Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1216 AM EDT Fri May 22 2020 Valid May 22/0000 UTC thru May 25/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Cut-Off Low impacting the OH Valley and northern Mid-Atlantic... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average Overall, the global models are in very good agreement with the details of the cut-off upper low drifting north now over the OH Valley which should turn east across the northern Mid-Atlantic region by Saturday and then head offshore. The 00Z NAM rather early in the period becomes slower than all of the global models in advancing the system eastward. Will prefer a non-NAM blend since the global models are tightly clustered in agreement. ...Deep upper trough/closed low reloading over the Western U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 60 hours Non-UKMET blend...after 60 hours Confidence: Average The latest guidance shows very good agreement in bringing a new large scale upper trough and associated closed low in across the Pacific Northwest and through the Intermountain West by this weekend. By early next Monday, the consensus of guidance supports a deep trough edging toward the Plains with a closed low center most likely over the central Rockies. Model mass fields are in good agreement until about 60 hours when the 12Z UKMET suggests the closed low focusing farther north up across WY, where as the remaining guidance suggests it will be down over western or even southwest CO. The latest GEFS mean and ECENS mean favor the more southerly position by the end of the period, and actually even suggest the 00Z GFS could be a tad too far north as the 00Z NAM/12Z CMC and 12Z ECMWF are all a little farther south with the ensemble means. For now, will prefer a general model blend through 60 hours, and a non-UKMET blend thereafter. ...Shortwave lifting northeast across the Midwest by late Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS and 12Z ECMWF 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 NAM is a slower and somewhat deeper outlier with the energy as it crosses the Midwest. On the flip side, the 12Z UKMET is the weakest solution and also a tad more progressive than the model consensus. The best model clustering and ensemble support favors a solution toward a blend of the 00Z GFS and 12Z ECMWF, and so a blend of these solutions will be preferred with this shortwave. ...Shortwave lifting northeast across the southern Plains Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Average As the deep trough and associated close low evolves across the West this weekend and slowly encroaches on the High Plains, there will be a shortwave trough rounding the base of it and lifting northeast across the southern Plains on Sunday. The 12Z CMC is a tad stronger than the remaining guidance and is a bit out of tolerance with the other models with its energy lifting north across central OK by the end of the period, as the remaining models and ensemble means support more concentration of energy/troughing down over central and eastern TX. Will recommend a non-CMC blend 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 Orrison