Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 236 AM EDT Tue May 01 2018 Valid May 01/0000 UTC thru May 04/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z model evaluation including final preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low/surface low departing from the Northeast today... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similarly with this system. ...Weakening low amplitude shortwave(s) moving into south-central Canada today/tonight... ...Elongated surface trof with main surface low near the upper MS valley this morning and tracking through Ontario/Quebec through tonight... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average After adjustments toward the consensus by the 00Z CMC, relative to its 12Z run, the models now only show small scale differences such that a general model blend can be used for this system. ...Western trof/closed low ejecting into the central Plains on Thursday with deepening surface low in the central High Plains and lingering mid-level troughing across AZ/NM/NW Mexico... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 00Z CMC blend through 12Z/03 75% 00Z ECMWF, 25% 00Z GFS blend from 12Z/03-12Z/04 Confidence: Slightly above average, becoming slightly below average The 00Z CMC adjusted slightly toward the remaining model consensus with its surface low starting Thursday morning over the Plains, but it continues to lie on the northern end of the latest ensemble/deterministic guidance. As the accompanying shortwave over the central Plains nears the Great Lakes Friday morning, it begins to meet with a separate shortwave amplifying southward from Manitoba and Ontario. The 00Z ECMWF/UKMET/CMC remain more amplified with the northern shortwave (although a slightly weaker trend was noted compared to the 12Z cycles), while the 00Z NAM/GFS are flatter. Model trends are inconclusive, but the 12Z ECMWF mean appears to be a reasonable middle ground between the deeper and flatter solutions. This translates close to a 00Z ECMWF/00Z GFS blend, but with more weight on the 00Z ECMWF, concerning a surface low over lower Michigan and the corresponding cold front extending southwestward into the southern Plains. ...Mid-level shortwave approaching British Columbia Friday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 00Z ECMWF blend Confidence: Slightly below average Ensemble trends sped up with the progression of a shortwave off of the British Columbia coast Friday morning, with the 12Z/00Z ECMWF toward the faster side of the latest ensemble guidance. There is fair agreement among the non-ECMWF models, so that will be the preference at this time. Given the uncertainty of the source region over the open Pacific, confidence is slightly reduced. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto