Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 335 PM EST Tue Nov 27 2018 Valid Nov 27/1200 UTC thru Dec 01/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... Final 12Z Model Evaluation...listing Preference and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 12Z GFS / NAM Confidence: Average A cyclone, becoming stacked, will lumber into the North Atlantic. The upstream flow pattern over the CONUS briefly goes through a lower amplitude zonal flow phase, but with an energetic upper jet leaning from the Pacific into the Southwest states by Day 2. This jet will support two strong shortwave troughs, one that ejects toward the southern Plains by the end of Day 3, 00Z December 1st, and another that approaches the CA/OR coastline at that same time. The large and stacked cyclone should be well handled by the models, and consensus suggests the 00Z ECMWF and now again the 12Z ECMWF are too far north and too progressive over time. Within the more zonal regime the 00Z UKMET had emerged as somewhat an outlier in producing a deeper system and a closed surface low track from the Tennessee Valley to the mid Atlantic. The 12Z UKMET dampened this system, and is generally in step with the NAM/GFS-led consensus for timing and placement of the large scale features across the map, but is still on the fringe of the ensemble envelope over the eastern U.S. on Days 2 and 3. Ensemble means have been fairly steady from run to run, whereas the UKMET has not. The ECMWF has also tended to fall out of phase with the ensemble consensus in the East by Day 3, perhaps owing to its more progressive Atlantic cyclone. The 12Z ECMWF also trended quite flat with the wave approaching the Pacific coast. Given this is an energetic short wavelength trough within a pattern that favors digging, we prefer the deeper NCEP guidance. In the Plains, however, the ECMWF ends up being well clustered with the other global models. Overall, the WPC preference for the CONUS pattern is GFS and NAM, noting that the GFS has been quite steady the past few cycles through Day 3, and the relatively narrow spread in the ensembles speaks to somewhat greater confidence / predictability, at least on the large scale. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Burke