MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 244 PM EDT WED OCT 21 2015 VALID OCT 21/1200 UTC THRU OCT 25/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z FINAL MODEL EVALUATION...INCLUDING PREFERENCES AND CONFIDENCE ...CLOSED MID LEVEL SYSTEM CROSSING EASTERN CANADA... ...SURFACE FRONT CROSSING THE EASTERN UNITED STATES... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE MODELS (INCLUDING 12Z NAM/GFS) REMAIN IN GOOD AGREEMENT BOTH WITH RESPECT TO THE UPPER TROUGH/LOW MOVING ACROSS QUEBEC AND ATLANTIC CANADA THU INTO FRI...AND WITH THE ASSOCIATED FRONTAL BOUNDARY ACROSS THE NORTHEAST US. ...CLOSED MID LEVEL LOW OVER THE SOUTHWEST... ...LOW PRESSURE TRACKING TO THE GREAT LAKES SAT... PREFERENCE: BLEND OF THE 12Z GFS/12Z ECMWF CONFIDENCE: AVERAGE THE 12Z NAM IS CLOSE TO THE CONSENSUS WITH THE CLOSED LOW OPENING INTO A SHORT WAVE AS IT CROSSES THE ROCKIES DURING DAY 1. HOWEVER...ITS SLOWS WITH TIME (AS DID THE 00Z NAM)...AND BECOMES SLOWER THAN THE CONSENSUS WITH THE SHORT WAVE AND ITS SURFACE LOW BY DAY 2/3. THE 12Z GFS IS FASTER THAN THE 12Z NAM WITH THE SHORT WAVE AND SURFACE LOW...AND REMAINS CLOSE TO THE CONSENSUS THROUGH DAY 3 (THOUGH IT DOES BECOME FASTER THAN THE 12Z ECMWF DURING DAY 3). THE DIFFERENCES BETWEEN THE 12Z GFS/12Z ECMWF ARE RELATIVELY SMALL THROUGH DAY 3...SO A BLEND OF THESE SOLUTIONS I PREFERRED. ...LONG WAVE TROUGH APPROACHING THE PACIFIC NORTHWEST SAT... PREFERENCE: 12Z ECMWF/12Z CMC CONFIDENCE: BELOW AVERAGE A SHORT WAVE ORIGINATING NEAR 39N 160W ON DAY 1 DEEPENS INTO A LOW WAVE TROUGH AS IT APPROACHES THE PACIFIC NORTHWEST COAST LATE ON DAY 3. THERE ARE TWO DISTINCT CAMPS WITH RESPECT TO SOLUTION. THE FIRST IS THE FASTER 12Z NAM/GFS SOLUTIONS...WHICH ARE FASTER THAN THEIR RESPECTIVE 00Z SOLUTIONS. THE SECOND CAMP IS THE 12Z ECMWF/CMC...WHICH ARE SLOWER WITH THE DEVELOPING LONG WAVE...AND CLOSER WITH THE LONG WAVE POSITION AND ITS SURFACE REFLECTION. THE 12Z UKMET SPED UP A BIT THIS MODEL CYCLE...AND ITS SOLUTION IS IN BETWEEN THE TWO CAMPS. A SLOWER SOLUTION MAKES MORE SENSE WITH A DEVELOPING LONG WAVE TROUGH (AND THIS IDEA IS SUPPORTED BY THE 00Z ECMWF ENSEMBLE MEAN)...SO THE SLOWER SOLUTION IS PREFERRED. HOWEVER...GIVEN THE SPREAD IN SOLUTIONS...OVERALL CONFIDENCE IS BELOW AVERAGE. ...SHORTWAVE CROSSING THE SOUTHWEST STATES FRI AND SOUTHERN PLAINS SAT...... PREFERENCE: NON-12Z CMC CONFIDENCE: ABOVE AVERAGE THE 12Z NAM/GFS HAVE TRENDED SLOWER WITH THE SHORT WAVE EJECTED FROM A LONG WAVE TROUGH OVER THE WESTERN US....CROSSING THE SOUTHWEST STATES FRI AND SOUTHERN PLAINS SAT. THE 12Z GFS FOLLOWED A SIMILAR TREND...AND THE TWO SOLUTIONS ARE CLOSE WITH THE SHORT WAVE POSITION BY THE END OF DAY 3. THESE SOLUTIONS HAVE THE SUPPORT OF THE 12Z GEFS AS WELL. THE 12Z UKMET REMAINED ON THE SLOWER SIDE OF GUIDANCE WITH THE SHORT WAVE...AND THE 12Z ECMWF SLOWED ITS SOLUTION SO THAT IT IS NOW CLOSE TO THE CONSENSUS. THAT LEAVES THE 12Z CMC...WHICH IS FASTER AND MUCH WEAKER WITH THE SHORT WAVE...AS THE ODD MODEL OUT. BECAUSE OF THIS...A NON-12Z CMC SOLUTION IS PREFERRED. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... HAYES