223 FXUS63 KGRR 041050 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 650 AM EDT Sat Jul 4 2026 .KEY MESSAGES... - Thunderstorm chances both Today and Sunday - Period of quieter weather expected Monday and Tuesday - Chance for showers/storms mid week && .DISCUSSION... Issued at 423 AM EDT Sat Jul 4 2026 - Thunderstorm chances both Today and Sunday A fairly diffuse surface pattern is in place today with lighter winds and high dew point air remaining across the entire area. Multiple MCS`s in the past 24 hours driven by convectively induced meso vorts have pushed an outflow well south of the area into Illinois and Indiana. The upper pattern is zonal with no significant shortwaves moving through the flow. Convection today will be driven by diurnal heating and additional convective vort maxima. The main feature of note is convection in Iowa and Northern Missouri that the HREF picks up on and moves a shortwave our direction through the course of the day. Feel convection today will be 1) heat of the day driven developing overhead and 2) what can develop and advect in from the SW and W. The main signal in the HREF is heat of the day convection that develops in eastern Lower Michigan that migrates westward into Central and Eastern portions of our area including MOP/AMN and LAN. Given lighter deep layer shear today, less than 30 knots, agree with the SPC outlook that we are looking at general thunder. Severe threat is overall low. Heavy rain will remain possible today with high dew point/PWAT air and likely slow moving thunderstorms. A similar day on Sunday is expected with mainly diurnally driven convection. Low dew point air slides in from the north through the day and we feel the best chances for storms will be in the southeast half of the forecast area closer to a weak low moving through IN/OH. Again, general thunder outlook on Sunday with low severe weather risk. - Period of quieter weather expected Monday and Tuesday After an active weather period Monday and Tuesday will see quiet weather with ridging building in at the surface. GFS BUFKIT overviews at Grand Rapids are nearly devoid of moisture in the vertical profile. Confidence is high that we should be dry both days. - Chance for showers/storms mid week Our next chance for rain after the weekend will be in the Wednesday and Thursday time frame. At this point there is model disparity between the GFS and the ECWMF. The GFS brings a front through quicker from the northwest on Wednesday whereas the ECMWF holds off until into Thursday. At this point a bit early to tell the correct path given we are talking about a wave in zonal flow out on day 5 and 6. Confidence is low in terms of timing of the wave and its associated cold front. The front will bring a round of showers and storms when it moves through. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 649 AM EDT Sat Jul 4 2026 Rain has largely moved off to the east of the TAF sites as we approach 12z, but there still are some isolated showers that remain. VCSH should cover that threat. Next item of note are areas of MVFR ceilings (and some IFR) floating through the region this morning. These ceilings are due to time of day and a very moisture rich air mass. Expectation is for pockets of lower ceilings to be around through about 1530z and then they should have mixed out. Focus then shifts to the potential of thunderstorms this afternoon and evening. Latest model guidance is trying to show the highest concentration to the northeast of the TAF sites up towards Mt Pleasant and Saginaw and then to the southwest towards Chicago. Feel there is at least a chance of scattered activity this afternoon and evening (20z through 03z) so have kept the prob30 ground in the TAFs during that time frame. && .MARINE... Issued at 423 AM EDT Sat Jul 4 2026 Wind and wave conditions are expected to remain below advisory levels through the remainder of the holiday weekend. Waves will generally be 1-2 feet or less through Sunday night. Ridging will build in from the north in the latter half of the weekend which will actually pivot the winds from what have been southwesterly for some time to a north and east off shore flow. The only exception to the lower waves/winds will be in and near thunderstorms where conditions may briefly reach advisory levels. The main time frame where that could occur would be this afternoon and evening and storms redevelop in the heat of the day. Chances for storms over the lake though are relatively low today as compared to adjacent land areas. Bottom line, fairly high chances for good weather on the big lake today. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Duke AVIATION...Duke MARINE...Duke

NWS GRR Office Area Forecast Discussion