Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 205 PM EST Mon Mar 05 2018 Valid Mar 05/1200 UTC thru Mar 09/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation...along with model preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Central Plains/Midwest storm system today... ...Passing off to developing East Coast nor'easter by Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS/12Z UKMET and 12Z ECMWF Confidence: Slightly above average The models take the negatively tilting trough and evolving deep layer closed low ejecting out across the central/northern Plains off to the east through the Midwest on Tuesday. As this occurs, there will be an increasing degree of binary interaction with a closed low over Ontario with this separate closed low feature beginning to rotate around the north side of the Midwest storm. The models shows very good agreement through Tuesday in taking a sizable portion of energy/height falls with the Midwest system off to the east and toward the Ohio Valley. By Tuesday night, the upper trough should take on a negative tilt across the Ohio Valley and then the central Appalachians as a 130+kt 250 mb jet max rounds the base of the trough through the Tennessee Valley. This will ultimately allow the system to deepen further and all of the models show a closed low crossing the Mid-Atlantic region on Wednesday before then lifting up across or very near southern New England. The result will be surface low evolution that initially focuses over the upper Midwest but then evolves east-southeast across the Ohio Valley through Tuesday. On Tuesday night, the Ohio Valley low will weaken and secondary low pressure developing over the Southeast coastal plain will lift up off the Virginia Capes by early Wednesday and become the dominant low center. The low will deepen further through Wednesday and Wednesday night as the low lifts just offshore New Jersey, Long Island and adjacent areas of southern New England. On Thursday, the system will lift up across the Gulf of Maine. Model spread with the entire system is mostly centered on the East Coast/nor'easter evolution. The 12Z guidance has generally been shifting the low track farther west. The 12Z NAM which had been on the west side of the model consensus, has gained agreement from the 12Z UKMET in a solution that is farther west and especially as it relates to coastal areas of the northern Mid-Atlantic and New England. However, one concern right now with the NAM is that it is a bit stronger aloft than any other model by Wednesday evening and through Thursday with the nor'easter evolution. This results in a very strong deformation zone wrapping farther back to the west over the Northeast. The 12Z GFS at the surface is a little east of the NAM/UKMET cluster. The 12Z CMC has also trended a bit farther west, but is still generally a little east of the model consensus, with the 00Z ECMWF the farthest east solution. UPDATE: The 12Z ECMWF has trended in tandem with the other deterministic with a notable westward trend in the low track, and is very close to the model consensus. The westward shift in the guidance has been noted in consecutive cycles of the GEFS ensemble members with stronger clustering that is more supportive of the NAM/UKMET camp. This is likely related to the details of a persistent and relatively strong blocking ridge over eastern Canada. It is feasible that some additional westward shifting of the guidance may occur, and especially as it relates to the low track relative to New England since the guidance maintains this blocking pattern. Also, the guidance takes the closed low feature dropping south over Ontario down to the southeast toward the Ohio Valley by Thursday which may help to back the large scale flow enough for the New England closed low/nor'easter to track farther left. Overall, WPC will favor a general model blend through the period given the improved model clustering along the East Coast, but with the greatest weighting toward a blend of the GFS, UKMET and ECMWF as there are concerns that the NAM is too strong aloft. ...West Coast/Northwest U.S.... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 12Z ECMWF Confidence: Slightly above average The large scale flow pattern will consist a deep closed low near 38.5N 142.0W initially that advances off to the east and approaches the West Coast by late Wednesday and then moves inland across the Northwest U.S. through Thursday. Surface low will arrive across coastal Oregon on Thursday along with a well-defined cold front sweeping in across the coastal ranges. The 12Z NAM and 12Z CMC are a bit stronger with the arrival of the system as compared to the 12Z GFS and 12Z ECMWF. The 12Z UKMET appears overall to be tad too weak. The GFS/ECMWF solutions are very well clustered and has very good ensemble support and so will prefer a blend of the GFS and ECMWF at this time. Previous model trends at www.wpc.ncep.noaa.gov/html/model2.shtml Previous 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison