MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 200 AM EST TUE DEC 15 2015 VALID DEC 15/0000 UTC THRU DEC 18/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...INCLUDING THE NAM/GFS/UKMET/CMC/ECMWF AND FINAL PREFERENCES ...UPPER LOW MOVING THROUGH THE GREAT LAKES TONIGHT WITH ACCOMPANYING SURFACE LOW... ...SURFACE LOW DEVELOPING OFF THE NEW ENGLAND COAST EARLY TUE... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE NAM AND GFS ARE IN GOOD AGREEMENT WITH THE MODEL CONSENSUS RESPECT TO THE TIMING AND STRENGTH OF THE UPPER-LEVEL LOW AS IT REACHES THE NORTHEAST TUESDAY MORNING. A SURFACE LOW IS FORECAST TO DEVELOP OFF THE NEW ENGLAND COAST TUESDAY MORNING AS THE UPPER LOW APPROACHES. MODEL DIFFERENCES WITH RESPECT TO THIS FEATURE ARE ALSO VERY SMALL. A GENERAL MODEL COMPROMISE IS RECOMMENDED AT THIS TIME. ...LOW PRESSURE SYSTEM MOVING ACROSS THE PLAINS TUE/WED... PREFERENCE: NON-NAM COMPROMISE CONFIDENCE: ABOVE AVERAGE THE NAM DEEPENS THE UPPER-LEVEL LOW A LITTLE FASTER THAN MOST OTHER GUIDANCE TUESDAY NIGHT ACROSS THE CENTRAL PLAINS. THIS APPEARS TO MANIFEST IN A SURFACE LOW TRACK IN THE NAM SLIGHTLY TO THE LEFT OF CONSENSUS. THE GFS SOLUTION IS IN LINE WITH THE ECMWF/UKMET/CMC AND THE MODEL CONSENSUS. THIS CONTINUES AS THE SURFACE LOW LIFTS NORTH INTO ONTARIO WEDNESDAY NIGHT. GIVEN THE GOOD AGREEMENT SHOWN BETWEEN GUIDANCE OTHER THAN THE NAM...WILL MAKE A NON-NAM COMPROMISE THE PREFERENCE. ...SURFACE LOW DEVELOPING ALONG THE GULF COAST WEDNESDAY AND MOVING ALONG THE EAST COAST THURSDAY... PREFERENCE: GFS/UKMET/ECMWF CONFIDENCE: ABOVE AVERAGE FARTHER SOUTH ALONG THE COLD FRONT...A WAVE OF LOW PRESSURE IS FORECAST TO DEVELOP WEDNESDAY ALONG THE CENTRAL GULF COAST AHEAD OF A SHORTWAVE CROSSING THE SOUTHERN PLAINS. THE LOW IS THEN FORECAST TO LIFT NORTHEASTWARD ACROSS THE SOUTHEASTERN U.S. WEDNESDAY NIGHT AND THEN UP THE EAST COAST THURSDAY/THURSDAY NIGHT. THE GFS LIFTS THE SURFACE LOW NORTHEASTWARD A LITTLE QUICKER THAN THE NAM. THE ECMWF HAS NOW COME AROUND TO A SOLUTION SHOWN BY THE GFS/UKMET...WHICH IS A LITTLE FASTER AND CLOSER TO THE COAST RELATIVE TO ITS PREVIOUS RUN. AS MENTIONED IN THE PRELIMINARY DISCUSSION...THE SOLUTION SHOWN BY THE GFS/UKMET AND NOW THE ECMWF HAS ENSEMBLE SUPPORT AND THESE THREE MODELS WILL COMPRISE THE FINAL PREFERENCE. ...SHORTWAVE DIGGING SOUTH ACROSS THE NRN ROCKIES ON WED... PREFERENCE: GFS/ECMWF BLEND CONFIDENCE: AVERAGE A SHORTWAVE IS FORECAST TO MOVE SOUTHEASTWARD ACROSS THE ROCKIES ON WEDNESDAY BEFORE AMPLIFYING INTO A LARGER TROUGH OVER THE PLAINS THURSDAY INTO FRIDAY. THE 00Z ECMWF HAS BACKED OFF A BIT ON THE AMPLIFICATION OF THIS WAVE AS IT CROSSES THE ROCKIES...AND NOW RESEMBLES A SOLUTION MUCH LIKE THAT SHOWN BY THE GFS. THE NAM REMAINS ON THE FAST SIDE OF THE SPREAD WITH THIS WAVE...AND THE UKMET SEEMS A BIT FAST AS WELL. THE CMC MAKES UP THE SLOWER SIDE OF THE SPREAD. GIVEN THAT THE GFS AND ECMWF SOLUTIONS NOW APPEAR TO BE SIMILAR WITH RESPECT TO THE TIMING AND AMPLITUDE OF THIS WAVE...WILL RECOMMEND A BLEND OF THESE TWO SOLUTIONS. ...LARGE CLOSED LOW/PACIFIC FRONT NEARING THE PACIFIC NORTHWEST THU... PREFERENCE: TWO THIRDS GFS/ ONE THIRD ECMWF COMPROMISE CONFIDENCE: AVERAGE PACIFIC SHORTWAVE ENERGY WILL APPROACH THE NORTHWESTERN U.S. THURSDAY INTO FRIDAY. THE WARM FRONT WILL APPROACH THE NORTHWEST WEDNESDAY NIGHT/EARLY THURSDAY...SPREADING PRECIPITATION BACK INTO THE REGION. THE ECMWF HAS MOVED TOWARD THE NAM AND GFS WITH PUSHING THE WARM FRONT AND THE PRECIPITATION INTO THE NORTHWEST A LITTLE QUICKER WEDNESDAY NIGHT. AS THE COLD FRONT ARRIVES THURSDAY NIGHT...THE GFS AND NAM REMAIN SLOWER THAN THE ECMWF AND UKMET...BUT THE ECMWF HAS SLOWED THE FRONT DOWN AND HAS MOVED SIGNIFICANTLY TOWARD THE GFS. THE UKMET REMAINS ON THE FAST SIDE OF THE SPREAD WITH THE COLD FRONT. AS MENTIONED IN THE PRELIM DISCUSSION...THE 12Z ECMWF ENSEMBLE MEAN FROM YESTERDAY SUPPORTED THE SLOWER GFS TIMING FOR THIS FRONT. ADDITIONALLY...THE 00Z GEFS MEAN IS ACTUALLY EVEN SLOWER THAN THE DETERMINISTIC GFS RUN. GIVEN THE SHIFT OF THE ECMWF TOWARD THE GFS HERE...WILL ADJUST THE PRELIM PREFERENCE HERE TO INCLUDE SOME COMPONENT OF THE 00Z ECMWF. AT THIS POINT...A COMPROMISE BETWEEN THESE TWO SOLUTIONS SEEMS REASONABLE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RYAN