Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 122 AM EST Fri Dec 06 2019 Valid Dec 06/0000 UTC thru Dec 09/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/ECMWF blend with low weight inclusion of the UKMET/NAM Transitioning to ECENS/GEFS mean blend for Central/Eastern CONUS after 72hrs. Confidence: Slightly above average until 72hrs...slightly below afterward East of 100W. 07z update: The 00z UKMET/CMC both trended a bit faster in the northern stream, yet the CMC continues to have a very cold bias across the Rockies thermally to have much confidence in its QPF phase to incorporate in the blend, though the timing/placement of the trof looks more center to the overall spread. The 00z ECMWF trended a bit more connected/phased through the length of the trof, slowing in the northern stream, but picking up pace with the closed low in the Southwest. This places it in line with the GFS south, but slower in the north, particularly after 72hrs...further muddying the confidence into the Eastern third of the CONUS. So will start transitioning toward more of a general model blend in both the northern and southern streams, yet still weighting the 00z GFS/ECMWF higher in the blend...eventually transitioning to the 00z GEFS/12z ECENS mean blend for the Central/Eastern CONUS after 72hrs. ---Prior Discussion---- Model agreement continues to be very strong across the CONUS, particularly through 48hrs (08.00z Sunday). Model spread increases after this point as the large closed low off the N CA coast breaks down slowly with some infusion of northern stream energy, before the northern stream begins to decouple and accelerate eastward. This model spread is contingent on how much energy sheds southward and how fast the lead northern stream slides into the Northern Plains. The 12z ECMWF/ECENS have shown the most run to run consistency, however, did depict a slightly faster solution through the northern Plains, atypical of its bias. The sticking point was the strength of the jet behind the wave to the strength/amplification swinging out of the Arctic with a more concentrated Arctic cold pool, which no other solution appeared to depict as strong. The 00z GFS, however, shifted almost in sync with the EC/ECENS mean with a stronger Arctic shortwave, faster translation through the Northern Plains...building confidence toward a blend with GFS incorporation (ECMWF/GFS blend). The reinvigorated closed low, will drop south along the CA coast, with more typical timing differences... as the 00z GFS/12z UKMET outpace the 12z ECMWF/NAM. The GFS however, did trend a bit slower adding additional confidence toward the slower ECMWF/NAM. However, the known bias of the ECMWF/NAM are slower more compact solutions by the end of Day 3...especially as the ECENS mean/GEFS mean are more progressive. As such a 00z GFS/NAM and ECMWF blend is more favored in the southern stream, even as pieces emerge into the Central CONUS. By the end of Day three, a broad but deepening surface low/trof extends from the Great Lakes to the Southern Plains, under influence of the northern stream digging across the Plains, and broad height-falls/ broad 250mb jet provide large scale, less focused ascent by 12z Monday. While the larger scale pattern is coming into agreement, small timing, placement differences of the internal shortwave features/pieces lead to large variation in the QPF/thermal profiles across the eastern US. This even includes, uncertainty in the axis of strengthening Eastern Atlantic return flow (weak shortwave), affecting the Eastern Carolinas Monday morning. This would favor hedging toward the ensemble means to pull out meaningful/best clustering of axis of QPF/forcing at relatively low confidence at this point (even though the larger scale pattern is agreeable. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina