Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 308 PM EDT Mon Mar 16 2020 Valid Mar 16/1200 UTC thru Mar 20/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep upper trough/closed low impacting the West... ...Cyclogenesis over the central High Plains Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 60 hours Non-NAM and non-CMC blend...after 60 hours Confidence: Slightly above average 19Z update: No significant changes to the earlier preference with the latest 12Z guidance now available. A deep upper trough and embedded closed low along the West Coast will continue to settle south over the next couple of days, and then begin to pivot inland into the Intermountain West by Wednesday which will foster lee-side cyclogenesis over the central High Plains. The guidance is in good agreement through about 60 hours, but thereafter a few of the models diverge on the ejection of the mid-level energy and subsequent surface low development across the central Plains. The 12Z NAM along with the 00Z CMC are ahead of the rest of the deterministic models and ensemble means, and also therefore have a stronger/deeper surface low that is further to the northeast compared to the GFS/ECMWF/UKMET solutions. The consensus favors a slower approach at this time and therefore, beyond 19.00Z (60 hours), a non-NAM and non-CMC blend is preferred while a general model blend is sufficient prior to that. ...Trough arriving over the northern High Plains Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Average 19Z update: With the rest of the 12Z guidance available, the GFS now appears to be a bit of an outlier with the progression of the trough over the northern High Plains. The ECMWF/UKMET slowed down somewhat, not to the degree that the NAM/CMC suggest, but enough to now favor more of a non-GFS approach at least for the mass fields. Positively tilted northern stream energy is expected to slip down into the northern High Plains by mid-week. As noted by the previous discussion, the 12Z NAM continues to be slower/deeper than the rest of the guidance. The 12Z GFS has slowed somewhat, and is a bit behind its 06Z GEFS mean, but isn't as deep as the NAM. The CMC mirrors the NAM idea of a slower/deeper solution while the ECMWF is still a weaker and more progressive solution. Its phasing/interaction with the southern stream energy coming out of the central Rockies remains unclear and likely will dictate how progressive the eventual troughing is. For now, will not make drastic blend preference changes, and continue to favor a GFS/ECMWF/UKMET blend. If the later 12Z ECMWF/UKMET trend slower, than more incorporation of the NAM and CMC would be plausible. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Taylor