Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1145 AM EST Fri Nov 29 2019 Valid Nov 29/1200 UTC thru Dec 03/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation and Preliminary Preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep closed low forming in the Plains... ...Handing off to a Northeast Coastal Low on Day 3... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 12Z GFS / 00Z ECMWF...emphasis on the ECMWF A deep upper trough pulling into the plains will spawn cyclogenesis, resulting in a deep closed system that is forecast to slide eastward through the short range period. As height falls cross the Appalachians we should see a handoff to a newly forming coastal low / Nor'eastern on Day 3, Monday. In recent days the ECMWF and ECMWF Ensemble have proven more consistent and served as a baseline for this storm. The NCEP solutions, however, were becoming more usable. The 12Z NAM and GFS show a large scale evolution that is very similar to the ECMWF. The thermal fields are of interest, given the anticipated winter weather impacts. Certainly by 48 hours, 12Z Sunday, the NAM strongly indicates its typical cold bias, with 850 mb cold air of greater magnitude and more expansive than the other models. Noting that the thermal fields in the operational ECMWF are strongly supported by the ECMWF ensemble mean, we have more trust in the European as a baseline. The GFS looks more reasonable than the NAM in this respect. The main question mark is slightly warmer air, 850-700mb, the GFS indicates along the warm front in the Midwest and then near the low track throughout its journey to the East Coast. It would not be unusual for air to verify a bit on the warm side of the spread near the low track, but for now we would place a majority emphasis on the ECMWF. ...Western U.S. and Northern Rockies/Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 12Z GFS / 00Z ECMWF...emphasis on the ECMWF Another deep trough and wet storm system will dig into place near the West Coast. Through Monday this system sits beneath mean shortwave ridging over the Pacific Northwest, with northern stream shortwaves amplifying downstream over the Northern Rockies and northern Plains. Looking at the flow pattern across the Pacific and North America, the 00Z ECMWF and Canadian models, as well as the 06Z GFS, look quite similar. Most of the flow features are large scale and predictable, but the northern stream offers some challenging shorter wavelengths, and interacting shortwaves that gyrate around the west coast trough do present some questions. The 12Z NCEP models began a trend in holding onto the definition of a tight upper low that retrogrades southwest out of Oregon. The NAM seems to show a more reasonable trend, while the GFS was much slower and represented a stark change from its 06Z run. On the other hand, the NAM solution is so messy and unsupported in the northern stream, through the Northern Rockies, that it is hard to recommend in our preference. Fortunately, the NAM/GFS thermal fields are very similar to the ECMWF over the western U.S., for forecasting precip type. But for shortwave timing and large scale forcing, we recommend emphasis on the ECMWF. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Burke