MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1246 AM EDT THU APR 02 2015 VALID APR 02/0000 UTC THRU APR 05/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ INITIALIZATION ERRORS WITH THE NAM/GFS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. CLOSED LOW NEAR THE PACIFIC NORTHWEST THIS WEEKEND ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z NAM / 12Z ECMWF COMPROMISE CONFIDENCE: AVERAGE THE ENSEMBLE SPREAD IN THE 500 MB HEIGHTS IS STILL QUITE LARGE OUT HERE BY 12Z/05...BUT IT APPEARS THE 00Z GFS COULD BE TOO FAST WITH THE BASE OF THE UPPER TROUGH MOVING ACROSS THE WEST COAST AT THE END OF THE SHORT RANGE PERIOD. WE WILL LEAN TOWARD THE PREVIOUS PREFERENCE WITH A SLIGHT ADJUSTMENT TOWARD THE 00Z NAM GIVEN ITS SOLUTION FITS IN CLOSELY TOWARD THE MIDDLE OF THE LATEST MODEL SPREAD. SHORTWAVE OVER THE SOUTHWEST REACHING THE PLAINS BY FRI MORNING ASSOCIATED COLD FRONT REACHING THE EAST COAST FRI NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS...12Z UKMET...12Z ECMWF COMPROMISE CONFIDENCE: SLIGHTLY ABOVE AVERAGE THERE ARE SOME RELATIVELY MINOR SPEED/TRACK ISSUES WITH THIS SYSTEM...WITH THE 00Z NAM/CMC SHOWING A SLOWER PROGRESSION WITH THE UPPER TROUGH AND RELATED COLD FRONT. THE 00Z GFS...12Z ECMWF AND 12Z UKMET SHOW A SIMILAR TIMING WHICH MORE CLOSELY RESEMBLES THE ENSEMBLE MEANS COMPARED TO THE NAM/CMC. SHORTWAVE TROUGH AXIS MOVING ENEWD FROM THE N-CNTRL U.S. TODAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE GUIDANCE SHOWS GOOD AGREEMENT WITH THESE SYSTEMS. COLD FRONT MOVING ACROSS THE N-CNTRL U.S. SAT/SUN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON 00Z NAM COMPROMISE CONFIDENCE: AVERAGE BY THE END OF THE SHORT RANGE PERIOD...12Z/05...THE NAM ENDS UP ON THE NRN SIDE OF THE LATEST DETERMINISTIC SPREAD WITH THE FRONTAL BOUNDARY ACROSS THE NRN PLAINS. OUTSIDE OF THE NAM...THE REMAINING MODELS WHEN BLENDED TOGETHER REPRESENT AN ACCEPTABLE COMPROMISE. MID-UPPER LEVEL SHORTWAVE REACHING THE SOUTHWEST SAT NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS / 12Z ECMWF BLEND CONFIDENCE: AVERAGE THE TIMING DIFFERENCES WITH A MID-UPPER LEVEL SHORTWAVE REACHING THE SOUTHWEST DO NOT REALLY SHOW UP UNTIL SUN MORNING. THE MODEL SPREAD IS NOT TOO LARGE...AND AT THIS TIME...GOING TOWARD THE MIDDLE SEEMS BEST GIVEN THE LARGE SCALE FLOW DOES NOT REALLY SUPPORT A SLOWER/AMPLIFIED NOR FASTER/ZONAL PATTERN. THEREFORE...THE 00Z GFS/12Z ECMWF COMPROMISED POSITION SHOULD REPRESENT THE BEST MIDDLE GROUND AT THIS TIME. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO