Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1150 PM EST Tue Dec 31 2019 Valid Jan 01/0000 UTC thru Jan 04/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z model evaluation with preferences/confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low entering Mexico and weakening Wednesday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average Latest guidance has trended better with the closed upper level low over Mexico and its transition/weakening over the next 24-36 hours. Earlier differences between the GFS/ECMWF seem to have lessened and now there is reasonable agreement and clustering with the early 00Z guidance. Beyond 36 hours, the energy becomes absorbed into the developing longwave positively tilted trough across the central US associated with incoming shortwave energy from the Pac NW and central Rockies. Overall, given the improved consistency and model agreement, a general model blend is preferred. ...Amplifying longwave trough across the central U.S. Thursday evening... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 03.00z, then GEFS/ECENS mean blend Confidence: Slightly below average A longwave trough will develop over the Great Plains Thursday into Friday with its associated surface low tracking from the southern Plains toward the Ohio Valley and Great Lakes. There remains fairly good agreement aloft with the 500 mb height evolution but sizable differences at the surface with the low track/strength from 03.00Z onward. The ECMWF and ECENS low plots are on the southern/southeastern spread, while the GEFS/CMCE are further north/northwest. These differences become amplified by the end of the forecast period, with a much below forecast confidence by Day 3. As such, will lean on the GEFS/ECENS for Day 3 given the forecast spread. ...Shortwave trough and surface low approaching Pacific Northwest Friday/Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: GFS/NAM Confidence: Slightly below average There remains a fair amount of spread and timing differences with the approach of the next shortwave trough for the Pacific Northwest in the Friday/Saturday time frame. The trend has been for a faster solution with the low track, which favors the GFS/NAM compared to the non-NCEP solutions which are slower. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Taylor