MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1158 PM EST SUN FEB 05 2017 VALID FEB 06/0000 UTC THRU FEB 09/1200 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 INITIALLY OFFSHORE THE PACIFIC NORTHWEST... ...SHORTWAVE/SURFACE CYCLONE REACHING THE WEST COAST TONIGHT... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE MODELS ARE IN GOOD AGREEMENT IN AT LEAST PARTIALLY PHASING THE UPPER LOW OFFSHORE THE PACIFIC NORTHWEST WITH A SEPARATE SOUTHERN STREAM SHORTWAVE FARTHER SOUTH THAT IS CURRENTLY APPROACHING THE WEST COAST. THIS WILL RESULT IN A ROBUST LOW CENTER MOVING INTO WESTERN OR TONIGHT AND THEN EASTERN WA EARLY MON...WITH A TRAILING COLD FRONT THAT WILL IMPACT AREAS AS FAR SOUTH AS NORTHERN AND CENTRAL CA. THE MODELS ARE NOW RATHER WELL CLUSTERED WITH RESPECT TO TIMING AND INTENSITY...SO A GENERAL MODEL COMPROMISE WILL BE PREFERRED. ...SHORTWAVE CROSSING THE FOUR CORNERS REGION TONIGHT... ...SURFACE LOW DEVELOPING OVER THE CENTRAL PLAINS LATE MON... PREFERENCE: 12Z UKMET/12Z CMC/12Z ECMWF BLEND CONFIDENCE: AVERAGE TIMING DIFFERENCES EMERGE LATE MONDAY AS THIS SHORTWAVE EMERGES INTO THE CENTRAL PLAINS AND A SURFACE LOW DEVELOPS. THE GFS REMAINS A TAD FASTER THAN THE MODEL CONSENSUS...WITH THE REMAINING MODELS CLUSTERED A BIT SLOWER. THE 12Z UKMET/CMC/ECMWF ARE WELL CLUSTERED THROUGH MON AND REFLECT THE MODEL CONSENSUS...AND SO A BLEND OF THE 12Z UKMET/12Z CMC AND 12Z ECMWF WILL BE PREFERRED. ...AMPLIFYING TROUGH ACROSS THE UPPER MIDWEST/GREAT LAKES THROUGH WED... ...DEEPENING SURFACE LOW LIFTING FROM THE MID MS VALLEY TO QUEBEC... PREFERENCE: 12Z UKMET CONFIDENCE: AVERAGE THE SYSTEM MOVING ACROSS THE WEST COAST THROUGH MON WILL CROSS THE NORTHERN INTERMOUNTAIN WEST/NORTHERN ROCKIES LATE MON/MON NIGHT. ON TUES AS THE UPPER TROUGH MOVES INTO THE NORTHERN PLAINS AND MIDWEST IT WILL BEGIN TO PHASE WITH THE SOUTHERN STREAM ENERGY FARTHER SOUTH ACROSS THE TN VALLEY, RESULTING IN RAPID WAVE AMPLIFICATION AND SURFACE LOW INTENSIFICATION TUES NIGHT ACROSS THE GREAT LAKES. THE GFS AND NAM ARE INITIALLY ON THE FAST SIDE OF THE SPREAD AS THE SURFACE LOW CROSSES THE GREAT LAKES LATE TUES AND MOVES INTO SOUTHEASTERN ONTARIO. THE 12Z ECMWF MAKES UP THE SLOW SIDE OF THE SPREAD. THE 12Z ECMWF ENSEMBLE MEAN AND 18Z GEFS MEAN ARE VERY CLOSE IN TERMS OF LOW TRACK AND TIMING TUES AND WED, INDICATING A GOOD CONSENSUS SOLUTION THAT IS A BIT SLOWER THAN THE 00Z GFS BUT FASTER THAN THE 12Z ECMWF. THE 12Z UKMET SOLUTION IS VERY CLOSE TO THIS CONSENSUS THROUGHOUT THE PERIOD, AND IS THE PREFERENCE AT THIS TIME. ...FRONTAL WAVE AFFECTING THE WEST COAST MON NIGHT THROUGH TUES... PREFERENCE: GFS/12Z ECMWF BLEND CONFIDENCE: AVERAGE A FRONTAL BOUNDARY WILL LINGER OFF THE WEST COAST DURING THE MON-WED TIME FRAME. A SERIES OF WEAK UPPER-LEVEL WAVES WILL TRAVERSE THE REGION SOUTH OF A PERSISTENT ELONGATED UPPER TROUGH OVER WESTERN CANADA. THE FIRST SIGNIFICANT WAVE ALONG THE FRONT SHOULD APPROACH THE WEST COAST MON NIGHT/EARLY TUES. MODELS HAVE COME INTO BETTER AGREEMENT COMPARED TO THIS TIME YESTERDAY ON A WELL DEFINED BUT RELATIVELY WEAK SURFACE LOW APPROACHING THE COAST. THE 12Z UKMET WAS THE FASTEST SOLUTION IN BRINGING THE LOW TO THE COAST WHILE THE NAM IS CLUSTERED WITH THE 12Z ECMWF/UKMET AS WELL AS THE 18Z GEFS MEAN ON THE SLOW SIDE, WITH THE GFS IN THE MIDDLE. GIVEN THAT THE CONSENSUS SEEMS TO BE WEIGHTED MORE TOWARD THE SLOWER SIDE, WILL LEAN IN THIS DIRECTION WITH THE PREFERENCE, WHICH WILL BE A GFS/12Z ECMWF BLEND AT THIS TIME. ...LOW PRESSURE/FRONT APPROACHING THE WEST COAST WED NIGHT... PREFERENCE: GFS/NAM/12Z ECMWF ENS MEAN/18Z GEFS MEAN BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE THE MODELS SHOW A DEEP UPPER TROUGH AND A STRONG SURFACE LOW EVOLVING WELL OFFSHORE THE WEST COAST BY WED. THIS SYSTEM WILL INTERACT WITH THE ELONGATED UPPER TROUGH OFF THE COAST OF BRITISH COLUMBIA, AT WHICH TIME SPREAD INCREASES SUBSTANTIALLY. THE EXACT TIMING WITH WHICH ANY INTERACTIONS/PHASING OCCUR MAKES A SUBSTANTIAL DIFFERENCE IN THE SPEED WITH WHICH THE SURFACE LOW APPROACHES THE COAST. THE NAM AND GFS ARE GENERALLY IN THE MIDDLE OF THE SPREAD WITH RESPECT TO THE TIMING, IF NOT A BIT TOWARD THE SLOW SIDE. THE 12Z UKMET/CMC PHASE THE SYSTEMS QUICKER AND BRING THE SURFACE LOW TO THE COAST MUCH FASTER. THE ENSEMBLE MEANS (12Z ECMWF ENS/18Z GEFS) FAVOR THE SLOWER CAMP OF SOLUTIONS, AND ARE ACTUALLY BOTH QUITE CLOSE TO THE NAM/GFS. THUS, WILL FAVOR THE NAM/GFS ALONG WITH THE ENSEMBLE MEANS AT THIS TIME. ...DEVELOPING LOW PRESSURE ACROSS THE SOUTHERN MID-ATLANTIC LATE WED... PREFERENCE: 12Z ECMWF/12Z UKMET BLEND CONFIDENCE: AVERAGE MODELS ARE IN GENERAL AGREEMENT THAT A WAVE OF LOW PRESSURE WILL DEVELOP ALONG THE TRAILING FRONTAL BOUNDARY ACROSS THE SOUTHERN PLAINS WED MORNING. AS THIS MOVES EAST, ENERGY WILL TRANSFER FAIRLY QUICKLY INTO A NEW SURFACE LOW WHICH SHOULD FORM SOMEWHERE ACROSS THE SOUTHERN MID-ATLANTIC WED NIGHT. THE NAM APPEARS TO BE TOO FAST WITH TAKING THIS MID-ATLANTIC LOW NORTHEASTWARD, WHILE THE GFS IS TOO FAR NORTH AND WEST WITH THE LOW TRACK. THE 12Z ECMWF ENS MEAN/18Z GEFS MEAN BOTH SUPPORT AN EVOLUTION SIMILAR TO THAT SHOWN BY THE 12Z ECMWF/UKMET. THUS, WILL PREFER A BLEND OF THESE SOLUTIONS AT THIS TIME. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RYAN