Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 144 AM EST Thu Jan 16 2020 Valid Jan 16/0000 UTC thru Jan 19/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Central to Eastern US system... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/18z GEFS/12z ECMWF/UKMET blend Confidence: Slightly above average As the close low fills along Vancouver Island, the upstream jet digs the tail end of the shortwave and sharpens the trof entering central CA later today (Thursday). The latitude of the depth of the trof appears to be handled at this point. As it progresses across the Rockies, timing with respect to subtle shortwave in advance of the trof in the subtropical stream has tightened in spread but small timing/amplification differences remain. The 12z CMC is slower in the subtropical stream supporting a stronger, southern track (faster cold front across the Southern Plains into Lower MS Valley. The 00z GFS/NAM both are a bit faster and swing the base of the trof though the Central Plains into the Midwest a bit sharper with more negative tilting compared to the ECMWF/UKMET. This allows the NAM to become much stronger by Day3 as well leading to a different location to development of a secondary coastal low off the New York Bight by 19.00z Sun. The 18z GEFS mean suggests the GFS is too sharp/fast relative to the ECMWF/ECENS but overall this timing/spread is not too bad, especially as the UKMET is a bit slower too. As such a 00z GFS/18z GEFS and 12z ECMWF/UKMET blend is preferred at slightly above average confidence. ...Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average (by Day 3...above prior). As the closed low currently near the Pacific NW fills, it becomes highly sheared under the influence/approach of the next very strong/compact wave that is also quite broad. Guidance has tightens overall with the timing/placement of the wave with only small variance in vertical tilt of the cyclone as a whole. Here the 12z ECMWF/ECENS mean continues to lag (greater vertical tilt) and a typical retention/slow weakening of the occluded low as the system swings along the Pacific NW coast Sat, this is opposed by the faster GFS, that due to faster trailing shortwave ridging is a bit slower to drop the frontal zone down the OR/CA coast by the end of the forecast period. This is fairly small, but moderately uncertain as both typical negative biases are in play. As such will split the difference and focus on the ensemble means that are more middle ground. So a general model blend will be preferred at slightly above 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 Gallina