Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 220 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/00Z 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 stronger than the GEFS mean. Multiple CMC runs had been west of the model consensus regarding the main upper low over south-central Canada, but the 12Z CMC is now much closer to the consensus and can be part of the blend. The NAM remains on the stronger side of the guidance. A blend of the UKMET/ECMWF/CMC should serve well as a starting point in the forecast process. Troughs approaching the Pacific Northwest through Sunday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: NAM/UKMET blend Confidence: Limited-Moderate Shortwaves rotating around the broad Gulf of Alaska Gyre will keep an active weather pattern in place going into the weekend off the Pacific Northwest Coast. The first perturbation to move through is expected to reach the British Columbia coast Friday night, along with a well defined surface low and trailing cold front. Except for a slightly slower cold front with the 12Z UKMET, the models are in decent agreement on this system. The second storm system begins approaching the region by Sunday night, and there are more noteworthy differences in the timing and evolution of this event. The GFS is faster with the surface low and a little ahead of the GEFS mean, whereas the ECMWF is much slower and well to the west. The CMC is suggesting the low track farther south and considerably weaker with little ensemble support. There is reasonably good agreement among the NAM and UKMET with this low, and between the GFS and ECMWF solutions. This blend should serve well as a starting point, along with some of the 12Z GEFS mean. Hamrick Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml