Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 136 AM EST Thu Jan 17 2019 Valid Jan 17/0000 UTC thru Jan 20/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation...with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 36 hours 12Z ECENS mean...Western U.S. after 36 hours Blend of the 00Z ECMWF/12Z ECENS mean and 00Z GEFS mean...Eastern U.S. after 36 hours Confidence: Average...Western U.S. and offshore the West Coast Below average...Eastern U.S. Model solutions show only minor differences during the initial 36 hours of the forecast period across the CONUS, which includes the deep layer cyclone offshore the West Coast that lifts gradually north off the West Coast through Thursday, and also the progressive shortwave and associated surface low that lifts from the southern Plains to the OH Valley and lower Great Lakes through Thursday night. Thus a general model blend should suffice through about 36 hours. However, by around 12Z on Friday, more substantial differences in the model mass fields begin to emerge. In particular the 00Z GFS and 00Z CMC are seen as slow outliers with the next negatively tilted trough and intense surface low offshore of the Pacific Northwest which ultimately advances northeast into British Columbia on Saturday as a trailing cold front crosses the coastal ranges of western WA/OR. The 00Z NAM for its part appears too weak with its surface low evolution. The 00Z ECMWF has trended a bit weaker from its very strong 12Z solution and has strong support now from the 12Z ECENS. The 00Z UKMET is also very close to ECMWF/ECENS mean camp. Meanwhile, farther east, the guidance continues to struggle with the details of the amplifying shortwave trough that ejects out across the central/southern Plains on Friday and then advances east across the OH/TN Valleys and the southeast U.S. Saturday into Sunday. The 00Z NAM and 00Z GFS are on the faster side of the guidance as the energy advances east of the lower/middle MS Valley, and the 00Z GFS overall is a bit north of all of the guidance with the low track and is also seen as being a bit faster than the 00Z GEFS mean. The 00Z UKMET/CMC/ECMWF solutions are conversely a bit slower but are noted to have trended a bit more progressive with this latest cycle. Overall, the UKMET remnains the slowest solution. The 12Z ECENS mean generally favors the slower consensus, and is quite close to the deterministic ECMWF. There remains a fair amount of ensemble member spread with the low track when looking into the ensemble plots of the GEFS/Canadian guidance, and to some extent the ECENS suite which suggests a limited degree of confidence in the details of the low track timing and latitudinal placement as it moves into the eastern U.S. this weekend, but there has been at least a modest convergence of the guidance with the 00Z cycle. Based on the latest available trends and guidance, a solution toward the 12Z ECENS mean will be preferred across the Western U.S. and offshore the West Coast after 36 hours, with a solution toward a compromise of the 00Z ECMWF/12Z ECENS mean and 00Z GEFS mean across the Eastern U.S. after 36 hours. The incorporation of the GEFS mean will be out of respect for the more progressive trends at least seen out of the NAM/GFS solution over the last 24 hours. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison