MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1204 PM EDT TUE MAY 26 2015 VALID MAY 26/1200 UTC THRU MAY 30/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES UPPER LOW OVER THE PACIFIC NORTHWEST... PREFERENCE: BEFORE 00Z FRI...NAM OR GFS OR ECMWF AFTER 00Z FRI...GFS OR ECMWF CONFIDENCE: ABOVE AVERAGE MODELS SHOW GOOD AGREEMENT THROUGH 00Z FRI...BY WHICH TIME THE NAM DISPLAYS SOME GRID-SCALE FEEDBACK ALONG THE COLORADO/KANSAS BORDER...WHICH THEN INTERACTS WITH SOUTHERN PORTIONS OF THE UPPER LOW AS IT MOVES OUT OF THE NORTHERN ROCKIES. THUS...THE NAM IS CONSIDERED USEFUL UNTIL ABOUT 00Z FRI...BEFORE BECOMING LESS USEFUL WITH A SWITCH TO EITHER THE GFS OR ECMWF AFTER 00Z FRI. LOW PRESSURE NEAR IOWA... SHORTWAVE TROUGH OVER WEST TEXAS... SHORTWAVE TROUGH OVER THE CENTRAL GULF COAST... MODELS SHOW GOOD LARGE-SCALE AGREEMENT. REFER TO THE QPFPFD FOR MORE INFORMATION ON RAINFALL. SHORTWAVE TROUGH CROSSING THE S. ROCKIES THU-FRI... PREFERENCE: EQUAL BLEND GFS/ECMWF CONFIDENCE: ABOVE AVERAGE DUE TO QUESTIONABLE INTERACTIONS WITH THE NORTHERN STREAM...THE NAM GRADUALLY MOVES TOWARD THE FAST EDGE OF THE GUIDANCE...AND THUS IS DISCOUNTED IN FAVOR OF A GFS/ECMWF BLEND WHICH HAVE THE BULK OF ENSEMBLE SUPPORT. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... JAMES