Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 231 PM EST Wed Nov 20 2019 Valid Nov 20/1200 UTC thru Nov 24/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low crossing the Four Corners into the Plains Friday/Saturday... ...Potential northern stream shortwave crossing the north-central U.S. Friday night... ...Surface low moving from the lower Mississippi Valley into the central Appalachians Friday night into Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/12Z UKMET/00Z ECMWF mean blend Confidence: Below Average ...17Z update... The 12Z UKMET/CMC joined the ECMWF/GFS camp regarding the northern stream shortwave tracking through the north-central U.S. Friday night. There remain timing differences though, with the 12Z CMC slower than the relatively similar 12Z GFS/ECMWF/UKMET. The 12Z ECMWF shows a perceived improvement to its 00Z cycle in that there is less interaction between the northern and southern stream waves across the eastern third of the nation by late Saturday with the corresponding surface low in about the same position but with a weaker 850-500 mb strength and less cold air in its wake. Blending the 12Z ECMWF with the 00Z ECMWF mean and 12Z UKMET are closest to the ideal middle ground solution preferred at this time. ...previous discussion follows... A complex interaction of features along with above average model spread and poor run to run consistency results in below average confidence regarding the evolution of a storm system moving from the Southwest to the Tennessee Valley. The ensembles are in better agreement with the track of the closed low over southern California this morning. However, the 12Z GFS appears to be faster with the track of this feature starting on Friday. To the north, there is potential interaction with a shortwave trough which originates south of Alaska. As this trough moves east and encounters a strong mid-level ridge over British Columbia. The 12Z NAM, 00Z UKMET and 00Z CMC are in agreement that the shortwave is slightly slower/stronger with the bulk of the energy moving into Washington/Idaho/Montana early Friday. Meanwhile, the 12Z GFS and 00Z ECMWF are in agreement that the shortwave is a bit faster allowing it to track through/atop the ridge and into Minnesota by Saturday morning. Ensembles show the 12Z GFS as a strong outlier, however, the 12Z GFS initialization (12Z/20) matches slightly closer to observed water vapor imagery regarding the shortwave compared to the more westward 12Z NAM. For this reason, feel the 12Z GFS/00Z ECMWF idea is more likely to verify but to a weaker degree than depicted by the 12Z GFS and even the 00Z ECMWF. The 00Z ECMWF mean tempers the amplitude of the 00Z ECMWF enough to be used as a favorable blend for the preference. ...Remainder of the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non-12Z NAM blend Confidence: Average ...17Z update... Despite some minor timing adjustments, no significant changes were noted with the 12Z ECMWF/UKMET/CMC compared to their previous 00Z cycles. ...previous discussion follows... The models show good agreement with the remainder of the systems impacting the lower 48, specifically with a deepening mid-level trough/low forecast to affect the upper Mississippi Valley and New England on Thursday and Friday and a closed low expected to form offshore of the West Coast and drop southward this weekend. The only exception across the lower 48 is with a 500 mb shortwave to reach the central Plains tonight, with a related surface low tracking into the Great Lakes region on Thursday. The 12Z NAM was noted to be faster with the track of this low as well as to be colder in the wake of the low/cold front. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto