629 FXUS63 KGRR 141720 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 120 PM EDT Fri Aug 14 2026 .KEY MESSAGES... - Multiple chances of showers and storms tonight into Sunday - Cooling off and drying out later Sunday through Tuesday - Stronger system possible Wednesday && .DISCUSSION... Issued at 319 AM EDT Fri Aug 14 2026 - Multiple chances of showers and storms tonight into Sunday Another night, and another round of convection just to our south over Illinois and Indiana where they don`t need any more damaging storms or rainfall. Up our way, we remain under a somewhat humid air mass, with little to no rain chances for one more night. We do see some minor changes in the upper air pattern that will bring the better shower/storm chances to Lower Michigan as early as tonight, and keeping the chances in until Sunday. We see upper heights build a bit as the long wave trough over the Western U.S. moves east a little, and we see some short waves come out of the long wave trough. This change will allow a short wave/MCV over Western KS early this morning to move toward the area late Friday night/Saturday. As the MCV approaches, the moisture advection with the low level jet will weaken as is typical at that time of the day. This will bring a few showers and maybe a rumble of thunder in Saturday morning. We see instability build through Saturday as the front moves north and the very warm and moist air mass moves back over the area, coinciding with diurnal peak heating. We see the instability continue to build Saturday evening as the low level jet with the next wave pushes right at the area. It looks like this will be the favored time and into Sunday morning for the best chances of showers and storms. CAPEs are shown to climb above 2000 J/kg Sat evening, and maybe even up to 3,000. Synoptic scale shear may be on the lower side, which would limit severe potential a bit. There may be some better mesoscale deep layer shear associated with the short waves/MCV. That is a bit uncertain at this time, but there is a potential of some strong to severe storms Sat evening/night. There may be some training of storms also with somewhat of a persistent low level jet causing some backbuilding. - Cooling off and drying out later Sunday through Tuesday The low jet jet from Saturday night will push east by daybreak Sunday morning, and the cold front will be poised to steadily move through the area as the upper flow pushes it. Any lingering rain and clouds early will slowly improve in the afternoon behind the cold frontal passage. We will see upper ridging build in behind the system on Sunday, and bring dry weather as the low level flow from the north advects drier weather overhead. Dew points will go down, and temperatures will not be nearly as warm. - Stronger system possible Wednesday The upper ridge will control the weather for Monday and Tuesday, but we will have nearly a zonal upper jet over the northern half of the country. What this will do is allow additional short waves ride it right into the region. There has been a wave shown to bring rain chances in for late Wednesday and Thursday. The latest data indicates that this wave may be stronger with a stronger jet supporting it as it traverses the country. The sfc low is shown to be relatively stronger, and potentially more impactful. We will see another break in the weather then for Thursday as the Wednesday system clears all of the moisture out of the area. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 115 PM EDT Fri Aug 14 2026 Visible satellite shows some cu over the southern terminals and mainly high clouds along the I-96 terminals. Clouds will lower overnight as low pressure moves toward the state. Included some light rain at AZO late in the period, but don`t think it will reach BTL nor JXN by 18z. A better chance of light rain will arrive across the southern terminals after 18z. Look for MVFR cigs to develop late in the period. && .MARINE... Issued at 319 AM EDT Fri Aug 14 2026 Our next possible set of marine headlines look to arrive Saturday afternoon into much of Sunday ahead of, and behind a frontal system. Until Saturday afternoon, the gradient will remain light as it has been for the past few days. Winds should stay below 20 knots and waves below 3 ft until Saturday afternoon. Waves will build later Saturday and more so Sunday with cooler air coming in on the backside of the system, and an onshore flow. Once the system moves by over the weekend, we should see a few days with lower winds and waves. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...NJJ AVIATION...04 MARINE...NJJ

NWS GRR Office Area Forecast Discussion