FXUS63 KGRR 031851 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 251 PM EDT Thu Jul 3 2025 .KEY MESSAGES... - Scattered Showers and Storms Possible Today and Friday - Showers and Storms Possible Saturday Night into Sunday - Hot Weekend, Then Slightly Cooler && .DISCUSSION... Issued at 246 PM EDT Thu Jul 3 2025 - Scattered Showers and Storms Possible Today and Friday Visible satellite imagery has showed significant cumulus development across much of the CWA in recent hours, except for areas in the lake shadow. A few showers and storms have already been observed across Kent and Allegan Counties. Mesoscale forcing may result in additional scattered showers and storms through the evening, with increasing mid-level heights and the lack of strong convergence tempering more widespread convection. The best chance of isolated showers and storms is areas east of US131 and south of M20. There are two potential sources for a few showers and storms for Independence Day. First will be driven by weakening storms crossing the lake from Wisconsin. If these storms can survive the crossing, they would reach the lakeshore Friday morning, with the best signal between Allegan and Muskegon Counties. The second is for mesoscale convergence to develop in the afternoon supporting additional potential for shower and storm development. Even though West Michigan will be in the peak of low-level height rises, the ample instability may bring precipitation to areas near and east of US131. However for many, Independence Day will remain dry. - Showers and Storms Possible Saturday Night into Sunday A mid-level wave driving a cold front across West Michigan will lead to the potential for areas of showers and storms Saturday Night into Sunday. Mid-level winds are weak keeping shear marginal. However with PWATs above the 90th percentile of model climatology heavy downpours are possible and isolated storms may contain gusty winds. However this latter possibility in particular is dependent on frontal timing with the NAM/GFS still running ahead of the ECMWF. The difference between models is less than yesterday but still enough that timing and available instability are uncertain. - Hot Weekend, Then Slightly Cooler The building ridge and associated return flow into the weekend will bring hot weather to the area this weekend. Temperatures in the upper 80s to low 90s with mid 60s dewpoints will produce heat indices in the low 90s Friday and well into the 90s for Saturday and Sunday away from the lake. This does bring at least moderate concern for heat stress for those vulnerable to heat, such as those active outdoors or without air conditioning. Dewpoints fall into the mid 50s to low 60s behind Sunday's cold front keeping heat indices in the 80s during this time. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 127 PM EDT Thu Jul 3 2025 A weak frontal boundary bisects the Lower Peninsula this afternoon and may be enough to pop a shower or weak storm yet this afternoon. However, chances are low enough at the terminals to preclude a mention in the TAFs. Otherwise, diurnal cu will dissipate with sunset. Given increasing dewpoints, it's possible that some patchy early morning fog may develop for an hour or two but will burn off quickly after sunrise. && .MARINE... Issued at 127 PM EDT Thu Jul 3 2025 High pressure over Michigan will drift east Saturday. Southwest flow will increase as this occurs and waves will build to 3 to 5 feet north of Holland by Saturday afternoon. Swim risk will rise accordingly with lowest swim risk near South Haven and highest north of Muskegon. Prior to Saturday afternoon waves will aob 2 feet. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Air Quality Alert from midnight tonight to midnight EDT Friday night for MIZ050-056-057-064-071. MARINE...None. && $$ DISCUSSION...Thomas AVIATION...04 MARINE...04