Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 512 PM EDT Tue May 26 2020 Valid May 26/1200 UTC thru May 30/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Latest Preferences and Confidence...Updated ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Overall Pattern across the continental U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 12Z Thursday, then 12Z GFS/UKMET/ECMWF blend Exception: 12Z ECENS/GFS/NAM for southeast U.S. coastal low Confidence: Moderate-High The overall weather pattern across the nation will be featured with a large trough and upper low situated across the Plains, and upper level ridge axes across both the West Coast and East Coast to begin the forecast period Tuesday afternoon. The broad upper low slow tracks towards the east from northern Texas to over Arkansas by Thursday, with the block pattern preventing things from becoming more progressive. Meanwhile, a northern stream trough initially over south-central Canada is forecast to amplify over the few couple of days, and will herald a pattern change for much of the central and eastern U.S. by the end of the week as a relatively strong cold front tracks southward from Canada, bringing a high quality airmass for much of the north-central U.S. to close out the week. This building trough will be amplified enough to exert its influence on the southern U.S. closed low, which will then evolve into a phased synoptic scale trough from the Deep South to the Great Lakes by Friday afternoon, and the disturbance off the Florida coast will also lift towards the north. By the end of the forecast period, a well developed upper low approaches central and southern California, which will eventually bring an end to the current heat wave across much of the Desert Southwest and California. Models overall are in very good agreement through about 12Z Thursday nationwide, with some minor differences emerging beyond that. The 12Z NAM tends to hold onto the closed low over the Mid-South a little longer than the remaining guidance, which favors a quicker progression to an open wave that merges with the northern stream trough. It also becomes stronger with the shortwave crossing the Great Lakes. The CMC is noted as slightly stronger with the upper ridge across the Desert Southwest, but otherwise in good agreement with the evolution across the east-central U.S. Model agreement is above average with the upper low approaching California by the end of the week, and a multi-deterministic blend will work quite well for that region. And for the disturbance near the East Coast, the ECMWF begins to stray more towards the northwest with the low on Wednesday across Georgia, whereas the 12Z ECENS is closer to the model consensus in keeping the low closer to the South Carolina coast, before slowly dissipating. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick