Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 156 AM EST Mon Dec 02 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/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. The UKMET which had been 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, has trended a little farther east, but remains on the west side of the model spread. The 00Z GFS is also on the west side of the model spread and rather close to the UKMET. The 00Z CMC and 00Z ECMWF trended a bit farther east and are reasonably close to the 00Z NAM and hires HREF guidance per the 00Z ARW/ARW2 and 00Z NMMB going through 36 hours. After 36 hours, the global models do come into better agreement as the system exits the Gulf of Maine and lifts across southeast Canada. Accounting for a bit of an eastward shift/trend in the low pressure track with the latest hires model suite, and with the global models overall following suit, 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 00Z ECMWF thereafter given favorable clustering and support from the 00Z GEFS mean. ...Upper low offshore the West Coast through Tuesday... ...Energy then crossing the Southwest on Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 36 hours Non-UKMET blend...after 36 hours Confidence: 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 00Z UKMET tends to be a little slower and south of the multi-model consensus as the system approaches the Southwest and advances inland. Will prefer a general model blend through 36 hours, and a non-UKMET blend thereafter. ...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 GFS/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 00Z CMC and 00Z UKMET edge stronger than the remaining guidance as the trough amplifies in across the Northeast. The UKMET also becomes a bit slower than the other models with its timing. On the other hand, the 00Z NAM becomes the most progressive solution which is in part related to its handling of upstream shortwave energy over south-central Canada. The better model clustering and ensemble support resides more with the 00Z GFS and 00Z 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 UKMET/ECMWF and 12Z ECENS mean 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 00Z CMC global is the slowest solution. The 00Z GFS, 00Z UKMET and 00Z ECMWF all split the difference with timing, but at the surface there is latitudinal spread with the surface low. The ECMWF and UKMET are north of the GFS, with the 12Z ECENS mean supporting the ECMWF/UKMET camp. The 00Z GEFS mean has trended toward the ECMWF/UKMET cluster overall, and so based on the latest trends, a blend of the 00Z UKMET/ECMWF and 12Z ECENS mean will be preferred with this system. Confidence remains limited. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison