Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 120 PM EDT Fri Mar 22 2019 Valid Mar 22/1200 UTC thru Mar 26/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS Evaluation Including Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Mid-level shortwave trough axis crossing the West Coast Saturday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 00Z ECMWF blend Confidence: Slightly above average The 00Z ECMWF and its ensemble mean stood out from the remaining deterministic/ensemble consensus with this feature making it appear to be a less likely solution. The ECMWF is stronger and more amplified with vorticity in the base of the trough and ends up translating the southern portion of the upper trough into Utah and Colorado whereas the remaining guidance lifts the energy north into Montana. Trends do not favor the ECMWF solution but ensemble spread remains fairly large at this point lowering confidence a little below average. ...Closed low moving from the Central Plains on Saturday to the East Coast on Monday while weakening with eastward extent... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS, 00Z ECMWF, 00Z UKMET blend Confidence: Average Timing differences are noted with this feature with the 12Z NAM/GFS faster than the 00Z ECMWF/UKMET/CMC showing up Sunday morning. The 12Z NAM is fastest with the mid-level wave, while the 00Z CMC is slowest. None of these models are outside of the ensemble spread and while a slight trend to be faster like the 12Z NAM/GFS is warranted, do not want to go toward the extremes of the model spread. A blend of the 12Z GFS, 00Z ECMWF/UKMET appears reasonable. Some caution is advised with the 00Z ECMWF beyond 12Z/25 from the Lower Mississippi Valley into the Southeast given differences with a shortwave referenced in the above section. The slower and more amplified 00Z ECMWF across the South is slower to move moisture out of the region. ...Closed low approaching the West Coast Trough and Coastal Low in the East... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/00Z ECMWF blend (weighted toward ECMWF) Confidence: Average Timing differences are seen with the next system to reach the West Coast on Monday. Ensemble spaghetti height trends have a history of showing the faster GFS/GEFS trending slower toward the ECMWF in cases like this. Therefore, since we are again seeing a faster 12Z NAM/GFS track with this system, and the amplified nature of the flow in place, will recommend a slower solution between the 12Z GFS/00Z ECMWF but with more weight toward the 00Z ECMWF. ...Remainder of the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average Systems elsewhere across the CONUS showed reasonable agreement with just some minor timing differences. Therefore, a general model blend is preferred outside of the three systems discussed above. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto