403 FXUS63 KGRR 250602 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 202 AM EDT Thu Sep 25 2025 .KEY MESSAGES... - Substantial fog expected again Thursday morning - Lesser rain chances on Thursday - Dry and warmer into the weekend and next week && .DISCUSSION... Issued at 350 PM EDT Wed Sep 24 2025 - Substantial fog expected again Thursday morning The 12Z DTX sounding showed a very deep saturated layer that is not liable to go anywhere anytime soon. The ground remains quite soaked from rain yesterday as well. Widespread fog seems likely again tonight, especially east of US-131. Widespread visibilities below a quarter of a mile are what we issue dense fog advisories for and there likely will be at least some spots in the generally favored areas that achieve this. Regardless, people can expect very comparable visibility restrictions Thursday morning that they observed this morning. - Lesser rain chances on Thursday Flow becomes somewhat more phased with the passage of a trough across northern Ontario at the same time the very positively tilted trough over our area trends closer to neutral and starts progressing eastward. The vast majority of available guidance shifts PoPs to our eastern forecast area closer to the US-127 corridor for the day. However, the 12Z HRRR does show a signal for afternoon shower development along a north-south axis west of US-131, apparently associated with a lake breeze convergence boundary. There is not much corroborating evidence for this among other model guidance, except perhaps for the 24/06Z REFS, which shows a weak (~10 percent) signal for measurable precipitation during this time in this area. The good news is that conditional instability should be negligible; hence, no thunderstorms are anticipated with any isolated showers that do manage to develop. - Dry and warmer into the weekend and next week The upper low/trough responsible for the rain chances on Thursday will be pushed well SE of the area by Friday. Upper ridging will be building over the area from the NW, with one small short wave trough trying to spill over the building ridge. This short wave will produce a non-zero chance of an isolated shower on Friday over the higher terrain of Central Lower, and maybe where some enhanced lake breeze convergence may be found. Most of the moisture will be swept out by Friday, so most areas should stay dry. Confidence is quite high, and only increasing then for an extended dry period from Saturday through the end of this forecast period on Wednesday, and likely beyond. Initially the upper ridge will be broad in nature across much of the middle portion of the 48 states, with upper lows over the SE and SW portions of the CONUS. This will ensure plenty of subsidence, with temperatures mild in nature. We will see temperatures warm to almost 80F early next week as the upper ridge builds a bit over the area and heights rise. This ridge will become more entrenched with the upper low over the SE and possible tropical systems over the Western Atlantic, and a long wave trough reinforcing the lower heights over the SW. The only change expected around mid-week next week might be a slight cooldown of temperatures. This would be the result of the strong sfc ridge to our north pumping in slightly cooler air in from the NE. && .AVIATION /00Z TAFS THROUGH 00Z FRIDAY/... Issued at 201 AM EDT Thu Sep 25 2025 Conditions and vsbys continue to drop as most TAF sites have dropped to MVFR with many already at IFR. Latest satellite shows clearing mid levels and increasing clouds at the low levels. Have adjusted timing for fog but widespread IFR/LIFR fog and low stratus are still expected by 09Z. Some areas of dense fog are likely but timing and placement is uncertain enough to cap minimum visibilities at 1/2 mile. LAN, AZO, and BTL are the most likely terminals to see dense fog. There are a few factors that could reduce the ability for fog to become dense. One is increase in high clouds from the south. The other is the persistent winds. That wind and high clouds could decrease moisture from settling and temps dropping. Fog should likely begin lifting and dissipating after daybreak with the low- cloud deck climbing to VFR by Thursday afternoon. After the fog lifts, there remains the potential for scattered showers tomorrow afternoon into early evening. Mainly affecting the eastern TAF sites. && .MARINE... Issued at 700 PM EDT Wed Sep 24 2025 Have expanded the Small Craft and Beach Hazards Statement south to St. Joseph/Van Buren County based on webcams as the extended duration of 20 knot winds has allowed hazardous waves to move further south into this region. Original discussion below for reference. *** Original Discussion*** The driver of our current marine pattern is the enhanced pressure gradient between an Upper Great Lakes high and Ohio Valley low. There looks to be localized enhancement of winds due to the lake breeze this afternoon between Whitehall and Holland with MKGM4 reporting 20-25 knot winds. Webcams suggest waves are likely in the 3-5 foot range near Grand Haven and Mona Lake as well. Will go ahead and issue a Small Craft Advisory/Beach Hazards Statement this afternoon from Whitehall to Holland/Muskegon and Ottawa Counties through late this evening given this. A similar brief increase in the wind across this region is expected Thursday afternoon to around 15 knots, slightly weaker than today, which should keep waves a bit lower. Lighter winds are then expected Friday into the weekend. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Duke AVIATION...Ceru MARINE...Thomas