Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 149 PM EST Sat Dec 15 2018 Valid Dec 15/1200 UTC thru Dec 19/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 12Z UKMET blend Confidence: Slightly Above Average ...19Z update... Changes in the 12Z ECMWF/UKMET/CMC relative to their previous cycles were small but the 12Z UKMET did adjust slightly in the direction of the remaining 12Z model consensus. The 12Z ECMWF adjusted temporarily weaker and farther offshore with the surface low near the New England coast Monday morning but outside of this perceived unfavorable shift, The 12Z ECMWF is similar to its previous cycle and can be used as part of a blend in the overall model preference.. ...previous discussion follows... A progressive, quasi-amplified pattern will be in place over the lower 48 over the next three days with a lot of the active weather focusing across the West after a deep closed low (currently over the Tennessee Valley) exits the eastern U.S. Across the West, a large closed low will open up as it crosses the West Coast Monday morning, followed by a quick moving shortwave to glance the Pacific Northwest late Monday with fast/zonal flow in its wake aimed into Oregon through Tuesday. Model agreement is fairly good through 84 hours (Tuesday evening) with ensembles and trends showing only small differences and changes from run to run. Perhaps the one model that stands out both east and west is the 00Z UKMET with a displaced mid-level and surface low off of the Northeast on Monday and off of the Northwest on Tuesday, differing from the remaining deterministic consensus and the agreeable ensemble means. One other difference worth noting is with the timing of a longwave trough axis across the West on Monday into Tuesday with the 12Z NAM, 12Z GFS and 00Z CMC faster while the 00Z ECMWF and 00Z UKMET are slower. Upstream flow is rather fast moving and overall trends have generally been a bit quicker which makes sense given the pattern...but prefer to stay toward the middle for now given enough spread in the ensemble guidance as seen in the 564 dam height line at 500 mb. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto