Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 142 AM EST Wed Feb 19 2020 Valid Feb 19/0000 UTC thru Feb 22/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Initial Model Evaluation with Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Overall Pattern Across the CONUS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 36 hours; then UKMET/ECMWF/GEFS mean Confidence: Near average for most areas The pattern at the beginning of the forecast period Wednesday morning is featured with a West Coast ridge, zonal flow across the central/southern Plains and Gulf Coast region, and a longwave positively tilted trough dropping southeastward across the northern Rockies and the Dakotas. The trough will then reach the eastern U.S. by early Friday and induce surface cyclogenesis over the offshore waters between the Carolinas and Bermuda. With the upper level ridge axis progressing to the south-central U.S. by the weekend, a southern stream closed low aloft reaches California and heralds a pattern change for this region. Through Thursday morning, a general model blend will serve as a good starting point since there are relatively minimal deterministic differences and little in the way of ensemble spread. By Thursday evening, differences become apparent with the 500mb trough crossing the Ohio Valley and Midwest states, with the NAM and to a lesser extent the GFS becoming more amplified than the non-NCEP guidance suggests. This has implications for offshore surface low development east of the Carolinas, with the NAM being a northwestern outlier with the track of the low, thus bringing more impactful weather to the interior Southeast. The CMC becomes a little more progressive with the low track, with good agreement among the ECMWF, UKMET, and the ensemble means. For the longwave trough and developing closed low for the West Coast region, there is now better agreement with the shortwave crossing the Pacific Northwest Thursday evening compared to earlier model runs of the NAM and GFS. In regards to the closed low reaching southern California by Saturday morning, the UKMET is slightly more progressive but still close to the ensemble means, and the GFS is slightly slower. The CMC and ECMWF are closest to the model consensus. The main difference noted with the 00Z ECMWF compared to the 12Z run is a trend towards a more amplified upper level trough crossing the Ohio Valley and Southeast U.S., and the surface low off the coast of North Carolina to the northwest of its 12Z run and closer to the 00Z GFS. The EC mean is still farther offshore compared to most of the other guidance, with the 00Z GEFS mean depicting a reasonable compromise between the EC mean and the GFS/ECMWF. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick