Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1243 PM EDT Fri Mar 27 2020 Valid Mar 27/1200 UTC thru Mar 31/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Southwest to Great Lakes strong cyclone today to Monday...Secondary Mid-Atlantic coastal low late Sun/Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z NAM/GFS and 00z ECMWF blend through 30.00z 12z NAM and 00z ECMWF/ECENS blend thereafter Confidence: Slightly above average prior to 30.00z, average after Models continue to trend together especially through the Plains into the Great Lakes by late Sunday. The 00z CMC/UKMET show similar evolution but the timing remains slow relative to the increased clustering in the ECENS mean/GEFS and the operational NAM/GFS and ECMWF, with the 12z NAM, 00z ECMWF/ECENS mean showing the greatest congruence. The NAM does depict a slightly faster/stronger solution as well as the typical cold bias through the lowest layers, so this may be a p-type issue,(please refer to QPFHSD for additional winter weather); but will add the GFS/GEFS into the blend to account for some slower/southward members of the suite, including some older continuity. So a 12z GFS/NAM and 00z ECWMF blend preferred at slightly above average confidence. By late Sunday into Monday, the deep cyclone over the Great Lakes has fully matured and is starting to fill/weaken and shift toward coastal surface cyclogenesis. The typically faster GFS leads the charge again and may be a bit too fast initially allowing for the surface cyclone it wrap up closer to the coast/Gulf of Maine than other guidance members, with the NAM/ECENS mean more centralized in the overall guidance suite. As such will shift toward a 12z NAM/00z ECMWF/ECENS preference for the coastal low portion on Day 3. Confidence is average for this portion given model spread and sensitivity of timing difference in the weakening/filling phase transferring eastward. Combining pair of shortwaves along West Coast late Sat/early Sun, tracking through Southwest Mon...TX/OK Panhandle surface low Mon ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z NAM/GFS and 00z ECMWF blend Confidence: Slightly above average Currently, GOES-W WV depicts a compact shortwave west of WA state that is expected to dig southwest toward the Central CA coast early Sunday. Upstream a fast wave through the Gulf of AK will take the prior's place and shear into a sharper/full-latitude wave along the West Coast. The 00z CMC is the only deterministic member that is struggling with this evolution. The 12z GFS is a tad weaker than the remaining guidance but this does not seem to be a major issue, as the wave combines and progresses into an average length shortwave trof through the Southwest. The 12z NAM/GFS eventually show some faster progression, relative to the ECMWF. The timing of the jet streak undercutting and providing a broad diffluent pattern over the High Plains late Monday supports lee cyclogenesis across the TX/OK panhandle by 00z Tuesday. The 00z UKMET however, is slower with the jet exit region but also stronger with the low level return flow, supporting increased convective activity and upscale growth further south over the Permian Basin, which may occur but given better agreement on day 3, further north...will support a blend of the 12z NAM/GFS and 00z ECMWF at slightly above average confidence. Deep Gulf of AK gyre with first peripheral shortwave/associated surface triple-point/front entering PacNW Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS/06z GEFS and 00z ECMWF/ECENS blend Confidence: Average to slightly below average A favorable large scale set-up for broadening/upscale development across the Gulf of AK will be occurring through the weekend as a strong shortwave in broad cyclonic flow allows for a broader/larger cyclonic gyre to form across the Gulf of AK late Sunday. Along the periphery of the developing large scale wave, strong speed vorticity with embedded shortwave will press strong convergence along the occluded front near an enhancing triple-point near Vancouver Island toward the Juan de Fuca Strait. There is large model variance in the timing/strength of the wave and the gyre itself. The 00z UKMET/CMC are less favorable/less cyclonic across AK from the polar vortex to remain more flat and progressive to be more favorable especially given longer term trends in the ensemble suite toward a broader cyclone evolution. The 12z NAM suggest this as well, but is quite fast and shows some typical day 3 over-amplification of the wave compared to the GFS/ECMWF solutions. The 00z ECMWF is strangely much stronger and forward compared to the bulk of ECENS members which are closer to the GFS/GEFS overall. Still the timing/placement of the ECMWF along with the GFS/GEFS and ECENS mean suggest some confidence for a blend to be preferred. Confidence in the evolution is solid, but internal changes, run to run variations are likely to suggest confidence overall in the blend is average to slightly below average Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina