MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 108 PM EDT THU MAR 23 2017 VALID MAR 23/1200 UTC THRU MAR 27/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...PLEASE NOTE THAT THE NAM WAS UPGRADED TO A NEW VERSION 21/12Z CYCLE... 12Z NAM/GFS EVALUATION...INCLUDING PRELIMINARY PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...NORTHERN STREAM SHORTWAVE CROSSING SOUTH-CENTRAL CANADA TODAY... ...CLOSED LOW DIVING THROUGH SOUTHEAST CANADA BY SAT MORNING... ...COLD FRONT ADVANCING DOWN ACROSS THE GREAT LAKES/NORTHEAST... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS CONFIDENCE: SLIGHTLY ABOVE AVERAGE LARGEST DIFFERENCES DEVELOP ON SUN WITH THE MID-LEVEL TROUGH OVER SRN CANADA AND HOW THAT RELATES TO THE POSITION OF THE SURFACE BOUNDARY ACROSS THE NRN-MID ATLANTIC REGION. THE PRESENCE OF A STRONGER SHORTWAVE EMANATING FROM THE BRITISH COLUMBIA/ALBERTA BORDER THIS MORNING REACHING NEW ENGLAND SAT NIGHT ALLOWS FOR A DEEPER AND FARTHER SOUTH LOWER HEIGHTS ACROSS NRN NEW ENGLAND AND A FARTHER SOUTH SURFACE BOUNDARY. MULTI-CYCLE TRENDS IN THE ENSEMBLES HAVE BEEN TOO THE NORTH ALONG WITH THE DETERMINISTIC ECMWF...BUT BOTH LAG THE LARGER CLUSTERING TO THE NORTH. A FRONTAL POSITION NEAR THE 12Z GFS HAS MORE ENSEMBLE SUPPORT AND LIES NORTH OF THE ECMWF FOR SUN. ...STRONG UPPER TROUGH CROSSING THE SOUTHWEST/FOUR CORNERS TODAY... ...CLOSED LOW EVOLUTION OVER THE CENTRAL PLAINS FRI... ...ENERGY CROSSING THE MID MS/OH VALLEYS THROUGH SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS / 00Z ECMWF BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE AT 500 MB...THERE HAS BEEN A NOTABLE TREND IN THE GEFS ENSEMBLES TO ADJUST FASTER COMPARED TO SLOWER EARLIER CYCLES...SO MUCH SO THAT THEY HAVE PASSED THE ECMWF ENSEMBLES WHICH HAVE BEEN TRENDING SLOWER VALID LATE FRI. WHILE DIFFERENCES ARE RELATIVELY MINOR THROUGH ABOUT 00Z/26...THE 12Z NAM/GFS PULL AWAY FASTER THAN THE 00Z ECMWF/UKMET/CMC FOR SUN WITH THE 500 MB AND SURFACE COLD FRONT. THE 00Z UKMET BECOMES AN OUTLIER JUST AFTER 00Z/27. THE INFLUENCE FROM AN UPSTREAM KICKER TROUGH MAY BE THE DECIDING FACTOR IN THE TIMING OF THE DOWNSTREAM FEATURE. GIVEN TRENDS IN THE GEFS BUT STEADY CONSISTENCY IN THE ECMWF...CONFIDENCE IS LOWERED. GOING IN THE MIDDLE IS THE BEST APPROACH AT THIS TIME...REPRESENTED BY A 50/50 BLEND OF THE 12Z GFS AND 00Z ECMWF. ...NORTHERN STREAM TROUGH/COLD FRONT REACHING THE NORTHWEST THURS/FRI... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THERE ARE ONLY MINOR TIMING DIFFERENCES WITH THIS SYSTEM AND ITS ASSOCIATED COLD FRONT...THUS A GENERAL MODEL COMPROMISE IS PREFERRED TO SMOOTH OUT THESE SMALLER SCALE DIFFERENCES. ...SOUTHERN STREAM COMPONENT OF UPPER LEVEL TROUGH OVER THE WEST ON SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS / 00Z ECMWF BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 12Z NAM/GFS HAVE TRENDED QUICKER WITH THE TIMING OF THE UPPER TROUGH MOVING THROUGH THE FOUR CORNERS REGION SAT EVENING...AND ARE CURRENTLY FASTER THAN THE 00Z ECMWF/UKMET/CMC. SIMILAR TO THE 2ND SYSTEM DESCRIBED IN THIS DISCUSSION...TRENDS IN THE GEFS HAVE BEEN FASTER BUT THE ECMWF MEAN HAS BEEN INCONSISTENT. WHILE THE PREFERENCE IS TO GO IN THE MIDDLE OF THE SLOWER AND FASTER...WOULD NOT BE SURPRISED TO SEE LATER ARRIVING MODEL GUIDANCE TO JUMP ABOARD THE FASTER TRENDS SEEN IN THE 12Z NAM AND 12Z GFS. ...UPPER TROUGH REACHING THE WEST COAST SUN EVENING... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THERE ARE ONLY MINOR TIMING DIFFERENCES WITH THIS SYSTEM AND ITS ASSOCIATED COLD FRONT...THUS A GENERAL MODEL COMPROMISE IS PREFERRED TO SMOOTH OUT THESE SMALLER SCALE DIFFERENCES. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO