Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1215 AM EST Sat Feb 22 2020 Valid Feb 22/0000 UTC thru Feb 25/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS Evaluation with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed mid level low reaching the Rockies Sun...then weakening over the Upper MS Valley Mon... ...Surface low tracking from northeast NM into Mid MS Valley by Mon ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/12Z ECMWF blend Confidence: Average Trends in the ensemble guidance have generally shown convergence valid on Sunday with the closed low with a subtle shift to be slower. The 00Z GFS slowed down from earlier cycles but remains slightly quicker than the 12Z ECMWF, with the 12Z ECMWF mean between the 00Z GFS and 12Z ECMWF. Regarding strength, the 00Z GFS may be a bit too strong, while the 12Z ECMWF may be a bit too weak given ensemble mean averages appear to be in the middle of the two models. Meanwhile the 00Z NAM is strongest with the low-mid level low and fastest through Sunday, with the 12Z UKMET slowest followed by the 12Z CMC. Downstream across the Midwest, the 12Z CMC becomes the slowest deterministic model with the closed low. The preference is to be near the middle of the tightening model spread, which is near a blend of the 00Z GFS and 12Z ECMWF. While some of the differences observed for Sunday reduce later in the short range period, a 00Z GFS/12Z ECMWF blend remains consistent and preferred at all forecast hours. ...Weak mid level shortwave and attendant cold front reaching the Great Lakes Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM, 00Z GFS, 12Z ECMWF blend Confidence: Average The 00Z NAM, 00Z GFS and 12Z ECMWF are reasonably similar to one another and match best to the agreeable ensemble means with the surface and upper level reflection of this system. The 12Z UKMET/CMC are flatter and faster with the mid-level shortwave. Despite the agreement from the ensemble means to the often reliable GFS and ECMWF, coupled with the NAM's agreement, confidence is only above average with this system given some lingering differences in ensemble spaghetti plots as the trough moves across Ontario. ...Mid level shortwave crossing the Pacific Northwest Sunday...closing off over the Northern/Central Plains Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM, 00Z GFS, 12Z ECMWF blend Confidence: Slightly below average There is better agreement with this system compared to yesterday but differences remain as the shortwave nears the coast of the Pacific Northwest, and downstream into the Great Basin and Great Plains. The 12Z UKMET is likely too slow considering the remaining guidance as the shortwave approaches the Pacific Northwest early Sunday. There are minor timing differences outside of the UKMET, with the 00Z NAM/GFS slightly ahead of the 12Z ECMWF/CMC but a non 12Z UKMET blend will work through early Sunday across the Northwest. By Monday morning, the trough will advance inland, crossing the northern Rockies and eventually reaching the Great Plains for Tuesday morning. The initially slower 12Z UKMET ends up with a closed low near the Texas Panhandle Tuesday morning, but this seems like the outlier compared to the remaining guidance. The 00Z GFS winds up a bit faster (typical bias) and slightly stronger into the north-central U.S. with a closed low while the agreeable 12Z ECMWF/00Z NAM are a bit slower. Given the rather large spread, and a tendency for convergence of timing with subsequent cycles, a blend of equal weighting between the 00Z NAM, 00Z GFS and 12Z ECMWF blend is preferred. This puts a little more weight to the slower ECMWF/NAM. The 12Z CMC was excluded from the preference given it does not show as much of a defined closed low Tuesday morning across the Great Plains. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto