Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1225 AM EDT Thu Aug 15 2019 Valid Aug 15/0000 UTC thru Aug 18/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation...with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 18Z GEFS/12Z ECENS mean blend...North-Central U.S. Non-ECMWF blend...Southeast/Gulf Coast Non-NAM blend...Remainder of CONUS Confidence: Average The upper-level pattern starts off with strong ridging across the Southwest and northwesterly flow to its north, leading to broad troughing across the eastern half of the nation. The ridge becomes suppressed on Friday and into the weekend as upper-level troughing begins to impinge upon the Northwest, leading to broad quasi-zonal flow from the Pacific Northwest to the Northeast. Anomalous moisture will remain in place ahead of a slow moving front which will extend from the Mid-Atlantic region to the Gulf Coast, while impulses in northwest flow aloft keep the central Plains to the Midwest active with organized convection. There is broad agreement among the global models with the synoptic scale features across these two areas, but the 00Z NAM in general appears to be too amplified and therefore too wet with the energy it has digging down across the Midwest and into the Eastern U.S. through the period. Across the Southeast and eastern Gulf Coast region, the guidance continues to hint at a weak area of low pressure developing along the aforementioned front. The 12Z ECMWF in particular is strong outlier with this feature as it appears to be suffering from convective gridscale feedback. A non-ECMWF blend is suggested across this region. The guidance is reflecting some of its biggest disagreements with the troughing/closed low energy advancing through south-central Canada this weekend which impacts the evolution of a cold front across the northern Plains and upper Midwest. The 00Z NAM is notably farther north with its track of the closed low, and is farther north with its surface low feature as a result. The NAM leans on the slower side of the guidance with its frontal evolution. Meanwhile, the 00Z GFS is the fastest solution with its height falls and the surface front. The 12Z CMC/ECMWF solutions are a tad slower than the GFS, with the 12Z UKMET the slowest solution overall with the entire system. The 18Z GEFS mean and 12Z ECENS mean both actually offer a nice compromise solution to resolve the broader model spread, as both ensemble means are clustered fairly well with each other. A blend of these solutions would be closest to the CMC and ECMWF when comparing to the deterministic guidance. Elsewhere, the models actually show reasonably good model mass field agreement by the end of the period with respect to strong height falls dropping down across western Canada. Based on the current guidance, a non-NAM blend will be preferred across the CONUS, with exception to the north-central U.S. where a blend of the 18Z GEFS mean and 12Z ECENS mean will be preferred. Caution is also again urged with the ECMWF across the eastern Gulf Coast and the Southeast. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Orrison