MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 136 AM EST WED DEC 16 2015 VALID DEC 16/0000 UTC THRU DEC 19/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...INCLUDING THE NAM/GFS/CMC/UKMET/ECMWF AND FINAL MODEL PREFERENCES ...LOW PRESSURE SYSTEM MOVING ACROSS THE PLAINS/UPPER MIDWEST TONIGHT/WEDNESDAY... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE MODEL CONSENSUS IS GOOD AS THIS SURFACE LOW MOVES ACROSS THE NORTHERN PLAINS/UPPER MIDWEST ON WEDNESDAY. THE NAM AND GFS FIT WELL WITHIN CONSENSUS. A GENERAL MODEL MODEL COMPROMISE IS PREFERRED. ...SURFACE LOW DEVELOPING ALONG THE GULF COAST WEDNESDAY AND MOVING ALONG THE EAST COAST THURSDAY... PREFERENCE: GFS/UKMET BLEND CONFIDENCE: ABOVE AVERAGE MODEL SPREAD WITH RESPECT TO THE TIMING AND INTENSITY OF THIS FEATURE IS NOW RELATIVELY LOW. THE NAM AND GFS ARE BOTH WITHIN THE AREA OF CONSENSUS...WITH THE NAM SLIGHTLY FASTER WITH THE LOW RELATIVE TO THE GFS. THE ECMWF CONTINUES TO SHOW A SLOWER/WEAKER AND FARTHER OFFSHORE SURFACE LOW OFF THE NEW ENGLAND COAST ON FRIDAY. THE UKMET AND CMC ARE IN LINE WITH THE GFS AND NAM...SHOWING A LOW CLOSER TO THE COAST AND A LITTLE STRONGER RELATIVE TO THE ECMWF. GIVEN THE CONTINUED SUPPORT FOR THE CAMP OF SOLUTIONS CLOSER TO THE COAST BY THE 00Z GEFS MEAN AND THE 12Z ECMWF ENSEMBLE MEAN -- WILL CONTINUE TO PREFER THIS OVER THE DETERMINISTIC ECMWF. ...SHORTWAVE DIGGING SOUTH ACROSS THE NRN ROCKIES ON WED... PREFERENCE: GFS/ECMWF BLEND CONFIDENCE: AVERAGE THE NAM SHOWS A SLIGHTLY MORE AMPLIFIED SOLUTION WITH THIS WAVE COMPARED TO THE THE GFS...WHICH IS CLOSE TO THE ECMWF IN TERMS OF TIMING/AMPLITUDE INITIALLY. AFTER 06Z THURSDAY...THE ECMWF SEEMS TO PUSH THE ENERGY SOUTHWARD A LITTLE MORE QUICKLY THAN THE GFS/NAM. THIS CAUSES HEIGHTS TO FALL A LITTLE FASTER ACROSS THE SOUTHERN PLAIN IN THE ECMWF...WHICH RESULTS IN A MORE AMPLIFIED SOLUTION COMPARED TO THE GFS BY 00Z FRIDAY. GIVEN THESE RELATIVELY MINOR DIFFERENCES...WILL PREFER A BLEND OF THE GFS AND ECMWF AT THIS TIME. ...LARGE CLOSED LOW/PACIFIC FRONT NEARING THE PACIFIC NORTHWEST THU... PREFERENCE: GFS/ECMWF THROUGH 18Z FRIDAY. ECMWF/UKMET AFTER 18Z FRIDAY CONFIDENCE: AVERAGE MODEL AGREEMENT HAS IMPROVED COMPARED TO THIS TIME YESTERDAY...WITH THE ECMWF NOW SIMILAR TO THE NAM/GFS WITH SPREADING WARM FRONTAL PRECIPITATION INTO THE NORTHWEST BETWEEN 00Z AND 06Z THURSDAY. AS THE COLD FRONT APPROACHES THE NORTHWESTERN U.S. LATER ON THURSDAY...SOME TIMING DIFFERENCES STILL EXIST. THE GFS/NAM AND NOW THE CMC CONTINUE TO SHOW A SLOWER ARRIVAL OF THE COLD FRONT TO THE COAST RELATIVE TO THE ECMWF/UKMET. WITH THE ARRIVAL OF THE 00Z RUN...THE ECMWF CONTINUES TO SLOW THE ARRIVAL OF THE COLD FRONT FURTHER...MOVING A LITTLE CLOSER TO THE GFS TIMING. THE UKMET IS PERSISTENT IN SHOWING A SOLUTION ON THE FAST SIDE OF THE SPREAD. WILL CONTINUE TO RECOMMEND A COMPROMISE BETWEEN THE GFS AND ECMWF FOR THE ARRIVAL OF THE FRONTAL SYSTEM. AS ADDITIONAL SHORTWAVE ENERGY AMPLIFIES THE TROUGH OFF THE WEST COAST FRIDAY NIGHT BEFORE IT MOVES INLAND...SOME DIFFERENCES WERE NOTED WHICH INFLUENCE PRECIPITATION ACROSS THE INTERMOUNTAIN WEST FRIDAY NIGHT/EARLY SATURDAY. THE GFS CONTINUES TO APPEAR FAST WITH MOVING THE WAVE TO THE COAST...WHICH RESULTS IN HEAVIER PRECIPITATION ACROSS THE INTERMOUNTAIN WEST DURING THIS TIME FRAME. THE NAM IS ALSO A LITTLE FASTER THAN MOST OTHER DETERMINISTIC SOLUTIONS WITH THIS WAVE. THE ECMWF AND UKMET HAVE BOTH SPED THIS WAVE UP FROM THEIR PREVIOUS RUNS...BUT THEY ARE STILL SLOWER THAN THE GFS. THE 00Z GEFS MEAN RESEMBLES A COMPROMISE BETWEEN THE ECMWF AND UKMET...SLOWER THAN THE DETERMINISTIC GFS. THUS...WILL RECOMMEND A ECMWF/UKMET BLEND AFTER 18Z FRIDAY AS THIS WAVE NEARS THE COAST. ...WAVE FORMING ON THE FRONTAL BOUNDARY ALONG THE EAST COAST ON FRIDAY... PREFERENCE: GFS/UKMET BLEND CONFIDENCE: AVERAGE THE ECMWF HAS BACKED OFF SLIGHTLY WITH ITS LATEST RUN ON THE INTENSITY OF THIS WAVE...AND NOW SHOWS A SOMEWHAT WEAKER WAVE THAT IS A HAIR FARTHER OFFSHORE RELATIVE TO ITS PREVIOUS RUN. BASED ON THE OVERALL RANGE OF SOLUTIONS...A SOLUTION WEAKER/TO THE EAST OF THAT SHOWN BY THE ECMWF STILL APPEARS LIKELY. THE GFS HAS SUPPORT FROM THE UKMET/CMC/GEFS MEAN AND TO A LESSER DEGREE THE NAM. ADDITIONALLY...THE ECMWF REMAINS CLOSER TO THE COAST THAN ITS 12Z ENSEMBLE MEAN. THUS...WILL CONTINUE TO RECOMMEND A GFS/UKMET BLEND AS THIS REPRESENTS A COMPROMISE BETWEEN THE FASTER AND SLOWER OF THE OFFSHORE CAMP OF SOLUTIONS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RYAN