865 FXUS63 KGRR 011742 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 142 PM EDT Wed Jul 1 2026 .KEY MESSAGES... - Hot and Humid Conditions Continue - Chances for Thunderstorms Next Several Days && .DISCUSSION... Issued at 404 AM EDT Wed Jul 1 2026 - Hot and Humid Conditions Continue Will maintain the ongoing Heat Warning as is through Thursday. Conditions do not look to change much in terms of heat index values given the combination of warmth and humidity. 850mb temperatures remain near or above +20C right through Friday actually. Depending on cloud and precipitation trends we may need to extend the headline into Friday. A combination of GFS and ECMWF MOS numbers is likely the way to go which puts highs in most areas in the 90 to 95 degree range at least through Thursday. Overnight lows will not provide any relief with multiple sites yesterday tying record warm lows, AZO and BTL at 76 degrees. The old records were set in 2018 at both sites. Dew points are in the 72 to 75 degree range across the area at 400am and this will not change much either the next day or two. There is a chance of seeing the dew points rise a bit as the stationary boundary sags our direction. Heat index values look to top out in the 100 to 105 range at many locations today and tomorrow (possibly Friday). Bottom line the Heat Warning looks good. - Chances for Thunderstorms Next Several Days Convective trends the next few days are not as straight forward as the heat forecast. The focus this morning is on the convection in the Plains states over SD/MN and IA at 400am. This complex of storms is expected to move east and potential take aim on Central Lower Michigan late this afternoon and evening. Models also indicate the potential for development ahead of the complex with these storms also possibly moving into Central Lower. The trusty HREF is not showing significant activity into our forecast area the next 24 hours with some convection certainly possible in the northern half of the forecast area (or near/north of I-96). The factor that may be more telling than the convection allowing models however the low level jet. All models show an increase in the 850mb LLJ this afternoon and especially this evening. So, we will rely on the conceptual model that an increasing LLJ in Southwest Lower Michigan usually yields shower/thunderstorm development. The main time frame of concern will be this afternoon and evening near/north of I-96 with wind being the primary hazard along with locally heavy rain given PWAT values of 1.5+ inches. Beyond today, additional shower and thunderstorm chances look to continue off and on through Sunday. A stationary boundary sags into the region from the north from Today into Thursday and likely remains nearby through Sunday. This front will likely be a focus for storms as will periodic largely convectively driven shortwaves working through a southwest flow initially that transitions to zonal with time. SPC has Central Lower Michigan in an enhanced risk for severe weather today and portions of the area in a slight risk for Thursday. Confidence in the morphology of the convection is not high the next 48 hours but there is potential for severe weather for sure. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 142 PM EDT Wed Jul 1 2026 No significant changes for this update. We expect about a 90 percent chance of VFR conditions at all the terminals though 00Z...except for 75 percent at MKG. We currently are watching a supercell thunderstorm over Wisconsin that has about a 30 percent chance of making it across Lake Michigan and a lesser chance than that of affecting the MKG terminal prior to 21Z. We expect synoptic wind gusts to resume shortly and last into early evening. Predictability for thunderstorms after 00Z remains poor with a wide variety of model solutions. We carried a PROB30 for some terminals after 06Z tonight for remnant, outflow-driven convection. But again, there remains is a lot of uncertainty involved. && .MARINE... Issued at 404 AM EDT Wed Jul 1 2026 At this time have decided to hold off on a Small Craft Advisory and Beach Hazards Statement for mainly tonight, but it will be close to criteria north of Grand Haven. It looks to be trending towards a typical sunrise surprise type of event. In these events, the overnight low level jet aides in developing surface winds that in turn builds a wave field. The waves look to be likely 2-4 feet with chances increasing for 3-5 footers. Given this is an increase and its borderline will hold off for now, but mariners can expect some choppy conditions early Thursday morning north of Grand Haven. Conditions look to be below advisory levels later Thursday and into Friday. The outlook for the holiday weekend on the big lake looks good at this point with lighter winds and lower wave conditions typical of mid summer. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Extreme Heat Warning until 8 PM EDT Thursday for MIZ037>040- 043>046-050>052-056>059-064>067-071>074. MARINE...None. && $$ DISCUSSION...Duke AVIATION...TJT MARINE...Duke

NWS GRR Office Area Forecast Discussion