MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1129 PM EST WED DEC 23 2015 VALID DEC 24/0000 UTC THRU DEC 27/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...INCLUDING THE NAM AND GFS ...DEEP LOW CENTER EXITING NORTHEAST AWAY FROM THE GREAT LAKES REGION... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE MODELS ARE IN EXCELLENT AGREEMENT WITH THE DETAILS OF THE DEEP LOW CENTER EXITING THE GREAT LAKES REGION ON THURS. WILL PREFER A GENERAL MODEL COMPROMISE. ...LOW AMPLITUDE SHORTWAVE/SURFACE LOW CROSSING THE CENTRAL PLAINS/MID MS/OH VALLEYS THROUGH THURS/FRI... PREFERENCE: 12Z ECMWF CONFIDENCE: AVERAGE THERE ARE SOME DIFFERENCES WITH THE PLACEMENT OF THIS LOW...WITH THE 00Z GFS AND 00Z NAM A LITTLE FASTER THAN THE MULTI-MODEL CONSENSUS. THE 00Z NAM ALSO TENDS TO HANG ON TO A SLIGHTLY DEEPER LOW CENTER THROUGH THURS NIGHT AND EARLY FRI OVER THE OH VALLEY. THE NON-NCEP MODELS ARE MORE STRONGLY CLUSTERED. WILL PREFER A NON-NCEP CONSENSUS LED BY THE 12Z ECMWF. ...NORTHERN STREAM TROUGH SKIRTING THE NORTHERN PLAINS/UPPER MS VALLEY SAT AND SUN... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE GUIDANCE INDICATES A NORTHERN STREAM TROUGH DROPPING DOWN ACROSS THE NORTHERN PLAINS AND UPPER MS VALLEY THROUGH SAT AND SUN. THERE ARE SOME MINOR TIMING DIFFERENCES WITH THE TROUGH EVOLUTION...BUT WITH REASONABLY GOOD AGREEMENT ON DEPTH. WILL PREFER A GENERAL MODEL COMPROMISE WITH THIS SYSTEM. ...SURFACE LOW EJECTING ACROSS THE CENTRAL PLAINS/MID MS VALLEY AND TO THE NORTHEAST FRI TO SUN... ...STRONG SURFACE FRONT LEFT DRAPING FROM THE NORTHEAST TO THE SOUTHERN PLAINS BY SUN... PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF AND 12Z UKMET CONFIDENCE: AVERAGE THE MODELS INDICATE A LEAD SHORTWAVE IMPULSE EJECTING EAST OUT OF THE BASE OF A DEEPENING TROUGH OVER THE WESTERN U.S. BY FRI AND THIS SHORTWAVE ENERGY WILL GENERATE A LOW CENTER OVER SOUTHEAST CO BY LATE FRI. THE LOW WILL THEN ADVANCE EAST THROUGH THE MID MS/OH VALLEYS AND INTO THE NORTHEAST SAT AND SUN. IN THE WAKE OF THE LOW CENTER BY SUN WILL BE A STRONG FRONTAL ZONE DRAPED FROM THE NORTHEAST ALL THE WAY BACK DOWN TO THE SOUTHERN PLAINS. THE 00Z GFS HAS TRENDED A BIT SLOWER WITH THE EVOLUTION OF THE LOW CENTER AS IT MOVES THROUGH THE OH VALLEY AND NORTHEAST AND CLUSTERS QUITE WELL WITH THE 12Z UKMET AND 12Z ECMWF. THE 12Z CMC AND TO AN EXTENT THE 00Z NAM ARE WEAKER/FLATTER WITH THE LOW VERSUS THE MODEL CONSENSUS. WILL PREFER A BLEND OF THE 00Z GFS/12Z ECMWF AND 12Z UKMET...AND THIS BLEND HAS STRONGER SUPPORT FROM THE 12Z ECENS MEAN AS WELL. ...DEEP UPPER TROUGH CLOSED LOW OVER THE INTERMOUNTAIN WEST/FOUR CORNERS REGION THURS TO SUN... ...SURFACE LOW EVOLVING OVER THE SOUTHERN HIGH PLAINS/RIO GRANDE VALLEY... PREFERENCE: GENERAL MODEL COMPROMISE...THROUGH 60 HOURS BLEND OF THE 00Z GFS/12Z ECMWF AND 12Z UKMET...AFTER 60 HOURS CONFIDENCE: AVERAGE THE GUIDANCE SHOWS VERY GOOD AGREEMENT WITH THE IDEA OF A DEEP TROUGH AMPLIFYING OVER THE WESTERN U.S. FRI AND SAT...WITH ULTIMATELY A DEEP CLOSED LOW CENTER DROPPING SOUTHEAST THROUGH AZ BY EARLY SAT AND INTO FAR NORTHERN MEXICO BY EARLY SUN. THE STRONG HEIGHT FALLS WILL BE INTERACTING WITH A STRONG FRONTAL ZONE SITUATED OVER THE SOUTHERN PLAINS SAT AND SUN AND WILL FOSTER SURFACE CYCLOGENESIS OVER THE RIO GRANDE VALLEY BY SAT NIGHT AND SUN. GIVEN THE STRONG MASS FIELD AGREEMENT WITH THE TROUGH/CLOSED LOW...A GENERAL MODEL COMPROMISE WILL BE PREFERRED THROUGH 60 HOURS...WITH A BLEND OF THE 00Z GFS/12Z ECMWF AND 12Z UKMET THEREAFTER BASED ON STRONGER MODEL CLUSTERING WITH THE SURFACE LOW AND FRONTAL ZONE PLACEMENT OVER THE RIO GRANDE VALLEY. ...SHORTWAVE TROUGH/FRONT APPROACHING THE PACIFIC NORTHWEST ON SUN... PREFERENCE: 12Z ECMWF CONFIDENCE: AVERAGE A SHORTWAVE TROUGH AND ASSOCIATED FRONTAL ZONE WILL BE APPROACHING THE PACIFIC NORTHWEST BY SUN. THE 12Z UKMET IS A FASTER OUTLIER WITH THIS SYSTEM. THE 00Z NAM AND 00Z GFS ARE THE SLOWEST AND DEEPEST. THE 12Z ECMWF AND 12Z CMC SPLIT THE DIFFERENCE. WILL PREFER THE 12Z ECMWF AT THIS POINT WHICH HAS BETTER SUPPORT FROM THE LATEST GEFS MEAN AND ECENS MEAN. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON