576 FXUS63 KGRR 171755 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 155 PM EDT Mon Aug 17 2026 .KEY MESSAGES... - Showers and storms late Tuesday into Wednesday - Next round of precipitation Friday night through Saturday && .DISCUSSION... Issued at 144 PM EDT Mon Aug 17 2026 - Showers and storms latter half of Tuesday into Wednesday Today`s quaint and idyllic summer time weather, fueled by surface high pressure, will be driven out, over hill and over dale, by a southward progressing upper level low. That low, situated over northern Ontario, will move through bush and through brier, over park and over pale, bringing with it a system with good barotropic flow. As the low treks southward the upper level trough will deepen and a mid level long wave trough with a corresponding surface trough will make its way across WI and through the Great Lakes tomorrow. This will swing a cold front through Lower Michigan Tuesday night into Wednesday. The questions through this forecast period is how widespread showers will be, and the potential for thunderstorms. Scattered showers remain likely for the area late Tuesday. PWATS are currently around 1.5 inches. With a moist mid level, little directional shear and the good barotropic flow mentioned above, any showers and storms will be efficient rainers. Given that potential, WPC has portions of the area in a marginal risk for excessive rainfall. Latest storm total QPF`s are only in the 0.25 to 0.50 inch range, but that could be significantly higher if; thunderstorms develop,the front stalls as it moves southward and if there is any storm entrainment through Tuesday night. Some rainfall could linger well into Wednesday if the front stalls. Other wise, clearer skies with fair weather will return Thursday. - Another chance of precipitation Friday night through Saturday More tumultuous weather is on its way late this week as there is an increasing consistent signal for a deepening upper level wave that will move through the Great Lakes Friday night and Saturday. Latest mid range ensembles shows less anomalous moisture associated with this system. However, there is great incongruity between the solutions. So while precipitation will be possible it is to early to nail down specifics. There remains the potential for rounds of showers beginning Friday and through the first half of the upcoming weekend. However, it could become just a mid summer`s night dream. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 114 PM EDT Mon Aug 17 2026 Visible imagery shows sct-bkn diurnal cu across the region. This will dissipate leaving some cirrus overnight as winds diminish. VFR expected through the period. && .MARINE... Issued at 154 PM EDT Mon Aug 17 2026 Winds and waves will remain calm through tonight and the first half of Tuesday. Increasing southwesterly flow will build waves Tuesday afternoon with the potential for a small craft advisory. This could be short lived given that the winds quickly shift due to frontal passage. The greatest area of concern is near shore waters north of Holland between 18Z and 00Z. However, given the marginal timing and conditions have held off on an SCA for now. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Ceru AVIATION...04 MARINE...Ceru

NWS GRR Office Area Forecast Discussion