Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1225 AM EDT Wed Aug 05 2020 Valid Aug 05/0000 UTC thru Aug 08/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Longwave trough from the Great Lakes to the Gulf Coast... ...Closed mid level low over Ontario... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The model guidance is reasonably well clustered with the broad longwave trough tracking across the eastern U.S., and weakening as it does so. Otherwise, there is generally good model agreement and continuity with the evolution of the closed mid-level low center as it crosses Ontario into Quebec before reaching Newfoundland by Thursday. Based on the above, a general model blend is again preferred. ...Shortwave crossing the Northern Plains/Upper Midwest... ...Energy lifting into the Northeast by Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in very good agreement taking shortwave energy currently over southern Manitoba down to the southeast across northern Plains on Wednesday before then tracking it across the Upper Midwest and Great Lakes region going through Thursday. On Friday, the energy should then begin to lift up across the Northeast. The model spread is rather minimal through most of the period, although the 00Z NAM/GFS solutions are a tad faster than the 12Z non-NCEP models as the energy arrives across the Northeast by Saturday. For now, a general model blend will still be preferred. ...Southern stream trough moving into CA... ...Closed low development by Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Above average The models are in good agreement bringing a broad upper trough and hints of a closed mid-level circulation in across northern CA on Wednesday. Gradually the trough will advance farther south, but there will be additional upstream shortwave energy offshore that should maintain a trough axis over CA through the period, including likely development of a closed mid-level low center near or just offshore of central CA by late Friday. The 12Z UKMET tends to have a more elongated mid-level low center offshore of CA by the end of the period. The remaining guidance is well clustered on a more symmetrical feature, so a non-UKMET blend will be preferred with this energy. ...Mid-level trough crossing the Pacific Northwest... ...Closed low development over Alberta/Saskatchewan... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS and 12Z CMC Confidence: Slightly above average The models are in very good agreement in taking an evolving longwave trough from the British Columbia/Pacific Northwest coast early Thursday into southern Alberta by early Friday. As it does so, the mid-level trough will be taking on a negative tilt and amplifying with the expectation of a closed low center forming over southern Alberta Friday before then advancing east into Saskatchewan. The 00Z NAM ends up a tad farther south with its trough axis and closed low evolution. Meanwhile, the 12Z UKMET is generally the farthest north with the energy. The 00Z GFS, 12Z CMC and 12Z ECMWF are better clustered, although the ECMWF may be a tad too fast as its energy crosses southern Canada by late in the period. The latest GEFS mean and ECENS mean favor the GFS/CMC cluster a bit more overall, so a GFS/CMC blend will be preferred with this trough. ...Surface low development over the central Plains Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Above average An area of low pressure is expected to develop by Saturday along a front over the central Plains. The 12Z CMC appears to be a tad too far east with its front and low center placement. The remaining guidance is reasonably well clustered a bit farther back to the west, so a non-CMC blend will be preferred for the time being regarding the surface low and front. 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