Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1242 AM EDT Mon Mar 11 2019 Valid Mar 11/0000 UTC thru Mar 14/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS Evaluation Including Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Upper trough departing from the Great lakes/Northeast through Monday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average Only minor differences remain with this system, with a general model blend recommended to smooth out any smaller scale discrepancies. ...Large closed low forming just offshore of California this morning and tracking through Arizona/New Mexico, reaching Kansas on Wednesday... ...Associated deep surface low in the Central Plains on Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS, 12Z ECMWF blend Confidence: Slightly above average The 12Z CMC stands out as a deterministic outlier but within the ensemble spread concerning the track of its 500 mb low into New Mexico by Wednesday morning. It appears an upstream wave, discussed below, has some affect on the initial timing of the negatively shortwave trough expected to reach the southern and central Great Plains Wednesday morning. The flatter 12Z CMC across the Southwest is also the slowest with the ejection of the lead shortwave into the Great Plains. The 12Z ECMWF is a bit more amplified across the Southwest Wednesday morning and a bit faster to eject the lead shortwave into Kansas and Oklahoma, with the 00Z NAM/GFS and 12Z UKMET somewhere in the middle. The ECMWF ensembles have been fairly consistent, just a slight slowing trend while the 12Z and 18Z GEFS members are noticeably slower to bring the leading edge of the 552 dam height line at 500 mb into the Midwest on 00Z/14. The surface low track however, shows remarkable agreement for a Day 3 forecast with the GEFS members a bit south of the ECMWF members, with a favored middle ground in line with a blend of the 00Z NAM, 00Z GFS, 12Z ECMWF and 12Z UKMET. Some of the timing differences noted aloft favors simply a 00Z GFS/12Z ECMWF blend to place a a position within the favored middle ground. Ensemble heights at 500 mb show enough differences that confidence is only slightly above average despite the very good surface low agreement, meaning that shifts in the clustering are possible over the next 24-48 hours. ...Progressive upper trough approaching the Pacific Northwest Tuesday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 12Z CMC blend Confidence: Average The 12Z CMC continued to favor a slower surface low track nearing the central coast of British Columbia early this morning and worth mentioning, this difference has little affect on weather across the northwestern U.S. Amplitude differences with the mid-level trough begin to show up over the western U.S. Tuesday night with the 12Z CMC flatter and the 12Z ECMWF a bit deeper. This system acts as a kicker to the lead shortwave discussed above, with the past 4 12/00Z cycles of the ensemble guidance showing a slight trend to be weaker through 12Z/13. At this time, better ensemble support exists for a non 12Z CMC blend. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto