020 FXUS63 KGRR 030816 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 416 AM EDT Fri Jul 3 2026 .KEY MESSAGES... - Thunderstorm chances continue through the holiday weekend - Warm and humid conditions to persist && .DISCUSSION... Issued at 415 AM EDT Fri Jul 3 2026 - Thunderstorm chances continue through the holiday weekend Thunderstorm chances will continue each day from today through Sunday across Southwest Lower Michigan. We are in a marginal/slight risk of severe weather today and a general thunder risk for Saturday/Sunday via the Storm Prediction Center. A diffuse stationary boundary remains in place across the Southern Great Lakes this morning which is being augmented by thunderstorm outflow. Rich boundary layer moisture remains in place which will aid moderate instability once again today and over the weekend as well. It is not until we get into Sunday night and Monday before we get into less humid/unstable air. Thunderstorms today will be driven by weak shortwaves moving through the upper flow and localized convergence at the surface. The SPC HREF shows a lull during the morning hours in the wake of the current activity with a diurnal boost to the activity this afternoon and evening, especially for areas near and south of I-96. Machine learning output via Nadocast shows wind as the clear main threat. Saturday and Sunday the thunderstorm chances continue with Saturday`s threat being driven by convective vort`s and Sunday`s by a stronger wave moving through. Instability is still fairly significant both days with the GFS showing north of 2,000 j/kg of MUCAPE. Cannot rule out severe weather either day, especially on Sunday when convection will get more of a synoptic boost from a mid level wave and a surface cold front. Heavy rain potential will exist today through Sunday as well with PWAT values near 2 inches all three days. The flooding threat would be short term excessive rain where storm drains will not be able to keep up with the volume of water. - Warm and humid conditions to persist 850mb temperatures remain warm today and on the forth. Highs today will still reach the 90s over much of the area. 80s will be more common on Saturday. We will maintain the current Heat Advisory as is. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 216 AM EDT Fri Jul 3 2026 VFR weather is in place across most of the region at 06z. The exception is in some very localized thunderstorm activity across the Southern Great Lakes stretching from Northern Illinois into Southern Lower Michigan. Isolated to scattered thunderstorms are expected to continue across Southern Lower Michigan the rest of the night impacting the I-94 TAF sites. The I-96 TAF sites will likely remain north of the activity. A lull in the showers/storms will likely occur during the morning hours of Friday after sunrise. During the afternoon and evening we expect another round of showers and storms to mainly affect the I-94 TAF sites between roughly 20z and 03z. Winds will be southwest at 5-15 knots today with some gusts to around 20 knots in the afternoon. && .MARINE... Issued at 415 AM EDT Fri Jul 3 2026 A fairly light wind regime is expected for the holiday weekend. Winds for the most part will be in the 5 to 15 knot range from today through Sunday. There is a brief window this evening where southwest winds increase aloft and some of this wind could mix to the surface. On Saturday we may see a southwest wind of 10 to 20 knots develop. Overall though it looks like waves of 1-3 feet or less through the holiday weekend given the lighter winds. We therefore are not expecting any wind/wave events to advisory levels. We will see occasional thunderstorms today through Sunday, some mariners and beach goers alike (both of which will be plentiful this weekend) will need to keep an eye to the sky for the threat of lightning. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Heat Advisory until 8 PM EDT this evening for MIZ046-051-052- 056>059-064>067-071>074. MARINE...None. && $$ DISCUSSION...Duke AVIATION...Duke MARINE...Duke

NWS GRR Office Area Forecast Discussion