Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1202 PM EDT Tue Apr 10 2018 Valid Apr 10/1200 UTC thru Apr 14/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...with Model Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Northern stream wave moving through New England by tonight... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Models are in very good agreement with this system, and a general model blend is preferred with high confidence. ...Southern stream shortwave moving over the Southeast and reaching the Atlantic Coast by Wednesday morning... ...Slow-moving front in the vicinity of Florida... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Models continue to move into good agreement with this system and the surface ridge building in behind the front. Therefore, a general model blend is preferred. ...Shortwave or lobe of the Hudson Bay low digging into Great Lakes Wednesday and reaching Canadian Maritimes Thursday... ...Weak surface low passing just north of the Canadian border... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS; 00Z UKMET; 00Z ECMWF Confidence: Slightly above average There is fairly good agreement with this system, particularly as the shortwave rotates into the Great Lakes. More divergent model forecasts are seen by Wednesday Night as the shortwave reaches the Atlantic coast. The 00Z CMC shows considerably less amplitude to the wave and has very little support from other models. The 12Z NAM, however, shows a more amplified wave, and the difference between the 500mb heights from the CMC to the NAM by 12.06Z is as much as 50-60m in some spots. The preference is to lean toward the remaining models which form a strong consensus close to the ensemble means. ...Lead shortwave and associated surface wave passing northeast through the Pacific Northwest today... ...Secondary shortwave just behind, reaching the northern Rockies by Wednesday and Great Lakes Thursday... ...Surface low development over the Northern Plains Wednesday, tracking through the Great Lakes Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM; 12Z GFS; 00Z ECMWF Confidence: Slightly above average The GFS, NAM, and ECMWF are clustered fairly close with surface low position and timing with this system, and the preference leans toward a blend of the three given the favorable convergence. The 00Z CMC shows considerably more downstream ridging over the Great Lakes and Northeast, and the sharper wave leads to a surface low that is deeper and a little slower than the other models are depicting. The 00Z UKMET is also on the slower end, particularly as the low moves through the Great Lakes. Both the CMC and UKMET are slower than the GEFS and ECMWF ensemble means. ...Trough and associated surface front arriving on the West Coast on Wednesday, reaching the Plains by Friday with closed low developing aloft... ...Strong lee cyclogenesis over the central Plains Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z UKMET; 00Z ECMWF; 00Z ECMWF Ensemble Mean Confidence: Average Over the past several model cycles, the preference has been to lean closer to the ECMWF ensemble mean and similar models given the consistency it has shown, and that will be the preference here as well. The most similar deterministic model seems to be the 00Z UKMET, which is very close with its mass fields aloft, as well as surface low progression (albeit slightly deeper than the ensemble mean). The 12Z NAM and 12Z GFS push the trough out into the Plains faster, and both are faster than even the 06Z GEFS mean. The 00Z CMC shows a weaker upper level low developing eventually, as it does not concentrate higher vorticity values in the base of the trough like the other models do. The timing is not too different from the ECMWF and UKMET, but the structure of the trough is considerably different. Finally, the 00Z ECMWF is also reasonably close to its ensemble mean, and it is included in the preference. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Lamers