Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 254 PM EDT Fri Jul 24 2020 Valid Jul 24/1200 UTC thru Jul 28/0000 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 tracking from the Northwest into the north-central U.S. through the weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A mid-level closed low/shortwave trough will track through southwestern Canada through Saturday with a cold front at the surface and extending into the northwestern U.S. As this energy reaches the northern Plains late in the weekend, it will phase with some southern stream energy lifting through the Front Range and central Plains, which will allow the trough to deepen over the northern Plains and upper Midwest. The latest guidance has come into very good agreement and clusters well enough that a general model blend will be preferred through the period. ...Tropical Storm Hanna... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Official NHC track Best Model Proxy: 12Z GFS/UKMET/ECMWF blend Confidence: See latest NHC products The latest model guidance continues to show fairly good clustering with the track and speed of the T.S. Hanna over the next 24 hours as the system approaches and ultimately makes a landfall along the south-central Texas coastline. The 12Z GFS, 12Z UKMET and 12Z ECMWF are quite close or perhaps locally a tad south of the 15Z NHC track of Hanna, with the 12Z NAM and 12Z CMC a bit farther north and a tad faster leading up to landfall. Some strengthening of the mid-level subtropical ridge north of Hanna should steer the system more westward by Saturday and then west-southwestward Saturday night as the system crosses through the lower Rio Grande Valley. On Sunday, Hanna should be weakening over northeast Mexico. ...Upper low/trough over California... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A broad upper trough and embedded closed low over CA will generally remain in place through early next week, with some tendency for the energy to begin lifting north by the end of the period. Overall, the models are in good agreement through the period with the handling of this energy, so a general model 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