456 FXUS63 KGRR 031453 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 1053 AM EDT Thu Sep 3 2026 .KEY MESSAGES... - SPC Slight Risk for severe weather over much of the area today - Thunderstorm chances may linger into Friday - Dry weather expected over the weekend && .UPDATE... Issued at 1052 AM EDT Thu Sep 3 2026 A fairly active midday into afternoon period is likely with additional thunderstorms developing across Wisconsin and central/northern Lake Michigan, moving east per the 850-300mb mean flow. An MCV is noted southeast of Madison. SPC mesoanalysis indicates morning CIN should erode especially away from the lakeshore region around 16z or so, with SBCAPE values of 2000-3000 J/kg and DCAPE values around 1000 J/kg ahead of both the MCV and developing convection near Green Bay. Either one of these areas may get better organized after moving past the lake in the 16z-18z time frame. 12z CAM max convective gusts indicate a signal for potential 60+ mph gusts especially from 18z onward east of US 131. Given substantial instability and also the present SPC large hail parameters overhead, quarter size hail or larger is also possible. && .DISCUSSION... Issued at 400 AM EDT Thu Sep 3 2026 - SPC Slight Risk for severe weather over much of the area today The pattern continues to support the threat of thunderstorms over the next 24 hours, including both today and tonight. At the surface we have essentially a stationary boundary stretching from east/west near the I-96 corridor. Dew points to the north are in the 60s and are in the 70s to the south. MUCAPE values are stratified correspondingly with 2,000 j/kg in place to the south and 500-1,000 to the north. The upper flow pattern will likely bring in convectively induced vorticity maxima from the west today (the IA/MN convection). Tonight models suggest a NW to SE moving shortwave that may bring additional storms to the area. The best LLJ orientation and magnitude occur early this morning through sunrise and again tonight coming up. Confidence in the evolution remains on the lower side today/tonight, but we do feel we will likely see additional storms this morning, additional chances this afternoon, followed by more storms tonight. Wind appears to be the main threat per machine learning data like NadoCast which is supported by the SPC outlooks. Early afternoon soundings via the HRRR in Ottawa County are indicating 1,100 j/kg of DCAPE which shows the potential for damaging winds. PWAT values continue to be high both today and tonight with 2.0 values both forecast periods. Storms have the potential to be moving quickly, but rainfall rates will likely be high given deep summer values of PWAT. If storms can train over certain areas or if motion is slower than anticipated hydro concerns will increase (localized short term flooding). - Thunderstorm chances may linger into Friday Models indicate the potential for some storms lingering into Friday morning in a northwest flow aloft just downstream of the plains upper ridge. SPC has a marginal threat for severe weather in our far southwest which makes sense given the moisture will be pooled in this area as the front likely sags to the southwest. - Dry weather expected over the weekend The patterns looks to try and dry out this weekend as high pressure builds in from the north and northeast. BUFKIT moisture overviews this weekend are starkly drier than what we have seen all this week. && .AVIATION /12Z TAFS THROUGH 12Z FRIDAY/... Issued at 711 AM EDT Thu Sep 3 2026 Scattered thunderstorms have developed this morning near a stationary front that is located over Lower Michigan. This scattered activity will likely continue for the next few hours. Additional storms will likely move in midday and during the afternoon. These storms will likely be associated with the activity that is moving eastward out of MN/IA. VFR weather is expected for the most part outside of the thunderstorm activity. We are seeing some light fog this morning, but it will lift by 14z. && .MARINE... Issued at 400 AM EDT Thu Sep 3 2026 The surface pattern remains fairly benign the next few days with lighter synoptic scale winds expected. Winds should remain at or below the 5-15 knot range which will result in waves of 2 feet or less through Saturday. No advisory level wave events are expected. The one item to keep an eye on though is the threat of thunderstorms and stronger winds associated with them. We will be in a pattern conducive for storms and wind today. Winds and waves can obviously be higher in and near thunderstorms and mariners will need to remain alert to this threat. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ UPDATE...Hoving DISCUSSION...Duke AVIATION...Duke MARINE...Duke

NWS GRR Office Area Forecast Discussion