Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 240 PM EDT Thu May 28 2020 Valid May 28/1200 UTC thru Jun 01/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Amplifying northern stream trough across the Great Lakes and Northeast through Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/UKMET/CMC blend through 00Z/31, then a general model blend Confidence: Slightly above average A northern stream, mid-level shortwave trough initially over south-central Canada and the upper Mississippi Valley is forecast to amplify and track east into Saturday. As energy in the base of this trough translates eastward, some timing differences develop with the 12Z GFS fastest and 00Z CMC slowest. The 12Z CMC sped up from its 00Z run and the 12Z ECMWF nudged only slightly faster. Meanwhile the 12Z UKMET remains similar with timing compared to its previous 00Z cycle. The 12Z ECMWF/UKMET/CMC fit the timing of the ensemble means best while the 12Z NAM is close but a slight bit slower. This mid-level shortwave will quickly brush northern New England Saturday morning. On the heels of the advancing shortwave across the Northeast, additional amplification of a longwave trough over the eastern half of Canada into the Great Lakes and northeastern U.S. is expected. From Saturday night into Sunday night, a -1 to -1.5 standardized 500 mb height anomaly will set up over the northern Mid-Atlantic and Northeast in association with the upper level trough. This is good model agreement with the depth and timing of the trough for the latter half of the weekend, resulting in a general model blend from late Saturday through Sunday. ...Closed low over Arkansas and Missouri that becomes absorbed by northern stream flow... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The 12Z models show similarly with this system. ...Closed upper level low that reaches northern Mexico on Friday and becomes slow moving through the weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average A compact closed upper level low, quickly tracking south into the southern High Plains this afternoon, is expected to reach northern Mexico Friday morning and slow its movement before briefly stalling through Saturday morning. A slow drift of the 500-300 mb upper low toward the south and west across north-central Mexico is forecast on Sunday. While there are some minor timing/placement differences among the 12Z deterministic guidance, stronger trends in the 12Z UKMET/CMC allows for their inclusion into a general model blend for the preference. ...Post-Tropical Cyclone Bertha... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average All of the latest guidance is in good agreement with taking the surface low associated with Bertha toward the north into southeastern Quebec late Thursday evening. Dissipation of the remnant low is forecast through Friday morning ahead of an approaching cold front. ...Subtropical closed low reaching central California by Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through Saturday morning, followed by a 12Z NAM, 12Z GFS and 12Z ECMWF blend Confidence: Average 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 00Z UKMET shows more amplification with an upstream trough axis over the eastern Pacific, interacting more with the CA closed low resulting in a merged trough axis just west of CA/OR late Saturday afternoon and west of the model consensus into Sunday morning. Meanwhile, through Saturday night, the 00Z CMC shows slightly more separation between the two features. While some minor longitude differences exist among the 12Z NAM and the 12Z GFS/00Z ECMWF, a blend of these 3 models is recommended given their agreement with one another and the latest ensemble guidance. No significant changes were noted with the 12Z ECMWF/UKMET/CMC compared to their previous 00Z cycles. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto