Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1136 PM EST Mon Dec 31 2018 Valid Jan 01/0000 UTC thru Jan 04/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS Evaluation...with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall pattern across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM, 00Z GFS, 12Z ECMWF blend Confidence: Average After the departure of a deepening surface low and accompanying mid-level shortwave from off of New England today, two significant shortwave troughs remain across the lower 48, one in the form of a closed low over the Four Corners region and the other a southward amplifying shortwave through in south-central Canada. There is strong ensemble agreement that these two features do not phase but there are still some timing and placement differences with the southern stream system across the lower Mississippi Valley. Lastly, a progressive shortwave trough is expected to reach the Pacific Northwest coast Thursday night. Ensemble and deterministic trends with the closed low tracking into the southern Plains continue to show some slight slowing compared to yesterday but spread continues to shrink and there is relatively good agreement. However, the 12Z UKMET/CMC are faster than a preferred blend of the GEFS/ECMWF ensemble means. The 00Z NAM, 00Z GFS and 12Z ECMWF show decent agreement with the ensemble means and one another but the 00Z GFS ends up a bit farther south than the ensemble mean position near the lower Mississippi Valley Thursday night, so a blend closer to the 00Z NAM and 12Z ECMWF is preferred with less GFS weight. The northern stream shortwave track through the Great Lakes Wednesday night has good support from the 00Z NAM/GFS and 12Z ECMWF with average spread remaining in the latest ensembles. Across the Pacific Northwest, the 12Z CMC stands out toward the faster side of the latest ensemble members with much stronger support for a slower track near the 00Z NAM/GFS and 12Z ECMWF with the 12Z UKMET a bit on the faster side. Between the NAM/GFS/ECMWF, the NAM is a bit slower and south with the surface low offshore Thursday night, with better ensemble support for a 00Z GFS/12Z ECMWF blend. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto