Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 147 AM EST Mon Mar 02 2020 Valid Mar 02/0000 UTC thru Mar 05/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Confidence Intervals ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Any initialization errors in the NAM/GFS do not seem to degrade their short range forecasts. Shortwave crossing the Upper Midwest/Great Lakes by Monday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The guidance shows agreeable solutions with this feature. A compromise of the 00z UKMET, 00z GFS, 00z NAM, 00z Canadian, and 00z ECMWF is preferred here. Shortwave over the northern Plains/Midwest by Tuesday Weak surface wave/energy lifting over crossing the OH Valley Deepening low center over northern New England by Wednesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: GFS/UKMET compromise Confidence: Slightly below average There is greater than normal dispersion near the low streaking up the Ohio Valley into the Northeast over the next few days, both within the 12z global ensemble guidance and 12z/00z deterministic guidance. The 00z NAM/18z GEFS mean lie on the east side while the 00z Canadian/00z ECMWF lies on the west side. Due to the above uncertainty, which is due to progression and depth issues, chose a solution closest to the middle of the spread, which would be a 00z UKMET/00z GFS compromise. Confidence in this solution is slightly below average. Shortwave approaching British Columbia on Tuesday Amplifying in the northern Plains early Thursday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-Canadian blend Confidence: Average As a ridge amplifies upstream, a shortwave moving along the western US/Canadian border begins to amplify. The guidance disagrees on the amplification expected and the latitude of the bundle of energy/possible closed low Thursday morning. The apex of the developing shortwave ridge in the stream to its north is ~68N which argues for a possible closed low ~48N, right where the 00z UKMET/00z GFS have it. However, the wavelength in the northern stream of the Westerlies is long, which argues for a more open shortwave. The above may explain the variance in the guidance. While the 00z Canadian has become sharper aloft, the base of the shortwave becomes so far south that its corresponding surface low is on the southern fringe of the 12z global ensemble guidance -- probably too far south. A compromise of the 00z NAM, 00z GFS, 00z UKMET, and 00z ECMWF is preferred with confidence no better than average. Southern Stream system moving from northern Mexico through the Southeast Monday into Thursday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average The guidance (outside of the NAM) has trended stronger aloft and more northwest with the surface low track near the Gulf coast and Deep South since this time yesterday. Progression issues in the deterministic guidance are quite small considering the broad 12z global ensemble spread seen in the 5640 meter 500 hPa height line spaghetti plots. The 12z ECMWF ensemble mean is showing an interesting issue that is normally associated with strengthening lows, both tropical and otherwise -- allowing deeper offshore solutions to weight the mean surface low solution offshore despite equal dispersion onshore and offshore the Gulf coast. Prefer a compromise of the 00z ECMWF, 00z UKMET, 00Z Canadian, 00z NAM, and 00z GFS until the guidance stabilizes with confidence no better than average. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Roth