Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1231 PM EDT Fri Sep 28 2018 Valid Sep 28/1200 UTC thru Oct 02/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Preference for the Entire CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model preference Exclusion: Non-UKMET in Pacific NW after 01/00z. Confidence: Above average Best Hrcn Rosa Proxy: 12z GFS Global scale upper level trof continues to dominate the northern half of the North American continent through the early period with broadly zonal flow from MT to NY given the breadth of the wave. Internally, the lead wave is already out of the CONUS with the lingering frontal zone crossing the Gulf of Maine down into the Carolinas and hugging the Central/Western Gulf Coast; the second wave is currently starting to amplify across NW Canada as it starts to swing through Central Canada to the Northern High Plains by Sat. Models are very strongly agreed upon with the mass fields as it shifts eastward and starts to completely break down the global trof by late Sunday. So for the Central US/Southern Plains and Eastern third, a general model blend is supported at above average confidence. Across the Pacific into the West, a mature Rex block is set up between 130-140W, and Hurricane Rosa is south of 20N. Models have come to a stronger consensus of the apex ridge to slightly retrograde into AK, supporting some troughing over BC and allowing eastward advancement of the closed low into N CA/OR by late Sat. This wave is now fairly well agreed upon as it shears into the increasingly confluent flow in the Snake River and Northern Rockies by late Sun. However, the UKMET starts to advance the northern stream trof a bit too much across Vancouver island into the Pacific Northwest. While the 12z NAM and GFS both show greater amplification of the wave off shore/connecting to a Pacific stream closed low by 84hrs, this is fairly consistent with the overall ensemble run to run trends an gels with the CMC/ECMWF even if they are still a bit broader and east. As such a non-UKMET blend is suggested in the Pacific NW for Day 3. The 12z GFS trended a bit faster toward 72-84hrs with respect to its 00z/06z iterations and also now appears to be aligned extremely well with the official 15z NHC forecast track as well as general intensity. The degree of shearing/interaction with the approaching closed low out of the North Central Pacific seems reasonable as well for QPF, to suggest the 12z GFS as the best proxy to the NHC forecast. The 00z UKMET/ECMWF and CMC all have utility and could be blended with the GFS to be a solid proxy to the official forecast as well, as it is clear the 12z NAM remains significantly east of track and fast. Of note: the UKMET would be fast and west, ECMWF is slow and west, CMC is slightly east but weak compared to the GFS. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina