473 FXUS63 KGRR 021115 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 715 AM EDT Wed Sep 2 2026 .KEY MESSAGES... - A couple rounds of showers/storms today - Additional showers/storms on Thursday - Storm chances could linger into Friday/Saturday && .DISCUSSION... Issued at 335 AM EDT Wed Sep 2 2026 - A couple rounds of showers/storms today MUCAPE values early this Wednesday morning are a very respectable 1,500 to 3,000 j/kg. Upstream convection continues to fill in, in an east/west zone across Wisconsin. A weaker low level jet around 30 knots is driving this convection. We expect it to continue to slide east and/or develop over our CWA from I-96 to the north. Cannot rule out severe weather this morning given the aforementioned instability and deep layer shear of 40 knots. Both hail and stronger wind gusts are possible. Some high resolution models indicate a few swaths of severe wind. We will be monitoring as the activity continues to build in. Given westerly upper flow that will result in training of cells as well as a persistent influx of high PWAT air from the south, heavy rain is certainly possible. Another round of showers and storms is possible this afternoon and evening and SPC has much of our forecast in a Slight Risk for severe weather. MUCAPE values will recover to in excess of 2,000 j/kg with deep layer shear on the order of 30 knots. Machine learning schemes favor area off to our east into the Thumb more than our area, but additional severe weather cannot be ruled out. SARS sounding analogs via the HRRR show a fairly big signal for large hail. DCAPE values are in excess of 1,000 j/kg so severe gusts are also possible. Bottom line today could be an active day (both this morning and later this afternoon) with severe weather and heavy rain. A Heat Advisory has been issued for the I-94 corridor. This is the area in the CWA that has the best chance at hitting 100 apparent temperatures. It is valid from noon to 8pm this evening. - Additional showers/storms on Thursday Low level moisture remains parked over the area on Thursday with a surface front lingering. Additional rounds of showers and storms appear likely on Thursday although convergence of the low level jet does not look ideal. The low level jet weakens through the day. Shortwave activity will be working through the area however in zonal upper flow north of the ridge located in the Southeast U.S. The upper support combined with low level convergence associated with the front should be enough to drive additional activity. Details remain difficult to nail down however as convection today and tonight will affect the setup for tomorrow. We are in a SPC marginal for severe weather on Thursday. - Storm chances could linger into Friday/Saturday GFS and ECWMF ensemble data show quite a few members that support more showers and storms Friday and potentially into Saturday. The upper flow shifts to the northwest as a ridge develops in the plains states. There are indications that convective vorts will be driving southeast into our area during this period. So, the bottom line is we will see additional activity. With repeated rounds of showers and storms we will need to keep an eye on the threat of locally heavy rain. && .AVIATION /12Z TAFS THROUGH 12Z THURSDAY/... Issued at 715 AM EDT Wed Sep 2 2026 Threat for thunderstorms remains the main question mark today. Storms have remained north of the TAF sites overnight. Outflow boundaries from the storms to the north will push in this morning towards I-96. We have put VCTS in the TAF sites from 16z-20z to account for storms developing near these outflow boundaries today. VFR weather will largely prevail today and tonight outside of potential thunderstorms. && .MARINE... Issued at 335 AM EDT Wed Sep 2 2026 An overall lighter wind regime will result in waves of 2 feet or less for the next several days. Given a slack gradient waves production will be driven by localized increases in wind via thunderstorm outflows. Winds and waves will be higher in and near thunderstorms today through Friday. We are expected to remain below advisory levels through Friday. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Heat Advisory from noon today to 8 PM EDT this evening for MIZ071>074. MARINE...None. && $$ DISCUSSION...Duke AVIATION...Duke MARINE...Duke

NWS GRR Office Area Forecast Discussion