669 FXUS63 KGRR 121050 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 650 AM EDT Wed Aug 12 2026 .KEY MESSAGES... - Chance for Scattered Thunderstorms Today - Saturday and Sunday is the Next Good Chance for Storms - Seasonable Temperatures Expected && .DISCUSSION... Issued at 359 AM EDT Wed Aug 12 2026 - Chance for Scattered Thunderstorms Today High resolution models all have a signal for scattered storms today and the SPC outlook agrees with general thunder and a marginal risk across the forecast area. Looking at the 24 hour max reflectivity from the HREF there are two main zones for convection. The first is in the SPC marginal risk across Central Lower Michigan. Storms may both develop this morning and again this afternoon over Central Lower, peeling to the southeast into the thumb with time. The second area of focus is really just to the south and west of the area like yesterday. The RAP is showing 1000-2000 j/kg of MUCAPE at max heating. Stronger mid level winds are noted over Central and Northern Lower, so if there are chances for severe weather today it will likely be up in Central Lower with wind being the main threat. - Saturday and Sunday is the Next Good Chance for Storms We will largely be dry after this evening until we get to Saturday night and Sunday when our next system will be working through the state. A mid level shortwave looks to be the driver of this convection as it tops the Central Plains ridge and moves through the Great Lakes. Dew points surge into the 70s with MUCAPE values in excess of 2000 j/kg so stronger storms are certainly possible, especially given mid level flow around 40 knots. - Seasonable Temperatures Expected No major changes in temperature are expected. Highs look to be in the 80s right through the 7 day forecast. && .AVIATION /12Z TAFS THROUGH 12Z THURSDAY/... Issued at 649 AM EDT Wed Aug 12 2026 Main concern today is the fog and stratus that is in place across Southwest Lower Michigan. As expected widespread LIFR conditions are occurring as we approach 11Z. The fog/stratus will not lift at the same rate across the area due to the fact that the stratus is not of uniform depth. Some areas will see the fog lift by 14Z-15Z, but there will be pockets that likely persist into the afternoon. By late afternoon, VFR weather should prevail once again. The next threat we are watching today is the threat of thunderstorms. At this time we feel the bulk of the activity will stay to the north and south of the 6 TAF sites. We cannot rule out some scattered activity impacted an airport or two, but at this time confidence is not high enough to include. && .MARINE... Issued at 359 AM EDT Wed Aug 12 2026 Limited concerns in the next few days in terms of winds and waves. We are in a fairly slack pressure gradient through the remainder of the week so waves should be 2 feet or less. Otherwise, the two main concerns are fog and thunderstorms. Thunderstorms are possible today over Lake Michigan so mariners and beach goers will need to keep that in mind as winds and waves are usually higher in and near storms. Fog will remain a threat over the water until we can bring in drier dew points. That does not really happen this week so the threat of fog will continue. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Duke AVIATION...Duke MARINE...Duke

NWS GRR Office Area Forecast Discussion