Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 145 PM EST Thu Mar 01 2018 Valid Mar 01/1200 UTC thru Mar 05/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation...along with model preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Powerful nor'easter impacting the Mid-Atlantic/Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 12Z ECMWF Confidence: Slightly above average The models have come into considerably better agreement compared to recent days with the evolution of a major nor'easter that will be impacting areas of the Mid-Atlantic and Northeast tonight through early Saturday. The 12Z NAM and 12Z GFS have both trended stronger with the upper trough digging across the Ohio Valley that goes negative tilt over the northern Mid-Atlantic region and results in a very strong closed low center south of Long Island early Friday. Strong surface low pressure deepening through the Ohio Valley will be redeveloping just offshore the Mid-Atlantic and will become a very intense low center southeast of New England by late Friday and all of the models agree with that, but the NAM is likely wrapping its low center a bit too far to the north and west, and as a result has a strong mid level deformation zone wrapped farther back to the northwest which results in a heavier QPF axis farther back across especially southeast NY. The NAM also appears to have too much cold air in the boundary layer considering the degree of cold air initially in place, along with the fact that there will be very strong Atlantic inflow which will tend to moderate the thermal profiles in the low levels. Overall, the 12Z CMC appeared to periodically be too weak at least through Friday with the system. The better model clustering is noted with the 12Z GFS and 12Z ECMWF which also has better support from the 12Z UKMET and the latest GEFS mean and ECENS mean. ...Deep closed low impacting the Western U.S. through Saturday... ...Negatively tilted trough approaching the Plains on Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM consensus Confidence: Slightly above average The models all take a very strong closed low south and offshore the Pacific Northwest today which broadens out over the next couple of days while also moving inland across the Intermountain region. This will allow a broad trough to envelope all of the West through Sunday. The guidance though indicates that energy lifting out of the base of the trough by late Sunday will allow the trough to take on a negative tilt toward the High Plains region. There is reasonably good agreement with the guidance through about 60 hours, and then after that the 12Z NAM is a bit of a faster outlier in taking its energy out into the Plains which results in a faster frontal progression. The global models are reasonably well clustered at this time, and so a non-NAM consensus will be preferred. 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