A SHORTWAVE WHICH CONTINUES TO SHEAR/DECAY ACROSS THE NORTHERN ROCKIES WILL EVENTUALLY SPLIT WHILE CROSSING INTO THE ADJACENT GREAT PLAINS. THE GUIDANCE APPEAR SIMILAR ACROSS THE BOARD WHICH SUPPORTS A GENERAL MODEL COMPROMISE. ...INITIAL SHORTWAVE SWINGING THROUGH THE UPPER INTERMOUNTAIN WEST ON SATURDAY... PRELIMINARY PREFERENCE: NON-00Z CMC MODEL CONSENSUS FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE AMPLIFIED FLOW ACROSS THE EASTERN PACIFIC WILL MAINTAIN AN ACTIVE PATTERN OVER THE WESTERN U.S. FOR THE NEXT FEW DAYS. FIRST...THE INITIAL SHORTWAVE IS CURRENTLY SPINNING OFF THE PACIFIC NORTHWEST COAST. THE 00Z CMC IS A BIT SLOWER AS THE SYSTEM LIFTS ACROSS THE BRITISH COLUMBIA/ALBERTA BORDER. AS A RESULT...WILL FAVOR A NON-00Z CMC MODEL CONSENSUS. ...MORE SIGNIFICANT UPPER TROUGH AFFECTING THE WEST COAST LATE IN THE WEEKEND... ...EVENTUAL CLOSED LOW/ASSOCIATED FRONTAL ZONE MOVING TOWARD THE FOUR CORNERS REGION... PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/06Z GEFS MEAN FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE ON THE HEELS OF THE INITIAL SHORTWAVE MOVING INTO THE PACIFIC NORTHWEST...A SEPARATE CLOSED LOW DROPS DOWN ALONG THE WEST COAST BEFORE MOVING INLAND OVER NORTHWESTERN CA BY 02/1200Z. BY SUNDAY EVENING...THERE IS SOME FORECAST SPREAD WITH THE 00Z UKMET ON THE QUICKER END WHILE THE 00Z CMC REMAINS TO THE WEST AS IT SEEMS TO BE WITH MOST SYSTEMS ON THE MAP. ENSEMBLE SPAGHETTI PLOTS SHOW A DISPARITY BETWEEN THE GFS/ECMWF CAMPS WITH THE ECMWF ENSEMBLE SOLUTIONS BEING SOMEWHAT QUICKER. WILL STICK TOWARD THE SLOWER GROUP GIVEN THE TYPICAL BIAS OF MODELS BEING TOO QUICK EJECTING CLOSED UPPER LOWS. WPC WILL PLAY A SPLIT BETWEEN THE 12Z GFS/06Z GEFS MEAN. ...MID-LEVEL WEAKNESS ACROSS THE NORTHERN GULF OF MX BY MONDAY... PRELIMINARY PREFERENCE: 12Z GFS FORECAST CONFIDENCE: AVERAGE WELL IN ADVANCE OF HURRICANE MATTHEW WILL BE AN ELONGATED AREA OF LOWER HEIGHTS ACROSS THE GULF OF MX. GIVEN THE NATIONAL HURRICANE CENTER FORECAST HAS BEEN CLOSER TO THE GFS SOLUTION...WILL LEAN IN THAT DIRECTION GIVEN ITS SYNOPTIC INFLUENCE ON STEERING THIS TROPICAL CYCLONE NORTHWARD. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER