Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 157 PM EST Wed Jan 01 2020 Valid Jan 01/1200 UTC thru Jan 05/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation with final preferences/confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low entering Mexico and weakening through Thursday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 12Z GFS blend Confidence: Average Timing differences continue to exist with this system with the 12Z GFS fastest while the 00Z ECMWF/CMC are slower. Slight adjustments in the 12Z ECMWF/UKMET/CMC show better support for a non 12Z GFS timing. Ensemble spaghetti plots continue to trend slower through their 00Z/01 cycle. Prefer to stay toward the middle of the latest deterministic spread given placement closer to the middle of the ensemble distribution. ...Amplifying longwave trough across the central U.S. Thursday evening... ...Developing surface cyclone from Midwest to East Coast Friday to Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM/12Z ECMWF blend through 00Z/04 12Z NAM/GFS/ECMWF blend 00Z/04-00Z/05 Confidence: Below average Large uncertainty exists with this system given complex interactions of several vorticity maxima within two streams of flow. Ensemble spread is larger than average and run to run consistency has been poorer than usual. The 12Z GFS is unsupported with a broader longwave trough axis over the central U.S. on Friday compared to the remaining available guidance. The 12Z GFS also ends up with a more developed surface refection crossing into the Ohio Valley compared to the remaining guidance. As the trough continues to advance downstream, the 00Z ECMWF slows significantly with the 500 mb trough axis compared to the latest ensemble and remaining deterministic guidance. The 12Z GFS however, begins to align better with the GEFS/ECMWF means and with the 12Z NAM to some degree. Also worth noting is that the 12Z ECMWF adjusted faster with the longwave trough progression and closer to the broad consensus concerning the surface low track. Therefore, beyond 00Z/04, a blend including the 12Z GFS and 12Z ECMWF with the 12Z NAM is preferred. The 12Z UKMET/CMC remain toward the edges of the ensemble distribution with their surface evolution between the Ohio Valley and the East Coast and are not recommended. ...Shortwave trough and surface low approaching Pacific Northwest Friday/Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM/ECMWF blend Confidence: Slightly below average Timing differences continue to affect the Pacific Northwest with the next potent shortwave to reach the region Friday night. The 12Z GFS is faster and on the quicker edge of the ensemble guidance. Meanwhile, the 00Z UKMET/ECMWF are slower but their 12Z runs sped up. the 12Z CMC slowed down relative to its previous 00Z cycle. The 12Z NAM and 12Z ECMWF are better fits for the middle ground. Trends have overall been faster compared to yesterday but the 12Z GFS continues to appear to outpace the vast majority of models. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto