Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1214 AM EST Fri Mar 08 2019 Valid Mar 08/0000 UTC thru Mar 11/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS Evaluation Including Preliminary Preference and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Departing shortwave over the eastern U.S. today... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model compromise Confidence: Above average Only minor depth differences with the 700-500 mb shortwave exist with the 00Z NAM deepest and 12Z CMC flattest. Given the differences are small, a general model compromise is preferred. ...Shortwave in southern Alberta/Saskatchewan this morning, tracking east and merging with another shortwave from the north over Saskatchewan/Manitoba on Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 12Z CMC blend Confidence: Average Some minor timing differences remain with the lead shortwave moving into Manitoba Saturday morning, but the 12Z CMC was noted to be slowest and results in a more amplified/closed low solution for Sunday afternoon over south-central Canada. the 12Z CMC shows toward the deeper/slower side of the available ensemble spaghetti height members early Sunday. Greater support is in place for a broad non-12Z CMC blend. ...Surface low tracking across the Upper Midwest/Great Lakes this weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM, 00Z GFS, 12Z ECMWF blend Confidence: Slightly above average There has been convergence with this system compared to yesterday with the 500 mb shortwave and surface low track across the central U.S. into the Great Lakes. The 00Z NAM/GFS are slightly quicker with the upper trough axis and a bit east with the surface low position by 12Z/10 compared to the 12Z ECMWF/UKMET/CMC. While the 12Z ECMWF is more in line with the ensemble means, given gradual trends in the spaghetti height plots over the past 3 cycles to be faster, blending the 12Z ECMWF with the 00Z NAM/GFS seems best at this time. The 12Z CMC differs enough from the consensus due to differences with an upstream wave over Canada to bring the 12Z CMC solution out of line with the remaining consensus, contrary to trends. ...Closed low over Washington this morning, interacting with the next Pacific trough/surface low nearing California on Saturday, developing into a large closed low over or just offshore of California Monday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM, 00z GFS, 12Z ECMWF blend Confidence: Average Several pieces of energy coming out of the eastern Pacific will eventually carve out a deeper trough over the west coast late in the weekend, while interacting with a retrograding closed low over the Pacific Northwest. There is fairly good agreement with a surface low tracking south off of the West Coast and the eventual large closed low that develops near the California coast, but the 12Z UKMET is displaced farther inland compared to the remaining consensus at 500 mb. This is reflected in the ensemble spaghetti heights as well with a better consensus for a 00Z NAM, 00Z GFS and 12Z ECMWF blend with the 12Z CMC a secondary option. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto