Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 253 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: 00Z ECMWF The 00Z GFS and especially the 00Z UKMET/ECMWF solutions have trended faster with the northward and then north-northeastward advance of Tropical Storm Isaias up across the Carolinas, Mid-Atlantic and Northeast over the next 48 to 60 hours. Meanwhile, the 00Z CMC trended a tad slower from its previous run, with the 00Z NAM ultimately quite slow and definitely a slower outlier. The GFS and UKMET outpace the 03Z NHC track after about 24 hours, with the GFS a tad left of the NHC track. However, the 00Z ECMWF and to an extent the 00Z CMC are very close to the NHC track, with the ECMWF just a tad left of the NHC forecast. One concern with the CMC though is its erroneously weaker surface reflection of the storm. Regarding the 00Z HREF suite of guidance through 48 hours, the members are left of the NHC track with exception of the 00Z ARW which is closer and is just a tad left of the NHC forecast. Yesterday's 12Z ECENS mean is the only solution favoring the slowest guidance like the NAM, but the 00Z GEFS mean is faster and is generally a blend of the GFS, UKMET and ECMWF solutions which means it is just a little faster than 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 60 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/ECMWF Confidence: Slightly above 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 00Z UKMET gradually becomes a weaker and somewhat more progressive outlier with the energy. Meanwhile, the 00Z CMC still eventually ends up a tad slower and deeper with the energy as it digs down across the Midwest by the end of the period. The 00Z NAM/GFS/ECMWF solutions are generally well-clustered in between the UKMET and CMC solutions, so a blend of these models 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 thus a general model blend will be preferred. ...Upper trough approaching the Pacific Northwest Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM 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 00Z NAM is now a tad on the strong side with its height falls compared to the well-clustered global models. Therefore, a non-NAM 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