Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1142 PM EST Sun Dec 01 2019 Valid Dec 02/0000 UTC thru Dec 05/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep closed low impacting the Mid-Atlantic/New England... ...Surface low pressure lifting offshore the Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z NAM/HREF...through 36 hours Blend of the 00Z NAM/GFS and 12Z ECMWF...after 36 hours Confidence: Above average Differences with this system are relatively minor aloft, regarding the 500/700 mb closed low positions and strength. However, the 12Z UKMET is a bit slower and farther west with its closed low and surface reflection as the system lifts up offshore New England and through the Gulf of Maine on Tuesday. The 00Z NAM and the hires HREF guidance per the 00Z ARW/ARW2 and 00Z NMMB are rather well clustered with the evolution of the system, and collectively are taking low pressure just a tad east of the global model consensus which is best represented by a blend of the 00Z GFS and 12Z ECMWF at this point. Accounting for a subtle eastward shift/trend in the low pressure track with the latest hires model suite and the NAM/GFS solutions, the latest model preference will be toward a NAM/HREF blend through about 36 hours, and then a blend of the 00Z NAM/GFS and 12Z ECMWF thereafter. ...Upper low offshore the West Coast through Tuesday... ...Energy then crossing the Southwest on Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 36 hours Blend of the 00Z NAM/GFS and 12Z CMC...after 36 hours Confidence: Slightly above average There is rather good agreement with the evolution of the upper low offshore the West Coast through about 36 hours, but thereafter the 12Z UKMET tends to be a little slower and south of the multi-model consensus. Meanwhile, there is a period between about 48 hours and 72 hours when the 12Z ECMWF is on the north side of the guidance, although as the system then ejects across the Southwest later Wednesday, the ECMWF comes back into better agreement with the guidance outside of the UKMET. The 00Z NAM, 00Z GFS and 12Z CMC are clustered together rather well through the period, and are supported by the 18Z GEFS mean, and so a blend of these solutions will be favored after 36 hours, with a general model blend prior to this. ...Shortwave crossing the Northern Plains/Upper Midwest Monday... ...Amplifying across the OH Valley/Northeast Tuesday/Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 48 hours Blend of the 00Z NAM/GFS and 12Z ECMWF...after 48 hours Confidence: Above average The models bring a northern stream shortwave southeast across portions of the northern Plains and upper Midwest on Monday and then drop it down across the OH Valley and Northeast through Tuesday and Wednesday. The guidance is in good agreement with this evolution through 48 hours, but thereafter the 12Z CMC and to some extent the 12Z UKMET edge stronger than the remaining guidance as the trough amplifies in across the Northeast. The UKMET also becomes a little slower than the other models with its timing. The better model clustering and ensemble support resides more with the 00Z NAM/GFS and 12Z ECMWF, and so a blend of these solutions will be preferred after 48 hours. A general model blend will be preferred prior to this. ...Weak shortwave/low clipping the Northern Plains Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS/12Z UKMET and 12Z ECMWF Confidence: Below average The models support a weak shortwave and associated surface low/front clipping the northern Plains late Wednesday and through early Thursday. There is considerable model spread with this feature as the 00Z NAM is a faster and yet deeper outlier compared to the global models. Meanwhile, the 12Z CMC global is the slowest solution. The 00Z GFS, 12Z UKMET and 12Z ECMWF all split the difference with timing, but at the surface there is latitudinal spread with the surface low. The ECMWF is north of the UKMET and GFS, with the 12Z ECENS mean supporting the ECMWF. However, the 18Z GEFS mean looks nothing like the GFS/UKMET or ECMWF solutions and actually favors a solution closer to the NAM. Confidence is below average, but for now the best clustering of solutions would favor a blend of the GFS, UKMET and ECMWF given close proximity of the ECENS mean, so a blend of these solutions will be preferred. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison