MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1221 PM EST SUN NOV 29 2015 VALID NOV 29/1200 UTC THRU DEC 03/0000 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... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...SOUTHWEST-NORTHEAST ORIENTED UPPER LOW ACROSS THE WESTERN HALF OF THE CONUS... ...DEVELOPING SURFACE CYCLONE OVER THE CENTRAL PLAINS... PRELIMINARY PREFERENCE: THROUGH 02/0000Z: BLEND OF THE 12Z NAM/00Z ECMWF...THEREAFTER: 00Z ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: INITIALLY AVERAGE...THEN BECOMING BELOW AVERAGE WATER VAPOR IMAGERY THIS MORNING INDICATED A BROAD POSITIVELY-TILTED UPPER TROUGH ANCHORING AN EXTENSIVE SECTION OF THE WESTERN U.S. THIS REX BLOCK SET UP WILL GRADUALLY BREAK DOWN IN RESPONSE TO UPSTREAM HEIGHT FALLS AFFECTING THE WEST COAST. A VARIETY OF EMBEDDED SHORTWAVES ARE FORECAST TO CONTINUE ROTATING ABOUT THE UPPER LOW CENTER WITH A GRADUAL MOVEMENT TOWARD THE NORTHEAST IN TIME. MODELS SUGGEST SURFACE CYCLOGENESIS WILL TAKE PLACE ACROSS THE GREAT PLAINS WITH THE WAVE LIFTING TOWARD THE MIDDLE MS VALLEY/UPPER MIDWEST ON MONDAY/TUESDAY. BASED ON THE PAST SEVERAL RUNS OF GUIDANCE INCLUDING ENSEMBLES...THERE HAS TENDED TO BE A SPATIAL DIFFERENCE BETWEEN THE GFS/ECMWF CAMPS. THE GEFS SOLUTIONS CONTINUE TO BE DISPLACED SOUTH AND EAST OF THE ECMWF CYCLES WITH THE LATTER BEING MUCH MORE STABLE IN THE PAST FEW RUNS. WHILE THE 12Z GFS DID MAKE LARGE WESTWARD ADJUSTMENTS...THIS SOLUTION ALONG WITH THE 00Z CMC REMAIN TO THE EAST OF THE STRONGER ENSEMBLE SUPPORT. THROUGH DAY 2...02/0000Z...A COMBINATION OF THE 12Z NAM/00Z ECMWF APPEARS REASONABLE. COMPLEXITIES EXIST THEREAFTER REGARDING THE TRACK OF THE UPPER TROUGH ALONG WITH THE POTENTIAL SURFACE LOW FORMATION OFF OF NEW ENGLAND EARLY WEDNESDAY. WILL STAY MORE CONSERVATIVE GIVEN THE GROWING SPREAD AND FAVOR THE 00Z ECMWF ENSEMBLE MEAN FOR DAY 3. ...PROGRESSIVE NORTHERN STREAM CLIPPING UPPER NEW ENGLAND THROUGH MONDAY... PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: ABOVE AVERAGE THE ACTIVE NORTHERN BRANCH OF THE JET WILL CARRY A PAIR OF SYSTEMS WHICH ARE EXPECTED TO CLIP UPPER SECTIONS OF MAINE. THERE ARE SOME SUBTLE AMPLITUDE DIFFERENCES WITH THE SECOND FEATURE BUT THIS APPEARS TO BE WITHIN THE GENERAL NOISE OF SOLUTIONS. AS A RESULT...A GENERAL MODEL COMPROMISE WILL SUFFICE. ...PACIFIC SYSTEM SPLITTING OVER THE NORTHWESTERN U.S. ON MONDAY AFTERNOON... ...SHORTWAVE ENERGY EVENTUALLY TRACKING THROUGH THE SOUTHWESTERN STATES... PRELIMINARY PREFERENCE: THROUGH 02/0000Z: A NON-00Z CMC MODEL COMPROMISE...THEREAFTER: BLEND OF THE 06Z GEFS/00Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: INITIALLY AVERAGE...THEN BECOMING SLIGHTLY BELOW AVERAGE AMPLIFIED FLOW IN THE EASTERN PACIFIC WILL PROJECT A COMPACT SHORTWAVE TOWARD THE PACIFIC NORTHWEST COAST ON MONDAY. A GENERAL SPLIT IN THE FLOW SHOULD THEN OCCUR CARRYING PART OF THE SHORTWAVE TOWARD BRITISH COLUMBIA WHILE THE REMAINDER SPILLS INTO THE LONGWAVE TROUGH ACROSS THE SOUTHWESTERN U.S. THERE ARE TIMING DIFFERENCES WITH THE NORTHERN SPLIT BUT MOST OF THIS OCCURS NORTH OF THE INTERNATIONAL BORDER. MEANWHILE...THE 00Z CMC IS MOST OUT OF PHASE WITH THE SOUTHERN FEATURE BEING QUICKER/MORE AMPLIFIED. MOVING TOWARD THE MIDDLE OF THE WEEK...THE 06Z GEFS/00Z ECMWF ENSEMBLE MEANS ARE IN SUFFICIENT AGREEMENT WITH OTHER SOLUTIONS BECOMING FURTHER OUT OF PHASE. MOST NOTABLY...THE QUICKER 00Z CMC AND THE MORE ROBUST LOOKING 12Z NAM. WPC FAVORS A NON-00Z MODEL COMPROMISE THROUGH DAY 2...02/0000Z BEFORE MOVING TOWARD A 06Z GEFS/00Z ECMWF ENSEMBLE MEANS BLEND. ...ADDITIONAL PACIFIC SYSTEMS AFFECTING THE IMMEDIATE WEST COAST ON TUESDAY/WEDNESDAY... PRELIMINARY PREFERENCE: BLEND OF THE 09Z SREF/00Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: BELOW AVERAGE INTO THE TUESDAY/WEDNESDAY TIMEFRAME...A BROAD LONGWAVE TROUGH SETS UP ACROSS NORTHEASTERN PACIFIC. OVERALL...THERE ARE RATHER SIGNIFICANT DIFFERENCES...PARTICULARLY WITH THE TRACK OF ALL INDIVIDUAL FEATURES. SPAGHETTI PLOTS DEPICT QUITE A BIT OF SCATTER WITH THE TIMING OF THESE EMBEDDED SHORTWAVES. WILL FAVOR A COMBINATION OF THE 09Z SREF/00Z ECMWF ENSEMBLE MEANS GIVEN THEY SEEM TO BE MORE STABLE THAN THE GEFS MEAN WHICH APPEARS TO BE MUCH MORE OUT OF PHASE FROM MOST SOLUTIONS WITHIN THE SPAGHETTI DIAGRAM. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER