Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 147 AM EST Sat Dec 21 2019 Valid Dec 21/0000 UTC thru Dec 24/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preference and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS, 00Z ECMWF, 00Z CMC Confidence: Slightly Above Average ---06Z UPDATE--- The 00Z CMC is now included in the preference as it has trended closer to the GFS and ECMWF with timing of the low in the Southeast. The 00Z UKMET is now on the fast side with that low, and still digs a shortwave further south into the base of the West Coast trough. ---PREVIOUS DISCUSSION--- Models have continued to gradually converge on their mass field forecasts over the next few days as an amplified synoptic pattern sets up. For instance, the deterministic models place the surface low along the Gulf Coast and Southeast Atlantic Coast generally within 150 miles of each other. This has led to more similar QPF from the models, and a slight increase in forecast confidence. The most significant differences appear to be from the 00Z NAM and 12Z UKMET with the trough approaching the West Coast. Both models dig a shortwave much further south into the base of the trough, leading to a slower progression of the overall trough axis through the Southwest, and some variation in the QPF across the region. The 00Z GFS continues to progress the trough slightly faster to the east, which is a typical bias, but there is increasing overlap with some of the faster ECMWF ensemble members and therefore a blend of the GFS, ECMWF and CMC appears reasonable. For the closed low in the Southeast, the 12Z CMC continues to show a faster progression than the other models. It is also noteworthy that the ECMWF and GFS are faster than their ensemble means, suggesting the low may slow down further in future model runs. Therefore, the CMC is not preferred for its handling of this system. Overall, a blend of the GFS and ECMWF should offer a forecast with more substantial ensemble support, and a compromise in the timing of the trough is preferred through the West. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Lamers