Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1245 PM EDT Thu Jun 18 2020 Valid Jun 18/1200 UTC thru Jun 22/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Eastern U.S. closed low and coastal front ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Moderate-High The closed upper low currently over the central Appalachians will gradually weaken and remain nearly stationary through Saturday morning, and then is expected to slowly evolve into an open wave and eventually become absorbed by the westerlies by the end of the forecast period. There is excellent agreement in the latest model guidance with this evolution through Saturday evening. Afterward, as the open wave begins to become absorbed by the approaching trough from the Great Lakes region, the GFS and its ensemble mean become a little faster as the wave tracks towards the northeast. It is still close enough to the model consensus to include as part of a general model blend. Closed low developing over northern high plains ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z UKMET/ECMWF/ECENS blend Confidence: Moderate A closed upper low over Saskatchewan and Manitoba is expected to remain nearly anchored in place over the next few days as it gradually deepens with associated shortwave energy crossing the north-central U.S. this weekend, sustaining a slow moving cold front with multiple waves of low pressure along it. Model differences become apparent by 12Z Saturday with the 12Z GFS more amplified with the trough crossing the central and northern Plains, maintaining continuity from its earlier runs, but with limited support from the GEFS mean. Multiple CMC runs have been west of the model consensus regarding the main upper low over south-central Canada, and the NAM being on the stronger side of the guidance. A blend of the UKMET/ECMWF/EC mean should serve well as a starting point in the forecast process. Trough approaching the Pacific Northwest by Friday night ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: GFS/ECMWF blend Confidence: Limited-Moderate Another fast moving shortwave trough will approach the Pacific Northwest early Saturday which is then expected to remain in place through the weekend. The 12Z GFS is a little faster with the initial surface low coming onshore late Friday night and early Saturday, and the UKMET is closer to the consensus compared to its slower solutions yesterday. Given some of the timing issues, a blend of the GFS/ECMWF would likely yield a desirable result at this time. Hamrick Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml