Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1120 AM EST Tue Dec 24 2019 Valid Dec 24/1200 UTC thru Dec 28/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preference and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS/00z ECMWF blend Inclusions: Add 12z NAM in Northern Stream after 27.00z Add 12z NAM/00z UKMET with Closed low in West; Trend toward 2/3rd EC - 1/3 GFS by 28.00z in Southern Plains Confidence: Above average A deep latitude, but narrow trof across the Intermountain West is expected to expand/broaden to a global scale trof with the approach of shortwave energy out of the Gulf of Alaska late Tuesday into Wed. The lead shortwave energy currently across the Desert Southwest will lift northeastward generally weakening through the expanding larger scale trof but a weaker kicker wave in the southern stream will lift quickly behind and under influence of the broad diffluent pattern aloft amplifies to a relatively dry cyclone across the northern Red River. Models continue to consolidate in placement and strength, though the 12z NAM continues to be strongest/compact by late Thurs...and should be tempered or removed in the local area blend. After its passage, the active Gulf of Alaska stream, drives shortwave energy across Southern Canada. The 00z CMC is particular (and uncharacteristically fast) leading to less southward digging which is not supported through the ensemble suite. The 00z UKMET, while a bit less flat, is also progressive and should be removed from the suite. The 12z NAM, along with the 12z GFS/00z ECMWF are more in line with the overall trend within the ensemble suite depicting a sharpening across the Northern High Plains toward 28.00z. So would favor those within a blend after the initial shortwave on Wed. Along the western side of the broadening western large scale trof, a strong meridional jet streak and associated shortwave dig parallel to the West Coast eventually closing into a compact closed low along the Central CA coat by 26.12z. There is solid model agreement in this evolution through this time period, but the 00z CMC eventually digs too far south relative to the suite and becomes less favorable after 26.12z. Thereafter, as the closed low weakens and rolls through the Southwest, there is a typical timing difference that emerges with the 12z GFS/00z UKMET and lesser so the 12z NAM (trended a bit slower with this iteration) faster into the Southern Plains by 00z Sat, intersecting with return moisture further east than the ECMWF/ECENS solutions. This looks like a more typical orientation/predictable variation to support the slightly slower solution (more of a 2/3rd EC camp & 1/3 GFS camp blend) that verifies well and subsequent runs trend toward. As such confidence is slightly above average overall. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina