376 FXUS63 KGRR 182327 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 727 PM EDT Mon May 18 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 /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 724 PM EDT Mon May 18 2026 Showers and storms have moved east of the terminals and dry wx is expected the rest of the night. Southwest winds will be gusty overnight as we watch another line of storms develop to the west and move east. Models continue to show the line decaying toward morning when it approaches Lower MI and then redevelop during the afternoon when instability gets a bit stronger. The afternoon storms, should they occur, will mainly affect LAN/JXN and we include prob30 groups for this potential. && .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 from 2 AM to 8 PM EDT Tuesday for LMZ844- 845. Small Craft Advisory until 8 PM EDT Tuesday for LMZ846>849. && $$ DISCUSSION...Ostuno AVIATION...04 MARINE...Ostuno

NWS GRR Office Area Forecast Discussion