Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 134 AM EST Mon Dec 09 2019 Valid Dec 09/0000 UTC thru Dec 12/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Eastern CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z ECMWF/GFS blend (weight to EC) Confidence: Slightly above average 07z update: The 00z CMC is trending toward the better overall consensus but continues to still have a very cold thermal bias which has manifested consistently over the last few weeks and not verified well, but the mass/QPF fields are looking better to provide confidence toward a solution that is majority ECMWF blended with the GFS. ---Prior Discussion--- The global scale deep latitude trof is taking a more phased shape currently as presented by GOES-WV suite. The model guidance appears to have come into stronger consensus with respect to the timing of the northern stream shortwave and point where the southern stream shortwave decouple late Monday into Tues...and show strong timing/amplitude agreement aloft which translates to solid agreement in the depth/track of the surface wave and cold front. By late Tuesday, though the 12z CMC starts to fall out of tolerance in both the northern and southern stream. The southern stream, it is a bit stronger but also evolves into a more compact/deeper solution while the remaining sheared energy slides through the Appalachians into the Northeast in the other solutions. The 00z GFS and 12z ECMWF are in fairly solid agreement with only moderate differences noted in QPF. The 00z NAM shows a bit stronger inflection in this energy lifting through the Mid-Atlantic into the Northeast by end of Day 3 which is solid, but may be too wet, especially given the likely dynamic cooling, and potentially producing a bit too much snow...so a GFS/ECMWF solution is generally more favored but some localized inclusion of the UKMET/NAM may be employed if desired. ...Western CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00z GEFS with 00z GFS/ Confidence: Slightly below average 07z update: The 00z ECMWF trended even faster in the northern stream remaining generally north of the clustering; additionally with greater spacing difference north to south the southern stream shortwave was also slower and trended a further southward digging across the Southwest. While the CMC depicts a similar southern extent, its timing in both streams suggest the GFS/NAM timing may be a bit better. The UKMET is fast in both stream but supports the GFS more in both stream. However, the GFS is much faster than the 00z GEFS which is a split between the 00z GFS and ECMWF, close to the 12z ECENS mean. So will favor the GEFS a bit higher in a blend between it and the GFS. Confidence remains slightly below average given much of the energy is well upstream in the data assimilation poor Pacific. ---Prior Discussion--- In the West, a highly elongated shear zone/axis presses eastward reaching the Pacific Northwest midday Tuesday. The 00z/NAM both continue to be slightly faster in squeezing the trof and therefore stretching it NW to SE into terrain...opposed by the ECMWF (being slower with the upstream edge), rolls through the ridge more compact and then into the Northern High Plains a bit faster. Paired more with the UKMET/CMC but both are a bit more sharper. A secondary shortwave/speed max out of the Pacific, quick on the heels, amplifies along the Central West Coast and fills out the base of a progressive trof toward 12z Wed into Thursday. Typically, the ECMWF/ECENS mean assimilate the West a bit better, but the evolution here seems a bit less meteorologically sound given the shortwave, shape breaking through a tight ridge that would be better supported by the orientation of terrain naturally. So would be ok with a general model blend though, mass fields would suggest/support the GFS/NAM though by Thursday, the trof is nearly 60DM deeper than the CMC/UKMET/ECMWF across the West. This does not have much sensible weather differences through the end of the short-range period, so will favor a GFS/ECMWF/NAM blend to best represent the system(s), but with in a lower predictability regime, confidence is slightly below average. Additionally, this blend is not likely to be favored through Day 4/5 given this height/strength difference in the southern stream...please refer to WPC PMDEPD for additional information. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina