640 FXUS63 KGRR 152349 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 749 PM EDT Mon Sep 15 2025 .KEY MESSAGES... - Areas of Fog and Low Clouds Across Central Lower Michigan Tonight - Dry And Warm Through Friday - Showers Possible This Weekend && .DISCUSSION... Issued at 307 PM EDT Mon Sep 15 2025 - Areas of Fog and Low Clouds Across Central Lower Michigan Tonight Forecast soundings and persistence of the synoptic pattern suggest that tonight will be similar to this morning in terms of fog and low stratus development. Easterly flow will advect low-level moisture off of Lake Huron which will be trapped under the nocturnal inversion. Cannot rule out some locally dense fog similar to this morning, but that is not expected to be widespread. Any fog and stratus that develop will burn off in the hour or two after sunrise as the sun angle is still decently strong. - Dry And Warm Through Friday A Rex block pattern transitioning into pure large scale ridging is expected through Friday. This will keep conditions generally dry with one possible exception. A cold front is forecast to sink through the area Thursday into Thursday night. Some guidance such as the ECMWF/EPS wants a few showers to develop off of that front near US10. However, moisture quality looks to generally be poor with frontal passage so will keep rain chances in the 10-20 percent range across the US10 corridor. Highs will be in the mid to upper eighties areawide through Thursday before cooling some for Friday behind the cold front. - Showers Possible This Weekend Still a lower confidence scenario in forecast evolution Saturday into early next week. The going forecast favors a bit of a cooldown during this period as large scale troughing, possibly as a cutoff low, moves into the region. However with the weak flow aloft persisting, this brings into question how this low evolves and tracks. This troughing may lead to one or more periods of shower development this weekend into early next week. However between the relatively modest nature of the mid-level height falls, and poor moisture quality given the lack of a connection to the Gulf, any rainfall would be light. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 749 PM EDT Mon Sep 15 2025 We are expecting some shallow ground fog to develop in spots tonight, similar to last night. Last night both AZO and JXN had visibilities dip below VFR between 09z and 12z. Given no airmass change we expect a persistence forecast to likely work again. Like last night as well, we will see some stratus and fog develop across Central Lower Michigan towards daybreak. Otherwise VFR weather will be the rule with high pressure firmly situated across the area. A light northeast to east wind will continue. && .MARINE... Issued at 307 PM EDT Mon Sep 15 2025 No change to the overall pattern in the Great Lakes for this week when looking at the latest model guidance. Surface ridging and/or a slack pressure gradient will insure that we see waves of 2 feet or less through the end of the week. The next time frame that the wind picks up will occur on Friday when easterly winds freshen as stronger high pressure settles into the Great Lakes from the north. Even in that regime though with an off shore wind of 15 to 25 knots waves will remain low given limited fetch. Bottom line...some great end of season boating weather. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Thomas AVIATION...Duke MARINE...Duke

NWS GRR Office Area Forecast Discussion