Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 154 AM EST Wed Jan 29 2020 Valid Jan 29/0000 UTC thru Feb 01/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Split flow trough crossing the Great Plains today and reaching the Southeast Wednesday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Average The latest numerical guidance remains in decent agreement with the evolution of a shortwave which was over the Southern Plains at 29/00Z. As the wave tracks east, the 29/00Z NAM was slightly faster than the 28/12Z runs and well within the clustering of other 29/00Z model guidance. A general model blend should look very similar to any of the individual model runs while dampening the minor differences in amplitude and speed of propagation of the wave. ...Split flow trough in northern stream from the Upper Midwest to the Mid-Atlantic Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 29/00Z UKMET/Canadian blend Confidence: Average The numerical guidance got into better agreement with respect to the energy in the northern stream during the 28/12Z model runs. There were a couple of minor run to run differences in the NAM and GFS...but the overall solution changed little. That leaves the 29/00Z UKMET offered a solution that was a bit slower than model consensus through Thursday morning and the Canadian depicted a weaker wave than consensus which makes its way across parts of the Great Lakes/Ohio Valley and towards the Mid-Atlantic region. No reason to change preferences based on the 29/00Z guidance. ...Mid-level trough over the Pacific Northwest today and amplifying into the Desert Southwest Wednesday, reaching the Southern Plains Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 29/00Z GFS and ECMWF blend Confidence: Average Both the 29/00Z GFS and 28/12Z operational ECMWF showed shortwave energy dropping south and forming a closed low which makes its way into northern Mexico...an idea that was supported by the ECMWF ensembles...while the NAM and UKMET were both hedging towards a faster solution without the depth of the ECMWF/GFS. Will not make any changes to the earlier preference for the GFS/ECMWF blend. ...Mid-level trough entering British Columbia on Wednesday and amplifying southward into the Great Plains by Friday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 28/00Z ECMWF/GFS blend Confidence: Below average Uncertainty remained high as the models struggle with the southern end of a shortwave trough and how it evolves once it crosses through a ridge centered over southwestern Canada and the northwestern U.S.. While run to run consistency has been poor...there was a move by both the ECMWF and the GFS in their 29/00Z runs towards a solution that showed a more unified flow pattern setting up downstream of the western ridge, and the development of a closed low within that low over parts of the Southern Plains or Tennessee Valley by early Saturday morning. While the Canadian had been suggesting a low in previous model runs, it backed away towards the 28/12Z ECMWF idea. At this point, the idea of a broad mid-level trough with a low seems more reasonable given the amplitude of the upstream ridge. So will favor a blend of the 29/00Z GFS and ECMWF...although confidence in any particular detail is below average and will not be surprised at additional run to run changes. ...Leading edge of longwave trough, offshore of the west coast of Canada Friday evening and downstream atmospheric river into the Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 29/00Z NAM/ECMWF/UKMET blend Confidence: Average After the passage of a shortwave and accompanying cold front into British Columbia on the 30th, initially zonal flow into western Canada will begin to amplify as ridging increases ahead of an upstream shortwave near 40N 145W by 01/00Z. Ensemble means and the remaining deterministic consensus suggest that the 29/00Z GFS and 29/12Z CMC may be a bit too quick with the shortwave...so a blend of the 29/00Z NAM/ECMWF/UKMET remains closest to the relatively agreeable ensemble mean's position and the downstream atmospheric river moving into the Pacific Northwest. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Bann