Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 130 PM EST Sun Jan 12 2020 Valid Jan 12/1200 UTC thru Jan 16/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Large Scale Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Average 19Z update: The 12Z ECMWF/UKMET/CMC still are showing a slower progression of the polar vortex over interior western Canada through the period, solidly putting the GFS as a fast outlier at this point. The 12Z CMC did trend a tad faster toward the GFS solution, roughly a middle ground between the slowest (ECMWF) and fastest (GFS). The NAM/UKMET lie in the middle as well. With this in mind, will still lean towards a non-GFS blend preference. A broad large scale trough is expected to develop over the CONUS through the next few days as a result of a closed, slowly moving low settles across interior western Canada. A strong impulse riding the periphery of this feature lifts through the central US and Great Lakes region Monday/Tuesday followed by a couple different shortwaves mid week (another central US shortwave and then a Pacific Northwest low). The largest and most significant model differences are attributable to the polar vortex over western Canada and its progression (or lack of) eastward in the increasingly shearing, zonal flow by the end of the forecast period. The GFS has consistently been shearing the vortex too quickly eastward ahead of all the other available global deterministic guidance. Its 12Z solution remains way ahead of even the GEFS mean, which is also considerably faster than the non-NCEP guidance and the 12Z NAM as well. Across the Pacific NW toward mid-week, a stronger but also more amplified wave crosses the Alaskan Peninsula and upper Aleutians late Monday into Tuesday, a relatively flat downstream 'ridge' or lack thereof, allows for greater buckling of the flow that the lead portion of the wave support strong cyclogenesis by late Tuesday into Wed nearing 130W. Most of the guidance now has converged on this idea including the CMC. The GFS is a bit faster but has trended toward the consensus. A blend of the NAM/ECMWF and GFS seems appropriate but hedging toward the ECMWF/NAM given the GFS may be showing fast bias. Uncertainty, is obviously high given the progressive flow, but the agreement even at 84hrs is high enough to have average confidence in a NAM/ECMWF weighted blend. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Taylor