MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1144 PM EST SUN NOV 09 2014 VALID NOV 10/0000 UTC THRU NOV 13/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ================================================== 00Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES ================================================== NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT. ================================================== ...WINTER STORM AFFECTING THE NORTHERN U.S... PREFERENCE: BLEND OF *12Z* GFS/ECMWF/UKMET THERE IS NOT A LOT OF EVIDENCE YET TO TRUST TRENDS SEEN IN THE 00Z NAM AND GFS. FOLLOWING THE SURFACE LOW TRACK...THE NAM TRENDED FASTER AND FARTHER NORTH...BUT IS STILL ON THE NORTHWEST SIDE OF THE OPERATIONAL MODEL SOLUTIONS. THIS IS A COMMON BIAS IN THE NAM. THE GFS TRENDED MUCH FASTER AND ALSO FARTHER NORTH...PLACING IT OUT AHEAD OF THE NAM SOLUTION AND ALSO A LITTLE FORWARD OF THE 12Z UKMET. OVER THE LONG HAUL...SEVERAL MODEL CYCLES...WE HAD SEEN CONVERGENCE TOWARD A COMMON SOLUTION REPRESENTED BY THE 12Z GFS/ECMWF/UKMET...AND STRONGLY SUPPORTED BY THE ECMWF ENSEMBLE MEAN. ALTHOUGH SOME ADDITIONAL TRENDING IS ALWAYS EXPECTED...WE QUESTION THE MAGNITUDE OF THE TRENDS SEEN IN THE NEW NAM/GFS RUNS. WPC IS TAKING THE APPROACH OF MAINTAINING CONTINUITY WITH THE PREVIOUS FORECAST CYCLE...BUT PERHAPS GIVING A LITTLE MORE WEIGHT TO THE 12Z UKMET IN ORDER TO TREND JUST SLIGHTLY FASTER WITH THE PRECIPITATION SWATH. WE INVESTIGATED THE 21Z SREF...BUT FOUND IT TO BE TOO MUCH LIKE THE NAM. CLUSTERING ALGORITHMS REVEALED RELATIVELY LITTLE SPREAD IN THE SREF...WITH CLUSTERS CLOSELY MATCHING THE OPERATIONAL NAM OR BEING EVEN FARTHER NORTH AND WEST. ...COLD BLAST AND UPPER LOW SINKING INTO THE ROCKIES/PLAINS TUE/WED... PREFERENCE: 12Z ECMWF ENSEMBLE MEAN...APPROXIMATED 12Z ECMWF/UKMET BLEND HIGHLY AMPLIFIED FLOW OVER CANADA AND ESTABLISHMENT OF A BROAD COLD DOME IN THE ROCKIES AND CENTRAL U.S. SHOULD CAUSE COLDER HEIGHTS TO SINK SOUTHWARD TUE/WED. THE NAM/GFS HAVE TENDED TO BRUSH THE COLDER HEIGHTS MORE EASTWARD...EITHER UNDERESTIMATING THE DEPTH OF THE COLD AIR OR PERFORMING SOME PHASING WITHIN THE UPPER PATTERN OVER THE NORTHERN STATES. WPC PREFERS SOLUTIONS MORE LIKE THE 12Z ECMWF WHICH MAINTAIN SEPARATION OF THE GREAT LAKES STORM AND ANOTHER CLOSED LOW DROPPING INTO THE PLAINS. SPAGHETTI PLOTS SHOW THE ECMWF TO BE A LITTLE DEEPER AND FARTHER SOUTHWEST THAN THE ECMWF ENSEMBLE MEAN BY DAY 3...SO WE RECOMMEND BLENDING TOWARD THE 12Z UKMET TO ARRIVE AT A CONSENSUS. ...DEVELOPING CLOSED LOW OVER FLORIDA... PREFERENCE: BLEND OF 12Z PARALLEL GFS WITH 12Z ECMWF THIS SYSTEM WILL PRODUCE SOME PRECIPITATION OVER FLORIDA THROUGH MONDAY. WPC PRECIPITATION FORECASTS HAD FAVORED THE 12Z PARALLEL GFS. BASED ON THE CONSENSUS CORRIDOR OF ONSHORE FLOW AT 850 MB...WE ARE ADJUSTING PRECIPITATION SLIGHTLY NORTHWARD INTO NORTHEAST FLORIDA...MUCH LIKE THE 12Z ECMWF. OTHER MODELS SUCH AS THE 00Z NAM AND GFS OFFER RELATIVELY SIMILAR SOLUTIONS...AND COULD BE USEFUL HERE. ...SHORTWAVE TROUGH REACHING THE WEST COAST WEDNESDAY... PREFERENCE: BLEND OF 00Z NAM/GFS A LOW AMPLITUDE SHORTWAVE TROUGH IS FORECAST TO BREAK LOOSE FROM THE CENTRAL PACIFIC AND BRING PRECIPITATION TO NORTHERN CALIFORNIA AND ADJACENT AREAS BY DAY 3. MODELS ARE VERY SIMILAR FROM THE SURFACE TO 700 MB...BUT THE MORE RECENT RUNS OF THE NAM/GFS SEEM TO BE MAINTAINING BETTER DEFINITION OF THE MID LEVEL WAVE. THE 12Z ECMWF WAS PARTICULARLY AGGRESSIVE AT SPREADING PRECIPITATION INLAND THROUGH NORTHERN NEVADA GIVEN ITS FLAT AND FAST MOVING MID LEVEL WAVE. THE UKMET AND CANADIAN LOOKED MORE REASONABLE IN THE MID LEVELS...BUT OFFERED ESPECIALLY WET SOLUTIONS. WHILE THE GFS MAY ACTUALLY BE TOO DRY...BLENDING IT AND THE NAM WOULD YIELD SOMETHING CLOSE TO THE PRECIPITATION WPC IS SEEING FROM OUR IN-HOUSE PSEUDO BIAS-CORRECTED ENSEMBLE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... BURKE