221 FXUS63 KGRR 200640 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 240 AM EDT Thu Aug 20 2026 .KEY MESSAGES... - Dry and less humid today - Showers with some thunderstorms Friday into the weekend && .DISCUSSION... Issued at 240 AM EDT Thu Aug 20 2026 - Dry and less humid today Today should feature dewpoints ranging from the upper 40s over central interior Lower Michigan to the upper 50s farther south along the I-94 corridor. This will feel noticeably drier to many. Maximum temperatures will range from near 80 to the lower 80s, with maximum apparent temperatures about the same or even slightly less where dewpoints are lower. Another and more robust measure of potential heat stress, known as the WetBulb Globe Temperature (WBGT), gives a reading of lower 70s for this afternoon. So all of this is to say that it should feel relatively comfortable outside today. - Showers with some thunderstorms Friday into the weekend Certainty is growing that we will see showers and thunderstorms moving through the forecast area Friday night and exiting to the east of the area by Saturday afternoon, yielding a dry Sunday. The exception may be the immediate lakeshore, particularly the Sable Points area, where lower tropospheric cooling may be sufficient for lake effect sprinkles. The growing certainty is related to the most recently available ensemble guidance, which shows a mean solution of meridionally deeper upper troughing that`s particularly pronounced into the Ohio Valley region. The expectation still is that this trough will become a cutoff low centered somewhere over the north-central Great Lakes region. The more amplified solution at this location means more of an equatorward component of the flow aloft over Lower MI, which is a drier pattern and suggests precipitation will remain shunted east of our forecast area after Saturday afternoon. However, it should be noted that ensemble solutions from as recently as yesterday morning and afternoon showed a sizable number of members forecasting precipitation through Sunday. So, although there is growing confidence for a dry Sunday, this is far from certain. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 130 AM EDT Thu Aug 20 2026 Thanks to an incursion of drier air at lower levels the probability for maintaining VFR conditions through the period is greater than 90 percent, except for JXN and BTL, which have an estimated 30 percent chance of experiencing brief MVFR visibility restrictions towards sunrise. This reasoning is based upon the presence of a weak surface boundary in that area where greater dewpoints/RH values appear to be pooled. The probability of MVFR occurrence is too low to explicitly mention in the TAFs. The only other change was to introduce a cloud deck around 8000 feet this morning for the southern terminals associated with convective debris from thunderstorms to the west and southwest of the area. These clouds are high enough that they likely wouldn`t interfere with the previously mentioned possible fog production. Made minor adjustments to winds this update as well. Based on high resolution guidance, MKG may see lake breeze augmented winds more from the northwest this afternoon instead of the typical west-southwest direction. && .MARINE... Issued at 240 AM EDT Thu Aug 20 2026 No concerns in the short term. Winds and waves could meet Small Craft Advisory thresholds by Friday afternoon, mostly around the Sable Points, due to persistent and moderately strong winds from the south-southwest over Lake Michigan. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...TJT AVIATION...TJT MARINE...TJT

NWS GRR Office Area Forecast Discussion


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