022 FXUS63 KGRR 200504 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 104 AM EDT Mon Jul 20 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 /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 104 AM EDT Mon Jul 20 2026 Smoke continues to support MVFR conditions at AZO/MKG and IFR at GRR. Given persistence forecast from previous days, espect conditions to remain the same through the night if not deteriorate slightly near daybreak. Mixing then increases favoring VFR conditions at all terminals beginning mid to late morning. A line of storms potentially arrives from the west after 00z Tuesday, however existence of timing and storms remains uncertain. Given this have elected to go PROB30 at GRR/MKG to start and can re- evauate with future packages. Gusty winds from the south to around 20 knots are expected today, with locally higher winds and MFVR and lower conditions possible in any storms tonight. && .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...Thomas MARINE...Ostuno

NWS GRR Office Area Forecast Discussion