Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 116 PM EDT Wed Mar 11 2020 Valid Mar 11/1200 UTC thru Mar 15/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS Evaluation with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed Low Affecting the Southwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS, 00Z ECMWF, 00Z CMC blend Confidence: Slightly above average Ensemble spaghetti plots suggest the 00Z UKMET is too slow, along with the 12Z NAM regarding the weakening mid-level closed low as it tracks across the Southwest through Saturday morning. During the day on Saturday, the 12Z NAM becomes a significantly slower outlier with the mid-level shortwave, becoming 500-600 miles slower than the remaining model consensus later in the day on Saturday. The 12Z GFS, 00Z ECMWF and 00Z CMC agree reasonably well with one another and the ensemble means. ...Northern stream trough tracking from the northern Rockies, Upper Midwest toward the Northeast through Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/00Z ECMWF blend Confidence: Slightly above average Timing differences appear with an amplifying mid-level trough expected to track across the Great Lakes region Thursday night. The 12Z NAM is notably slower with the 00Z ECMWF/CMC a touch slower as well compared to the ensemble means. Meanwhile, the 12Z GFS is a little faster than the ensemble means regarding the 500 mb trough and associated speed shear enhanced vorticity max rounding the base of the trough. Ensemble scatter low plots show a fair degree of north/south spread with the surface low crossing the Great Lakes region into Ontario. The 00Z UKMET/CMC are toward the southern side of the low track spread, especially the 00Z UKMET. A blend of the 12Z GFS and 00Z ECMWF appears to be the best compromise for this system. ...Closed Low Developing Over Pacific NW Friday/Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 12Z NAM blend Confidence: Slightly above average The 12Z NAM is the only model to significantly stand out with an eventual closed low to affect the northwestern U.S. for the end of the week, with a deeper and slower progression. The non 12Z-NAM guidance is reasonably similar but the 12Z GFS is noted to be weaker with the 700 mb low in the Northwest compared to the rather agreeable 00Z ECMWF/UKMET/CMC. Despite the differences of the 12Z GFS, and colder low level air into Montana by Saturday morning/afternoon, when blended with the 00Z ECMWF/UKMET/CMC, a preferred blend is reached. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto