MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1206 AM EST SAT MAR 04 2017 VALID MAR 04/0000 UTC THRU MAR 07/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. SMALL MID-LEVEL CLOSED LOW CROSSING NEW ENGLAND EARLY TODAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE MODELS SHOW SIMILARLY WITH THIS SYSTEM. UPPER TROUGH REACHING THE WESTERN GULF COAST ON SATURDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z NAM...00Z GFS...12Z ECMWF COMPROMISE CONFIDENCE: AVERAGE RUN TO RUN CONTINUITY IN THE MASS FIELDS HAS BEEN DECENT SINCE YESTERDAY...BUT MINOR ADJUSTMENTS HAVE BEEN MADE. DIFFERENCES MAY END UP BEING A FUNCTION OF SMALLER...MESOSCALE DETAILS BEYOND THE SCOPE OF THIS DISCUSSION. FOR QPF PREFERENCES...SEE THE QPFPFD. THROUGH ABOUT 12Z/05...THE MASS FIELDS SHOW SIMILARLY BUT BEYOND THAT POINT IN TIME...THE 12Z UKMET/CMC SHOW TOWARD THE EDGES OF THE ENSEMBLE SPAGHETTI HEIGHTS. THEREFORE...A BLEND OF THE 00Z NAM...00Z GFS AND 12Z ECMWF IS PREFERRED GIVEN THEIR BETTER AGREEMENT WITH THE ENSEMBLE GUIDANCE. LONGWAVE TROUGH NEAR THE WEST COAST TODAY AND SUNDAY NEGATIVELY TILTED SHORTWAVE/LOW NEAR THE NORTHERN PLAINS MONDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 18Z GEFS MEAN / 12Z ECMWF MEAN BLEND CONFIDENCE: BELOW AVERAGE THE ENSEMBLE SPAGHETTI HEIGHTS SHOW BETTER AGREEMENT WITH THE ADVANCING TROUGH AXIS TODAY COMPARED TO YESTERDAYS RUNS BUT THEY CONTINUE TO WOBBLE BETWEEN FASTER AND SLOWER WITH EACH 12/00Z CYCLE THROUGH MON EVENING. CURRENTLY...THE 00Z GFS IS ON THE STRONGER SIDE WITH THE CORE OF THE MID-LEVEL LOW BY 00Z/07 AND IS ALSO FASTER WITH THE COLD FRONT MOVING THROUGH THE CNTRL CONUS. THE 12Z ECMWF IS QUITE A BIT WEAKER WITH THE CORE OF THE 500 MB LOW WITH THE ECMWF MEAN SUPPORTING STRONGER AND A BIT FASTER WITH THE COLD FRONT INTO THE CNTRL CONUS INTO TUE. THE 00Z NAM APPEARS TO BE A DECENT MIDDLE GROUND WITH THE TIMING OF THE COLD FRONT BUT ENDS UP DISPLACED FROM THE BETTER ENSEMBLE SCATTER LOW CONSENSUS WHICH REMAINS RELATIVELY CONSISTENT FROM THE PAST 2 CYCLES. THE TIMING IN THE 12Z UKMET/CMC ALSO APPEARS SLOWER THAN IDEAL WITH THE COLD FRONT AND THESE MODELS DO NOT MATCH THE BETTER ENSEMBLE LOW CLUSTERING SHOWN FOR THE SURFACE LOW TRACKING THROUGH THE PLAINS INTO S-CNTRL CANADA. THE CLOSEST MATCH TO THE IDEAL MIDDLE GROUND IS A BLEND OF THE 18Z GEFS MEAN AND 12Z ECMWF MEAN. CONFIDENCE IS BELOW AVERAGE GIVEN GREATER THAN AVERAGE ENSEMBLE SPREAD. POTENTIAL SURFACE LOW APPROACHING THE PACIFIC NORTHWEST TUE MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12z UKMET/CMC COMPROMISE CONFIDENCE: SLIGHTLY BELOW AVERAGE THE DETERMINISTIC MODELS ARE IN GOOD AGREEMENT IN SHOWING A SURFACE LOW STRENGTHENING IN ITS APPROACH TOWARD THE PACIFIC NORTHWEST TUE MORNING...SOUTH OF A SLOW MOVING SURFACE LOW LOCATED NEAR HAIDA GWAII. THERE IS ONLY MODEST ENSEMBLE SUPPORT FOR THIS LOW NEAR LONGITUDE 130W AT 12Z/07 BUT GIVEN THE GOOD DETERMINISTIC DEPICTION OF THIS FEATURE...AND THE PRESENCE OF A LOW AMPLITUDE SHORTWAVE IN FAST WEST-EAST FLOW LOCATED SOUTH OF A MID-LEVEL LOW IN THE GULF OF ALASKA...CONFIDENCE IN THIS FEATURE IS GREAT ENOUGH TO INCLUDE IN THIS DISCUSSION. THE ENSEMBLE SPAGHETTI HEIGHTS SHOW THE 12Z ECMWF AS DISPLACED NORTH WITH LOWER HEIGHTS ENTERING BRITISH COLUMBIA WHICH DISPLACES THE RELATED SHORTWAVE AND SURFACE LOW NORTH IN THE 12Z ECMWF. THE 18Z GEFS AND 12Z ECMWF MEAN SUPPORT A SHORTWAVE AND SURFACE LOW POSITION BETWEEN THE 12Z UKMET AND 12Z CMC. THEREFORE...A BLEND BETWEEN THE 12Z CMC AND 12Z UKMET IS PREFERRED. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO