Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 254 AM EDT Sat Aug 01 2020 Valid Aug 01/0000 UTC thru Aug 04/1200 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 the Mid-MS/TN/OH Valleys... ...Surface low crossing the OH Valley/Lower Great Lakes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z NAM/GFS/UKMET Confidence: Slightly above average Mid-level energy digging southeast across the mid-MS Valley will drive a trough in across much of the TN/OH Valley going through the weekend. This will be reinforced by Sunday by an intrusion of northern stream troughing dropping down across the Great Lakes region but a lead shortwave within the initial troughing will coincide with a surface low tracking across the MS River Valley into the OH Valley and eventually the lower Great Lakes and southeastern Canada through Sunday night. The 00Z NAM/GFS solutions and the 00Z non-NCEP camp of guidance are mostly in strong agreement on the synoptic scale set-up, along with the details of the ejecting shortwave and attendant surface low. However, the 00Z CMC gradually becomes a weaker outlier with the shortwave energy and surface low and will be dismissed. Additionally, from about 36 hours onward, the 00Z ECMWF begins to outpace every other piece of guidance with the forward progression of this system. The 00Z GEFS mean and yesterday's 12Z ECENS mean are strongly supportive of the well-clustered 00Z NAM/GFS/UKMET solutions, so a consensus of the latter camp will be preferred. ...Hurricane Isaias... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 03Z NHC advisory package Best model proxy: 00Z GFS The 03Z NHC forecast track of Hurricane Isaias is generally faster and to the right of all of the non-NCEP guidance (i.e. 00Z ECMWF/UKMET/CMC solutions) from 24 hours onward, and is generally closest to 00Z NAM/GFS blend through 48 hours. After 48 hours, the NHC track is closest ultimately to the 00Z GFS, but then ends much being notably faster as the 00Z GFS along with the remaining model suite have been trending slower with the system's ultimate recurvature to the north and northeast ahead of the upper trough moving into the OH/TN Valleys over the next couple of days. The 00Z HREF suite of guidance on the other hand, minus the NMMB, takes Isaias to the right of the NHC track through 48 hours. Please consult the latest NHC forecast advisory/discussion for more details. ...Northern stream trough setting up over the Great Lakes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Northern stream energy will be digging down across the Great Lakes region this weekend with suggestion of an elongated closed low developing a bit farther north over Ontario by Monday and Tuesday. The guidance has come into better agreement with the full 00Z cycle, as the CMC/UKMET solutions trended toward the 00Z NAM with placement of the closed low at the end of the period. The 00Z GFS/ECMWF solutions are a tad more elongated off to the northeast across areas of southeast Canada, but given the better clustering seen at this point, a general model blend will be preferred. ...Upper low/trough approaching the Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Average Model differences show up with the trough axis as it nears British Columbia and the Pacific Northwest late on Sunday and then advances inland across the far northern Rockies and adjacent areas of southwest Canada on Monday. The 00Z CMC ends up being on the weaker and more progressive side of the guidance as the energy advances inland. The 00Z UKMET and 00Z ECMWF both gradually end up a little slower than the 00Z NAM and 00Z GFS, but these solutions have trended toward each other with this cycle and suggest a small closed low advancing east across far southwest Canada going through early Tuesday. Will still prefer a non-CMC blend for the time being. 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