Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 315 PM EST Thu Jan 02 2020 Valid Jan 02/1200 UTC thru Jan 06/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Upper low over Mexico shearing to the northeast... ...Frontal wave impacting the Gulf Coast/TN Valley... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Only minor timing differences remain with the shortwave shearing eastward and the related weak surface low to track from MS toward the east. ...Amplifying longwave trough across the central U.S. ...Surface low from the Lower MS Valley to the Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GEFS/00Z ECENS mean (nearest to 12Z GFS/12Z ECMWF) Confidence: Below average The interaction between a northern stream and southern stream component embedded within a longwave trough progressing eastward from the central U.S. translates into a difficult forecast evolution. By 12Z/04, the 12Z GFS begins to push ahead of the remaining guidance with the southern stream axis of vorticity along the northern Gulf Coast, due to a more amplified northern stream component across the Midwest. However, 12 hours later, at 00Z/05, the 12Z NAM is fastest with its 500 mb trough axis over the eastern U.S., followed by the 12Z GFS/UKMET. The 12Z CMC was slowest with the 12Z ECMWF in the middle, but having nudged faster compared to its 00Z run. The 12Z UKMET also trended faster compared to its 00Z run. With a fair degree of confidence, it can be said that the 12Z NAM and 12Z CMC have a low likelihood of verifying. However, among the remaining 12Z GFS/ECMWF/UKMET, the resulting surface low shows moderate spread. While the ensemble scatter low plots are rather broad in their depiction valid 12Z/05, the 12Z GFS's surface low is on the northern side of the surface lows, while the 12Z UKMET is east/fast. The 12Z ECMWF is toward the south side but a significant number of ensemble surface low plots are west of the 12Z GFS/12Z ECMWF position, hence the rather agreeable 12Z GEFS and 00Z ECMWF means are west of their deterministic counterparts. The preference is to be between the 12Z GFS/12Z ECMWF but with a slightly westward track of their surface lows given ensemble mean placement. Due to poor ensemble agreement and poor run to run consistency in the guidance, confidence is below average. ...Shortwave trough/low impacting the Pacific Northwest... ...Energy ejecting out across the Plains/Midwest by Sat/Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF Confidence: Average The preference is to go toward the middle of the latest ensemble/deterministic model spread. The 12Z NAM is fastest followed by the 12Z GFS as the shortwave trough tracks east into the Northern Plains. The resulting cold front shows similarly, but the 12Z ECMWF appears to be in the favored middle ground position despite a slightly faster trend compared to its 00Z cycle. Even considering the faster 12Z NAM, model spread is relatively small through Sunday evening across the Upper Midwest and Southern Plains. ...Next mid-level trough axis to reach the Pacific Northwest by Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 12Z CMC blend Confidence: Average While some amplitude differences exist with an upper trough axis nearing the Pacific Northwest by Sunday, timing differences are greater. The relatively agreeable ensemble means support a faster timing when compared to the 12Z CMC. While minor differences exist among the remaining 12Z deterministic guidance, a non 12Z CMC blend appears reasonable for this system at this point in time. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto