Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1231 PM EDT Mon Mar 09 2020 Valid Mar 09/1200 UTC thru Mar 13/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS Evaluation and Regional Preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed Low Affecting the Southwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM and 00Z ECMWF/Canadian A closed low off Southern California will be slow to move eastward, interacting weakly with the northern stream, more zonal flow brushing across the top. Our preference is weighted more toward the ECMWF. Ensemble spaghetti plots viewed over several consecutive model cycles show a clear trend of the GEFS members and mean trying to move back toward the slower and more pronounced closed signature of the ECMWF members. The 00Z Canadian and now 12Z NAM also match quite well to the ECMWF and its ensemble. There is a shortwave in the northern stream that will tug a bit at the closed low Tuesday night/Wednesday, drawing it to the coast. But the 12Z GFS goes farther with this interaction, and leaves a more strung out trough hanging off the coast with no distinct low until it reforms rapidly on Thursday. These small scale shortwave details do not share any support from other models and are a pretty substantial change from earlier GFS runs. That being the case, we recommend caution with the GFS here after March 11/12Z. ...Northern Stream Flow... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z ECMWF/Canadian, with NAM/GFS viable to March 12/00Z Within generally progressive and broad scale flow, some amplification is expected across the north-central U.S. by midweek. Ensemble spaghetti plots dating back several cycles have shown the fast GFS to be either an outlier or at least setting the very edge of the solution envelope. Some details over the north Pacific also look a little spurious in the GFS, where as teleconnections / advection arguments would argue for a closed low forming more at the latitude reflected in the ECMWF, of 38 North, by March 13/00Z. For these reasons we favor the ECMWF...which was joined at 00Z by the Canadian run. In the 12Z cycle the NCEP models are getting closer, and maybe they will prove to be correct in depicting a stronger surface low over the Canadian Prairie Provinces. Beyond Day 2, however, the NAM and GFS still stand out as being a little fast over the Upper Midwest. Will re-evaluate after seeing any trends in the other global models this afternoon. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Burke