Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 224 PM EDT Wed Jul 08 2020 Valid Jul 08/1200 UTC thru Jul 12/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation with Model Preferences/Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Closed low moving east across south-central Canada through Friday Associated cold front crossing the northern Plains Wednesday/Thursday and the Great Lakes Friday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS/UKMET/ECMWF blend Confidence: Average 19z update: The ECMWF/UKMET continue to remain fairly agreeable and the GFS is a bit fast initially, becoming a bit more amplified (likely due to timing with the coastal low) but still much more tolerable compared to the NAM or 12z CMC which continue to be too amplified. As such, will keep with initial 12z GFS/UKMET/ECMWF blend preference. ---Prior Discussion--- A stronger than normal, fairly compact shortwave over South-Central Canada will continue to lift out toward NW Ontario; broad diffluence on the northeast side of dominant southwest ridge will support an MCS across the north-central Plains tonight that will grow upscale into a solid shortwave through the Midwest. The 12z NAM, possibly due to higher grid network, shows typical over development with a very strong/very compact wave that maintains itself through the Central Great Lakes Friday evening. This is enough to suggest the NAM is likely too aggressive at this point, especially compared to earlier runs. The 12z GFS and 00z ECMWF continue to anchor the suite otherwise, though typical timing differences manifest with the GFS fast and ECMWF slow. The 00z UKMET seems a solid middle ground that supports both the convective complex track/placement feeding on the low level jet on the edge of the strong cap; but also not building the resultant upscale shortwave in the manner of the NAM, and even the 00z CMC. As such, will favor a 12z GFS and 00z UKMET/ECMWF blend at average confidence (given the influence of convective features to the synoptic evolution, which is still a bit too chaotic to have high confidence). Low pressure moving northeast along Eastern Seaboard into this weekend ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z ECMWF/ECENS/GEFS/UKMET/CMC blend Confidence: Average to slightly above average 19z update: The 12z UKMET shifted north initially and presents a similar timing to the development of the surface wave as the ECMWF/initial preference. The UKMET remains a bit on the stronger side with the worst case scenario, but its placement/track timing look comparable to include into the preference. The 12z GEFS while shifting a bit west of the prior GEFS, remains similarly timed indicating the uncertainty in the formative stages, but still close to the initial preference for continued preference over the GFS itself. Likewise, the CMC is fairly similar, but weaker than the UKMET. As such, will favor a 12z ECMWF/UKMET/CMC/GEFS blend at average to slightly above average confidence. ---Prior Discussion--- A fairly weak shortwave is noted along the VA/NC border progressing east on GOES-E WV, along with the Gulf stream convection SE of Cape Fear. The combination is expected to grow upscale and support a weak surface wave off SC to lift north. The 12z NAM, possibly due to the small grid scale, rapidly develops the complex and cyclonically rotates it northward, even faster/deeper than the 00z solution. This further enhances into Day 2 and Day 3, with the approach of the upstream over-amplified shortwave across the Central Great Lakes/northern Ohio Valley, which is also not favored. The GFS continues a trend of left of cluster (including significantly from GEFS solutions) as well as fast, typical of negative bias keeping it out of the preference. The UKMET has been stubborn on lifting the more vertically aligned vortex northward and is delayed relative to the overall suite. While, not out of the realm of possibility and likely a worse-case scenario supporting stronger/deeper surface cyclogenesis as it clips SE New England by 12.00z; it is not favored in the blend at this time. This leaves the CMC and ECMWF along with GEFS/ECENS means solutions; the CMC seems to help the NAM/GFS case lifting north but does not go to the extreme in convection/depth of the mid-level cyclone; much more sensible within the longer term ensemble suite/trend but also close to the GEFS in timing (if a tad left, which is ok). The ECMWF/ECENS show greatest consistency but also a tad slow evolution, which is a typical negative bias...so cannot support a 100% ECMWF blend...but trends and other solutions make it fairly close. As such will favor an ECMWF dominant blend with inclusion of the CMC/GEFS and ECENS means to help account for uncertainty. Confidence remains average, given the influence of convective upscale growth/proximity to deep latent heat source and uncertainty of outflow/DPVA from approaching shortwave out of the Ohio Valley. Trough moving into the Pacific Northwest Thursday, over-topping the ridge into the Upper Midwest by Sat ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average 19z update: While the CMC continues to be a tad south of the faster NAM/GFS...it is more in line with the latitude of the ECMWF, now that it has picked up pace. The ECMWF, like the CMC, continue to be on the slower and therefore southern side of the guidance, but not sufficiently to suggest any departure. As such, will favor a general model blend at slightly above average confidence. ---Prior Discussion--- A middle to low amplitude shortwave progressively exits the Pacific NW by Friday going from positive to neutral to slightly negative tilt as it over-tops the core of the ridge in ID/W MT into Sat. Only the CMC is generally slow though the placement of the core of the shortwave as it transition through the wave shows modest spread before stretching across the Upper Midwest by late day Sat. The uncertainty with convective placement is still related to the cap strength and progression/placement relative the preceding wave and its convective activity on Thursday through Friday. The ECMWF being slower and later, allows for the cap to press further SW than the GFS/NAM/UKMET that had already exited a few hours early and allowed for the low level environment/cap to rebuild relative to the ECMWF. These are typical biases to suggest a middle ground between the two camps is preferred. As such a Non-CMC blend is preferred, which will tilt the overall blend closer to the increased members of the UKMET/GFS/NAM relative to the ECMWF with respect to QPF placement. Larger scale trof dropping into Pacific NW Saturday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average 19z update: The ECMWF trended a bit weaker/broader with the trof overall, but held with the position of the trof axis a bit faster than the GFS/NAM/UKMET. Overall, no significant differences in thinking to continue a general model blend preference though the moderate spread keeps the confidence at average. ---Prior Discussion--- Perhaps due to the later exit of the preceding shortwave, the ECMWF/CMC show shorter wavelengths and slightly increased ridging on Saturday, allowing for an eastward/faster progress of the longer, higher scale trof coming through the Pacific NW on Sat into Sunday. Given the moisture stream is generally upstream of the trof axis, this is a limited affect to the Pacific NW with respect to sensible weather. Additionally, longer term ensemble trend continue to migrate toward a central compromise with time, and suggest a general model blend is afforded by the end of day 3 in this region. Yet, the remains modest spread in the timing to have only an average confidence in this blend, given it is a bit more washed out due to the modest spread itself. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml This product will terminate August 15, 2020 with the 21Z issuance: www.weather.gov/media/notification/pdf2/scn20-58pmdhmd_termination. pdf Gallina