416 FXUS63 KGRR 241950 AFDGRRArea Forecast Discussion National Weather Service Grand Rapids MI Issued by National Weather Service Detroit/Pontiac MI 350 PM EDT Wed Sep 24 2025
.KEY MESSAGES...
- Substantial fog expected again Thursday morning
- Lesser rain chances on Thursday
- Dry and warmer into the weekend and next week
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.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.
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.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 205 PM EDT Wed Sep 24 2025
Ceilings continue to improve with a mix of IFR and MVFR ceilings across the TAF sites this afternoon. Expect conditions to improve to MVFR for all sites in the next 1-2 hours with many sites potentially reaching VFR for a time this evening. Isolated showers are possible in the vicinity of GRR/LAN for the next few hours and an isolated storm cannot be ruled out though confidence is too low for TAF inclusion. Beginning lake this evening, conditions will be favorable for widespread IFR to LIFR conditions across the TAF sites given the abundant moisture in the form of both fog and low ceilings. Dense fog is possible at LAN, JXN, AZO, and BTL where low level moisture is greatest. By late morning Thursday visibilities will begin to improve, however similar to today it`ll likely be into the early afternoon before conditions improve to MVFR or better for all of our sites except MKG. With winds just off the surface a bit higher at MKG would expect conditions to reach MVFR by mid morning.
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.MARINE... Issued at 350 PM EDT Wed Sep 24 2025
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.
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.GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement until midnight EDT tonight for MIZ050- 056. MARINE...Small Craft Advisory until midnight EDT tonight for LMZ846-847.
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DISCUSSION...NJJ/TJT AVIATION...Thomas MARINE...NJJ/TJT
NWS GRR Office Area Forecast Discussion