Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1122 PM EST Wed Dec 25 2019 Valid Dec 26/0000 UTC thru Dec 29/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS Evaluation with preliminary preferences/confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS initialization errors do not seem to degrade their short range forecasts. System approaching Pacific Northwest Sunday morning ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: GFS/UKMET compromise Confidence: Above average There are competing factors clouding the forecast picture across the Pacific Northwest and Plains/Midwest by Sunday. A system approaching the Pacific Northwest at that time has a building ridge seen in all the guidance in its wake, which should yield a strengthening system aloft moving towards the region. The 12z ECMWF was out of tolerance with this system as it moved a sharp shortwave out in advance of it which was not seen in any of the other guidance and likely led to too weak of a look with the system near 47N 130W Sunday morning (even when compared to its ensemble mean). A compromise of the 00z GFS/12z UKMET looks ideal with the Northwest system with above average confidence. System moving from the West into the Midwest Fri-Sun ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: ECMWF/UKMET/Canadian compromise Confidence: Average Downstream, the guidance is plagued with stream interaction as the system moving from the West into the Plains starts out unphased but becomes phased with time as a sharply amplified ridge building into western Canada. The quickest solutions with the Plains/Midwest system are the 00z GFS and 00z NAM. Since the flow overall is becoming more amplified, a slower solution in the Plains/Midwest is preferred by Sunday morning since the kicking influence of the system approaching the Pacific Northwest shouldn't be felt quite yet (over 15 degrees latitude/900 miles away). Prefer a compromise of the 12z ECMWF/12z UKMET/12z Canadian with the Plains/Midwestern system with average confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Roth