Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 325 PM EDT Tue Apr 16 2019 Valid Apr 16/1200 UTC thru Apr 20/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Full Latitude Trough/Low Crossing the CONUS Days 1-3... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend through Day 2, Non-NAM Blend Day 3. Confidence: Slightly Above Average The main weather maker across the CONUS through Friday is the long wave trough digging down the Great Basin today with the southern portion closing into a low as it crosses the southern Rockies late tonight into Wednesday. There is good agreement among the global deterministic models until late Wednesday when the 12Z NAM remains more amplified and the ECMWF is the least amplified on Day 2. The timing and strength of this trough/low has impacts on the heavy QPF across the southern CONUS in the Day 2/3 time frame. The northern stream portion of the trough digs down the Great Plains mainly Wednesday night which interacts with the southern stream portion mainly Thursday night. The 12Z NAM is the strongest with the resultant low on Friday which makes for a quicker close and the slowest progression than any other 12Z deterministic run. Thus the 12Z NAM is ruled out for Day 3. The closest agreement in the southeast CONUS in terms of both mass fields and QPF is with the 12Z UKMET/ECMWF. The 12Z GFS and CMC are not far off and are acceptable. Overall the 12Z consensus trough is a bit broader over the southeastern CONUS on Day 3 than prior runs. ...Pacific Northwest Days 2/3... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC General Model Blend Confidence: Above Average There are some timing and amplitude differences with the next short wave reaching the Pacific Northwest on Friday. The 12Z GFS remains faster than the consensus, with the 12Z CMC remaining the most amplified though all guidance is more amplified by late Friday than the prior run. The 12Z NAM is the slowest with the 12Z ECMWF more progressive than the 00Z. Since QPF is mainly topographically determined in the Pac NW the only notable difference among global deterministic guidance is the 12Z CMC which is the farthest south into OR, so a non-CMC blend is recommended for the Pacific Northwest for Days 2/3. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Jackson