Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 301 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 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 overall, but by the end of the period, the 00Z GFS and 00Z ECMWF both tend to focus their closed low a little north of the 00Z NAM, 00Z UKMET and 00Z CMC. The UKMET in particular made a notable southward shift from its previous run. The 00Z GEFS mean and yesterday's 12Z ECENS mean both tend to support the farther south consensus. However, since the GFS/ECMWF solutions are not outside the full ensemble spread, they are plausible solutions. So, based on this, a general model blend will be preferred for the period. ...Shortwave lifting northeast across the Midwest by late Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: 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 still seen as being a tad slower and deeper than the global models with this energy. The global models with the 00Z cycle are now very well clustered with their timing and depth, so a non-NAM blend will now be preferred with this system. ...Shortwave lifting northeast across the southern Plains Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Average As the deep trough and associated closed 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 00Z UKMET is a tad stronger than the remaining guidance with its energy pivoting across central and eastern TX, and actually suggests a convectively induced mid-level low center forming over south-central TX by the end of the period. The remaining guidance is at least a bit more subtle with this idea, and so a non-UKMET blend will be preferred with this shortwave energy concentrating across central and eastern TX. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison