Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 135 PM EST Sat Dec 07 2019 Valid Dec 07/1200 UTC thru Dec 11/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF; 00Z ECMWF Ensemble Mean Confidence: Average ---18Z UPDATE--- While the 12Z UKMET remained relatively consistent with its 00Z run, there were important trends on the CMC and ECMWF. The 12Z ECMWF slowed down to be more comparable with the GFS, while the 12Z CMC sped up considerably and is now a reasonably good match to the ECMWF with the southern stream wave digging through the Southwest and into the Southern Plains. The preference has been shifted to include the slower 12Z ECMWF scenario, but still blended with the 00Z ECMWF Ensemble Mean to incorporate the prior consensus. It may take another model cycle or two to determine whether the slower trend will continue or not. ---PREVIOUS DISCUSSION--- Models are showing some more substantial differences beyond 09.06Z (Sunday Night), particularly with how they handle a southern stream wave digging through the Southwest, and how that eventually phases with a larger, amplifying trough over the Central U.S. This is most notable in a relatively large spread in timing centered around 10.00Z (Monday evening) over the Southwest. Over the past few model cycles, the ECMWF and ECMWF Ensemble Mean have gradually converged around their positions depicted on the 00Z runs. Other models have been less consistent, with the UKMET trending faster and less amplified, and the GFS trending slower. The preference will be to lean toward the 00Z ECMWF and 00Z ECMWF Ensemble Mean, given the multi-run consistency they have shown, and the 00Z GFS given its relatively good alignment with the ECMWF ensemble envelope. Conceptually, the ECMWF also makes sense as the southern stream wave may have a tendency to deamplify and accelerate as it is overwhelmed by larger height falls from the longwave trough expanding over the central U.S. The 00Z CMC and many 00Z NAEFS members hang the southern stream wave back more over the Southwest, and the 12Z GFS has joined that cluster. This can't be completely discounted, but there is a lack of support from other global models. Finally, a preference centered around the 00Z GFS and ECMWF will provide consistency with the previous forecast, as that was the preferred model blend overnight as well. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Lamers