MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 159 PM EST TUE MAR 01 2016 VALID MAR 01/1200 UTC THRU MAR 05/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 12Z MODEL GUIDANCE ALONG WITH FINAL PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...RIBBON OF VORTICITY ACCELERATING FROM THE MIDDLE MS VALLEY TOWARD NEW ENGLAND... ...DEEPENING SURFACE LOW/ACCOMPANYING COLD FRONT... FINAL PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: ABOVE AVERAGE A COMPACT SHORTWAVE CURRENTLY MOVING THROUGH THE MIDDLE MS VALLEY HAS HELPED IGNITE AN EXPANSIVE BAND OF SHOWERS AND THUNDERSTORMS OVER THE TN/OH VALLEYS. FARTHER INTO THE COLD AIR...LIGHT/MODERATE SNOW WAS NOTED OVER THE GREAT LAKES REGION. THIS ENTIRE SYSTEM WILL CONTINUE ADVANCING EASTWARD WITH HEIGHT FALLS SLIDING THROUGH THE EASTERN U.S. BY 02/1200Z. THE PRIMARY MID-LEVEL VORTICITY SHOULD CONGREGATE OVER NEW ENGLAND WITH A SEPARATE BAND OF ENERGY SLIDING UNDERNEATH THE BASE OF THE TROUGH TOWARD THE CAROLINAS. GENERAL HEIGHT FIELDS ARE AGREED UPON WITH SUBTLE DIFFERENCES IN THE SURFACE LOW INTENSITY. OVERALL...ENSEMBLE LOW PLOTS HAVE SEEN SPREAD DIMINISH MARKEDLY WITH DECENT CLUSTERING ON WEDNESDAY MORNING ACROSS THE INTERIOR NORTHEAST. A GENERAL MODEL COMPROMISE SHOULD SUFFICE HERE. ...MIGRATORY SHORTWAVE MOVING FROM THE PACIFIC NORTHWEST INTO THE TN VALLEY THROUGH 04/0000Z... ...INITIAL SURFACE LOW/COASTAL CYCLONE DEVELOPMENT BY LATE THURSDAY... FINAL PREFERENCE: BLEND OF THE 12Z GFS/ECMWF FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE PROGRESSIVE FLOW ACROSS THE MID-LATITUDES WILL CARRY ANOTHER SHORTWAVE FROM THE PACIFIC NORTHWEST TOWARD THE CENTER OF THE COUNTRY. MODELS SEEM TO INDICATE A PAIR OF SURFACE WAVES WILL EVOLVE...ONE MIGRATING THROUGH THE LOWER OH VALLEY WHILE THE OTHER TRACKS ACROSS THE MID-SOUTH. UNCERTAINTY REVOLVES AROUND THE STRENGTH OF THESE LOWS ALONG WITH WHICH FEATURE WILL DOMINATE. RECENT ENSEMBLE LOW PLOTS HAVE CONTINUED TO SHOW THE GFS/GEFS SOLUTIONS SUPPORTING THE NORTHERN LOW WHILE THE ECMWF/ECMWF ENSEMBLE MEMBERS FAVORING THE SOUTHERN FEATURE. GIVEN BOTH HAVE DECENT ENSEMBLE SUPPORT...WILL KEEP BOTH SUITES IN THE MIX WITH THE PREFERENCE. EVENTUALLY THE GUIDANCE AGREE ON ALLOWING THE SOUTHERN STREAM LOW TO DOMINATE AND STRENGTHEN AS IT ENCOUNTERS THE GULF STREAM LATE IN THE FORECAST. THE 12Z NAM TAKES THE MOST INSIDE TRACK WITH THE COASTAL LOW STRENGTHENING RELATIVE TO THE SLIGHTLY MORE OFFSHORE CONSENSUS. EVENTUALLY THE 12Z/00Z CMC ALSO START CARRYING THE SYSTEM FARTHER WEST THAN MOST ENSEMBLE MEMBERS DEPICT. THE WPC PREFERENCE WILL CONTINUE TO SPLIT THE DIFFERENCE BETWEEN THE GFS/ECMWF CAMPS. THERE STILL APPEARS TO BE ENOUGH UNCERTAINTY IN THE FORECAST TO PLAY THIS MIDDLE GROUND. ...PACIFIC SYSTEM REACHING THE NORTHWESTERN U.S. BY 03/0600Z... ...EVENTUAL SHORTWAVE ENERGY REACHING THE UPPER MIDWEST... PRELIMINARY PREFERENCE: BLEND OF THE 12Z NAM/ECMWF FORECAST CONFIDENCE: AVERAGE A BROAD CLOSED CIRCULATION BEGINS TO EMERGE INTO THE FORECAST DOMAIN ACROSS THE NORTHEASTERN PACIFIC BY WEDNESDAY EVENING. AT THE LEADING EDGE OF THIS NEGATIVE HEIGHT ANOMALY WILL BE A BAND OF SHORTWAVE ENERGY ACCELERATING TOWARD THE PACIFIC NORTHWEST COAST. THIS SYSTEM SHOULD EVENTUALLY TRANSLATE DOWNSTREAM WHILE FLATTENING OUT THE WESTERN U.S. RIDGE. MODELS SEEM TO AGREE ON THE PATTERN THROUGH THURSDAY MORNING. FROM THIS POINT FORWARD...THE 12Z GFS/06Z GFS-PARALLEL END UP ON THE QUICKER SIDE WHICH FOLLOWS THE USUAL FAST BIAS OF THE GFS. MEANWHILE...THE 12Z/00Z UKMET FAVOR ADDITIONAL EROSION OF THE EASTERN EXTENT OF THE RIDGE WHICH MAY TOO AGGRESSIVE. A CONSERVATIVE SOLUTION WOULD SUGGEST A 12Z NAM/ECMWF WHICH WILL REMAIN THE PREFERENCE OF CHOICE. ...AMPLIFIED LONGWAVE TROUGH ANCHORING THE EASTERN PACIFIC LATE IN THE PERIOD... PRELIMINARY PREFERENCE: BLEND OF THE 12Z GEFS/00Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: AVERAGE TOWARD THE END OF THE PERIOD...A BROAD NEGATIVE HEIGHT ANOMALY WILL EXTEND OVER MUCH OF THE EASTERN PACIFIC WITH THE LEADING EDGE OF THE HEIGHT FALLS NEARING THE WEST COAST. THIS PATTERN WILL ULTIMATELY SET THE STAGES FOR A MULTI-DAY HEAVY PRECIPITATION EVENT ALONG THE WEST COAST FOR THE MEDIUM RANGE PERIOD. IN THE MEANTIME...THERE ARE SOME TIMING DIFFERENCES ON DAY 3 WITH DETERMINISTIC MODELS QUITE VARIABLE IN NATURE. WHILE ALL AGREE ON THE PATTERN...THESE TIMING ISSUES SUGGEST AN ENSEMBLE MEAN APPROACH WITH A RECOMMENDATION OF THE 12Z GEFS/00Z ECMWF ENSEMBLE MEAN. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER