Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1259 AM EDT Thu Mar 22 2018 Valid Mar 22/0000 UTC thru Mar 25/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM?GFS evaluation...including preliminary preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Departing Nor'easter from the Northeast Coast today... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model compromise Confidence: Above Average The models show similarly with this system. ...Mid-level trough crossing the Great Lakes today and reaching the Mid Atlantic on Friday while gaining some amplitude... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model compromise Confidence: Slightly Above Average Only minor placement differences exist with the latest model guidance concerning the center of the vorticity maximum within the base of the trough axis as it crosses the East Coast late Friday. No single model stands out enough to discount it, so a general model blend is preferred. ...Deep Trough / Closed Low offshore the Northwest thru Friday... ...Opening up into a series of shortwaves crossing the West Coast Friday night through Saturday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 12Z CMC Blend Confidence: Slightly Above Average The 12Z CMC is notably faster with the lobe of shortwave energy forecast to cross the West coast Saturday evening. Outside of this differences, the models are in fairly good agreement. ...Ongoing atmospheric river Event focused into California... ...Related shortwaves ejecting into the Southwest Thursday and Friday... ...Lee cyclogenesis on the Plains, consolidating into a surface low near Kansas Friday evening and moving east toward the southern Appalachians Saturday night... ...Surface low redevelopment off of the Mid-Atlantic coast early Sunday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/12Z ECMWF blend Confidence: Average Differences begin to appear in the models as a shortwave reaches the Plains on Friday, with the 00Z NAM showing a bit quicker than the latest consensus and north with the related warm front crossing the MS valley from northwest to southeast 00Z/24. The 00Z NAM continues to look quicker than the model and ensemble consensus going forward with decent agreement for a non-NAM blend considering previous model cycles. The 12Z CMC on the other side is a bit slower than the consensus. As Sunday morning approaches, surface low redevelopment is expected off of the Mid-Atlantic coast. Due to differences aloft in the 00Z NAM over the Northeast, with a more amplified extension of a closed low over the northern Mid-Atlantic, the NAM is not preferred despite a relatively favorable placement with respect to the ensemble scatter low plots. The 00Z GFS and 12Z UKMET appear toward the southern side of the ensemble spread with these models also a bit weaker. Through 12Z/25 at least, a 00Z GFS/12Z ECMWF blend will suffice for this system. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto