Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1233 AM EDT Tue Mar 12 2019 Valid Mar 12/0000 UTC thru Mar 15/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS Evaluation Including Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Upper trough crossing the Pacific Northwest Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models continue to be in good agreement as this system moves inland through Tuesday night. During the day on Wednesday, the mid-upper level trough axis merges with an existing closed low and associated negatively tilted trough axis discussed below. Through Wednesday morning, a general model blend is recommended across the West with this system. ...Closed low/negatively tilted mid-level trough axis crossing the Southwest Tuesday/Tuesday night... ...Large Great Plains closed low Wed-Thu with associated deep surface low tracking toward the Great Lakes late Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/12Z ECMWF blend Confidence: Slightly above average Differences in the model fields begin to appear around 12Z/13 with the 12Z CMC/UKMET a bit weaker with the shortwave amplifying into the back of the closed low/negatively tilted shortwave trough axis into Kansas and Oklahoma. The 12Z CMC is slowest with the main shortwave ejecting out into the Great Plains with the 12Z UKMET between the agreeable 00Z NAM, 00Z GFS and 12Z ECMWF. Overall, the 12Z CMC appears to be the model with the lowest likelihood of verifying. By 00Z/14, the 00Z NAM and 12Z UKMET are noted to be weaker with the surface low and displaced slightly east of the better ensemble consensus which trended slightly back to the west with the 12Z/11 cycle. The 00Z GFS/12Z ECMWF show some minor differences but are better aligned well with the latest GEFS/ECMWF mean positions at 500 mb and at the surface. Run to run continuity has been decent from the GFS and ECMWF but future minor wobbles in position and timing can be expected, just not likely deviating far from the 00Z GFS and 12Z ECMWF blend. ...Upper trough approaching CA late Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM/GFS and 12Z CMC blend Confidence: Slightly below average The models bring another shortwave trough toward CA on Thursday but this one is of much lower amplitude than the one currently near the Southwest and Pacific Northwest. Ensemble spread is fairly large with this next system but trends have been toward a more amplified system. The 12Z UKMET/ECMWF represent the slowest of the deterministic guidance, the 00Z NAM/GFS are fastest while the 12Z CMC is slightly slower/weaker than the 00Z NAM/GFS. The ensemble means show greater support for the middle to faster side of the model spread with a little more amplitude than seen in the 12Z ECMWF/UKMET. Therefore, will recommend a blend of the 00Z NAM/GFS and 12Z CMC at this time. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto