Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1248 AM EDT Sat May 30 2020 Valid May 30/0000 UTC thru Jun 2/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Initial Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Upper level trough and cold front across the Eastern U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: GFS/ECMWF/UKMET Confidence: High An amplifying upper level trough over the eastern U.S. will herald a change in the recent weather pattern, with a strong cold front ushering in a pristine airmass from the Great Lakes to the Mid-Atlantic, and also for the Northeast. By the end of the forecast period, the trough axis will likely be across the eastern Canadian provinces. With the exception of a slightly weaker 12Z CMC solutions, the guidance is in excellent agreement through about 12Z Monday. Beyond that, there are some differences regarding whether an upper low pinches off by Tuesday morning, with the GFS, ECMWF, and UKMET on board with this idea. The CMC and NAM continue to support the idea of an elongated trough with no closed low developing yet. Since there is decent ensemble plot support for the GFS/ECMWF/UKMET solution, this will be the preference. Upper level low that reaches northern Mexico on Friday night and becomes slow moving through the weekend ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Moderate-High A broad upper level low over northern Mexico, most evident above 250 mb, is expected to remain nearly stationary underneath the building ridge across the Plains, and slowly move northward by early Tuesday. There is enough model agreement here to merit a multi-deterministic model blend. Trough evolution along the West Coast ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/12Z UKMET/ECMWF for first shortwave General model blend (offshore western trough) Confidence: Moderate An upper level low with subtropical origins will reach northern California by midday Saturday, and then evolve into an open shortwave as it lifts north across the Pacific Northwest and eventually crosses the northern periphery of the Great Plains upper ridge over south-central Canada. When that system exits, the trough rebuilds across the West Coast region as the overall synoptic pattern becomes more amplified, and should eventually become a cut-off low situated off the coast of southern California by Tuesday morning. The GEFS ensemble members are slightly stronger than the ECENS members with the large scale trough developing by the end of the forecast period, and right now a general model blend should suffice. There is increasing model spread with the shortwave crossing southern Canada and confidence decreases beyond 12Z Monday, so therefore a blend of the GFS, UKMET, and ECMWF should be a good starting point. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick