Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 155 PM EST Thu Nov 28 2019 Valid Nov 28/1200 UTC thru Dec 02/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep closed low crossing the Intermountain West/Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM and 12Z ECMWF Confidence: Slightly above average ...19Z update... Only minor changes were noted with the latest 12Z ECMWF/UKMET/CMC compared to their previous 00Z cycles. The 12Z ECMWF adjusted slightly south with the mid and low-level low tracking across the middle of the nation which looks okay given some of the model spread noted below. The 12Z CMC is reasonably close to the preferred NAM/ECMWF blend, but the CMC ends up a bit faster than the deterministic models as the system approaches the East Coast. The 12Z UKMET remained weaker than ideal and is still not preferred. ...previous discussion follows... The 12Z GFS has been trended toward the preferred model consensus, but it remains stronger and initially a bit farther west with its low level low that forms in the central High Plains Friday night. The result is for significantly warmer air from the GFS in the low levels to be drawn northward into the north-central U.S. Friday night through Saturday. The ECMWF mean as well as the ECMWF have been fairly consistent with surface and 850 mb low positions over their past 4 12/00Z cycles. The strength of the 12Z NAM could be a bit weak but when blended with the stronger 00Z ECMWF, a favorable blend is reached. This blend applies to position as well with the 00Z ECMWF's surface low a bit toward the north side of the latest model spread. The 00Z UKMET appears too weak while the 00Z CMC position is off from the preferred consensus. This blend applies through Sunday evening as the storm system nears the East Coast with secondary low development along the northern Mid-Atlantic coast. ...Upper low approaching the West Coast by Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 00/12Z ECMWF Confidence: Average ...19Z update... Differences remain with the interaction of a smaller remnant closed low over the Pacific Northwest on Saturday and an approaching closed low from the eastern Pacific. The ECMWF/UKMET camp shows two main circulations but with a dominant one to the north, while the 12Z NAM/GFS show one circulation with the lobe of vorticity to the south moving more quickly toward the coast. A 12Z GFS and 00Z/12Z ECMWF blend remains the preference given the blends representation between the two camps. Ensemble spread remains fairly large at this point through Sunday. ...previous discussion follows... By Sunday, a new closed low will be evolving offshore of the West Coast along with low pressure at the surface. The 00Z CMC and 00Z UKMET both appear to be a tad too weak with this system as well as displaced from the favorable ensemble mean positions. The 12Z NAM appears to be displaced too far west on Sunday with the 00Z ECMWF closer to the coast. The 12Z GFS splits the difference but lies closer to the NAM position. The GEFS and ECMWF means support a middle ground, between the 12Z GFS and 00Z ECMWF concerning the 500 mb low. Regarding cold frontal timing, the 12Z NAM is slowest with the 00Z ECMWF toward the faster side. A blend of the 00Z ECMWF with the slightly slower 12Z GFS is preferred over the slower 12Z NAM given differences in position in the 700-500 mb low. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto