Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 105 AM EDT Fri Mar 23 2018 Valid Mar 23/0000 UTC thru Mar 26/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS evaluation...including preliminary preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave trough crossing the Mid Atlantic coast today... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Above Average The models show similarly with this feature. ...Deep trough / closed low offshore the Northwest today...opening into a Series of shortwaves moving into the Intermountain West this weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 00Z GFS, 12Z UKMET, 12Z ECMWF Confidence: Average The more significant differences with this feature are tied to a stronger mid-level shortwave forecast to reach the West Coast near 00Z/25. As this feature moves inland, the 00Z NAM shows less amplitude in the 500 mb heights compared to the remaining deterministic and ensemble consensus. The 00Z NAM is also slightly quicker here, but given the highly meridional flow pattern over the eastern Pacific, would tend to think a slower/more amplified progression would fit better to conceptual thinking. The ensemble spaghetti data also shows the 12Z CMC as faster with the leading shortwave as it crosses the Rockies. A 00Z GFS, 12Z UKMET and 12Z ECMWF blend fits well with the latest ensemble data. ...Southern stream shortwave currently over the Southwest...ejecting into the Plains this evening and deamplifying toward the East Coast Saturday night as stronger shortwave drops south into the northern Mid-Atlantic states... ...Lee cyclogenesis in the Plains; surface low moving across the middle Mississippi River valley on Saturday and redeveloping off of the Southeast coast early Sunday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS, 12Z ECMWF, 12Z UKMET blend with initial surface low 00Z NAM/12Z ECMWF/12Z UKMET blend with redeveloped surface low Confidence: Average Trends in the NAM have been slower since yesterday concerning the shortwave as it crosses the Mississippi valley. The 00Z NAM looks the strongest with the mid-level wave as it nears the Mississippi valley, but the more significant trend has been with the corresponding surface low which has trended south valid 00Z/25 compared to older model cycles. This trend has been noted in the ensemble scatter low plots as well but the NAM lies toward the north side of the ensemble guidance. Ensemble spread is more west to east valid 00Z/25 than north to south, so the NAM is considered too far north here. A blend of the 00Z GFS, 12Z ECMWF and 12Z UKMET looks like a better fit to trends and the latest ensemble guidance. Forecast models show a surface low redeveloping off of the Carolinas coastline late Saturday night/early Sunday morning. The GFS/GEFS are faster with a northern stream shortwave amplifying southward over the northern Mid-Atlantic region, which coincides with the surface low off of the Carolinas pushing out east more quickly into the Atlantic. While differences grow quite rapidly into the Atlantic, all models keep the impacts largely away from the coast as Sunday night approaches. Ensemble scatter low plots show greater support for a 00Z NAM/12Z ECMWF/12Z UKMET blend with the redeveloped surface low through 00Z/26. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto