Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 251 PM EDT Wed Jun 17 2020 Valid Jun 17/1200 UTC thru Jun 21/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 19Z Update: The 12Z CMC trended closer to the model consensus with the upper low lifting northward across the Appalachians, with the 12Z GFS noted as the most progressive by 00Z Sunday. There has been a slightly more amplified trend with the non-NCEP guidance with the trough crossing the central and northern Plains Friday night and Saturday, with the GFS still indicating the strongest solution. The CMC still remains west of the model consensus with the main upper low across south-central Canada and not much different from its 00Z run. Eastern U.S. closed low and coastal front ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 00Z Saturday, then non-GFS blend Confidence: Moderate-High The cut-off upper low that is currently parked over western North Carolina is expected to gradually lift north across the Appalachians and eventually reach the Northeast U.S. by this weekend as it slowly evolves into an open wave aloft. This is supporting a surface low over eastern North Carolina that is fueling convection and heavy rain for portions of the Southeast and Mid-Atlantic region. The models are indicating very good synoptic scale agreement on the progress of the upper level system through Friday evening, after which the GFS and its GEFS mean are a little quicker with the westerlies absorbing the trough. In contrast, the CMC tends to keep the closed low intact and farther south on Saturday. At the surface, the 00Z UKMET is slightly stronger with the low, but still within the realm of possibilities. Therefore, blending the ECMWF/UKMET/NAM should work well after 00Z Saturday. Closed low moving into the Northwest Tuesday into the Northern High Plains by Thursday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 12Z Friday, then 12Z UKMET/ECMWF/EC mean blend Confidence: Moderate The upper level low over the northern Rockies is expected to become absorbed by a second evolving upper low over south-central Canada by Thursday morning. This will sustain an occluded surface low and a slow moving cold front across the central and northern Plains through the end of the week. The two main differences noted in the guidance is a more amplified solution with the 12Z GFS across the Plains regarding height falls, and this also holds true for the NAM by Saturday morning. The 00Z CMC becomes displaced to the west of the model consensus by 12Z Friday with the closed low over south-central Canada, but it does not appear to affect QPF too much across the Plains. Therefore a blend of the 00Z ECMWF/UKMET/EC mean should suffice as a starting point in the forecast process. Trough approaching the Pacific Northwest by Friday night ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/NAM/GFS Confidence: Moderate A shortwave trough pivoting around a broad upper level gyre over the Gulf of Alaska is expected to reach the offshore waters of the Pacific Northwest and Vancouver Island by Friday evening, accompanied by a slow moving cold front. The 00Z UKMET is slowest in bringing this trough towards the British Columbia coast, and this is more evident with its surface low being much slower than the model consensus by 12Z Friday. By the end of the forecast period Saturday evening, the CMC is more amplified with the second shortwave trough to pivot trough the region. There is enough model agreement among the NCEP guidance and the ECMWF to merit a blend of those models with average confidence. Hamrick Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml