Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 242 PM EDT Thu Jul 09 2020 Valid Jul 09/1200 UTC thru Jul 13/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation with Final Preferences/Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low crossing Ontario through Sat... ...Associated cold front crossing the Great Lakes Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/12Z UKMET blend Confidence: Slightly below average The 12Z NAM/GFS are close to the consensus tracking the closed mid level low from ND into northern Ontario this afternoon into Sat, and are initially close with short wave energy south of it crossing the Upper Great Lakes (through about 11/00z). After that time, the 00Z NAM becomes flatter and a bit faster with the short wave, as it appears to be reacting to the mid level trough to its east. The 12Z GFS is closer to the consensus at that time, but also eventually flattens as it encounters the same mid level system. Both the 12Z ECMWF/UKMET have become stronger with the mid level system, closing it off at various points across the eastern OH Valley into western NY state in response to short wave energy dropping into it from eastern Ontario. Though the strength of the mid level system as changed, the timing is basically the same, so this pair remains the preferred solution. However, due to the change in strength, forecast confidence has been dropped to slightly below average. ...Low pressure moving northeast along Eastern Seaboard into this weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/12Z UKMET/12Z CMC blend Confidence: Slightly below average The 12Z NAM appears to be too fast with the surface low almost from initialization, though it tends to slow a bit toward 11/00z. However, both the 12Z NAM/GFS are faster with the surface low than much of the 00Z non-NCEP guidance, and remains so through 11/12z. The 12Z NAM/GFS are generally weaker with the surface system, and tend to draw it back westward toward the broad long wave trough crossing the Mid Atlantic and New England through the period. Though the trend in the 12Z non-NCEP guidance has been to bring the track of the surface low back west, it is still slower and further east than the 12Z NCEP guidance. The change in the 12Z ECMWF surface low track seems to be tied to how the mid level systems are interacting, as the 12Z ECMWF has closed off a mid level system over the eastern OH Valley. While the change in the 12Z ECMWF is concerning, it seems to have embraced the general westward shift all of the 12Z guidance. In the end, the preference has not change, despite the rather large change in the 12Z ECMWF. However, since it is not clear how the mid level interactions will ultimately impact the surface low track, forecast confidence is dropped to slightly below average. ...Trough moving into the Pacific Northwest Thursday night, crossing the ridge and moving across Upper Midwest by Sat, then diving into the OH Valley by Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 12Z NAM model blend Confidence: Slightly above average The 12Z NAM/GFS are close to the consensus with the mid level trough coming ashore across the Pacific Northwest this evening, which tracks across the Northern Rockies Fri morning, then reaches the Upper MS Valley Sat morning. After ingesting the non-NCEP guidance, it now appears as though the 12Z NAM is the westernmost outlier with respect to the speed of the short wave as it approaches the OH Valley, it has been dropped from the preference. ...Long wave trough closing off over western Canada Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average The 12Z NAM/GFS are close to the consensus taking a closed mid level low from the southern Gulf of Alaska this afternoon to a position along the northwest British Columbia coast 12/00z, as a long wave trough evolves to its south. The 12Z NAM/GFS slow a bit as they close off another mid level low over eastern British Columbia, whereas the non-NCEP guidance is a bit faster, closing it off over northern Alberta. Despite the differences with the mid level closed low, the short wave energy south of the closed low is in remarkably good agreement. Based on this, a general model blend is preferred, but because of the differences in the placement of the closed mid level low late over western Canada, forecast confidence is average. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml This product will terminate August 15, 2020 with the 21Z issuance: www.weather.gov/media/notification/pdf2/scn20-58pmdhmd_termination. pdf Hayes