456 FXUS63 KGRR 152346 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 746 PM EDT Wed Apr 15 2026 .KEY MESSAGES... - Rain and Thunderstorms into Thursday, Flooding Concerns Continue - Dry Friday, Rain and Thunderstorms Friday Night into Saturday - Colder and Windy Sunday && .DISCUSSION... Issued at 250 PM EDT Wed Apr 15 2026 - Rain and Thunderstorms into Thursday, Flooding Concerns Continue Instability is slowly building this afternoon, with thunderstorms intensifying to our south in the more favorable environment. The currently warned storm in Indiana is expected to remain south of the area and with the ongoing stratiform rain, our afternoon chances for severe weather are low. A lull is expected during the late afternoon and early evening before the low level jet picks back up bringing another round of scattered rain and thunderstorms. Effective shear of 40 to 50 knots and MUCAPE around 500 to 1000 J/kg should be enough for some stronger to severe storms. Overall the primary concern tonight will be damaging winds and heavy rainfall with lower chances for hail and winds. Risk for severe storms looks to taper off by 2am with lingering showers into Thursday morning. Instability will drop off overnight into Thursday morning limiting the lightning potential. As the upper level low approaches Thursday afternoon instability is expected to build. HREF mean surface based instability values around 500 to 1000 J/kg with shear values around 30 knots. Some stronger storms may develop with the best chances along and south of I-69, damaging winds and hail are possible. Rainfall amounts of 1 to 2 inches are likely through Thursday with isolated spots up to 3 inches possible. Flooding concerns will continue with rivers expected to worsen. Check the HYDROLOGY section for more information. - Dry Friday, Rain and Thunderstorms Friday Night into Saturday Dry conditions return for Friday with highs in the 70s under a brief period of high pressure. Southwest flow ahead of a deep trough with a strong low level jet will feed warm, moist air into the region. Thunderstorms are expected to develop Friday night and continue into Saturday. Depending on the timing of the cold front there could be a concern for strong to severe storms. The Day 4 outlook has shifted the 15 percent area further east likely due to the current trend for the front to move through during the early afternoon. - Colder and Windy Sunday Colder air moves in behind the low Saturday with lows Saturday night into Sunday dropping into the upper 20s to 30s. Breezy west to northwest winds will cause wind chills to be in the 20s Sunday morning. Temperatures may peak in the upper 30s to 40s, however wind chills are expected to remain in the upper 20s to 30s. && .AVIATION /00Z TAFS THROUGH 00Z FRIDAY/... Issued at 746 PM EDT Wed Apr 15 2026 Another forecast period full of impacts for aviation interests. We are starting the forecast period in a relative lull with VFR conditions. This will not last long as showers and storms over Wisconsin are steadily moving toward the area. These are expected to arrive at KMKG between 01-02z, and spread south and east thereafter. IFR to LIFR conditions are expected due to visibilities in rain and BR. Later in the night they will diminish in intensity a bit. KMKG and KGRR are likely to see lower ceilings and visibilities continue based on the track of the low. The other sites may see a brief reprieve to VFR. Additional showers and a few storms will move in Thursday morning for a few hours. The threat of thunder will be lower compared to tonight. This will gradually diminish Thursday afternoon, with lower clouds holding on to MVFR conditions for the area. && .MARINE... Issued at 250 PM EDT Wed Apr 15 2026 Dense fog continues to impact the nearshore waters, a Marine Dense Fog advisory is in effect through tonight. Rain and thunderstorms are expected to develop this evening and continue overnight before transitioning to mainly showers. Winds will shift to the northwest Thursday but remain below Small Craft Advisory Conditions. Friday dry conditions are expected with southerly winds building throughout the day into Friday night. Small Craft Advisory conditions are expected to develop and continue through the weekend. Thunderstorms will also be possible Friday night into Saturday. && .HYDROLOGY... Issued at 250 PM EDT Wed Apr 15 2026 Bottom line: The most significant flood in recent years continues to develop along the Muskegon River. Meanwhile, heavy rains last night are also likely now going to create another round of primarily minor flooding along the Grand River and associated tributaries. Another 1.5 to 2.5 inches of rain fell last night across a large portion of the area, with the exception of the headwaters areas of the Grand, Muskegon, and Kalamazoo watersheds (where closer to 1 inch of rain fell). Unfortunately, another 0.5 inches is expected tonight and tomorrow across a large area, with localized streaks of 1 to 3 inches. Along with the river flooding, urban and low lying areas will be prone to flooding due to any additional thunderstorms rains in the next day or so. 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 into Thursday as additional rounds of 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...RAH AVIATION...NJJ MARINE...RAH HYDROLOGY...AMD

NWS GRR Office Area Forecast Discussion