529 FXUS63 KGRR 130756 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 356 AM EDT Sat Jun 13 2026 .KEY MESSAGES... - Thunderstorms expected this evening into Tonight - Showers and storms Tuesday and Wednesday - Slightly cooler than normal through the 7 day forecast && .DISCUSSION... Issued at 356 AM EDT Sat Jun 13 2026 - Thunderstorms expected this evening into Tonight The main focus of the 7 day forecast is on thunderstorms this afternoon and evening and whether or not we have a severe threat with these storms. The bottom line up front is there are small chances for severe, especially this evening. We are in a SPC marginal threat for severe weather today and agree with that assessment. Really there are quite a few factors going for convection today. Starting aloft, there is a 100 knot upper level jet overhead with some suggestion for a slight coupled jet structure. At the very least we look to be in a right front quad of a jet streak which will aid overall lift today. At 500mb we have 50 knots of flow, so the upper level variables one looks for are there. At 850mb we have around 30 knots of wind which is more than enough to aid convective development. In terms of low level moisture, +13C 850mb dew points are sufficient for storms as are the middle 60s dew points that are forecast. Deep layer shear is around 40 knots with MUCAPE values of 1,000 to 2,000 j/kg. So there really is a lot going for severe weather this evening. Machine learning models like Nadocast are also showing a threat for wind and hail over much of the area. If there was one slight negative its that the moisture through the depth of the atmosphere is a little bit down from what could be there today. PWATs are around 1.6 which could be higher in the month of June, but that is plenty to work with as well. We expect scattered showers and storms to slowly work southward with an advancing cold front this evening and overnight. Chances increase up along U.S. 10 around 22Z. Again, hail to around 1 inch or so and wind gusts to around 60 mph look to be the main threats. - Showers and storms Tuesday and Wednesday A deepening 500mb trough will be in place over much of the forecast period a mid level shortwave and associated surface cold front will move through during this time frame. Monday, and Thursday/Friday look mainly dry at this point. - Slightly cooler than normal through the 7 day forecast Given the troughing and potential for clouds and showers feel our highs will be near to slightly below normal. Highs will be comfortable in the 70s with lows dipping into the 50s. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 156 AM EDT Sat Jun 13 2026 VFR weather will prevail at the TAF sites across Southwest Lower Michigan at least into the afternoon hours of Saturday. We really are not expecting any restriction to visibility or a substantial lowering of ceiling to MVFR until the evening hours. Cloud bases up to that time will likely be at or above 8,000 feet. During the evening a cold front will approach from the northwest and scattered showers and thunderstorms are expected to develop along and ahead of it. It is really the 22Z to 06Z time frame that we should see showers/storms sagging southward through the TAF sites. MVFR and potentially even IFR will be possible during the heaviest activity, but this will not lower conditions for very long at any one location. Winds today will be gusty from the southwest at 14-27 knots. && .MARINE... Issued at 356 AM EDT Sat Jun 13 2026 Will leave the ongoing Beach Hazards Statement and Small Craft Advisory as is with this update. Considered bringing the headlines one zone further south to include Ottawa County beaches today, but in the end held off. Air temperatures will be higher than the water temperatures today, so the stability over the lake is a concern for how much wind is mixed down to the lake surface to build waves. Overall like the area we have selected for the Statement/Advisory. Expecting southwest winds of 15 to 25 knots north of Grand Haven where waves will build to 3 to 6 feet. Lighter winds and therefore smaller waves are expected from late tonight through the remainder of the weekend. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement through late tonight for MIZ037-043-050. MARINE...Small Craft Advisory until 2 AM EDT Sunday for LMZ847>849. && $$ DISCUSSION...Duke AVIATION...Duke MARINE...Duke

NWS GRR Office Area Forecast Discussion