Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 252 AM EDT Tue Jul 30 2019 Valid Jul 30/0000 UTC thru Aug 02/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation and Final Preferences/Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...East of the Mississippi River... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average ...07Z update... No significant model changes were noted with the 00Z ECMWF/UKMET/CMC compared to their previous 12Z cycles. ...previous discussion follows... Mid/upper-level troughing will generally remain over the eastern third of the nation with a northern and southern stream component. The northern stream component will track from the Great Lakes this morning to New England Thursday morning, with a cold front following along ahead at the surface. A southern stream component to to the trough will exist as a compact closed upper level low over the Gulf of Mexico or an elongated trough extending northward into the Gulf Coast states. While minor model differences exist with these features, they are small enough to allow for a general model blend as a preference. ...Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM/00Z ECMWF/00Z UKMET blend Confidence: Average ...07Z update... Despite ensembles trending away from a stronger trough offshore of the Washington/Oregon coasts Friday morning, the 00Z ECMWF/UKMET trended toward that idea while the 00Z CMC stayed similar to its previous cycle regarding strength. Given some of these deterministic trends, including that of the 00Z GFS which is still likely too strong, will adjust the preference to include these recent trends. ...previous discussion follows... Outside of the 12Z UKMET, the models have converged closer with the evolution of the closed low, located just off of the British Columbia coast this morning, as it reaches the West Coast. The closed low is expected to move inland into central British Columbia Wednesday night while a shortwave trough axis, extending southwest of the closed low, nears the coasts of Washington and Oregon early Friday morning. The 12Z UKMET is a slow outlier with the shortwave trough/closed low nearing Washington/Oregon Friday morning and the 00Z GFS is a strong outlier. A blend between the 00Z NAM and 12Z ECMWF is closest to the relatively agreeable ensemble means and will be preferred at this time. ...Southwest into the Great Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: near the 00Z ECMWF/UKMET Confidence: Below average ...07Z update... Despite some minor adjustments, the 00Z ECMWF/UKMET remained similar to their 12Z cycles concerning the vorticity max around the southwestern U.S. ridge and with the surface low/frontal boundary in the Plains. The 00Z CMC had some similarities to the ECMWF/UKMET, but was slower in its timing of the energy reaching the Dakotas. Therefore, the preference remains the same, but just to update with the 00Z cycles of the ECMWF/UKMET over their 12Z runs. ...previous discussion follows... There is generally good agreement on the strength and position of the southwestern U.S. ridge and on the idea for a convectively enhanced mid-level vorticity max to round the ridge Wednesday into Friday...tracking from western AZ to WY into the Dakotas. The GFS/ECMWF have had the best run to run consistency on the mid-level vorticity max with greater run to run changes noted in the NAM, UKMET and CMC. However, downstream into the Plains, the 12Z ECMWF/UKMET show better agreement with an area of low pressure at the surface in western KS o the latest ensemble scatter low plot clustering compared to the farther south 00Z NAM/GFS. For this reason, a 12Z ECMWF/UKMET blend is preferred, but confidence is low due to the uncertainties with convection and its influences on impulses rounding the southwestern ridge. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Otto