Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1244 AM EDT Wed Mar 13 2019 Valid Mar 13/0000 UTC thru Mar 16/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS Evaluation Including Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Large closed low/upper trough tracking from the Central Plains to the Great Lakes through Saturday morning ... ...Corresponding surface low through the Upper Mississippi Valley with trailing cold front... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/12Z ECMWF blend Confidence: Slightly above average The main feature to affect the lower 48 over the next couple of days will be tied to an ongoing upper trough axis swinging into the southern High Plains this morning with a corresponding surface low to move from Colorado into Kansas. A secondary upper trough over the western U.S. will amplify just south of the Plains system resulting in a large closed low by Thursday morning over the middle Missouri Valley. The surface low will track into Ontario and Quebec through Friday as the attendant cold front sweeps through the eastern U.S. Ensemble run to run continuity has been excellent and supports a surface low track slightly slower/west than the 00Z NAM, 12Z UKMET as the deep surface low tracks across southeastern Nebraska into Iowa and Wisconsin. Some timing differences develop with the trailing cold front through the Ohio Valley to the Gulf Coast due to some minor timing differences with the resultant longwave trough axis moving across the central U.S. by Friday morning. Regarding cold frontal timing, the 00Z GFS and 12Z ECMWF represent a similar solution and lie in the middle of the latest model differences. ...Relatively weak upper trough to reach the West Coast Thursday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS, 12Z ECMWF, 12Z UKMET blend through 12Z/15 12Z ECMWF/12Z UKMET blend 12Z/15 through 12Z/16 Confidence: Slightly above average The main feature to affect the lower 48 over the next couple of days will be tied to an ongoing upper Another shortwave will reach the West Coast early on Friday with a quasi-rex block setting up over the western U.S. for Saturday morning with troughing over the Southwest and ridging over the Northwest. The ensemble spread is smaller compared to yesterday but the 00Z NAM appears too weak with the feature aloft, and the 12Z CMC is a bit stronger than the remaining consensus. The strength and timing of the 00Z GFS, 12Z ECMWF and 12Z UKMET appears best with this system until about 00Z/15, at which point the 00Z GFS moves toward the faster side of the latest ensemble spaghetti heights. This tends to be a known bias for the GFS so staying closer to the 12Z ECMWF/UKMET is recommended between 12Z/15 and 12Z/16. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto