


Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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438 FXUS63 KGRR 110554 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 154 AM EDT Fri Jul 11 2025 .KEY MESSAGES... - Thunderstorms Friday and Saturday, Severe Possible - Lingering Showers and Thunderstorms Sunday, Mainly East - Dry Monday and Tuesday, Rain and Storms Wednesday && .DISCUSSION... Issued at 327 PM EDT Thu Jul 10 2025 - Thunderstorms Friday and Saturday, Severe Possible Overall there is uncertainty in the exact timing of rain and thunderstorms due to differences in the overall pattern features. However confidence is higher for showers and storms to move into western Michigan early Friday morning from the remnant MCV over western Wisconsin. This feature will cause thunderstorms to redevelop overnight and move through the area Friday morning. Some stronger storms are possible, but overall not expecting anything severe with the morning round. The morning convection looks to clear by the late morning/early afternoon. Depending on how quickly storms clear will impact our chance for afternoon thunderstorms which could be severe. At time time the main window would be during the late afternoon and evening hours. Mean HREF SBCAPE values are in the 1000-2000 J/kg range during the afternoon mainly sough of I-96. 0-3 km storm relative helicity values during that time are in the 100-200 m2/s2 range. Therefore there is enough spin in the atmosphere for stronger storms producing hail, gusty winds, and perhaps a tornado. This will be a higher concern with any remnant boundaries in the area from the morning round of thunderstorms. This matches up with the updated SPC outlook for Friday. Thunderstorms will also produce heavy rainfall with precipitable water values approaching 2 inches. Rainfall rates around an inch per hour are possible. Areas that see thunderstorms track repeatedly overhead could see higher rainfall amounts of 2 or more inches. This could lead to minor flooding especially in urban areas. Friday night thunderstorms will gradually diminish as we lose our daytime instability. Saturday a shortwave trough moves through the area bringing with it another round of rain and thunderstorms for the afternoon and evening. NBM 25th-75th percentile SBCAPE values range from 2000-3500 J/kg across much of the area, shear isn`t that great but with that amount of instability it won`t take much for a storm to become severe. - Lingering Showers and Thunderstorms Sunday, Mainly East Another shortwave through moves through Sunday which could spark additional showers and thunderstorms during the day. Highest chances are south and east of Grand Rapids but we`ll need to monitor for a westward trend. Overall not expecting the day to be a complete washout, but something to keep an eye on for those with any outdoor plans. - Dry Monday and Tuesday, Potential for Rain and Storms Wednesday High pressure builds in for the beginning of next week with highs in the 80s to low 90s and lows in the 60s to around 70. Wednesday into Thursday a deeper, more organized trough looks to move through the region. With the hot, moist environment it looks like another good set up for thunderstorms. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 154 AM EDT Fri Jul 11 2025 Convective trends are our main focus with the 06z set of forecasts. We are watching an area of rain with embedded thunder down toward Chicago and Milwaukee as of 0530z. This is moving toward the area, but is trending down for the time being. We do expect additional development to take place, and affect all of the terminals this morning into early afternoon. Showers are expected to move over KMKG by 10-11z, and then spread eastward from there through the morning. Thunder chances look to lag the showers by a couple of hours. We do expect conditions to drop down into the IFR category with the storms and heavier rain rates. These showers and storms are then forecast to move east of the terminals by 18z or so. There will be a relative break in the more widespread showers/storms after the morning batch moves out. The chance will not be zero of an isolated shower/storm popping up, but the coverage will be 10-20%, so have not included it in the forecast. We will be watching another potential wave of showers and storms moving into the area late evening to early overnight. This is a bit uncertain yet, but looks to favor the KMKG and KGRR terminals. Have mentioned thunder there, and left the rest of the terminals dry for now. We will fine tune this as trends unfold through the day with features. && .MARINE... Issued at 327 PM EDT Thu Jul 10 2025 Short range models presently favor winds and waves remaining below levels hazardous to small craft and beachgoers through the weekend. However a low (around 20 percent) chance of hazardous winds and waves exists later Friday into Saturday associated with a frontal boundary crossing the area. The other marine concern is that several rounds of showers and thunderstorms are likely through the weekend beginning early Friday. Locally higher winds and waves are possible in any storms, particularly later Friday and again on Saturday. Mariners and beachgoers should monitor the forecast this weekend. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...RAH AVIATION...NJJ MARINE...Thomas