895 FXUS63 KGRR 251038 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 638 AM EDT Tue Aug 25 2026 .KEY MESSAGES... - Patchy Fog into Mid Morning - Chance for Thunderstorms Wednesday, Some Strong - Warmer & More Humid Sunday into Early Next Week; Storms Possible && .DISCUSSION... Issued at 248 AM EDT Tue Aug 25 2026 - Patchy Fog into Mid Morning NBM hourly guidance as well as GFS MOS guidance continues to support a few hours of patchy fog mainly from 5am-9am this morning. Some could be locally dense. Low or zero dew point depressions, calm winds, and clear low/mid levels (just some scattered high clouds) should allow for some patchy fog. Will assess observation trends into mid morning, but confidence is not high that any headlines will be needed. - Chance for Thunderstorms Wednesday, Some Strong Model guidance continues to support scattered thunderstorms across the region Wednesday. Since we are now within 36 hours of the event, the CAMs are helping fine tune what the threat could be. 00z HREF guidance indicates a surface cold front will be located across western Lake Michigan by 18z Wednesday. Ahead of the front, the HREF mean is showing a plume of 1500 J/kg SBCAPE with maximum members indicating over 2000 J/kg. HRRR soundings for 18z at LAN show a bit more decent shear than previously indicated with 0-6km shear around 30 kts with decent directional shear in the 0-3km layer. Some of the Nam3km soundings look more ominous for low level shear ahead of the front. Overall, there appears to be enough shear and instability along with some low level curvature in the model hodographs to support some severe potential, including perhaps some clusters of storms with embedded strong winds or even some mini-supercells capable of a short duration tornado. Some questions exist about midday shower activity prior to peak daytime heating. Some CAMs do indicate scattered morning showers moving into western Lower MI, which could complicate pre-frontal storm development in this area. Indeed, models such as the HRRR push showers through GRR around the lunch hour and effectively end the storm threat for the day there. We`ll see how this pans out. The Nam3km would delay storms a bit, which could bring more of a severe weather threat to the area. If we had to highlight a particular region for strong storm development, it seems east of US 131 may have the best threat from 18z-00z Wednesday. As previously mentioned, a few diurnally driven showers and a thunderstorms may develop on Thursday mainly near and east of US 127 given residual instability and moisture left in the area underneath upper troughing. Currently NBM isn`t buying it, with POPs too low to mention a threat for rain. - Warmer & More Humid Sunday into Early Next Week; Storms Possible After we`ve gone through some fallish weather lately, it appears we`ll reverse course a bit late weekend into early next week as anomalous upper heights move in per ensemble guidance (500 mb heights in the upper 580s dm) as well as 850mb temps that could even touch 20C across southern Lower MI. This also occurs with climbing dew points and PWAT values, as well as an active low level jet pattern somewhere across the Midwest. Depending on where we sit with relation to the upper ridge and low level jet, periods of thunderstorms are certainly possible. && .AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 638 AM EDT Tue Aug 25 2026 Sporadic light fog may have some minimal impacts for the first hour or so of this TAF period, otherwise no significant weather is expected. VFR conditions today into tonight with very light winds and perhaps some scattered cu around 4k ft. A few showers may be pressing toward MKG at the tail end of the TAF period, but we have time to evaluate that risk. && .MARINE... Issued at 248 AM EDT Tue Aug 25 2026 Wednesday will be the next hazardous day for mariners and also lead to a high swim risk for many areas, especially Holland to the north. This occurs ahead of a cold front likely situated across western Lake Michigan around 18z Wednesday. Mariners will face increasing wind and wave activity, likely necessitating a Small Craft Advisory for Wednesday with 3 to 6 footers possible and SW winds 10-20 kts and gusts to 25 kts. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Hoving AVIATION...Hoving MARINE...Hoving

NWS GRR Office Area Forecast Discussion