Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1112 PM EST Fri Jan 10 2020 Valid Jan 11/0000 UTC thru Jan 14/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Exception: 12z ECMWF/CMC and 18z GEFS across Pacific NW/SW Canada Confidence: Slightly above average Current high meridional trof across the Central CONUS will continue to lift northeast and weaken across the Great Lakes into increasingly confluent flow. The trends have been toward a slightly faster and weaker system, breaking down the surface cyclone a bit faster than the last few days, the only remaining stronger/compact solutions remain the UKMET (though is faster) than the 00z NAM. It is not a tremendous difference in the spread, but would weight those solutions less or even remove them from the remainder of this system. After this wave, the large scale pattern broadens toward a large scale trof that dominates the northwestern two-thirds of of North America with a central hub/lobe of the polar vortex taking up residence across N BC/Alberta by Monday. Along this outer edge in the deeper westerlies, fast moving shortwaves will swing through the Rockies on their way through the Central Plains on late Sunday into Monday and then again on Tuesday, with a third potent Pacific wave entering Oregon Tuesday reaching the Great Basin by the end of the forecast period. The first wave that starts the broadening of the large scale trof is already a bit to compact/strong in the 00z crossing the Intermountain West, and while it is not terribly out of phase with the ensemble suite, it is a bit stronger and has negative effects on the broad return flow of the Gulf and intersection/overrunning. The 00z GFS, much like prior runs, shows some typical fast bias, but what is interesting is the placement/strength of the return moisture stream out of the Gulf (tighter 850-7H gradient further east) than the ECMWF/UKMET, while the mass fields are not too bad, this fast bias would suggest the GFS may be a bit too far east, though the ECMWF/UKMET may be too far west and a compromise may be best. This pattern continues with the next but weaker shortwave coming through Tuesday, with the GFS weaker and further east while the UKMET/ECMWF further west, with the CMC favoring the slower solutions over the GFS too. As the large scale vortex/cold pool anchors itself Monday, the internal wobble/binary interactions, show the GFS pull the cold air and therefore the centroid further east, a bit more than even the 18z GEFS suggests, so would be a bit leery of thermal profiles in the northern High Plains by late Mon/Tuesday, though the timing/track of the shortwave emerging from the Pacific/Gulf of AK appears to be congruent with the ECMWF/CMC to have some confidence. The 12z UKMET is also generally east with the center of the vortex by the end of Day 3, but unlike much of the other guidance is much too slow and very weak with the Pacific/Gulf of AK wave that it would not be in the preference across the Pacific NW on Day 3. So overall, a non-NAM blend is supported throughout the forecast period, but after the initial meridional trof lifts through the Northeast and broader trof develops with embedded shortwaves, would prefer to utilize the GEFS over the GFS in general in the preferred blend. Confidence remains well above average for the overall pattern, but the smaller scale but important placement/timing/depth issues in the 00z GFS/NAM and UKMET in the Pacific Northwest on day 3 reduce overall confidence to slightly above average for the entire blend. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina