Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1144 AM EST Sun Jan 26 2020 Valid Jan 26/1200 UTC thru Jan 30/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwaves crossing the Great Lakes/OH Valley through Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A shortwave currently digging southeast over the Midwest will race across the OH Valley by late Monday. It will then reach the Mid-Atlantic coast Monday night. In its wake, a second shortwave will also be dropping down from the Great Lakes region which will cross the OH Valley through Tuesday. The 12Z NAM occasionally appears to be perhaps a tad too strong, but the overall model spread is quite minimal, so a general model blend will be preferred. ...Split flow trough crossing the West coast today... ...Energy ejecting through the Southwest and Plains by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS/06Z GEFS/00Z ECMWF/00Z ECENS mean Confidence: Below average The models all take a progressive split-flow trough across the West today, with a southern stream portion of the energy then dropping down across the Southwest and amplifying into a closed low as it approaches the southern High Plains by early Tuesday. Meanwhile, the northern stream component of the trough will be over the northern High Plains by early Tuesday. The 00Z CMC remains a bit out of tolerance with the 12Z NAM/GFS solutions and the remaining 00Z non-NCEP models concerning both streams, and again suggests a surface low evolving over the southern Plains/lower MS Valley that tracks a bit north of the model consensus. The 12Z GFS suggests a somewhat more amplified southern stream evolution, with a relatively stronger surface low that crosses the lower MS Valley by early Wednesday. The 12Z NAM in time becomes the slowest solution, and the weakest with its surface reflection. The 00Z UKMET is also weak, but is more progressive. The differences with the northern stream energy are not as vast, but the NAM and ECMWF may be too amplified with this energy. Given the deterministic model spread with timing/depth of the energy crossing especially the southern U.S., the preference at this point will be to blend the latest GEFS/ECENS means and the 12Z GFS/00Z ECMWF solutions as a means of approximating the model consensus for both the northern and southern streams. ...Progressive upper trough over the Pacific Northwest Tuesday... ...Amplifying into the West on Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Average Yet another in a series of Pacific shortwave troughs will arrive on Tuesday across the Pacific Northwest, and then dig into the West on Wednesday, with the gradual development of a closed low over the Southwest late Wednesday. The 12Z NAM may be a tad too weak and fast as the energy initially comes into the Pacific Northwest, but then by late Wednesday appears to be a little too slow with its height falls pivoting toward the Southwest. The global models are overall in pretty good agreement with the larger scale mass field evolution, so a non-NAM blend will be preferred with this system for the time being. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison