Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 133 AM EST Tue Dec 10 2019 Valid Dec 10/0000 UTC thru Dec 13/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Eastern CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average 07z update: The 00z UKMET weakened the influence of the greater convective/slantwise instability activity across the Piedmont Wed morning that enhanced the jet a tad...this placed the mass fields more in line with the remaining guidance. Small mesoscale differences in dry/moist advection remain and still be needed to be ironed out, but synoptically in mass fields/frontal timing; a general model blend can be afforded. ---Prior Discussion--- The model guidance mass fields continue to tighten with the northern stream large scale cyclone and associated deep surface low in the Great Lakes currently. The attendant cold front is also well timed and placed through the mid-week including the very strong jet. Smaller scale, dry slot/moisture ribbons continue to come into tighter agreement as well but the 12z UKMET has a wet bias currently with this system and it looks it again along the East Coast/Piedmont region that feeds a bit upscale to the jet holding the trailing inflection/right entrance a bit to make it a bit less favorable. Other-wise the 00z GFS/NAM and 12z ECMWF continue to be very tight overall. Additionally, the Arctic shortwave/kicker is timed and shaped well to have increased confidence in the overall evolution through to end of week in the East. Confidence in a 00z GFS/NAM and 12z ECMWF Blend is slightly above average. ...Western to central CONUS (Gulf Coast Day 3)... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GEFS/ECMWF and 12z ECENS blend Confidence: Average 07z update: The 00z ECMWF trended a tad slower and therefore a bit further south in the southern stream, this was bolstered by a consistency in the 00z GEFS with the 18z GEFS, and away from the weaker/faster 00z GFS, to retain confidence in the ECMWF/ensemble initial preference. However, the southward trend does at least call into question the 00z NAM that is a bit more compact (slightly faster) that leads to a northward pull of Gulf moisture/forcing..so perhaps a bit less influence that initially thinking is warranted. The UKMET held serve, but the 00z CMC trended toward the GFS/UKMET side of the suite at the end of the forecast period (favoring stronger northern stream forcing), deflating some of the gained confidence from the GEFS. So a 00z GEFS/ECMWF and 12z ECENS mean blend is preferred at average confidence. ---Prior Discussion--- In the wake of the large Vortex that has dominated the Northeast portion of the continent, enhanced ridging exists along the West Coast, with an approaching southeast shortwave trof extension of a larger Alaskan closed low into the Pacific Northwest to N California by late Tuesday. This wave continues to stretch/elongate through the ridging helping to split the shortwave energy into a northern stream packet through the borderland Rockies as well a southern portion of the wave entering the Great Basin. The GFS has been trending best with the evolution of this situation with a stronger reflection in the southern stream while the northern wave keeps pace with weak phasing. Only the 12z UKMET is out of tolerance through the Rockies, still favoring a stronger northern stream which leads to a faster evolution and surge of the jet across the Central MS River valley toward the end of the forecast period... which deflates the subtropical shortwave lifting north and squashes the development of Gulf Coast system at the end of Day 3. Obviously, the UKMET is not favored in the evolution. With the 12z ECMWF/ECENS trending toward the GFS/GEFS evolution there was growing confidence. However, the 00z GFS shifted toward a weaker solution and starting looking more like the UKMET, becoming very weak and fast by the end of Day 3. While reducing confidence, hoping this is a one-off solution given its break from growing ensemble congruence. So will favor a 00z NAM/18z GEFS and 12z ECMWF/ECENS mean solution at average confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina