Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1148 AM EST Wed Jan 24 2018 Valid Jan 24/1200 UTC thru Jan 28/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... ...12Z NAM/GFS evaluation along with preliminary preferences... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Quick moving shortwave reaching the Mid-Atlantic coast tonight... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model compromise Confidence: Above average The models show similarly with this system. ...Mid-level shortwave weakening northeastward from northern Mexico through Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model compromise Confidence: Above average The models show similarly with this system. ...Large upper trough moving through the western U.S. today/tomorrow... ...Surface low near the U.S./Canadian border moving east with trailing cold front... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 00Z UKMET blend Confidence: Average More significant differences appear around 00Z/27 concerning the cold frontal timing through the Mississippi valley. The 12Z GFS continues to be faster with the overall upper trough progression across the center of the country, but has trended slower since Tuesday. Meanwhile, the 00Z ECMWF has been a bit slower with some trends to be faster over its past few runs. The 12Z NAM is a bit faster as well when compared to the 00Z ECMWF but not as fast as the 12Z GFS. Given the 00Z UKMET becomes a deeper outlier with the base of the trough by 00Z/28, it is not preferred. The 12Z GFS is the only model that does not show stronger vorticity energy in the base of the upper trough near 12Z/27 over the central Plains given its faster progression. However, the 00Z ECMWF is considered too slow/strong with this feature. The 12Z NAM ends up flatter with the trough axis near 00Z/28 compared to the remaining model consensus and ensemble data. Therefore, no single model is preferred, but perhaps a blend of the 12Z NAM, 12Z GFS, 00Z ECMWF, 00Z CMC will be able to smooth out individual issues seem in the deterministic guidance. ...Low amplitude mid-level shortwave nearing the Pacific Northwest late Friday night with accompanying surface low... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM/GFS blend Confidence: Slightly above average The 12Z NAM/GFS and 00Z ECMWF are in line with the latest ensemble data except the 00Z ECMWF becomes a stronger near-outlier with ridging off of the West Coast by 00Z/28. The 00Z ECMWF is otherwise usable until around 00Z/28 given its moisture axis is oriented away from the remaining model consensus. The surface low depicted in the ensemble data is represented by a blend of the 12Z NAM/GFS and 00Z ECMWF. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 MB forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto