Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 216 PM EDT Sun Jul 26 2020 Valid Jul 26/1200 UTC thru Jul 30/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Mid-upper level troughing over the northern CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average No changes to the previous thinking. Mid to upper-level energy over southern Canada is expected to close off before settling over Ontario later in the period, while the larger scale trough deepens over the Great Lakes region. At the surface, a pronounced cold front is forecast to march across the northern tier into the Great Lakes while upstream ridging builds over the Canadian Rockies. In the increasingly amplified pattern, the models have converged on a similar idea and show very good agreement through 84 hours with the synoptic pattern. ...Mid-level energy over California/Great Basin... ...Energy advancing southeast across the Plains by Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 72 hours Non-NAM blend...after 72 hours Confidence: Above average A broad upper trough and embedded closed low over CA will drift east-northeast over the next couple of days and cross into the Great Basin around the north side of the subtropical ridge over the Southwest and the southern Plains. This energy then is expected to actually amplify a bit over portions of the northern Rockies by Wednesday and then dig southeast out across the Plains. The models overall show good synoptic scale agreement through most of the period. However, the 12Z NAM does generally appear to be a tad too slow and too far north with its energy over the Plains on Wednesday. The 12Z NAM and 12Z GFS both may also be a tad too strong, but there is room for a somewhat stronger closed mid-level low to evolve over the central Plains by the end of the period considering the notable strengthening of the subtropical ridge over the Desert Southwest. A general model blend will be preferred through 72 hours, with a non-NAM blend thereafter given some of its energy placement concerns. ...Shortwave troughs approaching CA/Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Above average A pair of new shortwaves trough will be approaching the West Coast over the next few days, with one arriving over the Pacific Northwest on Tuesday, and one arriving across CA on Wednesday. Generally the models are in good agreement, with strong exception to the 12Z UKMET which is much too slow with the energy approaching CA on Wednesday. The UKMET overall ends up more out of phase relative to the other models with the energy over the Pacific Northwest and even a rather strong closed low that is situated south of the Gulf of AK at the end of the period. A non-UKMET blend will again be preferred 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