498 FXUS63 KGRR 191857 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 257 PM EDT Sun Jul 19 2026 .KEY MESSAGES... - Stormy Monday Night - Upper Troughing Continues && .DISCUSSION... Issued at 256 PM EDT Sun Jul 19 2026 - Stormy Monday Night A vigorous upper shortwave trough rounds the top of an upper high centered over Colorado tonight and then phases with troughing over eastern Canada on Monday. A surface low deepens as it moves north of Lake Superior Monday afternoon, with a trailing cold front to focus convection across Wisconsin. There is some uncertainty on the strength and timing of the convection as it crosses Lake Michigan and moves into Lower Michigan Monday evening. The hi-res convective-allowing models show several hours of spread on timing, from late afternoon to late evening, so confidence is low, but the forecast blend has the higher POPs moving in around midnight. Deep layer shear is forecast to be greater than 35 knots along with modest instability during the evening, waning overnight. The main threat appears to be downburst winds associated with bowing line segments along with large hail. The threat should be ending Tuesday morning as the cold front pushes south. - Upper Troughing Continues The large scale pattern of ridging across the SW CONUS and troughing across the NW CONUS should keep the Great Lakes region in a northwest flow pattern for the next week at least, with occasional cold front passages that could focus convection. THe next one appears to be next weekend. Overall, a cooler and drier than normal weather regime. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 158 PM EDT Sun Jul 19 2026 Main challenge with flight category continues to be smoke at ground level to 6,000 feet. Visibility is expected to range between 3SM and 8SM based on latest observations from the region. Not enough horizontal movement of air to get the smoke out of here through Monday morning, but there may be some exchange of cleaner air from the top of the scattered/broken 4,500 to 6,000 ft cumulus cloud layer this afternoon which is helping to slowly improve things. && .MARINE... Issued at 256 PM EDT Sun Jul 19 2026 Winds and waves will be increasing on Monday and a SCA/BHS will be needed from Monday into Wednesday. South winds on Monday will go west by Tuesday morning then northwest Tuesday afternoon, and then north Tuesday night, when gales are possible along with waves building over 6 feet. Conditions should rapidly improve on Thursday as high pressure builds in. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Air Quality Alert until midnight EDT tonight for MIZ037>040- 043>046-050>052-056>059-064>067-071>074. MARINE...None. && $$ DISCUSSION...Ostuno AVIATION...CAS MARINE...Ostuno

NWS GRR Office Area Forecast Discussion