Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 221 AM EDT Thu May 21 2020 Valid May 21/0000 UTC thru May 24/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Cut-Off Low Over Lower OH and TN River Valleys... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 60 hours Non-GFS blend...after 60 hours Confidence: Above average Overall, the 00Z NAM/GFS solutions and the 00Z non-NCEP models are in good agreement with the details of the cut-off upper low currently over the TN Valley which should lift north through the OH Valley on Friday before turning east across the northern Mid-Atlantic region on Saturday. However, gradually the GFS begins to accelerate the system offshore a tad faster than the remaining guidance and the latest ensemble means after 60 hours. Will prefer a general model blend through 60 hours, and then a non-GFS blend after 60 hours as the system moves offshore and out to sea. ...Deep upper trough/closed low over the northern Rockies... ...Secondary upper trough over the Pacific Northwest by Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 60 hours Non-UKMET blend...after 60 hours Confidence: Slightly above average The latest guidance shows very good agreement in taking the upper trough and associated closed low over the northern Rockies northward into southwest Canada over the next 24 hours. As this occurs, a new upper trough and associated closed low will be advancing southeast in across the Pacific Northwest. This energy will reload a full-latitude trough across the West by Saturday. By Sunday, the trough will begin to edge east toward the Plains. The models are in good mass field agreement through about 60 hours, but thereafter the 00Z UKMET is a bit more out of phase with the other deterministic models, especially with its closed mid-level low center over western WY at the end of the period. The UKMET is also perhaps still just a tad too slow in advancing energy off to the east toward the Plains. This slower evolution is also evident at the surface, as the UKMET is a tad slower than the remaining models with its frontal evolution. So, will prefer a general model blend through 60 hours, and then a non-UKMET blend thereafter. ...Shortwave lifting northeast across the Midwest by late Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Slightly above average Ahead of the deep layer troughing over the western U.S., the models allow a shortwave trough to lift northeast from the southern High Plains and across the Midwest by late Friday. The guidance favors some amplification of this system with a closed mid-level low center forming Friday night over eastern NE and then lifting through the upper Midwest on Saturday. The energy will then begin to weaken over the Great Lakes by Sunday as it attempts to crest the deep layer ridge forming and nosing northward by then over the OH/TN Valleys and Southeast. Overall, the 00Z UKMET is the weakest solution with this energy. The remaining guidance is reasonably well clustered, and so a non-UKMET 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 Orrison