Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 239 AM EDT Fri Jul 3 2020 Valid Jul 3/0000 UTC thru Jul 6/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Final Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 6Z Update: The CMC and UKMET both trended slower with the shortwave entering the Pacific Northwest on Day 3, and the ECMWF trended stronger. The NAM remains the most amplified with the first shortwave across Washington and British Columbia through Saturday night. The UKMET is still weaker with the Gulf Coast upper trough compared to the model consensus, with no overall change in the model preference. Trough over the Northeast U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/ECMWF blend Confidence: Moderate The upper low that is departing the Northeast U.S. Friday morning will be followed by another round of height falls by Sunday across New England, as a shortwave rotates around a broad upper level trough over eastern Canada. At the surface will be a weak back-door cold front that sinks south along the East Coast, and a second cold front crossing New England by Monday morning. The models are in decent agreement on the timing of the first front. For the next trough over the Northeast, the NAM is a bit more amplified by Sunday morning, with the CMC also on the stronger side of the guidance. The 12Z UKMET is indicating a slower passage of the trough axis, with a stronger ridge axis across the Great Lakes and Ontario. A blend of the GFS/ECMWF should work well as a starting point. Trough over the Gulf Coast region ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/NAM/ECMWF Confidence: Limited-Moderate Along the Gulf Coast, a broad trough will develop beneath the ridge expanding from the Plains to the Ohio Valley on Friday. This trough will then be amplified by mid-level impulses rotating atop the ridge and across 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 becomes anchored along the Gulf Coast and towards the Southeast U.S. The models generally agree that the trough will persist through the weekend but unlikely to close off. The UKMET is weaker with this feature owing to a stronger central U.S. ridge compared to the other guidance. However, is should be noted that confidence drops 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: 00Z CMC/ECMWF/EC mean Confidence: Moderate A large closed low pivoting across the Pacific Northwest and into western Canada will remain nearly in place as several vort impulses rotate cyclonically around each other to reinforce the trough. Through Saturday morning, the guidance is in very good agreement with the position and amplitude of this feature. By Saturday afternoon, the UKMET is quicker to lift out the trough across the Pacific Northwest, and the NAM/GFS are stronger with this trough across British Columbia and Alberta on Sunday. The next disturbance drops southeast along the coast by Monday morning, and the NAM is a stronger solution with that shortwave and a bit more progressive. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick