Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 331 PM EDT Tue Mar 19 2019 Valid Mar 19/1200 UTC thru Mar 23/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Trough and Developing Low in the East... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 12Z GFS/ECMWF/NAM Confidence: Average Considerable model spread persists through Day 3 with guidance still shifting the track of the coastal low expected to develop off the Mid-Atlantic Wednesday night and move over the Northeast through Friday. Both the operational 12Z ECMWF and 12Z GFS trended slower and farther inland compared to the previous run. The 12Z ECMWF is still farther inland than the 12Z GFS, particularly into Day 3, and is similar to the 12Z NAM. However, notable spread in both the 12Z GEFS and 00Z ECENS suggest uncertainty persists and further shifting of the track can be expected. Given the continued inland trend of the ECMWF and its similarity to the NAM, the preference will now include the 12Z NAM. The track of this low is sensitive to northern stream shortwaves that will be interacting, including a phase on Thursday and of particular concern is the reinforcing shortwave that reaches the Great Lakes Thursday night which will influence the track of the primary trough/low through Friday and where the phasing takes place over the weekend (beyond the current Day 3 outlook). The 12Z ECMWF slowed both features with this run, so the reinforcing northern stream shortwave is now technically slow in the 12Z ECMWF than the 12Z GFS, but the slower leading trough has shifted the track farther inland in the ECMWF than the GFS. The intensity of the components are similar among the 12Z GFS, ECMWF, and NAM resulting in similar QPF magnitude. The 12Z UKMET and CMC made considerable shifts in their surface low track closer to the guidance consensus, but remain considerable outliers. The preference has been updated to include the NAM with the GFS/ECMWF and the caveat that much is still to be determined with the timing and intensity of the interacting components of this low is still relevant. ...Low and approaching trough in the West... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Above Average An amplified/full-latitude trough currently off the West Coast comes ashore tonight before closing into a low over the Desert SW Thursday and swinging into the northern Rockies through Friday. Excellent agreement is seen with the mid/upper portions of the system among 12Z global guidance with this feature, so a general model blend is recommended. The next trough approaches the West Coast late Friday with good timing agreement among 12Z global guidance with the arrival of QPF into CA. A general model blend also holds for this second feature. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Jackson