Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1245 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 NAM/GFS Evaluation with Preliminary Preferences/Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low crossing Ontario through Sat... ...Associated cold front crossing the Great Lakes Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/UKMET/12Z ECMWF mean Confidence: 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. The 00Z ECMWF/12Z ECMWF mean/00Z UKMET have been consistent with the track of the short wave and its interaction with the mid level system downstream across New England, as well as its associated cold front. Based on the consistency, the abovementioned model blend is preferred with this system, but the spread in the NCEP versus non-NCEP guidance results in only average forecast confidence. ...Low pressure moving northeast along Eastern Seaboard into this weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/00Z UKMET/12Z ECMWF mean Confidence: 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. In contrast, the 00Z ECMWF/UKMET/12Z ECMWF mean keep a stronger surface low (driven mainly by convective processes) and track it northeast along with and just ahead of the mid level system. These models have been more consistent with the track of the surface low, though each as been faster with the track over the past three model cycles. At this point, the key to the track of the surface low will be whether the system remains stronger (favoring a track further east), or remains weaker and is pulled more westward by the mid level system. Based on continuity, the non-NCEP guidance is preferred with the surface track. However, based on the fair amount spread and its implications for the QPF, forecast confidence is average at best. ...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: General 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. This is close to the model consensus with respect to timing and strength, though the non-NCEP guidance becomes a bit faster as the short wave moves across the OH Valley by Sun. However, the differences are not sufficient to deviate from a general model blend for a 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