Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1239 AM EDT Thu Apr 26 2018 Valid Apr 26/0000 UTC thru Apr 29/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS evaluation including preliminary preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Mid-level shortwave lifting north along the New England coast today, interacting with a northern stream shortwave crossing the Great Lakes... ...Surface low departing from the Northeast today/tonight... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similarly with this system. ...Mid-level energy departing from the lower MS valley this morning and crossing the Southeast by Friday... ...Low pressure lifting from the Southeast to the Northeast Friday and Saturday... ...Phasing with northern stream energy over the Northeast by Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z NAM, 00Z GFS and 12Z ECMWF Confidence: Slightly above average The 12Z UKMET/CMC are a displaced off to the east relative to the better ensemble clustering regarding the surface low as it tracks through the Mid-Atlantic region early Friday. The 00Z NAM, 00Z GFS and 12Z ECMWF show better agreement to the ensemble low plots and the ensemble means. Regarding the phasing energy over the Great Lakes/Northeast for the weekend, there are some timing differences to speak of with the 12Z ECMWF a bit faster than the 00Z GFS, with the 00Z NAM in the middle. The 500 mb pattern shown by the 12Z UKMET is less amplified than the remaining consensus, so the 12Z UKMET is excluded here as well, despite its surface low looking to be in a reasonable spot. ...Positively tilted upper level shortwave crossing the upper MS valley and central Plains today, with the southern portion of the trough reaching the eastern Gulf Coast Friday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The models only show minor placement differences, with a blended approach yielding a solution near a blend of the ensemble means. Given differences are small, a general model blend can be used for this system. ...Closed low evolution toward the West Coast by Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM, 00Z GFS, 12Z ECMWF blend Confidence: Average Good agreement exists with this system until late Saturday, when the 12Z UKMET/CMC depict a sharper mid-level trough axis over the West, while also being displaced toward the southern side of the deterministic spread. The 00Z GFS is a bit faster to move the upper trough to the east, while the 12Z ECMWF is a bit slower. The 12Z ECMWF mean is between the faster and slower camps, and appears to be a decent fit at this time, along with the 00Z NAM, given typical biases in the GFS and ECMWF to be fast and slow, respectively. ...Weak southern stream shortwave ejecting out toward the southern High Plains by Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z NAM, 00Z GFS and 12Z ECMWF Confidence: Slightly above average The models eject a weak southern stream shortwave out of the Southwest and toward the southern High Plains by Saturday. The 12Z CMC and especially the 12Z UKMET are a bit stronger and better defined with the energy as it ejects out across eastern NM and western TX. The 12Z UKMET is a near outlier with respect to the latest ensemble spaghetti heights at 500 mb Friday evening. The 00Z NAM, 00Z GFS and 12Z ECMWF are all a bit weaker and sheared in their appearance, and fit better into the ensemble clustering. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto