Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 233 PM EDT Thu Aug 15 2019 Valid Aug 15/1200 UTC thru Aug 19/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Exception: Non-CMC across Northern Tier/S Canada Confidence: Average 19z update: Small adjustments were noted with the timing of the lead shortwave height falls progressing through the Northern Plains into the Great Lakes by 00z MON with the UKMET/ECMWF, with little negative affect to the increasing agreement, though toward the end of Day 3; the spread increases in a typical manner. As such no adjustment is suggested for this area with respect to these models. The CMC however, did slow further and therefore positions the closed low and surface reflection well west of the other guidance enough to suggest its removal from the blend outright. Confidence remains average for this area. ---Prior Discussion--- The upper-level pattern continues with strong Southwest Ridge and broad cyclonic flow along the much of the northern portion of the United States. This trof produces broadly northwesterly flow across the Northern Plains into the Great Lakes with embedded small scale shortwaves moving through it. The base of the trof is centered over the Ohio and TN valley, where it intersects with return easterly flow under the subtropical high near Bermuda (SW). The frontal/confluence zone at this intersection continues to remain fairly active but also very stationary, with weak waves along it. Models do not have a strong agreement on timing, but there is good agreement on the existence of a dominant wave emerging out of the Southeast Sat into Sunday into the Northwest Atlantic north of Bermuda along 40N into Sunday. The 12z NAM/00z UKMET are strong while the 12z GFS/00z ECMWF suggest more flat/strung out features, but overall the pattern/orientation/placement supports a general model blend for this area. Back into the northern stream, convectively induced shortwaves emerge from the Northern Rockies through the Central Plains into the Ohio Valley for the next few nights, before a stronger northern stream Canadian wave drops east of the Canadian Rockies into the Prairies, dangling a frontal zone across the northern High Plains into Dakotas due to the lead height-falls by early Saturday. The 00z UKMET is a bit north/slower with the frontal push but the 12z NAM/GFS have trended toward better agreement with the ECMWF; yet remain slightly faster typical of bias. The 00z CMC also appears a bit slower than consensus to suggest lower weighting especially by day 3 in the Northern Tier/Southern Canada, but otherwise a general model blend appears solid. As such a general model blend trending toward a non-CMC blend or a GFS/ECMWF heavy weighted blend will suffice. While this is shaping up a bit better in timing/placement...confidence remains average given the importance of convection (upscale growth). The far western portion of the large scale trof will also start to become a bit more amplified at the end of the weekend, though the NAM/GFS and CMC are most aggressive, the ECMWF, UKMET are a bit weaker, allowing for a slightly faster southward progression. Longer term trends suggest the former has a slightly preferred trend in the ensemble suite but not significant enough to support anything greater than a general model blend with maybe a slight increase/weight toward GFS/GEFS/ECENS and CMC solutions. Confidence is average. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina