321 FXUS63 KGRR 131834 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 234 PM EDT Mon Jul 13 2026 .KEY MESSAGES... - Hot and humid through at least Thursday with no rain expected - Cooler weather slowly filters in late week into the weekend - Rain chances begin starting Thursday night and increase by Sunday && .DISCUSSION... Issued at 234 PM EDT Mon Jul 13 2026 - Hot and humid through at least Thursday with no rain expected We issued a Heat Advisory earlier for the period of Tuesday afternoon and evening. Additional heat headlines are very possible through Thursday. Our dominating weather feature is a 600 dam 500 mb ridge that is centered just west of the state. This ridge has only strengthened its hold as it has built over the area today. 850 mb temps are around 19-20C this afternoon. The upper ridge will slowly build south of the area over the next couple of days. However, the core of the warmest air aloft (+25C) remains to our NW, and moves overhead Tuesday. Mid 90s F looks likely over most of the forecast area Tuesday, away from Lake Michigan. In addition, higher dew points are also moving in from the WNW, with upper 60s to near 70 expected. That will put heat indices in the lower 100s. The upper ridge axis and core of the warmest temps start to slip south of the area by Wednesday. However, with better mixing with the high moving away will likely keep highs in the mid 90s on Wednesday. The trend will continue with the ridge weakening, and 850 mb temps slowly cooling. We feel it is likely that Heat Advisory criteria (100F) will be met Tuesday and Wednesday, and maybe just a tad shy on Thursday as a weak front slips through with the lowering heights. Coordination with other offices brought a plan to deal with headlines daily, vs over the entire period. That is due to some signal in the models of trying to mix down much drier air. This would limit the heat indices a tad. - Rain chances start Thursday night with cooler temps filtering in That front that moves through on Thursday is quite weak, with very little convergence along it. However, it will gradually become a potential boundary to focus convection along it with the cap weakening with the lower heights settling in. Models are indicating that the first chances of rain may arrive as early as Thursday night with a weak wave embedded in the flow could act on the gradient of better instability. More clouds, lower heights, and cooler temps aloft will all lead to sfc temps slowly trending cooler through the weekend. We do not see high precipitation chances for the first half of the weekend. There is not really a well organized upper wave/sfc low until later Sunday. At that time, rain chances will be the best for the seven day period. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 206 PM EDT Mon Jul 13 2026 VFR is expected under a high pressure system and a hot and somewhat dry atmosphere. Winds will be between SW and W with gusts occasionally to 16 knots. && .MARINE... Issued at 234 PM EDT Mon Jul 13 2026 We are looking at a very low chance of wind/wave related headlines through most of this week. The big area of high pressure bringing this hot weather will also keep the gradient weak over the area through the week. There is a little bit of wind as the center of the high slips south over the period. The more stable conditions will keep lighter winds over the lake with less mixing. The next set of headlines looks to be around the Saturday time frame. That occurs as the next organized system is poised to approach the area. && .CLIMATE... Issued at 246 AM EDT Mon Jul 13 2026 Here are the high temperature records for July 13, 14, and 15. Location July 13 July 14 July 15 Grand Rapids 108 (1936) 102 (1936) 95 (2013) Lansing 99 (1936) 101 (1936) 99 (1977) Muskegon 93 (1995) 94 (1995) 93 (1995) Kalamazoo 109 (1936) 108 (1936) 103 (1936) Battle Creek 103 (1936) 104 (1936) 100 (1977) Holland 99 (1936) 98 (1995) 98 (1932) && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Heat Advisory from noon to 8 PM EDT Tuesday for MIZ037>040- 043>046-050>052-056>059-064>067-071>074. MARINE...None. && $$ DISCUSSION...NJJ AVIATION...CAS MARINE...NJJ CLIMATE...RAH

NWS GRR Office Area Forecast Discussion