242 FXUS63 KGRR 190633 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 233 AM EDT Tue May 19 2026 .KEY MESSAGES... - Severe Line of Storms moving out this evening - More storms on Tuesday - Frost/Freeze Wednesday Night across the North && .DISCUSSION... Issued at 215 PM EDT Mon May 18 2026 - Severe Line of Storms moving out this evening A line of storms that was well forecast by the Hi-Res ARW will be moving across the southern half of the forecast area this afternoon and moving off to the east this evening. Downdraft CAPE values of over a 100 J/kg in the airmass the line is moving through means downbursts with severe wind gusts to 60 mph are the main threat with this line. Scattered storms with isolated severe winds and/or hail are possible across the north. The severe threat winds down this evening as the line of storms moves off the the east with little to no additional QPF expected overnight with the atmosphere being effectively stabilized. - More storms on Tuesday Surface cold front moves southeast across the forecast area on Tuesday afternoon attended by scattered strong to severe storms as surface based CAPE approaches 1500 J/kg. Best chance for severe weather will be across the southeast forecast area where instability is greatest. Deep layer shear greater than 40 knots will also aid the cause. The cold front will move southeast of the forecast area during the evening, ending the threat with a much cooler airmass moving back in. - Frost/Freeze Wednesday Night across the North Canadian surface high building in on Wednesday and Wednesday night with dew points dropping into the 20s and 30s will lead to min temps cold enough for Frost/Freeze headlines across about the northern third or half of the forecast area. Temperatures moderate by the end of the week as low pressure moves up from the south bringing rain by Friday into Saturday. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 233 AM EDT Tue May 19 2026 Showers and storms are located upstream over Wisconsin and Illinois making slow progress to the east. We expect these decaying showers/storms to move into Western Lower Michigan between 10z and 12z. The decaying activity will move through the TAF sites during the morning. MVFR ceilings will also develop for places like MKG, GRR and AZO associated with the moisture increase. There will be a lull in the midday hours with a redevelopment of stronger storms for AZO, BTL, LAN and JXN between 20z and 02z. These storms will be capable of poor aviation conditions (IFR and lower) along with strong winds in excess of 40 knots. The showers and storms should taper off after 02z as a cold front presses south through the area. VFR weather is expected into the overnight. In general, winds will be strong today out of the south and southwest. Speeds will generally be between 15-30 knots. && .MARINE... Issued at 215 PM EDT Mon May 18 2026 No changes to the SCA. Winds and waves will remain hazardous to small craft through Tuesday. A cold front moves through late Tuesday and northwest winds could gust to 25 knots into Wednesday before diminishing Wednesday night as high pressure builds in. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for LMZ844>849. && $$ DISCUSSION...Ostuno AVIATION...Duke MARINE...Ostuno

NWS GRR Office Area Forecast Discussion