Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1239 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 and 12Z 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 12Z 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 12Z CMC gradually becomes a weaker outlier with the shortwave energy and surface low and will be dismissed. Additionally, from about 36 hours onward, the 12Z ECMWF begins to outpace every other piece of guidance with the forward progression of this system. The 18Z GEFS mean and 12Z ECENS mean are strongly supportive of the well-clustered 00Z NAM/GFS and 12Z 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 to the right of all of the non-NCEP guidance (i.e. 12Z 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. 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: Blend of the 00Z GFS and 12Z UKMET/ECMWF 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 12Z CMC ends up with a closed low well southwest of the model consensus by Tuesday and is spatially an outlier solution. The 00Z GFS and 12Z UKMET/ECMWF solutions are very well clustered with the details of the trough/closed low and have strong support from the 18Z GEFS mean and 12Z ECENS mean. The 00Z NAM for its part is a tad southwest of this multi-model consensus, but not to the extent of the 12Z CMC. The model preference will toward a blend of the 00Z GFS and 12Z UKMET/ECMWF camp. ...Upper low/trough approaching the Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Slightly below 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 12Z CMC ends up being a weaker and more progressive outlier with the energy as it advances inland. The 12Z UKMET and 12Z ECMWF both gradually end up on the slower and somewhat deeper side of the guidance by late Monday and Tuesday and suggest a closed low center crossing far southern British Columbia or near the border with WA state and far northwest MT. The 00Z NAM and 00Z GFS gradually do favor a closed low evolution but they are a little farther north and faster with this feature and place any closed low generally up across southern Alberta by the end of the period. The 18Z GEFS mean and 12Z ECENS mean are more supportive of the slower UKMET/ECMWF solutions, so there are some uncertainties with depth and timing of this energy toward the end of the period. For now, a non-CMC 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