433 FXUS63 KGRR 151801 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 201 PM EDT Wed Apr 15 2026 .KEY MESSAGES... - Severe storms have passed, flood risk continues - Thunderstorm chances again this evening - Further chances for storms late this week && .DISCUSSION... Issued at 308 AM EDT Wed Apr 15 2026 - Severe storms have passed, flood risk continues Front has passed to the west and the south with lingering showers and a few isolated storms along the I 94 corridor. Most of southwest Michigan is in the downsloping drier air. The boundary will continue to move to the south and east slowly overnight. A few clusters of storms are expected to follow along the stalled boundary and move along the I 94 corridor overnight into early this morning. The atmosphere is mixed over with little if any dynamics so further severe is not a concern. However, potential hydro concerns remain. The heaviest rainfall occurred north of the I 96 corridor with bullseyes of 2 to 4 inches of radar estimated rainfall. Latest CAMS do have a line of showers and storms through southern Michigan, but that boundary has shifted to the south. So will continue to watch for potential hydro threat this morning but the heaviest rainfall should be along the southern row of counties of Michigan . - Thunderstorm chances again Wednesday The thunderstorm chances will keep on coming. There is a greater potential for weak convection this morning. Any clouds and rainfall will inhibit any atmosphere recovery today. Temperatures are expected to get into the mid 70s with Dewpoints into the 60s. The mid to upper level dynamics are far weaker than the previous two days. That said, another surface low and corresponding frontal patter will move through the region tonight into Thursday. Mid level moisture and weak forcing will accompany that system into far southern Lower Michigan. The best LLJ and helicity will be in Indiana. If that forcing shifts to the north then there could be a better chance for severe Wednesday evening into Thursday. Due to the above conditions SPC has far southern Lower in a slight risk. Main threat will be wind. Given the wet pattern we have been in, hydro will remain a concern. Latest soundings are fairly moist with weak mid level flow, so definitely more of a rain sounding. There is quite a few areas of stable air so access to mid level moisture could be a concern. WPC continues to keep the region in a slight risk for excessive rainfall. - Further chances for storms late this week Michigan could see a reprieve from showers and storms Thursday into Friday. This break will probably be short lived as another large upper level system is trending to move through the region Saturday into Sunday. Latest mid range models are in fair agreement ion the passage of a large upper level low Saturday. that low should bring a system with decent QPF through Saturday. There remains a deepening elongated mid level trough associated with that upper level pattern. SPC does have southern Michigan outlooked for potential severe weather through this timeframe. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 201 PM EDT Wed Apr 15 2026 Current radar loop shows an area of rain moving east-northeast across northern Indiana and southern Lower Michigan with lightning presently confined to south of Michigan. This activity may brush our southeast terminals early this afternoon. Additional thunderstorms are developing over Iowa and will affect the terminals early tonight. Another factor is marine dense fog over Lake Michigan, which is already producing IFR/LIFR conditions at MKG with the onset of onshore flow. We expect a prolonged period of MVFR/IFR restrictions well into tonight with the thunder threat continuing towards and after 06Z. For the sake of brevity, have not provided much detail after that, but it`s looking likely that IFR ceiling restrictions will be common into and possibly beyond 12Z Thursday. && .MARINE... Issued at 333 AM EDT Wed Apr 15 2026 Thunderstorms are expected overnight with the potential for damaging winds and large hail. Higher waves will also be possible with any thunderstorm. Thunderstorms will gradually taper off in the southern zones Wednesday morning, but there is a chance they could linger through the day. Otherwise thunderstorm chances return late Wednesday afternoon into Wednesday night. && .HYDROLOGY... Issued at 250 PM EDT Tue Apr 14 2026 Bottom line: The most significant flood in recent years is likely upcoming on the Muskegon River, with several locations expected to pass Major flood stage. Another 1-2 inches of rain fell last night, primarily in upper/headwaters portions of the Muskegon River Watershed. This joins the previous 2-5 inches of rain in the area that is all finding its way toward the river. A significant and impactful flood on the Muskegon River will be developing over the next few days, with a crest expected in the Friday timeframe. Meanwhile, additional rounds of heavy rain are expected to shift south a bit starting today, with the Grand River basin the more likely to be impacted. With 1-2" across a large area, and locally 3"+ bullseyes expected, we are expecting some localized flooding to develop overnight tonight, especially if the thunderstorms track over urban areas repeatedly. This will also eventually get the Grand River water levels increasing again over the next few days. Currently, this looks like we`ll largely repeat the minor flooding (on the Grand River and tributaries) that occurred in the last few weeks. Further south, the Kalamazoo River has been a bit drier lately, so no flooding is expected to develop there, though urban and poor-drainage area flooding will definitely be possible over the next day or two as the thunderstorms move through. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Flood Watch through late Thursday night for MIZ037>040-043>046- 050>052-056>059-064>067-071>074. MARINE...Dense Fog Advisory until 8 AM EDT Thursday for LMZ845>849. && $$ DISCUSSION...Ceru AVIATION...TJT MARINE...Ceru HYDROLOGY...AMD

NWS GRR Office Area Forecast Discussion


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