Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1259 PM EDT Wed Apr 04 2018 Valid Apr 04/1200 UTC thru Apr 08/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS evaluation...including preliminary preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Upper Level Trough over the Great Lakes this morning wrapping into east side of Hudson Bay Low by tonight... ...Occluding surface low moving into Quebec today and tonight... ...Trailing cold front sweeping to the East Coast on Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similarly with this system. ...Peripheral shortwave around Hudson Bay low rotating south into the Northern Plains by late Thursday and digging into the Great Lakes Friday morning... ...Leading low amplitude shortwave dropping southeastward from western Canada, reaching the Great Lakes late Thursday... ...Associated surface cyclogenesis across the Great Lakes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 12Z NAM, 12Z GFS and 00Z ECMWF Confidence: Average The 00Z UKMET/CMC remain slower with the leading low amplitude shortwave moving across the Midwest Thursday night, while the 12Z NAM trended a bit faster with the 12Z GFS and 00Z ECMWF in the middle. Run to run changes are still occurring in the guidance but ensemble means support a broad blend of the 12Z NAM, 12Z GFS and 00Z ECMWF with this system...both aloft and at the surface. ...Low-amplitude shortwaves pushing into the Western U.S. in split flow through Friday... ...Surface low development over the Southern Plains Thursday associated with one of the waves, developing east into the Southeast for Saturday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: nearest to the 00Z ECMWF Confidence: Average No discernible differences or preferences with the lower amplitude waves are noted until early Saturday as one of the shortwaves begins to amplify east of the Plains. The 12Z GFS is much faster and flatter with this wave, resulting in a quicker surface low track across the Southeast and Mid-Atlantic coast. The 12Z NAM is also a bit faster and more amplified across the Southeast with the 500 mb trough axis. The 00Z ECMWF appears to be the closest match to the preferred solution, but a nudge toward the NAM/GFS cannot be ruled out in future cycles. ...Large upper level low and trough approaching British Columbia by Thursday with occluded marine surface low offshore... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The models show similarly with this system. ...Strong shortwave pushing toward the Pacific Northwest by Friday Night with new surface low development just south of the prior occluded cyclone... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 00Z CMC blend Confidence: Average Only the 00Z CMC stands out with a slower and less amplified wave approaching the West Coast. While the 12Z NAM/GFS remain quicker, the ensemble trends and latest means support a blend between the faster NAM/GFS and slower ECMWF/UKMET. These relatively minor timing differences outside of the 00Z CMC can be worked out with a 12Z NAM...12Z GFS...00Z ECMWF and 00Z UKMET blend. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto