Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1229 PM EDT Thu Mar 29 2018 Valid Mar 29/1200 UTC thru Apr 02/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...Including Model Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave trough over the Lower Mississippi Valley ejecting quickly northeast in convergent flow to New England by Friday... ...Secondary shortwave over the High Plains reaching the Mid-Atlantic by Friday... ...Surface low tracking from the Lower Mississippi Valley to the Northeast by Friday and associated cold front... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in reasonably good agreement with their mass field details concerning the evolution of the Lower Mississippi Valley shortwave trough and associated surface low evolution up across the Northeast through Friday. The guidance also is agreeable with the details of a relatively weak secondary shortwave that arrives across the Mid-Atlantic by Friday. Therefore, a general model blend will be preferred at this time. ...Shortwave over the Gulf of Alaska today, crossing the Northwest on Friday 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: 12Z GFS Confidence: Average The models bring a shortwave down from the Gulf of Alaska and across the Northwest by Friday and allow a surface low to drop southeast across Montana. This energy will then advance across the Northern Plains and Upper Mississippi Valley late Friday and early Saturday with a relatively compact and energetic low crossing the region and reaching the Great Lakes on Saturday. The low will lift across Ontario and Quebec through Sunday with a trailing cold front that will cross the Ohio Valley and Northeast. The 12Z NAM is a bit stronger than the global model consensus with the shortwave and tracks its surface low a little farther north than any other model. The 00Z UKMET is overall the slowest solution again, but has at least been trending more progressive. The 00Z ECMWF also is perhaps a tad on the slow side with its low evolution. The 00Z CMC is the farthest south and weakest with its low track. The 12Z GFS reflects a solution very close to the model consensus. The 06Z/00Z GEFS means favors the GFS solution and the 00Z ECENS mean is only a tad slower than the GFS. Given very good run to run continuity and overall ensemble support, the GFS mass fields will be preferred. ...Low-amplitude shortwave reaching the Oregon coast on Saturday, and shearing toward the High Plains by Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-ECMWF blend Confidence: Average Models generally agree that a low-amplitude shortwave will be pushing through portions of the West this weekend before gradually shearing out. The 00Z ECMWF does appear to be perhaps a little too strong and slow with this system as the remaining model consensus favors a somewhat more sheared/progressive wave. Will suggest a non-ECMWF blend with this feature for now. ...Large scale trough digging into the Northwest by late weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM, 12Z GFS and 00Z UKMET Confidence: 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 00Z CMC and to a lesser extent the 00Z ECMWF are not as amplified with the troughing as compared to the 12Z NAM, 12Z GFS and 00Z UKMET. The 06Z GEFS mean and 00Z ECENS mean tend to favor the more amplified consensus, and so will lean toward a blend of the NAM, GFS and UKMET as a result for now. ...Lingering trough and stalled surface front in the vicinity of Florida this weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 00Z ECMWF 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 00Z UKMET remains the weakest solution with the upper level energy, with the 12Z NAM the strongest and also the slowest. Will maintain continuity with a preference toward the reasonably well clustered 12Z GFS and 00Z ECMWF. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison