Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 253 AM EDT Sun Aug 02 2020 Valid Aug 02/0000 UTC thru Aug 05/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Mid-level trough digging across OH/TN Valleys... ...Surface low crossing the Lower Great Lakes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Mid-level troughing over the OH/TN Valleys will lift northeast and drive a surface low across the lower Great Lakes region on Sunday before then advancing into southeast Canada. The models are in good agreement and thus a general model blend will still be preferred. ...Hurricane Isaias... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 03Z NHC advisory package Best model proxy: GFS/CMC/UKMET/ECMWF blend The 03Z NHC forecast track of Hurricane Isaias is overall closest now to a multi-model blend consisting of the 00Z GFS, 00Z UKMET, 00Z CMC and 00Z ECMWF. Of these solutions, the GFS and CMC end up generally a little faster than the NHC track, especially after 48 hours, and with the UKMET and ECMWF a little slower. The ECMWF is also seen as being a bit left of the NHC track as the system makes a landfall across eastern SC and southern NC, and then advances northeastward across the remainder of the Mid-Atlantic coastal plain going through 72 hours. The 00Z NAM for its part ends up being the slowest and farthest west solution by the end of the period. However, all of the models support the system rapidly lifting through New England by the end of the period. Please consult the latest NHC forecast advisory package for more details. ...Northern stream trough setting up over the Great Lakes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 48 hours 00Z GEFS/12Z ECENS blend...after 48 hours Confidence: Average Northern stream energy will be digging down across the Great Lakes through Sunday with likely development of an elongated closed low a bit farther north over Ontario by Monday and Tuesday. By the end of the period, the 00Z GFS and 00Z ECMWF suggest a closed low north of the model consensus over Ontario, with the 00Z NAM farther south. The 00Z CMC and 00Z UKMET split the difference, but the 00Z GEFS mean and the recent 12Z ECENS mean cluster well and approximate the model consensus. The guidance is at least in good agreement through 48 hours, and so a general model blend will be preferred to that point, followed thereafter by a blend of the 00Z GEFS mean and yesterday's 12Z ECENS mean. ...Upper low/trough crossing the Pacific Northwest... ...Energy dropping down over the Northern Plains/Midwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z NAM/GFS/CMC Confidence: Average An upper trough will cross in through British Columbia and the Pacific Northwest late on Sunday and then well inland through Monday and Tuesday with the main focus of the height falls remaining across western and central Canada. However, the guidance supports some energy in the base of the trough separating out across the far northern Rockies and then advancing southeast by Wednesday across the northern Plains and Midwest. The 00Z NAM and 00Z GFS are on the stronger side of the guidance with this energy over the northern U.S. late in the period. The 00Z ECMWF and especially the 00Z UKMET are notably weaker. However, the 00Z CMC has trended toward the stronger NAM/GFS camp. In fact, the NAM, GFS and CMC would all support a mid-level closed low feature potentially dropping southeast across ND at the end of the period. The preference will be toward the NAM/GFS/CMC camp for the time being since there is a bit of a trend toward stronger energy separating out from the troughing over central Canada. ...Southern stream trough moving into CA by Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A southern stream trough is forecast by the models to move in off the Pacific Ocean by early Wednesday and cross much of California. The models are in very good agreement with the details of this system, so a general model blend will be preferred. 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: www.weather.gov/media/notification/pdf2/scn20-58pmdhmd_termination. pdf Orrison