137 FXUS63 KGRR 171753 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 153 PM EDT Sat Oct 17 2026 .KEY MESSAGES... - Areas of frost tonight - Warming trend with fair weather && .DISCUSSION... Issued at 153 PM EDT Sat Oct 17 2026 - Areas of frost tonight Saturday morning temperatures away from Lake Michigan were right around 32 degrees, plus or minus a few degrees locally, with areas of frost as expected. A more marginal setup for frost is expected tonight, mostly in southern Michigan. As the surface high pressure ridge migrates southeast of Michigan tonight, low-level southwest flow will increase to 15-25 knots. While the surface layer should decouple under strong radiational cooling, the increasing pressure gradient winds may keep some locations stirred up enough to prevent widespread frost. Model guidance on overnight lows tonight remains a few degrees higher compared to last night. The frost advisory for southern Michigan, where winds will be relatively weaker, will be the final one issued from the GRR WFO until spring. - Warming trend with fair weather The brief shot of cooler air is already exiting, to be replaced by a warmer mix of Pacific and Southwest continental air. 925-850 mb temperatures between this morning and Sunday morning will rebound about 10 degrees C and remain that way for several days. After a breezy Sunday, calmer winds are favored much of the coming week under weak upper-level flow and a tendency for subsidence and high pressure over the region. Normal high temperatures are now around 60 degrees, and the next several days will feature highs trending from the lower to the upper 60s. Ensembles are in good agreement regarding the forecast temperatures and drier conditions through at least midweek. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1248 PM EDT Sat Oct 17 2026 Clear skies are forecast through the TAF period as a dry airmass and surface high sit across the region. Wind is the only real item of note. First, A low-level jet will bring about 25 knots of LLWS overnight to the terminals, just below TAF thresholds. In addition, Winds pick up from the west or southwest this afternoon, becoming predominantly southwest by Sunday. Winds will be around 10 knots sustained, with MKG seeing gusts to 25 knots starting this afternoon, and GRR/LAN to around 20 knots late Sunday morning. && .MARINE... Issued at 153 PM EDT Sat Oct 17 2026 Deteriorating conditons are expected today into tonight, becoming increasingly hazardous for small craft from north to south, as southwest winds strengthen and waves build. An upgrade to a gale warning Sunday morning is possible for the nearshore near Big and Little Sable Points (north of Whitehall), as 25 to 30 knot winds could gust up to 35 knots. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Frost Advisory from 3 AM to 8 AM EDT Sunday for MIZ064>067- 071>074. MARINE...Small Craft Advisory from 8 PM this evening to 11 PM EDT Sunday for LMZ844>846. Small Craft Advisory until 11 PM EDT Sunday for LMZ847>849. && $$ DISCUSSION...CAS AVIATION...Thomas MARINE...CAS

NWS GRR Office Area Forecast Discussion