086 FXUS63 KGRR 151907 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 307 PM EDT Tue Jul 15 2025 .KEY MESSAGES... - Strong to Severe Storms Possible Wednesday Afternoon and Evening - Dry And Cooler Later Thursday And Friday - Showers and Storms Possible Saturday && .DISCUSSION... Issued at 259 PM EDT Tue Jul 15 2025 - Strong to Severe Storms Possible Wednesday Afternoon and Evening Dry conditions are expected the rest of today before showers and thunderstorms return to the forecast for Wednesday. Two rounds of thunderstorms are forecast, with both capable of damaging winds in the strongest storms. The first round of storms is expected to develop Wednesday afternoon off of the lake breeze, with scattered storms near and east of US131. The airmass will be quite humid with PWATs north of 1.5". Heavy rain and lightning are the greatest concerns with these storms. Although shear is poor, with mean SBCAPE values near or above 2000 J/kg, isolated wet microbursts cannot be ruled out. Attention then turns to the storms that will develop Wednesday afternoon across Wisconsin and Illinois. These storms will fire off of a cold front Wednesday and be aided by an MCV as they move eastward. These storms will become more linear with time, reaching the lakeshore in the mid to late evening. Compared to the daytime environment, increasing mid-level winds will support better shear, on the order of 25-35 knots. This is a conditional threat, as it is uncertain whether storms will survive the journey over the lake given the displacement of the mid-level jet to the north and lack of a low-level jet or robust EML. The best chance for any storms to survive appears to be near and north of I96 at this time being closer to the jet/MCV and having slightly better delta Ts. If storms can survive across the lake, damaging winds are possible with this line. We will monitor this closely over the next 24 hours. The cold front then arrives Thursday morning keeping the potential for at least scattered showers and storms in the forecast to start the day. Given the unfavorable morning timing of fropa, severe storms are not expected with the front itself. - Dry And Cooler Later Thursday And Friday Dry air filters into the area later Thursday into Friday with the arrival of surface ridging. Look for highs in the upper 70s to low 80s with decreasing cloud cover, especially for Friday. - Showers and Storms Possible Saturday Precipitation returns to the forecast Saturday with the interaction of a mid-level wave and a frontal boundary across the Ohio Valley. Exact timing and placement of the vorticity maxima remain uncertain at this range, though the overall pattern suggests that the best chance will be late Saturday into Saturday Night across the southern half to two-thirds of the forecast area. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 152 PM EDT Tue Jul 15 2025 VFR prevailing through late this evening. Lingering haze/smoke this afternoon but greater than 6 mile visibility, and a few cumulus clouds with bases around 4,000 feet. Scattered to broken clouds at 5,000 to 6,000 arrive late tonight, and scattered rain showers could develop during the early morning hours of Wednesday. Ceilings may descend to MVFR by mid day Wednesday, and scattered thunderstorms could develop. && .MARINE... Issued at 152 PM EDT Tue Jul 15 2025 Low swim risk and 1 to 2 ft waves through Wednesday with a wind component mostly from the south. Thunderstorms will attempt to cross Lake Michigan late Wednesday evening and some may be successful. If so, lightning and wind gusts greater than 30 or 35 knots would be possible. Small craft advisory and beach hazards statement (high swim risk) is likely for Thursday as winds strengthen from the north. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Air Quality Alert from midnight tonight to midnight EDT Wednesday night for MIZ050-056-057-064-071. MARINE...None. && $$ DISCUSSION...Thomas AVIATION...CAS MARINE...CAS

NWS GRR Office Area Forecast Discussion