Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1229 PM EST Tue Mar 06 2018 Valid Mar 06/1200 UTC through Mar 10/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS evaluation...along with preliminary 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: Blend of the 12Z NAM/00Z UKMET 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. The strength of the surface to 500 mb lows looks similar 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 older 00Z ECMWF/UKMET/CMC do not. Perhaps this is one reason why the 12Z NAM/GFS are farther west/inland with the surface low track compared to the 00Z ECMWF/UKMET/CMC? Regardless of this fact, the 12Z GFS looks to be on the western side of the available model spread while the 00Z ECMWF and 00Z CMC are more east. A favorable middle ground considering only minor trends is a blend of the 12Z NAM and 00Z UKMET for the surface low track through Thursday. ...Secondary surface low near Nova Scotia Friday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 00Z ECMWF blend 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. Outside of the farther west 00Z ECMWF, the deterministic models show decent agreement here for a non-00Z ECMWF blend. There is modest support for a 00Z ECMWF-like solution, but until greater deterministic guidance is seen for the westward 00Z ECMWF with this next surface low on Friday, a non-00Z ECMWF blend will be preferred. ...West Coast/northwestern U.S.... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 00Z ECMWF blend through 00Z/09 00Z 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, but the 00Z ECMWF appears to be a faster outlier with this system. The 00Z ECMWF mean is slower than the 00Z ECMWF as well, so there appears to be good support for a non 00Z ECMWF blend 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 00Z ECMWF appears to be the favorable middle ground with the 12Z NAM faster 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