


Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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194 FXUS63 KGRR 112358 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 758 PM EDT Fri Jul 11 2025 .KEY MESSAGES... - Chance of strong/severe storms tonight/Saturday - More storms possible middle of next week && .DISCUSSION... Issued at 312 PM EDT Fri Jul 11 2025 - Chance of strong/severe storms tonight/Saturday Radar shows a few light rain showers moving across the cwa. Mesoanalysis indicated a lot of juice remains in place. SBCAPE around 2500 j/kg south of I-96, but only 20 kts of shear. Additionally, a weak frontal boundary was draped over far southern Lower, but creeping northward. In many respects, this is the quintessential Michigan summer environment. We`re sitting on abundant moisture and instability and just looking for a catalyst for storm initiation. We may have to wait until later tonight for that to occur. While it`s possible that a storm or two could develop this afternoon along the frontal boundary or even in the presence of outflow boundaries from this morning`s convection...CAMs point toward storms rolling eastward from Iowa/Illinois later this evening 3z-6z ahead of an upper short wave that would interact with the weak boundary drifting northward through the cwa. This would mostly affect the northern/northwest half of the cwa. Despite instability waning this evening, the low level jet will be increasing which will increase shear to 30-35kts. Thus, it`s possible that a few storms tonight could be strong, perhaps severe. Heavy rainfall remains a threat too due to precipitable water values aoa 2 inches. A severe threat remains for Saturday too. SBCAPE is progd to be aoa 2500 j/kg along with 30 kts of shear. Additionally, a cold front over Wisconsin will be pushed east by a stronger upper trough. However, if convection develops, it will likely be along a prefrontal trough after 17z across the southeast cwa. If that occurs, severe storms are quite possible with torrential rain and strong winds; the eastern cwa remains in a Slight Risk for severe storms. Once the cold front pushes east Saturday night, we`ll see a few days of dry weather. - More storms possible middle of next week Once the high that builds over the Great Lakes Sunday moves east Tuesday, a weak trough/warm front will move north across the cwa Wednesday, ahead of low pressure in the Plains. We see a 40-60 percent chance of showers/storms with that boundary Wednesday/Wednesday night. It`s early yet to determine if a severe threat will develop with that boundary, but it`s possible. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 758 PM EDT Fri Jul 11 2025 A stationary front is situated east to west in the I-96 corridor region with easterly winds across Central Lower and southerly winds toward the MI/IN line. This front will become a focus for shower and thunderstorm development tonight. During the 03Z to 06Z time frame we expect showers and storms, at least in a scattered nature to move into the TAF sites. Showers and storms may linger through the night as the frontal boundary remains a focus for activity. Near and north of the boundary MVFR ceilings will develop overnight, these ceilings may affect KMKG and KGRR between 12Z and 18Z. On Saturday the focus will be on renewed thunderstorm development for areas south and east of KGRR. We expect storms to affect KBTL, KLAN and KJXN between 15Z and 22Z. && .MARINE... Issued at 312 PM EDT Fri Jul 11 2025 Generally expecting 1 to 3 ft waves during the weekend, though Saturday could sneak into 2 to 4 ft and moderate swim risk from Grand Haven and north with southwest 10-20 knot winds. Thunderstorms this afternoon in Wisconsin/Illinois will cross Lake Michigan late this evening but will gradually weaken. However, they could bring wind shifts and gusts over 30 knots. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...04 AVIATION...Duke MARINE...CAS