Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1127 AM EST Tue Nov 20 2018 Valid Nov 20/1200 UTC thru Nov 24/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM/GFS and 00Z ECMWF Confidence: Slightly above average The current pattern across the CONUS is rather amplified with a deep layer ridge over the Intermountain West and a longwave trough downstream across the Eastern U.S. Meanwhile, a longwave trough is also positioned just off the West Coast with a separate southern stream closed moving across southern CA. The latest guidance strongly agrees that an area of low pressure lifting up along the New England coast will deepen further through tonight and lift through the Canadian maritimes through Wednesday. In its wake, there will be another digging shortwave trough and associated low pressure which will drop across the Great Lakes region tonight and the Northeast through Wednesday. An anomalously strong high pressure in its wake will bring near record cold to the Northeast U.S. for Thanksgiving. Across the West, the deep layer ridge will break down and the offshore trough will advance east and well inland through Thanksgiving. This will set the stage for a well-defined atmospheric river event to impact the Pacific Northwest and especially northern CA. A series of shortwave impulses upstream will follow suit and arrive going into Friday. The lead trough axis will advance downstream across the Plains and MS Valley by Friday. The models are in good agreement with the large scale features, although the 00Z ECMWF and 00Z CMC are just a little slower than the model consensus and the latest GEFS mean and ECENS mean with the trough progression toward the MS Valley by Friday. Based on the latest trends and model clustering, a blend of the 12Z NAM/GFS and 00Z ECMWF will be preferred across the CONUS. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison