Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 104 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: Slightly 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. There is some modest spread with the track of the surface low as the 00Z NAM/GFS solutions are a tad left of the 12Z non-NCEP model guidance, but there is sufficient clustering that a general model blend can be preferred with this energy. ...Hurricane Isaias... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 03Z NHC advisory package Best model proxy: Closest to the 00Z GFS The 03Z NHC forecast track of Hurricane Isaias is overall closest to the 00Z GFS, but after about 48 hours, the GFS ends up being somewhat faster than the NHC track. The 00Z NAM/12Z UKMET and 12Z ECMWF all end up being slower as the system makes a landfall across eastern SC and southern NC, and then northeastward across the remainder of the Mid-Atlantic coastal plain going through 72 hours. The 12Z CMC for its part is even faster than the GFS, and ends up left of the NHC track. 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 60 hours Non-GFS blend...after 60 hours Confidence: Slightly above 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 ends up with a closed low north of the model consensus over Ontario. The guidance is at least in good agreement through 60 hours, and so a general model blend will be preferred to that point, followed thereafter by a non-GFS blend. ...Upper low/trough approaching the Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z NAM/GFS 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 support 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 12Z CMC/ECMWF solutions are weaker and faster, with the 12Z UKMET slower. The preference will be toward the NAM/GFS 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