449 FXUS63 KGRR 181025 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 625 AM EDT Sat Jul 18 2026 .KEY MESSAGES... - Scattered Showers and Storms Saturday Morning/Early Afternoon - Showers and Storms With Severe Weather Possible Monday Night - Dry and Cooler Mid to Late Week && .DISCUSSION... Issued at 234 AM EDT Sat Jul 18 2026 - Scattered Showers and Storms Saturday Morning/Early Afternoon A cold front sits across Central Wisconsin based on surface observations and will reach the area early this morning and sweep southeast through early afternoon. Short range model guidance shows a broken line of storms is likely to develop. Forecast soundings suggest MLCAPE over 2000 J/kg with MUCAPE over 3000 J/kg. Deep layer shear is marginal around 25-30 knots, but mid-level winds around 35 knots and DCAPE around 1000 J/kg suggests a damaging wind threat in any storms that organize. The greatest potential is across our southeast forecast area where surface based instability builds ahead of the front. Around 100 effective SRH suggests a low but not zero risk of a tornado if an embedded supercell can develop. Smoke then filters back in this afternoon/evening behind the front. - Showers and Storms With Severe Weather Possible Monday Night High pressure moves into the region behind the front keeping things dry for Sunday ahead of the next system. Attention then turns to Monday Night as a shortwave drives a cold front across the area. MUCAPE north of 1000 J/kg and ample low and mid-level jets suggest that storms along this front could be severe, with damaging winds as the favored hazard given anticipated mode. The caveat to this is that nocturnal timing is less favorable with increasing low-level stability with time. However, given the thermodynamic and kinematic parameter space, trends will need to be monitored. - Dry and Cooler Mid to Late Week Northwest flow and surface ridging then set in behind the cold front bringing dry and cooler conditions to the area. As 850mb temps fall into the lower 10s to upper single digits C, highs will fall to near 80F mid to late next week. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 625 AM EDT Sat Jul 18 2026 Have kept PROB30s in place for thunderstorm potential given radar trends and matching short range model guidance suggesting the best storm coverage will be east of the terminals closer to the surface low. Storms should clear the area by shortly after 18z with MVFR and lower conditons and gusty winds possible in any storms. JXN has seen a small pocket of fog/low clouds that likely continues to have intermittent impacts until clearing an hour or two after daybreak. Winds gust to 20 knots ahead of the front driving shower and storm chances from the southwest, switching to northwest behind it. Smoke also returns behind the front, though confidence in the extent of visibility impacts is low. Have maintained VFR for now but similar to previous days this is a complicated forecast with several potential outcomes. && .MARINE... Issued at 234 AM EDT Sat Jul 18 2026 A Beach Hazards Statement and Small Craft Advisory are currently in effect for a two part hazardous wind and wave event this morning through Sunday morning. Southwest winds and waves increase to 15-20 knots late tonight into Saturday morning with 3-5 foot waves. Behind the front this afternoon/evening sees winds increase from the northwest to around 20 knots with 3-6 foot waves keeping waves hazardous. Winds then go offshore tonight causing waves to subside. A break in winds and waves then is expected until later Monday into Tuesday when winds and waves increase again potentially becoming hazardous. In addition, isolated thunderstorms are possible again today with storms possible again Monday night. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Air Quality Alert until midnight EDT tonight for MIZ037>040- 043>046-050>052-056>059-064>067-071>074. Beach Hazards Statement through late tonight for MIZ037-043-050- 056-064-071. MARINE...Small Craft Advisory until 4 AM EDT Sunday for LMZ844>849. && $$ DISCUSSION...Thomas AVIATION...Thomas MARINE...Thomas

NWS GRR Office Area Forecast Discussion