617 FXUS63 KGRR 280039 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 839 PM EDT Mon Jul 27 2026 .KEY MESSAGES... - Severe Thunderstorm Risk This Afternoon - Rain and Thunderstorm Chances Return Friday into the Weekend && .DISCUSSION... Issued at 131 PM EDT Mon Jul 27 2026 - Severe Thunderstorm Risk This Afternoon A Severe Thunderstorm Watch is in effect until 8PM this Evening. The areas of interest are the storms that will move in from Wisconsin and over Lake Michigan into the area. Additional development ahead of the line is possible with remnant boundaries in the current unstable high shear environment. The highest threat for severe thunderstorms will be along and west of US-131 with lower confidence further east as instability decreases. All hazards will be in play with effective shear values around 50 knots, ML CAPE values increasing to 3000 J/kg, and 0-3km SRH values around 100 to 200 m2/s2. Overall guidance hasn`t had a great grasp on thunderstorm development and evolution. We are in a high risk low confidence situation. If storms are widespread through this afternoon and clear this evening, the rest of the night should be largely dry. If the environment isn`t worked over we could see additional development overnight. - Rain and Thunderstorm Chances Return Friday into the Weekend As the shortwave responsible for today`s thunderstorms moves east, pressure heights increase with dry conditions expected through most of the week. Temperatures will largely be in the 80s each day with lows in the 50s and 60s. Rain and thunderstorm chances increase Friday into Saturday with another trough. Chances may linger into Sunday depending on how fast the trough clears the area. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 735 PM EDT Mon Jul 27 2026 East-west oriented front over the upper Great Lakes will sag southward overnight, passing south of Lower Michigan by daybreak. Per current radar trends, scattered showers/storms may accompany front over the next several hours, though current TAFs do not include any precipitation. The strongest and more widespread storms are expected to remain over NE Lower MI. This will need monitored. Winds will become north behind the front tonight. And with a moist boundary layer and today`s rainfall, some low clouds and fog are expected to develop -- generally MVFR ceilings/vsbys. The clouds and lift will lift early Tuesday, with VFR weather from late morning or early afternoon onward. Winds will remain from the north, with gusts to around 20 kt expected. && .MARINE... Issued at 838 PM EDT Mon Jul 27 2026 Webcams and observations suggest earlier thunderstorms and associated winds have already caused advisory/beach hazards level waves to develop along the nearshore. Have bumped up the Small Craft Advisory/Beach Hazards Statement to start this evening. --- Original Discussion--- 131pm Monday June 27, 2026 Severe thunderstorms this afternoon will bring a risk for damaging winds, hail, and waterspouts. This risk is expected until 8pm with it ending earlier to the north. Wave heights of 2 to 3 feet are expected into this evening, but higher waves will be possible with any thunderstorm. Tonight northerly winds behind the low pick up to 25 to 30 knots and will bring building waves of 4 to 7 feet. These conditions will linger through Tuesday. A Small Craft Advisory and Beach Hazard Statement are in effect. Northwest winds Wednesday afternoon may bring another period of Small Craft Advisory, Moderate to High Swim Risk conditions for areas between Whitehall and South Haven. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement through late Tuesday night for MIZ037- 043-050-056-064-071. MARINE...Small Craft Advisory until 2 AM EDT Wednesday for LMZ844>849. && $$ DISCUSSION...RAH AVIATION...Smith MARINE...RAH/Thomas

NWS GRR Office Area Forecast Discussion