Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 145 AM EST Tue Jan 07 2020 Valid Jan 07/0000 UTC thru Jan 10/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Southern stream trough/low over the TN Valley... ...Surface low impacting the Mid-Atlantic/Northeast on Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A compact, progressive shortwave trough currently advancing toward the TN Valley will be gradually amplifying on Tuesday as it crosses the Mid-Atlantic region. This will allow an attendant wave of low pressure to deepen as it crosses from the TN Valley to the lower Chesapeake Bay/VA Tidewater region by Tuesday evening. The system will then quickly exit out to sea southeast of New England through early Wednesday. Overall, the models are in very good agreement with the system, with very modest differences with respect to timing/depth, and so a general model blend will be preferred. ...Northern stream trough crossing the Northeast by Wed... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models advance a northern stream upper trough and attendant cold front across the Great Lakes on Tuesday, and then through the Northeast on Wednesday. Very good model agreement is seen with this on the large scale, so a general model blend will be preferred with this energy as well. ...Parade of shortwaves crossing the Pacific Northwest... ...Energy advancing east across the Plains/Midwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Slightly above average By late Tuesday and into Wednesday, there will be another shortwave trough and front crossing the coast of the Pacific Northwest. On the large scale sense, the timing/strength appears very agreeable between the various deterministic models. As this system traverses the Intermountain West and then the High Plains by early Thursday, there will be another shortwave crossing the Pacific Northwest that will then dive southeast toward the Four Corners region late Thursday and Friday. There is a bit more spread seen in the guidance with this latter system, as the 00Z NAM appears a tad too progressive. Farther north, the initial system will drive cyclogenesis out across the northern Plains which will cross the Upper Midwest and Great Lakes. The NAM appears to be too far north with its low track, with the 00Z ECMWF perhaps occasionally a little too slow and the 00Z GFS a little too fast. Overall, the NAM is generally the solution that is more out of phase with the model consensus, so a non-NAM blend will be preferred with the succession of shortwaves advancing through the Pacific Northwest and ejecting downstream toward the Plains and Midwest, and this should address some of the modest timing differences noted. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison