Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1259 AM EDT Mon Aug 03 2020 Valid Aug 03/0000 UTC thru Aug 06/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave/low center exiting the lower Great Lakes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The guidance is in very good agreement on the details of the exiting shortwave/surface low over the lower Great Lakes region, so a general model blend will be preferred with this system. ...Tropical Storm Isaias... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 03Z NHC advisory package Best model proxy: 18Z GEFS mean The 03Z NHC forecast track of Tropical Storm Isaias is generally in between the faster 00Z GFS/12Z CMC solutions and the slower 00Z NAM/12Z UKMET and 12Z ECMWF solutions. However, the NHC track is overall a bit to the right of all of the global model guidance through 48 hours as the storm approaches and makes landfall across the Carolinas and lifts through the Mid-Atlantic states. The same applies to all of the 00Z HREF suite of guidance through 48 hours, although the 00Z ARW is fairly close a tad left of the NHC track. Thereafter, as the system advances rapidly through the Northeast, the UKMET/ECMWF solutions bring their tracks a bit east of the NHC track. The 12Z ECENS mean still favors the slower guidance, but the 18Z GEFS mean does a nice job of favoring a compromise between the faster and slower global model camps, and appears to be the best model proxy at this time to the latest NHC track even though the GEFS mean is a tad left of the NHC forecast. Please consult the latest NHC forecast advisory package for more details. ...Broad trough from the Great Lakes to the Gulf Coast... ...Closed low over Ontario... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A broad trough extending from the Great Lakes down to the central Gulf Coast on Monday will be key in allowing Tropical Storm Isaias to lift north and then north-northeast up along the Eastern Seaboard over the next 48 to 72 hours. The models are in good agreement in maintaining the broad trough through the period, but with some stronger northern stream energy over the Great Lakes region favoring a closed low evolution up over Ontario. Sufficient agreement is noted with the global models such that a general model blend can be preferred. ...Upper trough crossing the Pacific Northwest Monday... ...Energy dropping down over the Northern Plains/Midwest for Tuesday/Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z NAM/GFS and 12Z ECMWF Confidence: Average An upper trough will cross in through the Pacific Northwest on Monday and cross far southwest Canada before then dropping southeast and digging across the northern Plains and Midwest Tuesday and Wednesday. The 12Z UKMET gradually becomes a weaker and somewhat more progressive outlier with the energy. Meanwhile, the 12Z CMC does the opposite and becomes a slower and deeper outlier. The 00Z NAM/GFS and 12Z ECMWF are all well clustered in between these camps, and thus a blend of these solutions will be preferred. ...Southern stream trough moving into CA by Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in very good agreement with this energy, and a general model blend will be preferred. ...Upper trough approaching the Pacific Northwest Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Above average A relatively deep trough will be approaching the Pacific Northwest by late Wednesday and the models are overall in very good agreement with their timing and depth. However, the 12Z CMC is perhaps a tad too slow by Thursday as the energy begins to advance inland. Therefore, a non-CMC blend will be preferred with this next trough. 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