Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1152 AM EST Wed Nov 27 2019 Valid Nov 27/1200 UTC thru Dec 01/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS Evaluation with Preliminary Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/12Z NAM blend Confidence: Average An amplified pattern across the lower 48 is in place at the start of the period with a potent closed low over the upper Midwest and a second closed low over the Pacific Northwest coast. As the eastern closed low tracks east through Thursday, with only minor differences, the flow transitions toward a deep trough over the western half of the nation with anomalous ridging downstream over the East for Thursday and Friday. A mid-level low will eject out into Nebraska/South Dakota on Saturday as a portion of the mid-level low hangs back over the Pacific Northwest. Another closed low will near the West Coast late Saturday. The biggest differences in guidance lie with the large western closed low with the 12Z GFS standing out significantly from the remaining deterministic guidance. The GFS tracks the center of the mid-level closed low a bit farther south and ends up slightly faster than the remaining model consensus on Friday. As a strong surface low develops in the Great Plains Friday night into Saturday, the GFS surface low tracks farther west/north while also being stronger than the remaining model guidance. Low level warm air wraps up significant farther north through the north-central U.S. than non-GFS guidance. While the 12Z GFS is not an outlier with respect to the ensemble distribution, lack of consistency and support from the GFS warrants caution in its solution. The ECMWF mean and deterministic ECMWF have been fairly consistent and match closer to a non-GEFS/GFS blend of models with the bigger picture evolution of the storm system. The 12Z NAM is closest to the 00Z ECMWF but the surface low in the NAM is slightly weaker than ideal and the 12Z NAM may be too cold in the lower levels. The 00Z UKMET/CMC look okay at times, but deviate enough from the preferred model blend to exclude them from being included in the preference. Lastly, the closed low approaching California and Oregon late Saturday shows fair agreement among the latest models, but the 12Z NAM, 12Z GFS and 00Z ECMWF match closest to the agreeable ensemble means while the 00Z UKMET/CMC differ on timing. Interaction with the remnant Pacific Northwest portion of mid-level energy favors more of a 12Z NAM/00Z ECMWF blend over the 12Z GFS. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto