377 FXUS63 KGRR 041914 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 314 PM EDT Thu Jun 4 2026 .KEY MESSAGES... - Periods of showers and thunderstorms Friday through Saturday - Potential chances for rain early next week - Building heat mid to late next week && .DISCUSSION... Issued at 220 PM EDT Thu Jun 4 2026 - Periods of showers and thunderstorms Friday through Saturday Convection upstream in the Plains states tonight driven by an increasing low level jet will try to spill eastward into Western Lower Michigan after about 500am in a decaying non-severe mode. HREF 4hr reflectivity shows areas from Holland northward standing the best chance at rainfall through 800am. After 800am, the area of rain will spread eastward through the GRR forecast area. During the midday into the afternoon on Friday with some building weak instability (500-1000 j/kg) we expect convection to increase, initially on the southern end of the activity which will occur south of I-96 and then over much of the area. The activity in the afternoon will be aided by a weak shortwave trough in the mid levels. It is not out of the question that there may be strong to severe storms Friday afternoon and evening across Southern Lower Michigan especially. Near and south of I-96 stand the best chance at severe storms during this time. Given stronger winds noted at both 850mb and 500mb, damaging winds will likely be the bigger severe threat. Machine learning tools like Nadocast also support winds being the primary threat. There will likely at least somewhat of a lull in the activity Friday night as the low level jet and its associated convection peel off to the east. We have been monitoring the chance for additional convection on Saturday ahead of the southward moving cold front. The front may be a bit quicker in the latest model runs and we wonder how much airmass recovery can occur before it begins to push out of the area. The threat area on Saturday will be near/south of I-96 once again, especially down towards I-94. Deep layer shear near the front is fairly strong 30-40 knots so severe weather is not out of the question. - Potential chances for rain early next week Early next week and potentially into the middle of the week, models are trying to show an upper low moving into the mean ridge position aloft over the Great Lakes. At this point will side towards the ECWMF which does not have as pronounced of an upper low. At this point we have low pops in the forecast from Monday night into Wednesday. Could see these pops needing to be lowered with time with the ridge holding firm. - Building heat mid to late next week The upper ridge builds after Wednesday with heights pushing into the 590s late in the week. If that verifies and it is our current forecast that it will, we are looking at highs in the 90s. Even early in the week highs will remain in the 80s so summer warmth looks like it is here. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 1259 PM EDT Thu Jun 4 2026 VFR continues into tonight ahead of a front that will move through the region on Friday. Showers and possibly a few thunderstorms could begin impacting mainly MKG/GRR/AZO by 18z Friday. Given some uncertainty regarding intensity and coverage, PROB30s are the appropriate way to handle the threat until getting into the 16z-18z time frame for these sites when SHRA may be predominant. With questions regarding the degree of instability present, will hold off mention on TSRA for now through the 18z ending of these TAFs. && .MARINE... Issued at 220 PM EDT Thu Jun 4 2026 We will be issuing a Small Craft Advisory from Holland northward to Manistee. South winds increase tonight and into Friday to a point where south winds of 15 to 25 knots should become common. Some gusts should push towards 30 knots at times. This will push waves into the 3 to 5 foot range. The Small Craft Advisory may need to be expanded in area to the south and in time as there is some indication that winds could hang on a bit longer and/or be aided by thunderstorms. A period of lighter/offshore winds will occur Saturday night into Sunday. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Small Craft Advisory from 8 AM to 11 PM EDT Friday for LMZ846>849. && $$ DISCUSSION...Duke AVIATION...Hoving MARINE...Duke

NWS GRR Office Area Forecast Discussion