Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 144 PM EST Thu Mar 05 2020 Valid Mar 05/1200 UTC thru Mar 09/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation with final preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deepening northern stream low moving out of the Great Lakes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/UKMET/ECMWF (slightly less weight on ECMWF) Confidence: Slightly above average ...19Z update... The 12Z non NCEP guidance all trended slightly in direction Friday night and Saturday (12Z ECMWF, westward...12Z UKMET, slightly westward...12Z CMC, slightly northward), but the biggest adjustment was in the 12Z ECMWF. The 12Z ECMWF jumped west near the already western 12Z CMC surface low track late Friday night into Saturday morning. The CMC remains farthest west throughout the short range period, but the preference and thinking remains the same. This thinking is near the 12Z GFS/UKMET with some slight incorporation of the 12Z ECMWF given recent trends in the deterministic guidance. With the ensemble means east of the deterministic consensus, there is a chance the deterministic runs will jog a bit farther east again with the 00Z/Friday cycle. ...previous discussion follows... The ensembles continue to exhibit run to run changes with the upper trough crossing the Great Lakes and East Coast for Friday/Friday night as well as the surface low offshore. There has been a westward shift from the ECMWF/CMC/GEFS ensembles valid Friday morning and Friday evening with the upper trough and surface low over their past 3 12/00Z cycles. However, the trends have not been so large as to reach that of the CMC...even Wednesday's cycles of the CMC which were considered too far west. Currently, the non 00Z CMC guidance shows reasonably similar, but the surface to 850 mb low is much weaker in the 12Z NAM compared to the remaining consensus through Friday evening. The 00Z ECMWF is also a little weaker with its low, while the 12Z GFS and 00Z UKMET are more developed and a little west of the 00Z ECMWF low track. Given proximity to the Gulf Stream and recent trends in the deterministic guidance toward the west and to be somewhat stronger, more weight toward the 12Z GFS and 00Z UKMET is preferred, but with some inclusion of the weaker/more-east 00Z ECMWF included to account for potential shifts in the guidance back in the other direction. This 3-way blend of the 12Z GFS, 00Z UKMET and 00Z ECMWF is preferred at this time. ...Longwave trough moving into the West Coast Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average ...19Z update... The 12Z CMC sped up its timing of the shortwave trough axis moving across the West Coast on Saturday. Little change was noted with the 12Z ECMWF/UKMET compared to their previous cycles, so the preference has been updated to include the 12Z CMC as a general model blend. ...previous discussion follows... A deepening longwave trough dropping from the Gulf of Alaska will approach the Pacific Northwest today and then extend down towards the CA coast Friday before lifting inland by the weekend. There is reasonable agreement among all of the deterministic guidance, but the 12Z GFS is slightly faster with the mid-level trough axis crossing CA/OR on Saturday compared to the remaining consensus. The 00Z CMC was noted to be slower with this trough axis. While the 12Z GFS is a little faster, it is not unreasonable given the ensemble distribution, but the 00Z CMC does stand out more. A general model blend may be fine across the western U.S., but at this time, we prefer to leave out the slower 00Z CMC given greater support for a faster timing. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto