Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1258 PM EDT Thu Jul 02 2020 Valid Jul 02/1200 UTC thru Jul 06/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Preliminary Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Eastern U.S. trough ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend, less weight on the CMC D3 Confidence: Above average early, average D3 Two features of interest embedded in the persistent eastern CONUS trough. The first is across New England where a wave of low pressure and back door type cold front will sag southward late Friday into Saturday. The GFS is a bit faster than the remaining consensus, but not outside the typical spread by D3, so a general model blend is acceptable. Along the Gulf Coast, a broad trough will develop beneath the ridge expanding from the Plains into the Mid-Atlantic on Friday. This trough will then be amplified by mid-level impulses rotating atop the ridge and into the Gulf Coast. While discrepancies exist in the timing, intensity, and placement of these smaller scale shortwaves/MCVs, the end result is a broad and modest trough that gets stuck along the Gulf Coast and towards the Southeast CONUS. The CMC closes off a low along the central Gulf Coast by Sunday, and while the position of this feature is similar to the central trough axis from the remaining guidance, it is the only model indicating a trough of that strength. Otherwise, a blend of the remaining models should suffice. However, is should be noted that confidence drops considerably by Sunday due to interactions with the smaller scale shortwaves, and possible surface low development beneath this trough. Deep upper trough/closed low across the Pacific Northwest and western Canada ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS or CMC blend Confidence: Slightly above average A large closed low pivoting across the PacNW and into western Canada will spin nearly in place as several vort impulses rotate cyclonically around each other to reinforce the trough. Through Saturday, the guidance is in very good agreement with the position and amplitude of this feature. However, by late D2 into D3, the GFS becomes more amplified with a subsequent shortwave ejecting from the base of the trough and northeast towards Alberta, Canada, while the CMC lags this feature leaving a flatter overall trough. The GEFS is well aligned with the other guidance (ECMWF/ECENS/NAM/UKMET) which suggests the GFS is too amplified. The GFS also leaves a higher QPF signal due to its stronger impulse, and for this reason is removed from the preference. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Weiss