MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1122 PM EST SUN FEB 19 2017 VALID FEB 20/0000 UTC THRU FEB 23/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...INCLUDING THE NAM AND GFS ...CLOSED LOW DEVELOPMENT NEAR NORTHERN NEW ENGLAND/NOVA SCOTIA THROUGH MON... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE MODELS ARE IN GOOD AGREEMENT WITH THIS SYSTEM THROUGH MON...SO WILL PREFER A GENERAL MODEL COMPROMISE. ...SHORTWAVE CROSSING OUT INTO THE NORTHERN PLAINS... ...UPPER TROUGH EJECTING OUT OF THE SOUTHWEST INTO THE PLAINS... ...ENERGY REACHING THE UPPER MIDWEST MON NIGHT... ...SURFACE LOW PRESSURE/COLD FRONT CROSSING THE PLAINS/MIDWEST THROUGH TUES... PREFERENCE: NON-NAM CONSENSUS CONFIDENCE: AVERAGE A NORTHERN STREAM TROUGH EJECTING OUT ACROSS THE NORTHERN PLAINS ON MON COUPLED WITH THE NORTHERN PORTION OF THE SOUTHERN STREAM TROUGH EJECTING OUT OF THE SOUTHWEST WILL WORK IN TANDEM TO DRIVE LOW PRESSURE ACROSS THE DAKOTAS EARLY MON AND THEN UP TOWARD HUDSON BAY ON TUES AS A TRAILING COLD FRONT CROSSES THE PLAINS/MIDWEST AND GREAT LAKES. THE 00Z NAM BECOMES A BIT SLOWER THAN THE MODEL CONSENSUS WITH THE ENERGY IN THE SOUTHERN STREAM THAT GETS PULLED NORTHEAST IN TANDEM WITH THE NORTHERN STREAM TROUGH AND ENDS UP WITH A SLOWER FRONTAL PROGRESSION. THE REMAINING MODELS ARE REASONABLY WELL CLUSTERED... WITH THEIR MASS FIELDS...AND SO WILL PREFER A NON-NAM CONSENSUS. ...SHORTWAVE/SURFACE LOW APPROACHING CROSSING THE WEST COAST ON MON... PREFERENCE: BLEND OF THE 00Z GFS/12Z UKMET AND 12Z ECMWF CONFIDENCE: ABOVE AVERAGE THE 00Z NAM IS A TAD SLOWER WITH THE SHORTWAVE/SURFACE LOW ARRIVING EARLY MON ACROSS WESTERN OREGON COMPARED TO THE WELL-CLUSTERED 00Z GFS/12Z UKMET AND 12Z ECMWF. THE 12Z CMC IS A WEAK OUTLIER SOLUTION. THEREFORE...WILL PREFER THE MODEL CONSENSUS WHICH CLOSEST TO A 00Z GFS/12Z UKMET AND 12Z ECMWF BLEND. ...SHORTWAVE/SURFACE LOW CROSSING THE WEST COAST MON NIGHT/EARLY TUES... ...SURFACE LOW REACHING THE NORTHERN PLAINS/UPPER MIDWEST BY WED... ...SURFACE LOW/COLD FRONT CROSSING THE GREAT LAKES BY THURS... PREFERENCE: BLEND OF THE 00Z GFS/12Z UKMET AND 12Z ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 12Z CMC IS THE MOST PROGRESSIVE WITH THE NEXT IN A SERIES OF SHORTWAVE/SURFACE LOWS THAT IMPACT THE WEST COAST BY MON NIGHT AND EARLY TUES. THE 00Z NAM ON THE OTHER HAND IS THE SLOWEST SOLUTION...WITH THE 00Z GFS/12Z UKMET AND 12Z ECMWF CLUSTERED IN BETWEEN. THE MODELS TAKE THIS ENERGY QUICKLY INLAND AND OUT INTO THE NORTHERN PLAINS BY WED WITH A PROGRESSIVE SURFACE LOW THAT THEN TRAVELS ACROSS THE UPPER MIDWEST THROUGH WED. BY THURS...THIS SURFACE LOW WILL BE DEEPENING WHILE CROSSING THE GREAT LAKES REGION AS TRAILING COLD FRONT APPROACHES THE OH VALLEY. THROUGH THE LATER STAGES OF THE PERIOD...THE 12Z CMC REMAINS A PROGRESSIVE OUTLIER...WITH THE 00Z NAM SLOWER AND TOO DEEP OVER THE GREAT LAKES. THE 00Z GFS/12Z UKMET AND 12Z ECMWF CLUSTER IN BETWEEN. WILL PREFER A BLEND OF THESE SOLUTIONS AT THIS TIME. ...LONGWAVE TROUGH FINALLY REACHING THE WEST COAST BY WED... ...LOW PRESSURE DEVELOPING OVER THE CENTRAL/SOUTHERN HIGH PLAINS... PREFERENCE: BLEND OF THE 12Z UKMET AND 12Z ECMWF CONFIDENCE: ABOVE AVERAGE...BECOMING AVERAGE BY WED/THURS A LONGWAVE TROUGH WILL MOVING ACROSS THE WEST COAST ON WED AND BEGIN TRAVERSING THE INTERMOUNTAIN REGION. THIS WILL LEAD TO AN ELONGATED AREA OF LOW PRESSURE DEVELOPING OVER THE CENTRAL AND SOUTHERN HIGH PLAINS ALONG A FRONTAL ZONE EAST OF THE ROCKIES. THE 00Z NAM AND 12Z CMC TEND TO BE PERHAPS A LITTLE DEEPER/SHARPER WITH THE TROUGH AS IT ARRIVES OVER THE WEST WITH THE 00Z GFS/12Z UKMET AND 12Z ECMWF A LITTLE FLATTER. TOWARD THE END OF THE PERIOD...THE 00Z GFS IS THE FLATTEST SOLUTION WITH ITS HEIGHT FALLS OVER THE INTERMOUNTAIN REGION...AND BY THEN THE 12Z CMC IS THE SHARPEST. CONSEQUENTLY...THE 00Z GFS IS A BIT WEAKER BY EARLY THURS WITH ITS LEE-SIDE CYCLOGENESIS. THERE IS A BIT BETTER MODEL CLUSTERING BETWEEN THE 12Z UKMET AND 12Z ECMWF BY THE END OF THE PERIOD..AND SO WILL LEAN TOWARD THIS CONSENSUS. ...SOUTHERN STREAM TROUGH/CLOSED LOW EVOLUTION NEAR THE GULF COAST... PREFERENCE: BLEND OF THE 12Z ECMWF/18Z GEFS MEAN AND 12Z ECENS MEAN CONFIDENCE: AVERAGE THERE REMAINS SOME SPREAD WITH THE CLOSED LOW EVOLUTION THAT IMPACTS THE WESTERN AND CENTRAL GULF COAST AREA TUES THROUGH THURS. THE 12Z CMC AND 12Z UKMET BOTH BECOME A LITTLE SLOWER THAN THE MODEL CONSENSUS AS THE ENERGY PUSHES OUT INTO THE GULF OF MEXICO...WITH THE 12Z CMC ALSO A BIT FARTHER SOUTH. THE 00Z GFS PLACES MORE ENERGY A BIT FARTHER NORTH...WITH THE 12Z ECMWF IN BETWEEN THE CMC/UKMET CAMP AND THE GFS. THE 00Z NAM IS A BIT WEAKER AND MORE PROGRESSIVE WITH THE ENERGY. THE 12Z ECMWF FOR NOW HAS BETTER ENSEMBLE SUPPORT...AND SO WILL BLEND THE ECMWF WITH THE LATEST GEFS MEAN AND ECENS MEAN. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON