Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1236 AM EDT Tue Apr 07 2020 Valid Apr 07/0000 UTC thru Apr 10/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Initial Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Surface wave moving through Great Lakes late Tue/Wed then sliding offshore along 40N Wed/Thurs ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend (weighted heavy to 12z ECMWF/ECENS) Confidence: Average A weak surface wave currently in SD, will progress through the Great Lakes later today between the stronger deeper closed lows over the Southwest and Eastern Canada but also prior to the stronger upstream Pacific wave. So, the mass fields do not indicate strong mid-level shortwave with this feature but dual jet structure) and low level jet warm advective processes maintain it well before it grows deeper offshore south of Long Island by Wed, along the base/favorable cyclonic curvature aloft from the Eastern Canadian cyclone. The 00z NAM is clearly stronger/more amplified aloft initially, a perhaps a tad north within the ensemble surface cluster, but is paired with the 12z UKMET to give some increased credence. The 00z GFS continues to be fast relative to the suite and the CMC is very slow. The ECMWF/ECENS mean are more central to the packing and will receive greatest weighting in the preference, but to account for some uncertainty, will support a Non-CMC blend at average confidence. Upper Trough Digging Across Great Lakes; Surface Low Developing Off New England Coast Day 3 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/12z ECMWF blend Confidence: Average Strong Omega block initially over Northern Canada, will direct Pacific jet to undercut it through central Canada. Binary shortwave interactions will lead to rapidly developing/devolving cyclones along the shear axis until reaching the Upper Great Lakes/Midwest by late Wed into Thursday, starting to strongly amplify aloft to a deep closed low that will swing through the Lower Great Lakes by Thursday. In the process a strong embedded shortwave will drive height-falls/negative tilting through the Mid-Atlantic and help transfer the center of the upper low to a much stronger closed deep cyclone in New England/Gulf of Maine by 00z Friday. A clear outlier manifest early, mainly in the initial setup from the downstream wave: the 12z CMC. A weaker core through Manitoba/W Ontario and slower exiting wave combine to accelerate the nose of the jet and associated new triple point low faster and further south with the fastest cold front through the Mid-Atlantic/East Coast, which is not preferred. On the opposite side of the spectrum, the 00z NAM is very strong with the initial center low/occluded surface wave in Ontario, which leads to the triple-point and upstream shortwave to dig south and develop slower. This is paired with the UKMET, but unlike the NAM, it rapidly deepens the surface wave along the Gulf of Maine, likely with over-aggressive latent heat release and feedback to cyclone deepening (which the UKMET has a known bias toward) to be the strongest solution by the end of Day 3. The 18z GFS which had been slow/delayed due to initial interaction with a faster southern stream closed low; no longer has this connection and trended slightly faster in the 00z run, just outpacing the ECMWF and now is more in line with the 18z GEFS. Given the ECMWF/ECENS mean show solid consistency and are central to the overall suite, the GFS combined with the ECWMF seems an appropriate blend, while keeping the door open toward a stronger solution with future cycles. Confidence is average given the dynamic evolution, harder predictability (undercutting the Omega Block to the north). Slow moving southern stream (S CA/Desert Southwest) closed low. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model through 09.12Z; 12z CMC/ECENS mean and 00z GFS/NAM blend Confidence: Above average becoming Average after 09.12z Deep closed low off Central CA will continue to slide south along the CA coast late Wed. Models continue to handle a similar evolution through this point. As the inner core differences grow, with timing/magnitude, the resultant binary interaction differences magnify as the typically do mainly late Thursday. The consistent outlier, GFS, has seen a significant shift back west with the 00z run, and while it is quicker to break down the cyclone, it is quite central to the placement as well as hinting at the proper orientation of the internal wave, relative to the remainder of the guidance suite, particularly the 12z ECENS mean. The 18z GEFS was more sensible than the 18z GFS, but given the adjustment seen, it would not be surprising to see the 00z GEFS shift back toward the ECENS mean later. The 00z NAM, while stronger, typical of the late-term bias, looks sensible in placement/timing as the ECENS mean and the 00z GFS and 12z CMC, providing some confidence in a blend of these solutions. The 12z UKMET is now the clearest outlier, showing a typical negative bias of over-amplifying a vorticity center, which sends the overall closed low wobbling back west well outside of the CMCE/ECENS/GEFS suite, and is not considered for the preference, at this time. The 12z ECMWF is similarly unbalanced favoring a westward wobble on Day 3; and is a distinct westward member of the entire 12z ECENS suite. When this occurs, it is typical to not verify very well and reduce its confidence toward inclusion. As such, a general model blend is supported through 09.12z but transitioning to a 12z CMC/ECENS mean and 00z GFS/NAM blend. The aforementioned concerns with the GFS/NAM are likely to offset in the blend to have some confidence; yet, it is only considered average after 9.12z. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina