FXUS63 KGRR 091730 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 130 PM EDT Fri May 9 2025 .KEY MESSAGES... - Dry and Mostly Sunny Through Monday, Slight Chance of Showers Saturday - Chances for Thunderstorms Middle to Late Next Week && .DISCUSSION... Issued at 340 AM EDT Fri May 9 2025 - Dry and Mostly Sunny Through Monday, Slight Chance of Showers Saturday High pressure will be largely over the region with mostly clear skies and warming temperatures through the weekend, though interrupted by a weak cold front on Saturday. Going with a slight chance of showers on Saturday... Models show a moist layer in the mid levels above the PBL, around 5,000 to 10,000 feet, which may be within a shallow conditionally unstable layer. As a result, a few higher-based, lower-topped showers could develop with enough rain that could survive the trip through drier air closer to the ground. - Chances for Thunderstorms Middle to Late Next Week Better moisture arrives Tuesday and sticks around for a few days. The NBM has dew points reaching the lower 60s. Average CAPE values among the ENS, GEFS, and CMC ensembles increase from Tuesday into Thursday or Friday, with a majority of members producing rain at some point during that time frame. Early next week, there is likely a split upper-level jet across the central US, with a broad ridge in the northern stream, and a cutoff low the southern US / Gulf region, forming a Rex block type of pattern. For Tuesday-Wednesday, the southern low should slowly migrate toward the Ohio Valley or southern Great Lakes. Scattered showers and thunderstorms should develop as a result, with a tendency for them to be more diurnally driven (occurring mostly during the afternoon). Wind shear appears rather weak, as do mid- level lapse rates. This should limit severe weather potential. Instead, deep moisture through the convective layer and slow- moving cells would favor localized downpours and highly variable rainfall totals. For Thursday-Friday, a deeper upper-level trough from the Dakotas approaches the western Great Lakes. Stronger surface fronts are expected, along with the potential for steeper mid-level lapse rates and increasing shear. This time frame would have some possibility for severe storms if this were to verify. It's still a week away, though confidence is a little higher than usual given low spread in the ensembles regarding the synoptic pattern evolution. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 126 PM EDT Fri May 9 2025 Mainly clear skies are expected through the period. A weak cold front will move across central Lower around 12z bringing a sct-bkn mid cloud layer that will quickly move through. There may be a passing shower with this cloud deck but probably not; showers were left out of the TAFs. && .MARINE... Issued at 340 AM EDT Fri May 9 2025 Light offshore winds this morning will become onshore during the day as a lake breeze develops. On Saturday, winds and waves may become hazardous to small craft, as north winds strengthen to 20-25 knots over mid Lake and near the Sable Points. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...CAS AVIATION...04 MARINE...CAS