Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 252 AM EDT Thu May 28 2020 Valid May 28/0000 UTC thru May 31/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Amplifying northern stream trough across the Great Lakes and Northeast ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/UKMET/GFS blend Confidence: Moderate-High 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 into the weekend. The main model difference continues to be with the 00Z CMC that is considerably more amplified, and this is similar to its recent 12Z run. The NAM is also stronger, but not to the degree of the CMC. There is enough agreement among the ECMWF/UKMET/GFS to merit a blend of those three models. Closed low over Arkansas that becomes absorbed by northern stream flow ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Moderate-High The broad upper low initially over Arkansas slowly lifts northeastward to southern Illinois by Thursday evening, before becoming absorbed and merged with the building trough from the Great Lakes region. A general model blend works here before the system merges. Tropical Depression Bertha ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Deterministic consensus with greater weighting to 00Z NAM is close to 3Z WPC advisory Confidence: refer to WPC advisory Bertha made landfall along the central coast of South Carolina Wednesday and is currently tracking inland across the Appalachians. As the system weakens, it is forecast by WPC to move northward across West Virginia and then western Pennsylvania before dissipating. Currently, a NAM/GFS blend is close to the 3Z WPC advisory for Bertha before the system weakens and merges with an advancing mid-level trough over the Great Lakes region late Thursday. Subtropical closed low reaching central California by Saturday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through Saturday morning, then 00Z ECMWF/UKMET blend Confidence: Moderate-High The models show good agreement on the track of a closed low approaching central/northern California by Saturday, but differ with timing by Saturday morning and beyond. The 12Z CMC becomes slower with bringing the system inland and south of the ensemble means. By Saturday night, the GFS becomes faster in bringing the shortwave northward on the west side of the building western High Plains ridge, and the NAM indicates the strongest solution as the feature lifts northward across the Pacific Northwest. A general model blend works well through Saturday morning, after which a 00Z ECMWF/UKMET blend would work. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick