MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1148 PM EST MON DEC 14 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 AND PRELIMINARY PREFERENCES ...UPPER LOW MOVING THROUGH THE GREAT LAKES TONIGHT WITH ACCOMPANYING SURFACE LOW... ...SURFACE LOW DEVELOPING OFF THE NEW ENGLAND COAST EARLY TUE AND MOVING ALONG THE EAST COAST THURSDAY NIGHT... PRELIMINARY 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... PRELIMINARY PREFERENCE: GFS/12Z ECMWF/12Z UKMET BLEND CONFIDENCE: ABOVE 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 12Z ECMWF/UKMET AND THE MODEL CONSENSUS. THIS CONTINUES AS THE SURFACE LOW LIFTS NORTH INTO ONTARIO WEDNESDAY NIGHT. ...SURFACE LOW DEVELOPING ALONG THE GULF COAST WEDNESDAY AND MOVING ALONG THE EAST COAST THURSDAY... PRELIMINARY PREFERENCE: GFS/12Z UKMET BLEND CONFIDENCE: 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 AND THE 12Z ECMWF. HOWEVER...THE 12Z ECMWF ENSEMBLE MEAN IS ACTUALLY CLOSER TO THE GFS THAN TO THE 12Z DETERMINISTIC ECMWF. BY EARLY FRIDAY MORNING...THE GFS SHOWS THE SURFACE LOW JUST OFF THE MAINE COAST...WHILE THE 12Z ECMWF IS FARTHER OFFSHORE AND A LITTLE SLOWER. AGAIN AT THIS POINT...THE 12Z ECMWF ENSEMBLE MEAN IS VERY SIMILAR TO THE GFS...AS IS THE 18Z GEFS MEAN. THE NAM IS A LITTLE CLOSER TO THE COAST RELATIVE TO THE 12Z ECMWF...BUT STILL APPEARS TOO SLOW WHEN COMPARED TO THE GFS AND THE AFOREMENTIONED ENSEMBLE MEANS. GIVEN THE ENSEMBLE SUPPORT FOR THE SLIGHTLY FASTER AND CLOSER TO THE COAST GFS SOLUTION...THE PREFERENCE IS FOR THAT SOLUTION AT THIS TIME. ...SHORTWAVE DIGGING SOUTH ACROSS THE NRN ROCKIES ON WED... PRELIMINARY PREFERENCE: GFS/12Z ECMWF/12Z UKMET BLEND CONFIDENCE: AVERAGE THE NAM AND GFS APPEAR TO BE ON OPPOSITE SIDES OF THE MODEL CONSENSUS WITH RESPECT TO THE TIMING IF THIS WAVE. THE GFS APPEARS SLOW RELATIVE TO CONSENSUS AS THIS SHORTWAVE CROSSES THE NORTHERN INTERMOUNTAIN WEST ON WEDNESDAY...WHILE THE NAM APPEARS TO BE ON THE FAST SIDE. BY THURSDAY...HOWEVER...THE GFS APPEARS TO CATCH UP TO THE TIMING SHOWN BY THE 12Z ECMWF. BY 00Z FRIDAY...SOME DIFFERENCE EMERGE OVER THE PLAINS AS THE SHORTWAVE AMPLIFIES INTO A LARGER UPPER-LEVEL TROUGH. AT THIS TIME...THE 12Z ECMWF IS MORE AMPLIFIED THAN ANY OTHER DETERMINISTIC SOLUTION. GIVEN THE OBSERVED DIFFERENCES WITH TIMING AND AMPLITUDE...AN INCLUSIVE BLEND SEEMS APPROPRIATE AT THIS POINT...ESPECIALLY AS THE SHORTWAVE EVOLVES INTO A LARGER SCALE FEATURES. THEREFORE...A BLEND OF THE GFS ALONG WITH THE 12Z ECMWF/UKMET IS RECOMMENDED AT THIS TIME. ...LARGE CLOSED LOW/PACIFIC FRONT NEARING THE PACIFIC NORTHWEST THU... PRELIMINARY PREFERENCE: GFS CONFIDENCE: BELOW 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 NAM AND GFS BOTH PUSH THE WARM FRONT INLAND FASTER THAN THE 12Z ECMWF AND UKMET. THE 12Z ECMWF ENSEMBLE MEAN APPEARS TO LOWER SURFACE PRESSURES ACROSS THE NORTHWEST A LITTLE FASTER THAN ITS DETERMINISTIC SOLUTION...WHICH LENDS SOME SUPPORT IN THE GFS/NAM DIRECTION. AS THE COLD FRONT ARRIVES THURSDAY NIGHT...THE GFS AND NAM ARE SLOWER THAN THE 12Z ECMWF/UKMET. THE 12Z ECMWF ENSEMBLE AND 18Z GEFS MEANS BOTH LEND MORE SUPPORT TO THE SLOWER GFS/NAM SOLUTION WITH THE ARRIVAL OF THE COLD FRONT THURSDAY NIGHT. GIVEN THAT THIS SYSTEM IS STILL WELL OUT IN THE PACIFIC AT THIS TIME...CONFIDENCE IS BELOW AVERAGE PENDING THE ARRIVAL OF FURTHER 00Z GUIDANCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RYAN