335 FXUS63 KGRR 172338 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 738 PM EDT Fri Apr 17 2026 .KEY MESSAGES... - Line of Storms Crosses Area Tonight, Strong to Severe Possible - Cooler Sunday, Drier Pattern Ahead && .DISCUSSION... Issued at 253 PM EDT Fri Apr 17 2026 - Line of Storms Crosses Area Tonight, Strong to Severe Possible Storms out west across the upper Mississippi Valley will traverse east through the evening reaching the lakeshore near 9am. HREF/RAP guidance is less bullish on CAPE than yesterday with MUCAPE on the order of 500-1000 J/kg by the time storms arrive thanks to a warm nose just off the surface. 30-45 knots of deep layer, and 0-3 km shear will be sufficient for the potential of storms remaining organized as they approach. Damaging winds in any bowing segments are the main concern, with a non-zero, but low, risk of tornadoes. The greatest risk will be near and west of US131 where the earlier arrival will support better instability lessening with eastward extent. Showers and garden variety storms will follow the primary line continuing through daybreak. Widespread rainfall of 0.25-0.75" is expected with isolated totals to around 1.5 inches. The progressive nature of the storms should limit areal flooding concerns but any training or heavier swaths will bring that potential given saturated soils. - Cooler Sunday, Warmer and Drier Pattern Next Week Colder air filters in behind the cold front with 850mb temps falling into the negatives. This will also support breezy conditions later Saturday with gusts to 30-35 mph. Highs in the 40s and lows in the 20s to low 30s between Sunday Morning and Monday will be a notable change from recent patterns. The bright side is the incoming ridging and northwest flow will be much drier than we have been of late. Dry weather is likely until late next week when the approach of our next system brings precipitation back into the forecast. Temperatures then rebound into the 60s and 70s. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 738 PM EDT Fri Apr 17 2026 Thunderstorms from the west will move east tonight from 01Z to 08Z from west to east. Thunderstorms may contain gusts 25 to 35 knots with higher gusts possible for the western TAF sites. MVFR ceilings move in with the thunderstorms and may fall to IFR levels briefly into Saturday morning. Low visibilities of 1 to 3 SM are also likely with heavy rain. Low level wind shear of 40 to 50 knots will also be present as the low level jet from 03 to 12Z Saturday. Northwest winds behind the front Saturday will build through the day with gusts 25 to 30 knots. Ceilings will also begin to lift and scatter out Saturday afternoon and evening. && .MARINE... Issued at 253 PM EDT Fri Apr 17 2026 Webcams show that fog has dissipated across the nearshore waters so will be ending the Marine Dense Fog advisory with this package. Winds and waves increase to levels hazardous to small craft tonight and continue through the weekend. A Small Craft Advisory goes into effect this evening continuing into Sunday. A line of thunderstorms is expected to cross the lake this evening. Wind gusts to 34 knots are possible as this line moves through. && .HYDROLOGY... Issued at 253 PM EDT Fri Apr 17 2026 Major flooding continues on the Muskegon River. The good news is that the river at most locations will be cresting within the next 24 hours (Upstream areas of the river including Evart crested earlier today). It will likely take until late next week for all locations to come under flood stage, so the recovery process will be slow. Meanwhile, water levels continue to rise on the Grand River, and confidence is increasing that this will end up being another minor flood event, slightly higher and worse than the one that happened earlier this month, but not a record flood at any locations. However, some of the lowest and easily flooded locations on the river like Comstock Park and Robinson Township will have moderate to possibly major flooding. A final round of rain moves back into Lower Michigan tonight, and is expected to drop around one-half inch of rain over a large area, with locally higher streaks of 1"+ possible at some locations. Given the saturated soils everywhere, this could result in some renewed minor flooding, primarily impacting roadways. Thankfully, this expected rainfall is not anticipated to make the river flooding significantly worse at any locations. Beyond this next round of rain, we dry out for at least the better part of a week going forward, which will be a very welcome chance for the rivers to begin the slow process of recovering to more normal levels. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Small Craft Advisory until 8 AM EDT Sunday for LMZ844>849. && $$ DISCUSSION...Thomas AVIATION...RAH MARINE...Thomas HYDROLOGY...AMD

NWS GRR Office Area Forecast Discussion