Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 249 PM EDT Fri Mar 30 2018 Valid Mar 30/1200 UTC thru Apr 03/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...Including Model Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Surface low lifting northeast through New England today and associated trailing cold front down the East Coast... ...Secondary shortwave pushing from the Mid Mississippi Valley to the Mid Atlantic behind primary cold front... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models handle the mass field details of these systems similarly and so a general model blend will be preferred. ...Shortwave digging into the Northwest today with a surface low dropping down over Montana... ...Surface low evolution across the Upper Midwest/Great Lakes through Saturday... ...Trailing cold front sweeping across the Northeast by Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models have come into considerably better agreement over the last 12 hours compared to model cycles 24 to 48 hours ago with this system. Earlier runs of the NAM and ECMWF which were north of the more consistent GFS have come into agreement on a farther south solution and are close or perhaps just a shade north of the GFS with today's 12Z cycle. The only model that may still be out of tolerance at this point is the 12Z CMC which appears to be a little too weak, but overall a consensus approach will be preferred and thus a general model blend to resolve the smaller scale detail differences that remain. ...Low-amplitude shortwave reaching the Oregon coast on Saturday... ...Shearing downwind toward the High Plains by Sunday and Mid Atlantic by Sunday Night... ...Surface wave activity from the Lower Mississippi/Tennessee Valleys to the Mid-Atlantic... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM, 12Z GFS and 12Z ECMWF Confidence: Average...becoming below average The models generally agree that a low-amplitude shortwave will be pushing through portions of the West this weekend before gradually shearing downstream across the central High Plains on Sunday and then all the way to the Mid-Atlantic region by early Monday. The models are in good agreement with this feature on the large scale going through early Sunday, but then there are more meaningful differences noted by Sunday night and Monday as the remnant vort energy translates downstream toward the Mid-Atlantic region. Generally the 12Z NAM, 12Z GFS and 12Z ECMWF tend to hang onto a bit more definable vort energy and thus a bit more defined surface wave development along a front that will extend from the lower Mississippi valley northeast across the Tennessee Valley and to the southern Mid-Atlantic region Sunday into Monday. The 12Z CMC trended slightly toward the more defined consensus, with the 12Z UKMET at this point the weakest/flattest. There is support in particular from the euro ensemble members for a better defined surface wave, and growing support from the latest GEFS members. So will lean toward the more developed consensus as per the NAM, GFS and ECMWF solutions. Confidence in the exact details remains limited though by the late Sunday and Monday time frame. ...Large scale trough digging into the Northwest by late weekend... ...Surface cyclogenesis over the High Plains Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 12Z ECMWF Confidence: Slightly above average Additional height falls will be digging toward the Northwest U.S. by late in the weekend, as a strong shortwave trough over the northern Gulf of Alaska amplifies southeastward across British Columbia. The models have come into better agreement on the idea of a rather strong trough dropping into the Northwest by Sunday night but there remains some differences with the depth and progression. The 12Z UKMET is a bit deeper than the model consensus and gradually the 12Z NAM supports a somewhat more progressive trough. The faster NAM in particular results in a more progressive surface low evolution across the northern High Plains on Monday as low pressure develops in the lee of the Rockies. The NAM aside from being more progressive appears in general to be too far north with at least its initial wave that impacts the Dakotas. Generally the better model clustering and ensemble support resides with the 12Z GFS and 12Z ECMWF, and a blend of these solutions will be preferred. ...Lingering trough and stalled surface front in the vicinity of Florida this weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Slightly above average The models stall out a front across the Florida Peninsula this weekend as a weak mid level trough traverses the eastern Gulf of Mexico, the Florida Keys and Cuba. The 12Z NAM overall is the slowest solution with the trough, with the remaining models rather well clustered. Will prefer a non-NAM blend with 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 Orrison