Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1258 AM EDT Mon Mar 12 2018 Valid Mar 12/0000 UTC thru Mar 15/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z model evaluation...including model preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave energy crossing the TN Valley... ...Surface low tracking across the Gulf Coast States on Sunday... ...Strong surface low development offshore the East Coast... ...Phasing with strong Great Lakes height falls/closed low... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS and 00Z UKMET Confidence: Average The models take the vigorous shortwave trough currently crossing the TN Valley down to the east-southeast and then offshore the Southeast U.S. coastline by late Monday. As this occurs, strong cyclogenesis will be taking place off the Mid-Atlantic coast, with low pressure then expected to lift north-northeast and offshore New England through Tuesday as the shortwave trough pivots northeast ahead of the strong northern stream height falls/closed low dropping down across the Great Lakes region. Complete phasing of this energy will occur by Wednesday as the Great Lakes closed eventually captures the shortwave ejecting off the East Coast. The 00Z NAM becomes a bit of a stronger outlier with the evolution of cyclogenesis off the East coast with stronger 500/700 mb low evolution and surface reflection as the system approaches southern New England. The NAM also tends to tuck its surface low a little to the left of the model consensus and closer into the coast. The 12Z UKMET and to a lesser extent the 12Z ECMWF had reflected the weaker solutions and both of these models track their initial shortwave trough/energy farther offshore the East Coast through the period before phasing occurs. The 12Z CMC is closer to the 00Z NAM with its low track and is occasionally even west of the NAM, but is not as strong. The 00Z GFS with this run trended a little farther east and is close to the ECMWF low track, but is definitely deeper. The latest 00Z UKMET solution has come and is much different from its 12Z run. The latest UKMET is stronger and is very close to the GFS, except perhaps a little deeper as the system moves up offshore New England. The GFS/UKMET cluster is currently in between the 18Z GEFS mean and 12Z ECENS mean for low track, but seem reasonable for intensity considering gradual degree of phasing. Will favor a blend of the 00Z GFS and 00Z UKMET at this point, given the concern over the NAM in particular being a little too far west and too deep. ...Shortwave over the Great Basin/northern Rockies... ...Energy shearing southeast across the High Plains by Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models all take a shortwave trough out of the Great Basin and then over the northern Rockies through early Monday. Thereafter, the guidance takes the energy around the crest of the large scale ridge axis developing over the West and drops the energy down over the High Plains where it will gradually shear out. The models show decent agreement with timing and depth and a general model blend will be preferred at this point. ...Large closed low/trough approaching the West... ...Surface cyclones offshore the West Coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 36 hours 00Z GFS/12Z ECMWF blend...after 36 hours Confidence: Slightly below average A large deep layer closed low offshore the West Coast will be moving east over the next few days and will approach the West Coast by Tuesday and then begin to spread height falls inland on Wednesday as multiple shortwaves rotate around the base of the trough and lift northeast. This will bring surface low pressure up off the Pacific Northwest on Monday, and then with a new area of low pressure attempting to consolidate by Wednesday offshore as additional energy digs into the base of the trough and arrives across the West Coast. The guidance is reasonably well clustered through 36 hours with the first low offshore. Thereafter, the better model clustering is much more focused on the 00Z GFS and 12Z ECMWF with the next surface low and the upper trough axis arriving along the West Coast. The 12Z CMC along with the 18Z GEFS mean and 12Z ECENS mean support this cluster. The 00Z UKMET appears too weak and the 00Z NAM much too strong. Will lean toward a blend of the GFS and ECMWF as a result. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison