716 FXUS63 KGRR 200530 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 130 AM EDT Thu Aug 20 2026 .KEY MESSAGES... - Drier and Comfortable Air on Thursday - Showers and Chance of Scattered Thunderstorms Late Week && .DISCUSSION... Issued at 258 PM EDT Wed Aug 19 2026 - Drier and Comfortable Air on Thursday The more humid air has been nudged south of the area along a weak cold front, and dew points are trending into the upper 40s to 50s for much of the area, especially in Central Michigan. With dew points still in the 60s this afternoon near I-94 and favorable lapse rates 850-700 mb, there is a slight chance for low-topped and isolated showers to develop this afternoon or tonight, especially closer to Jackson, as portrayed in a few of the HREF member CAMs. - Showers and Chance of Scattered Thunderstorms Late Week Global models continue to depict an upper-level trough digging from western Hudson Bay toward Michigan Fri-Sat, then cutting off a low over the central/northeast Great Lakes region Sun-Mon. Slightly warmer and more humid air should briefly nose back in on Fri before the next weak cold front passes through Fri night. Scattered showers and thunderstorms may develop in the vicinity of the front amid CAPE around 1000 J/kg (some ECE members depict MUCAPE as high as 2000 J/kg). Deep layer shear may be relatively modest, around 20 knots, limiting the severe weather potential. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 130 AM EDT Thu Aug 20 2026 Thanks to an incursion of drier air at lower levels the probability for maintaining VFR conditions through the period is greater than 90 percent, except for JXN and BTL, which have an estimated 30 percent chance of experiencing brief MVFR visibility restrictions towards sunrise. This reasoning is based upon the presence of a weak surface boundary in that area where greater dewpoints/RH values appear to be pooled. The probability of MVFR occurrence is too low to explicitly mention in the TAFs. The only other change was to introduce a cloud deck around 8000 feet this morning for the southern terminals associated with convective debris from thunderstorms to the west and southwest of the area. These clouds are high enough that they likely wouldn`t interfere with the previously mentioned possible fog production. Made minor adjustments to winds this update as well. Based on high resolution guidance, MKG may see lake breeze augmented winds more from the northwest this afternoon instead of the typical west-southwest direction. && .MARINE... Issued at 258 PM EDT Wed Aug 19 2026 Waves and swim risk remain low with light winds tonight and Thursday. Then Friday and through the weekend, there will likely be some medium-high swim risk areas, with winds increasing in the vicinity of low pressure slowly trekking across the Great Lakes. Beaches north of Grand Haven on Friday should have the higher swim risk, due to south winds. Northwest winds are favored Saturday and Sunday. Scattered thunderstorms are possible over the lake from late Friday into early Saturday. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...CAS AVIATION...TJT MARINE...CAS

NWS GRR Office Area Forecast Discussion