FXUS63 KGRR 030748 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 348 AM EDT Thu Jul 3 2025 .KEY MESSAGES... - Slight chances for showers or isolated storm today and July 4 - Holiday weekend heat - Showers and storms possible Saturday night through Sunday && .DISCUSSION... Issued at 348 AM EDT Thu Jul 3 2025 - Slight chances for showers or isolated storm today and July 4 A weak front becoming oriented NW-SE and flow-parallel is mostly stalled out over Lower Michigan today. It may have a better pronounced moisture difference on either side of it than a temperature difference. Some afternoon surface convergence over southern portions of Mid Michigan today may assist in popping up isolated showers. The threat of storms will be tempered by midlevel height rises and warming temperatures around 10-15 kft / around 0 Celsius which will limit instability at and above that level. For July 4, all of the latest HREF member models show spotty precip over Western/Mid Michigan, worth adding some 20 percent PoPs / slight chance showers or storm during the day. Elevated thunderstorms may be ongoing in the morning over Wisconsin, fed by southwesterly warm air advection. Some models take storms across Lake Michigan during the morning but those solutions may be too aggressive. Additional surface-based development may occur over Mid Michigan during the afternoon within a zone of low-level convergence. The day-by-day increasing low-level heat and moisture may just counter-balance the upper-level ridging, which yields more modest lapse rates and skinny CAPE, offering some chances of localized showers/storms but again with a tempered overall threat. - Holiday weekend heat A building upper-level ridge is expected over the Midwest and Great Lakes Fri-Sat, July 4-5. Temperatures near 90 on July 4 with dew points in the mid 60s will yield a heat index in the lower to mid 90s. On Saturday, temperatures are favored to reach in the lower 90s in most locations away from the Lake Michigan shore, and heat index values may reach the mid to upper 90s. Whether or not this reaches the traditional "heat advisory" criteria, the impacts of heat and humidity will be at least of moderate concern for people active outdoors or without air conditioning. - Showers and storms possible Saturday night through Sunday An upper-level trough and surface cold front passing through late Saturday night through Sunday may touch off areas of thunderstorms. While rain is not a guarantee everywhere, the high PW environment with increasing wind shear may produce some heavy downpours along with a marginal severe wind threat. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 153 AM EDT Thu Jul 3 2025 Earlier showers and thunderstorms have dissipated and skies have returned to mostly clear. VFR will be prevalent but may have to deal with some localized visibility reductions due to shallow fog in spots prior to sunrise (10 to 11Z). Scattered cumulus clouds around 5,000 feet will tend to develop by mid day. Latest short term models suggest showers in the vicinity of BTL, LAN, and JXN this afternoon, mainly between 19 and 23Z. && .MARINE... Issued at 135 PM EDT Wed Jul 2 2025 Waves will remain aob 2 feet through Friday before southwest winds increase Saturday. Waves will increase to 2-4/3-5 ft north of Whitehall Saturday afternoon and a small craft advisory may be needed then. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...CAS AVIATION...CAS MARINE...04