Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1149 PM EST Wed Nov 21 2018 Valid Nov 22/0000 UTC thru Nov 25/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS Evaluation...with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z NAM, 00Z GFS and 12Z ECMWF Confidence: Slightly Below Average The synoptic scale pattern starts off with longwave troughing along the West Coast, a deep closed low centered over eastern Quebec with troughing extending down the East Coast with ridging centered between the two troughs over the Great Plains. Shortwaves embedded within the western longwave trough will progress downstream into the central and eastern U.S. through Sunday morning, allowing cyclogenesis near the East Coast and central Plains on Saturday into Sunday. There are large differences in the deterministic and ensemble guidance regarding a shortwave that crosses the lower to middle Mississippi Valley early Saturday morning and a lower amplitude wave off of the coast of the Southeast and how these features affect surface low development/track. Given poor run to run continuity and model agreement, confidence is lowered compared to average but a broad blend of the 00Z NAM, 00Z GFS and 12Z ECMWF with the thinking that the 12Z ECMWF is probably too strong with its surface low near the New England coast 12Z/25. The other significant shortwave for the central Plains shows moderately large spread in the ensembles, but by 12Z/25, the 12Z ECMWF mean is faster than the 12Z ECMWF and the 18Z GEFS is slightly slower than the 00Z GFS. This argues for a middle ground/ensemble mean approach, led most by the 00Z NAM, 00Z GFS and 12Z ECMWF, noting that the 12Z ECMWF is likely too slow given its placement among the remaining model guidance. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto