Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 129 AM EDT Wed Mar 18 2020 Valid Mar 18/0000 UTC thru Mar 21/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep upper trough/closed low impacting the West... ...Low pressure traversing the High Plains/Midwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS, 12Z CMC and 12Z ECMWF Confidence: Average A deep and elongated upper trough with multiple closed low centers will pivot well inland across the Intermountain West by Wednesday which and set the stage for lee-side cyclogenesis over the central High Plains. In particular, the closed low center currently situated near the base of the trough west of the Baja Peninsula will quickly eject northeast across the Southwest on Wednesday and arrive over the central High Plains by early Thursday and be the dominant player in deepening surface low pressure across this region which should lift northeast toward the upper Great Lakes by early Friday. The 00Z NAM is again somewhat stronger and faster than the global model guidance with this system, and suggests a low track a tad northwest of the global model guidance relating to its track across the Midwest and upper Great Lakes. The 12Z UKMET overall does still appear to be too slow with its height fall progression and also ends up with a notably flatter/weaker surface wave evolution. While still awaiting arrival of the 00Z non-NCEP models, the better clustering tends to be toward the 00Z GFS, 12Z CMC and 12Z ECMWF for most of the period, and so a blend of these solutions will be preferred for now. ...Closed low/energy lingering over the Great Basin Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average The latest GOES-17 Airmass RGB and AMV data show a well-defined and somewhat elongated closed low over western NV which is embedded in the aforementioned deep Western U.S. trough axis. This particular low center does not eject east over the next few days and instead gets left behind over the Great Basin. The 00Z NAM tends to place the system a tad east of the global models. All of the models weaken the system by Friday, and suggest the energy will elongate more east/west and shear out on Saturday. A non-NAM blend will be preferred with this energy. ...Series of troughs arriving over the northern High Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS, 12Z UKMET and 12Z ECMWF Confidence: Slightly above average The models bring a series of northern stream shortwave troughs down toward the northern High Plains, with one arriving by late Wednesday, and then an additional one on Friday. The 00Z NAM overall is a tad slower and deeper than the global models with the initial system, and then this model along with the 12Z CMC tend to be a little slower and deeper with the second one. Will prefer the clustering of the 00Z GFS, 12Z UKMET and 12Z ECMWF with these shortwaves as they arrive across the northern Plains and advance east toward the Upper Midwest and Great Lakes region. ...Trough arriving over southern CA by Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Below average A new surge of height falls will be dropping down off the West Coast by the end of the week as a deep closed low center evolves south from the Gulf of AK. Ahead of this closed low will be a separate and smaller closed low center that gets caught up in the the larger scale cyclonic flow off the West Coast and gets slingshotted east toward southern CA as a progressive shortwave trough. The 12Z UKMET is the slowest and deepest solution with this system. The 12Z ECMWF is also on the slower side of the guidance, but has some ensemble support from the ECENS mean. The remaining guidance led by the 00Z GFS and 00Z NAM are a bit more progressive and has more support from the GEFS mean. Will suggest a non-UKMET blend at this point, but with limited confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison