MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1155 AM EST TUE FEB 21 2017 VALID FEB 21/1200 UTC THRU FEB 25/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS MODEL EVALUATION...INCLUDING PRELIMINARY PREFERENCES ...SHORTWAVE CROSSING THE GREAT LAKES/OHIO VALLEY TODAY... ...SURFACE LOW PRESSURE/COLD FRONT CROSSING THE REGION THROUGH TONIGHT... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE MODELS ARE IN GOOD AGREEMENT WITH THE EVOLUTION OF THIS SYSTEM. A GENERAL MODEL COMPROMISE IS PREFERRED AT ABOVE AVERAGE CONFIDENCE. ...SOUTHERN STREAM CLOSED LOW EVOLUTION FROM THE GULF COAST TO THE FL KEYS... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE MID/LATE MORNING WV/IR IMAGERY SHOWING DEVELOPING CLOSED LOW OVER THE WEST CENTRAL GULF COAST. GOOD MODEL AGREEMENT WITH DEVELOPING AN ANOMALOUSLY STRONG CLOSED LOW ACROSS THE LOWER MS VALLEY/CENTRAL GULF COAST THROUGH TONIGHT...WITH THE FEATURE CUTTING OFF FROM WESTERLIES AND DIVING SE ACROSS THE EASTERN GULF OF MEXICO WED...TOWARD SOUTH FLORIDA/FLORIDA KEYS BY EARLY THURSDAY. THE GUIDANCE HANDLES THE EVOLUTION OF THE SYSTEM SIMILARLY FOR LATER THU AND FRI...WITH GENERAL AGREEMENT IN PROGRESSING THE SYSTEM NORTH OF THE STRAIT OF FLORIDA TOWARD THE BAHAMAS BY EARLY FRIDAY BEFORE THE LOW FILLS/WEAKENS OFF THE SOUTHEAST COAST FRIDAY NIGHT. THE NEW 12Z NAM REMAINS A BIT FASTER THAN THE REMAINDER OF AVAILABLE GUIDANCE...WITH THE 12Z GFS AND THE ECMWF ON THE SLOW SIDE OF THE GUIDANCE ENVELOPE. HOWEVER...THERE IS OVERALL VERY LITTLE SPREAD WITH THIS FEATURE WITH DECENT TO GOOD MASS FIELD AGREEMENT THROUGH THE PERIOD SUCH THAT A GENERAL MODEL COMPROMISE WILL SUFFICE THROUGH THE FORECAST PERIOD. GIVEN RELATIVELY LOW SPREAD AND GOOD RUN TO RUN CONTINUITY...FORECAST CONFIDENCE IS ABOVE AVERAGE WITH THIS SYSTEM. ...SHORTWAVE/SURFACE LOW OVER THE PAC NW/INTERMOUNTAIN WEST TODAY... ...SURFACE LOW REACHING THE NORTHERN PLAINS/UPPER MIDWEST TONIGHT/WED ...SURFACE LOW/COLD FRONT CROSSING FROM THE NORTHERN/CENTRAL PLAINS TO THE GREAT LAKES WED/THU... PREFERENCE: 00Z UKMET/ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE MODELS ARE ALSO WELL CLUSTERED WITH THIS LATEST PAC NW SHORTWAVE AND ASSOCIATED SURFACE LOW...WHICH WILL IMPACT THE WEST COAST THROUGH TONIGHT. GOOD MODEL AGREEMENT IN EJECTING THE SHORTWAVE NORTHEAST WED/EARLY THURSDAY. THE ASSOCIATED SURFACE WAVE AND ATTENDANT SURFACE COLD FRONT WILL QUICKLY TRAVERSE THE NORTHERN GREAT BASIN/NORTHERN ROCKIES TODAY...BEFORE PUSHING ACROSS THE DAKOTAS TONIGHT. THE SYSTEM IS EXPECTED TO INTENSIFY A BIT ON WED AS IT APPROACHES THE UPPER MIDWEST. THE 12Z GFS HAS TRENDED TOWARD THE ECMWF IN DEPICTING A SLIGHTLY MORE SHEARED/WEAKER WAVE...BUT THE GFS REMAINS A BIT FASTER THAN THE 00Z ECMWF/UKMET. THE 12Z NAM IS NOW A STRONG/SLOW OUTLIER WITH THE SYSTEM 00Z CMC TRENDED SLOWER BUT OVERALL REMAINS THE WEAKEST AND IS A LITTLE SLOWER THAN THE GFS AS THE LOW CROSSES THE NORTHERN PLAINS/UPPER MIDWEST. THE 00Z UKMET AND 00Z ECMWF BOTH IN BETWEEN THE SLOW NAM AND THE FASTER GFS/CMC CAMP. GIVEN THE TREND OF THE 12Z GFS TOWARD THE ECMWF CAMP WITH MASS FIELDS...WILL LEAN TOWARD A COMPROMISE BETWEEN THE UKMET AND ECMWF AT THIS TIME TO APPROXIMATE THE MODEL CONSENSUS. ...BROAD LONGWAVE TROUGH FINALLY REACHING THE WEST COAST WED... ...ADDITIONAL NORTHERN STREAM SHORTWAVE CROSSING THE PACIFIC NORTHWEST... ...DEVELOPING SURFACE LOW OVER THE CENTRAL/SOUTHERN HIGH PLAINS MOVING TOWARD UPPER MIDWEST LATE THU/FRI... PREFERENCE: 00Z ECMWF/06Z GEFS MEAN CONFIDENCE: SLIGHTLY BELOW AVERAGE A LONGWAVE TROUGH WILL FINALLY BEGIN TO DROP SOUTHEAST ACROSS THE WEST COAST ON WED/EARLY THU...MOVING INLAND AND TRAVERSING THE INTERMOUNTAIN WEST BY THU/THU NIGHT. LEAD SHORTWAVE CROSSES NORTHERN CA AND THEN EJECTS EAST ACROSS THE GREAT BASIN AND THE CENTRAL ROCKIES. MEANWHILE...AN ADDITIONAL NORTHERN STREAM SHORTWAVE WILL BE DIGGING SOUTHEAST ACROSS THE PACIFIC NORTHWEST ON THE HEELS OF THE INITIAL SURGE OF HEIGHT FALLS AND WILL HELP TO BROADEN THE OVERALL LONGWAVE TROUGH THROUGH THE PERIOD. THE INITIAL SURGE OF HEIGHT FALLS ARE WELL RESOLVED BY MODELS AND GOOD FORECAST CONFIDENCE THAT THIS WILL LEAD TO SURFACE CYCLOGENESIS ACROSS THE CENTRAL/SOUTHERN HIGH PLAINS ALONG A FRONTAL ZONE EAST OF THE ROCKIES LATE THURSDAY. HOWEVER...THE MODELS STILL DIVERGE TO SOME DEGREE WITH RESPECT TO THE EVOLUTION OF THE LONGWAVE TROUGH ACROSS THE PLAINS...WITH RESULTANT IMPACTS REGARDING SURFACE LOW PRESSURE TRAVERSING THE CENTRAL PLAINS TOWARD THE MID MISSISSIPPI RIVER VALLEY LATER THU AND FRI. THE 12Z GFS TRENDED A BIT SLOWER WITH THE EVOLUTION OF THE SYSTEM...BUT REMAINS THE STRONGEST SOLUTION WITH THE LOW PRESSURE LIFTING FROM EASTERN IA TOWARD THE UPPER MIDWEST BY FRI MORNING. THE 00Z ECMWF DID TREND A BIT STRONGER TOO AND IS ONLY A LITTLE WEAKER THAN THE GFS. THE GFS REMAINS IS A BIT FARTHER NORTH WITH ITS LOW TRACK...WITH THE 06Z GEFS ESSENTIALLY A COMPROMISE SOLUTION OF THE TWO AT THIS TIME. THE 12Z NAM REMAINS SLIGHTLY WEAKER AND IS A FAST OUTLIER WITH THIS SYSTEM. THE 00Z UKMET AGAIN BECOMES THE SLOWEST WITH THE 00Z CMC IN BETWEEN THE ECMWF AND UKMET TRACKS. BASED ON THE 06Z GEFS MEAN...THE 12Z GFS STILL APPEARS SLIGHTLY TOO FAR NORTH WITH ITS LOW TRACK...BUT SPATIAL DIFFERENCES ARE DIMINISHING WITH TIME. THE 00Z ECMWF HAS SHOWN BETTER CONTINUITY...AND ALIGNS WELL WITH THE 06Z GEFS MEAN AND IS NOW A BIT NORTH-NORTHWEST OF THE 12Z ECENS MEAN. GIVEN THE TRENDS STARTED/CONTINUED WITH THE 12Z GFS...WILL STICK WITH A BLEND OF THE ECMWF AND LATEST GEFS MEAN AS A COMPROMISE AT THIS POINT...WITH CONFIDENCE LIMITED GIVEN THE OVERALL DETERMINISTIC MODEL SPREAD. ...ADDITIONAL HEIGHT FALLS OVER THE PACIFIC NORTHWEST ON FRI/SAT... PREFERENCE: 06Z GEFS/00Z ECENS CONFIDENCE: AVERAGE THE MODELS SHOW SOME ADDITIONAL SHORTWAVE ENERGY SETTLING SOUTH OVER TOP THE STRONG UPPER LEVEL RIDGE/HIGH OVER THE GULF OF AK AND DROPPING DOWN ALONG AND OFFSHORE OF THE PACIFIC NORTHWEST. THERE ARE SOME TIMING DETAIL DIFFERENCES...THE ECMWF BEING A BIT STRONGER/SLOWER THAN THE 12Z GFS. HOWEVER...THERE IS DECENT CLUSTERING AT THIS TIME RANGE BETWEEN THE TWO...AND THEY APPEAR TO BE CONVERGING WITH THEIR HANDLING OF THIS FEATURE. IN THE INTERIM...WILL BLEND GEFS AND ECENS AT AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... MONTEFUSCO