302 FXUS63 KGRR 171758 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 158 PM EDT Fri Jul 17 2026 .KEY MESSAGES... - Smaller rain chances into this evening and Saturday - Good rain chances late Monday into early Wednesday && .DISCUSSION... Issued at 158 PM EDT Fri Jul 17 2026 - Smaller rain chances into this evening and Saturday The wildfire smoke remains at the forefront of weather related items this afternoon. It continues to hold in for the time being, but confidence is increasing per coordination with Michigan EGLE that there will be a temporary improvement later today through Saturday morning as stronger winds from the SW likely push the smoke out. This occurs as the front dropped through on Wednesday moves back north as a warm front as a low moves through the area. We will see warmer air and additional low level moisture move back in, and create some instability for a few showers/storms late this afternoon and this evening. MU CAPEs are expected to push 2,000 J/kg early this evening. Any mesoscale boundary could touch off a shower/storm. Deep layer shear is very weak, under 20 knots. This will favor pulse type storms with locally heavy rainfall for 20-30% of the area. We should see a break then tonight and first thing Saturday morning. By late morning, the front will steadily start pushing through the forecast area, and start to develop scattered to numerous showers/storms along it. MU CAPEs are forecast to increase to almost 2500 J/kg by early afternoon. The front is expected to be near GR around noon, and then push out of the area by 3 pm per the latest consensus of guidance. Deep layer shear along and ahead of the front continues to be weak, 20 knots or less. DCAPEs are shown by forecast soundings to approach 1000 J/kg, so can`t rule out some isolated microbursts with some of the better storms. The storms should just get going better as they look to exit the area. The storm potential will end with the passage of the front, with NW winds spreading in. These winds have the potential to bring some additional smoke in from the MN and Wrn Ontario fires, but how much is the big question. The Michigan EGLE has extended the Air Quality Alert for the state through Saturday with this in mind, expecting that Unhealthy for Sensitive groups will at least be affected. - Good rain chances late Monday into early Wednesday We will see short wave ridging aloft settle in on Sunday, with the general flow from the WNW. This will bring in cooler weather, along with the potential of some smoke. Dry conditions will continue into the first half of Monday. The next formidable short wave aloft, and sfc reflection will approach the area Monday afternoon. We will see shower/storm chances increase as as the low level jet ahead of it noses into the area. Not much instability initially is weak. Best chance for thunder will be Monday night and Tuesday morning when the instability axis is overhead. The front moves by Tuesday afternoon, ending the better convective potential. It does look like some shower potential stick around into Wednesday as the upper trough lingers over the region until Wednesday afternoon. After that, high pressure will return, and bring back cooler and drier weather for the rest of the week. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 158 PM EDT Fri Jul 17 2026 Visibility reductions due to smoke to slowly improve over the course of the TAF period...but current expectations are at least another 8-12 hours of impacts to terminal before smoke begins to move off. Some showers, maybe a rumble of thunder over the next 6 hours or so but only confident enough to keep prob30 in for a couple locations. && .MARINE... Issued at 158 PM EDT Fri Jul 17 2026 We will be hoisting Small Craft Advisories and Beach Hazards Statements for the entire lakeshore from overnight tonight through Saturday night. Winds will increase this evening ahead of the front, but should remain just under criteria. It will be right along and then behind the front that criteria should be met pretty easily with a decent gradient and a good surge of cooler air coming in. Winds will eventually turn offshore from the NE Saturday night. Waves will subside at that point. Conditions will settle down for a couple of days for Sunday and Monday as high pressure moves through. The next period of higher winds and waves will come in late Monday into Tuesday associated with the next system to affect the area. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Air Quality Alert until midnight EDT Saturday night for MIZ037>040-043>046-050>052-056>059-064>067-071>074. Beach Hazards Statement from late tonight through late Saturday night for MIZ037-043-050-056-064-071. MARINE...Dense Smoke Advisory until 8 PM EDT this evening for LMZ844>849. Small Craft Advisory from 2 AM Saturday to 4 AM EDT Sunday for LMZ844>849. && $$ DISCUSSION...NJJ AVIATION...Maczko MARINE...NJJ

NWS GRR Office Area Forecast Discussion