605 FXUS63 KGRR 090807 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 407 AM EDT Tue Jun 9 2026 .KEY MESSAGES... - Scattered showers and storms today - Strong to severe storms possible Wednesday and Thursday - Turning cooler for Friday through Monday && .DISCUSSION... Issued at 407 AM EDT Tue Jun 9 2026 - Scattered showers and storms today Scattered convection continues to occur even at this hour (3am) due to a slight increase in the low level jet and weak instability that remains in place. We are not expecting anything widespread through daybreak but showers and a few storms will continue to percolate given the hi-res models showing a 25-35 knot LLJ through daybreak. The focus will then turn to the afternoon and evening as the low level jet redevelops across the southern half of the forecast area (I-96 southward). The low level jet will be a focus for convection across the southern CWA, while a mid level shortwave trough will bring an increase in storms for the eastern half of the forecast area. So, much of the area will see showers and storms this afternoon and evening, once the morning low clouds lift. Deep layer shear is not strong today so not expecting organized severe weather. SPC has us in general thunder and that matches out thinking. - Strong to severe storms possible Wednesday and Thursday Strong to severe storms will be possible both Wednesday and Thursday. The Storm Prediction Center has the area in a Slight Risk on Wednesday and an Enhanced Risk on Thursday. A warm front will lift through the area on Wednesday which will provide a focus for convection. The LLJ ramps up to 35 to 45 knots at least with some models showing a convectively enhanced jet of over 50 knots. A couple rounds of storms appear possible during the afternoon/evening and into the overnight. We are most likely looking at a linear system moving our direction from WI/IL with wind being the primary threat. Deep layer shear is not all that strong Wednesday afternoon/evening, but upper level diffluence will aid the maintenance of the storms. MUCAPE values will likely reach the 2,000 to 3,000 j/kg range. Thursday the parameter space is even better which is why the SPC has us in a Enhanced Risk for severe weather. MUCAPE values will increase to 3,000+ j/kg with deep layer shear increasing to better than 40 knots in the evening. Given the CAPE/shear balance and values all hazards are in play. The cold front looks to be the primary forcing mechanism and it moves through the area Thursday night. PWAT values in the 1.75 to 2.00+ range will make heavy rain and localized flooding a threat with all storms this week. The highest moisture content will be Thursday into Thursday night when torrential downpours are possible. - Turning cooler for Friday through Monday We turn cooler behind Thursday nights cold front. Friday and Saturday, temperatures may remain near normal. By Sunday and Monday however we will likely be slightly below normal. Highs on Monday will likely hold in the middle 70s. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 212 AM EDT Tue Jun 9 2026 2 main concerns the next 24 hours...the potential for low ceilings and threat of thunderstorms. Low ceilings are expected to develop and/or spread into the area over the course of the remainder of the night and into the morning hours of Tuesday. Ceilings will likely dip to IFR at most TAF sites during the 09z to 16z time frame. We expect improving ceilings during the afternoon on Tuesday as the low ceilings lift/spread northward. As for thunderstorms, there are two distinct time frames, one is the rest of tonight and the other is this afternoon. For the remainder of the night the storms should be scattered and on the weak side. This afternoon, stronger storms are anticipated. KAZO, KBTL, KLAN and KJXN will be most affected. Storm chances are highest at these TAF sites from 18Z to 23Z. && .MARINE... Issued at 407 AM EDT Tue Jun 9 2026 Winds and waves look to remain below advisory levels today, tonight and through Wednesday morning. It is during the afternoon on Wednesday when winds and waves begin to ramp up. By Wednesday evening Small Craft Advisories and Beach Hazard Statements will likely be needed. The increase in winds will be due to a tightening pressure gradient between a Plains trough and a high of the middle Atlantic coast. Waves will reach the 4 foot threshold in the evening and through the overnight from Holland northward. There is the potential for dense marine fog today given very moist air moving over colder lake waters. Holding off on a Marine Dense Fog Advisory at this point, but we will be monitoring webcams. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Duke AVIATION...Duke MARINE...Duke

NWS GRR Office Area Forecast Discussion