Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 133 AM EST Sun Dec 08 2019 Valid Dec 08/0000 UTC thru Dec 11/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Large scale trof that dominates the bulk of the CONUS through Wed... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z ECMWF/ECENS mean blend with some lower weighted 00z GEFS/GFS Confidence: Slightly above average 07z update: The overall agreement in the northern stream mass fields continue, but the Arctic shortwave still remains much more uncertain, with the CMC still much more amplified/compact that other solutions. In the southern stream, the ECMWF remained quite similar but the 00z GEFS mean continues to hedge more toward the ECMWF/ECENS mean solution than the 00z GFS specifically. So, will continue with initial preference of ECMWF/ECENS mean with some 0z GEFS/GFS in the blend particularly in the southern stream portion of the larger global trof. ---Prior Discussion--- A large scale global trof is developing currently with a deep closed vortex over northern Hudson Bay, a northern stream shortwave sliding down the Canadian Rockies that will sharpen and accelerate across the Plains Monday drawing a southern High Plains lee surface cyclone up the surface trof into the Great Lakes, as it deepens into a strong cyclone across Quebec by early Tues; with an attendant cold front that extends back toward the Lower MS Valley Tues. The southern portion of the frontal zone is expected to slow, as the closed low currently off the West Coast slides into the Southwest. For the most part, the guidance has come into solid agreement in the evolution/placement of these features with exception to the strength/shape of the remaining portion of the southern shortwave as it crosses the southern Plains late Tues into Wed. The 18z GFS had been very compact and abnormal within the suite, however, the 00z run, while still strong/compact, is much better and closer to the remaining guidance...particularly the most consistent ECMWF/ECENS mean. The 12z UKMET is extremely weak/sheared and therefore accelerates through the southeast, this places the UKMET out of balance feeding into the northern stream as well...making it less preferable in the northeast as well by 00z Wed. The 18z GEFS is more in line with the ECENS mean and 12z ECMWF...so would provide stronger confidence toward the ECMWF solution across the southern stream. But overall, a GFS/ECMWF blend is supported overall. Behind the main height-falls, a strong compact cold pocket originating from N Nunavut is expected to descend in the open northerly flow. It is the CMC is that is very cold and very strong with the associated shortwave in this Arctic stream that drops into MN/Dakotas by 00z Wed...and is clearly out of place in the ensemble suite. The UKMET is a bit stronger/faster like the CMC, though more tempered...but still less favored...so much like the prior long wave trof, an ECMWF/GFS blend is preferred though some incorporation of the 00z NAM is acceptable for higher resolution desires, particularly for developing Lake Effect. ...Approaching elongated/stretched shortwave entering Pacific NW late Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~ Preference: 00z GFS/GEFS blend Confidence: Average 07z update: Little change was noted in the newer 00z guidance, with the ECMWF still faster than the initial preference. The 00z UKMET/CMC were trending a bit more compact like the ECMWF but still remain slower and more on par with the timing of the GFS, yet still not ideally matched the GFS/GEFS. So will continue a preference of the GFS/GEFS at average confidence. ---Prior Discussion--- In the West...a progressive ridge builds in Monday to Wed ahead of the next system. A large global scale closed low sheds off its southern periphery shortwave energy that squeezes into the ridge allowing for north-south elongation, impacting the Canadian and Pacific Northwest Coast to about Cape Mendocino by 11.00z. There the ECMWF is uncharacteristically, fast and compact moving through the ridge...and while supported by a bulk of ECENS members, it does not appear correct given the stretching environment enhanced by the orientation of the higher terrain...so is less favored overall. The 00z NAM while moving about the same rate as the GFS/GEFS... is very strong, with the energy and therefore very sharp in the mass fields. So would hedge toward the GFS/GEFS by the end of Day 3, particularly in the Northwest and into the Northern US Rockies. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina