Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 134 AM EST Wed Dec 11 2019 Valid Dec 11/0000 UTC thru Dec 14/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Larger scale CONUS (Confidence discussion)... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The broad global trof that has dominated the eastern half of the NA continent gives way toward a more zonal pattern over the next few days, lead by smaller shortwave energy packets along the remaining NW-SE stretched trof currently entering the West Coast (one north along the Vancouver Island/Puget Sound and southern near Cape Mendocino in N CA). Eventually, the lead northern and southern stream waves progress into the Plains before giving full way to a strong Pacific jet with numerous very short wavelength/low amplitude wave parade into the Pacific Northwest, midday Wed to late Friday with the approach of a deeper latitude shortwave trof entering Sat. High confidence in general model blend will exist for the remaining global scale trof and frontal zone crossing the East Coast/Northeast today, afterward however, the timing/spacing of numerous smaller scale features and their interactions lead to large internal variations, with moderate to high differences in the sensible weather predictability even though the large scale evolution of a broadly negative tilt trof and Southeast surface low development is agreed upon. So bottom-line, confidence is slightly below to below average for the internal precise placement of important weather elements as the system comes together by the weekend. ...Northern Stream shortwaves across Northern Tier into Great Lakes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~ Preference: Initially 00z GFS/NAM and 12z ECMWF thru 13.06z 00z GEFS/NAM/ECMWF and 12z ECENS after Confidence: Slightly above average 07z update: The ECMWF trended faster/tighter with the secondary shortwave in the Northern tier, though a bit stronger though the base of the trof, much like the NAM (though a tad faster). The GEFS still encapsulates the GFS without going as aggressive as the operational run; as such will keep with initial preference. ---Prior Discussion--- The northern stream, starting with the shortwave entering the PacNW at this time, is better handled through the short-range period...with a solid consensus/general model blend working across the northern tier into the Great Lakes by Fri. On its heels, though, there is more variation, mainly in timing spacing between the Pacific shortwave energy and the digging Arctic cold air. Here the ECMWF, NAM and GFS are solid in timing, but the GFS shows a typical though minor to moderate fast bias with the cold air and therefore greater amplification. The 00z NAM, while spaced nicely, shows a greater reflection of the wave in the height fields, but that seems to be the only negative impact. So would be shifting more toward a 18z GEFS mean, 00z NAM, 12z ECMWF blend solution for this system but at average to slightly above average confidence. ...Southern Stream/developing Southeast surface low Fri/Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/NAM/ECMWF blend (with some GEFS/ECENS mean) Confidence: Slightly below average 07z update: The 00z ECMWF and UKMET both trended slightly faster with the initial wave as well as stronger with the upstream shortwave through the Central Plains on Sat, leaning toward the GFS evolution. While both are lighter/less sharp with the redevelopment of the deformation zone in AL/TN on Sat than the GFS...there is growing evidence toward this. Additionally the GEFS was shifting this way as well, providing additional confidence. The UKMET while still strongest/deepest with the shortwave energy was more elongated through the negative tilted larger scale trof, but still favors a the center of the surface wave along the spine of the Southern Appalachians. So while the UKMET is not used in the blend it can provide confidence toward a GFS/ECMWF blend (with some inclusion of the GEFS/ECENS mean to account for still moderate to high spread/run to run variations). Confidence is slightly below average. ---Prior Discussion--- The southern stream systems/energy are more uncertain, mainly driven by the uncertainty in models handling the internal waves of the zonal jet. Initially though the lead wave is a bit more certain in its timing through the 00z GFS trended a back toward a stronger and further south solution which shortens the spacing from the northward returning subtropical shortwave and associated moisture/instability flux out of the Gulf Thursday. The tighter solution of the GFS leads to a longer retention of the wave relative to a more favorable 00z NAM/12z ECMWF and CMC solutions that fit the ensemble suite better; the UKMET remains unresolved with the wave (well too weak). Getting the initial setup is going to be critical toward the evolution/internal sensible weather across the Southeast up the East Coast by 12z Sat...because the shortwave emerging from the 150kt 250H jet out of the Pacific/Intermountain West, interact and lead to a general larger scale negative tilt to the 5H pattern. The GFS being stronger upstream, enhances the deformation zone across AL into TN greater than the ECMWF which is weaker and more progressive leading to more moisture/flux convergence out of the Gulf and eastern Atlantic across the Carolinas. The 00z NAM which has initial conditions a bit more favorable initially than the 00z GFS; does evolve a stronger more compact upstream wave (though in line with typical negative Day 3 bias), and is a split between the GFS and ECWMF camps. The CMC is uncharacteristically progressive with the entire large scale trof and is dismissed as the wave should be waiting for the larger scale height-falls emerging from the strong upstream jet. So all considered, will be favoring the ECMWF/ECENS mean across the Southeast by the late week/Sat, though incorporating the NAM may help hedge the moderate to high internal uncertainty. ...West... ~~~~~~~~~~~ Preference: 00z GFS/NAM/ECMWF Confidence: Average 07z update: Small timing adjustments slightly faster in the ECMWF (north too), and little substantial changes in the UKMET/CMC, keep average confidence on the initial NAM/GFS/ECMWF blend ---Prior Discussion--- As stated in CONUS discussion above, parade of small amplitude shortwaves in strong zonal jet make deciphering a preference extremely difficult given the spacing to waves may be below 6hrs and where synoptic forcing hits orographic forcing enhancement is best handled by a general model blend and hit hazards at longer time scales such as 12/24hr packs. Still, toward the end of the train, a stronger/greater amplitude shortwave tracks through with some moderate neutral to negative tilt orientation late Friday into early morning Sat with an associated surface cyclone. Remarkably, the global guidance is fairly agreeable with the timing and mass fields as a whole, providing some confidence. The large differences are the width of the upper level system, with the GFS a bit more slower and broader supported more by the CMC while the NAM/ECMWF are well placed/shaped but narrower and the UKMET is most narrow and negatively tilted. Will hedge more of a compromise between the 00z NAM/GFS and 12z ECWMF. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina