Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 215 PM EST Tue Mar 06 2018 Valid Mar 06/1200 UTC thru Mar 10/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation...along with final preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Series of shortwaves in the vicinity of the Northeast U.S. closed low... ...Developing Northeast coastal low Wednesday and Wednesday night... ...Secondary surface low near Nova Scotia Friday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 12Z GFS blend Confidence: Slightly above average Regarding the surface low forecast to track north along the Northeast coast on Wednesday and Wednesday night, ECMWF/GEFS/CMC ensemble trends have not shown much in the way westward/eastward trends since yesterday, but perhaps a subtle shift to the west valid 00Z/08 and 12Z/08. The deterministic guidance has also only shown minor movement since yesterday except the UKMET which has trended west since yesterday through its 00Z/06 cycle and then slightly east with its 12Z/06 cycle. The strength looks similar regarding the surface to 500 mb lows in all of the guidance except early in the forecast regarding a sub-5280 m low situated over Iowa at 12Z. The 12Z NAM/GFS, RAP show a 5280 m contour valid 12Z/07 over the Ohio valley whereas the 12Z ECMWF/UKMET/CMC do not. Considering only minor trends in the guidance through today's 12Z cycle, The 12Z GFS surface low track looks to be on the western side of the available model spread while the remaining 12Z guidance is similar to one another. The result is a warmer surface to 850 mb layer in the 12Z GFS compared to the remaining guidance. A growing consensus seems to be for a non 12Z GFS solution for this system through Thursday. ...Secondary surface low near Nova Scotia Friday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z UKMET Confidence: Slightly above average While the initial surface low is impacting New England Wednesday into Thursday, another surface low is forecast to develop over the western Atlantic on Thursday and track north-northeastward. The 12Z ECMWF nudged east from its previously farther west 00Z cycle, but the differences is minor. The 12Z UKMET and 12Z CMC trended westward from their previous cycles with the 12Z UKMET now west of the 12Z NAM/GFS. However, the 12Z CMC is nearer to the 12Z NAM/GFS and given the latest ensemble guidance, the 12Z UKMET is nearest to the 12Z GEFS mean and 00Z ECMWF mean with both the GEFS and ECMWF means near one another in position by 00Z/10. The preference has shifted westward to the 12Z UKMET which is a compromise position between the westward and eastward low tracks. ...West Coast/northwestern U.S.... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 00Z/09 12Z ECMWF between 00Z/09 and 00Z/10 Confidence: Average Two features are worth noting which will impact weather along the western U.S. through Friday. A closed low is expected to weaken over the Pacific Northwest on Thursday, and the 12Z ECMWF slowed somewhat from its previously faster 00Z cycle as the system comes ashore early Thursday morning. Given the 00Z ECMWF mean was slower than the 00Z ECMWF, this shift by the 12Z ECMWF appears to be in the right direction through 00Z/09 which is the point at which the shortwave weakens considerably as it tracks over land. A second shortwave is expected to drop southward British Columbia coast on Thursday and interestingly enough, the 12Z ECMWF appears to be the favorable middle ground with the 12Z NAM faster than and 12Z GFS slower than the favored ensemble means and middle ground. This next wave will impact the timing of the cold front dropping down the coast of Oregon and California. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto