438 FXUS63 KGRR 171029 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 629 AM EDT Thu Sep 17 2026 .KEY MESSAGES... - Scattered Showers and Isolated Storms This Morning - Heavy Rain Possible This Saturday && .DISCUSSION... Issued at 257 AM EDT Thu Sep 17 2026 - Scattered Showers and Isolated Storms This Morning Regional composite radar imagery shows convection developing associated with a Low-level jet overrunning the stationary front to our south. The best coverage will be south, however rain showers are possible into this morning, especially south of I96. Instability is pretty marginal but cannot rule out isolated storms. Conditions then dry out later today into Friday as high pressure takes over as the main driver of our weather. - Heavy Rain Possible This Saturday On the heels of this breif dry window comes widespread precipitation Friday Night into Saturday. A ample southerly LLJ forces the front south of us back north as a warm front. In conjunction with marginal instability and PWATs near 2" this is a favorable setup for high rainfall efficiency. Some question based on low placemenet and convective track as to where exactly the heaviest rain falls, however heavy rain is likely. High confidence in rainfall north of 1" across much of the area, with NBM probabilities of > 2" north of 60% in spots. Overall the slight ERO from WPC remains in good shape. && .AVIATION /12Z TAFS THROUGH 12Z FRIDAY/... Issued at 628 AM EDT Thu Sep 17 2026 Low stratus has set in across the area. Most sites are IFR, with LIFR at AZO/BTL with patchy fog across those terminals as well. Conditions will slowly improve through the day, with the southernmost TAF sites (AZO/BTL/JXN) being last to scatter out to VFR this evening. Likely to be some adjustments needed to exact improvment times due to dependence on upstream showers providing pockets of enhanced moisture. Winds will be predominantly from the east to northeast today. && .MARINE... Issued at 257 AM EDT Thu Sep 17 2026 Can`t rule out an isolated thunderstorm over the southern waters tonight, however chances are low. The next hazard of note is Friday Night into the weekend. Increasing winds will support gusts aoa 22 knots, though the easterly flow does favor the better waves remaining over the open waters. A Small Craft Advisory may be needed. Thunderstorms are also possible over the waters Saturday. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Thomas AVIATION...Thomas MARINE...Thomas

NWS GRR Office Area Forecast Discussion