


Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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836 FXUS63 KGRR 160808 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 408 AM EDT Thu Oct 16 2025 .KEY MESSAGES... - Potential for some light precipitation tonight into Friday - A wet and windy weekend - Another system set for Tuesday/Wednesday && .DISCUSSION... Issued at 408 AM EDT Thu Oct 16 2025 - Potential for some light precipitation tonight into Friday Today will bring rather calm and quiet weather to the region as high pressure is in place both at the surface and aloft. The initial push of warm air advection in advance of our next system comes tonight into Friday morning. The best moisture transport occurs across Northern Lower Michigan. The SREF pops almost always seem superior to other guidance and will follow its lead here. We will carry small pops across Central Lower Michigan to account for showers that will be moving across the area tonight into tomorrow morning. - A wet and windy weekend A cold front will be located just west of the area in the Friday night and Saturday time frame associated with the initial wave moving into Canada today from the Plains. A little bit less in the way of precipitation is expected initially now, with a period of dry weather expected as we away for energy to drop into the base of the upper trough as we head into Saturday night. A deep low is expected to from in the Great Lakes this weekend, but the energy that drives and deepens that low is currently all the way up in the Gulf of Alaska west of British Columbia Canada. It has a long way to traverse before it induces a strong deepening low into Sunday over the Great Lakes. So, while the nearby cold front will have some rain associated with it on Saturday, the bulk of the activity gets going with the upper wave begins to round the base of the upper trough to our west Saturday evening. Using the GFS, the surface low deepens from 998mb in Iowa Saturday evening to 989mb just north of Lake Huron Sunday evening. This is a strong low for sure, but nothing that out of the ordinary by the standards of fall Great Lakes systems. The backside high is not abnormally strong either, around 1020mb. The expectations are for a windy system this weekend with sustained winds likely in the 20-30 mph range with gusts of 40-50 mph. WE are likely looking at the potential of a Wind Advisory on Sunday at least for portions of the area. Given the dynamics in play with a strong upper jet over 100 knots and the moisture return of 60+ F surface dewpoints, thunderstorms are expected in the warm sector Saturday night into Sunday morning. WPC QPF totals are in the 1-2 inch range over the next 5 days with most of that coming this weekend. We should be able to handle that rain without issues given lower river levels. - Another system set for Tuesday/Wednesday Another system is expected into mid next week in the Tuesday and Wednesday time frame. The deep upper trough of this weekend is followed by an even deeper upper system as we head into next Wednesday. The upper trough has a reinforcing shot of cold air with 850mb temperatures dipping to below zero C. Widespread rain showers are expected along with blustery conditions. Fall has arrived! && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 204 AM EDT Thu Oct 16 2025 Surface high pressure is sprawled across the Great Lakes tonight which is resulting in light winds and clear skies. We have some occasional ground fog occurring, formed through radiational cooling processes, but most sites are VFR. We expect VFR weather to continue throughout the next 24 hours actually as the high will only have slipped slightly to the east during that time. The cloud bank that is off to our west early this morning with cloud bases of 3,500 to 8,000 feet will remain west of the TAF sites today. Some high level cirrus clouds will filter in from the west after sunrise with bases at or above 20,000 feet. In the 00z to 06z time frame this evening we will see clouds spread in from the west with bases around 10,000 feet. Winds through the TAF period of 06z to 06z will be light, either calm (like this morning) or east to southeast around 5 knots today. && .MARINE... Issued at 408 AM EDT Thu Oct 16 2025 Lake Michigan is quiet this morning with offshore winds around 10 knots and 1 foot waves. Winds will become even lighter today so no marine concerns through sunset. Tonight winds begin to pick up out of the south at about 10 knots as surface high pressure slips away to the east of the Great Lakes. On Friday winds will likely increase to Small Craft Advisory (SCA) strength as the gradient tightens between the retreating high and low pressure in the Northern Plains. 15 to 30 knot south winds look like a reasonable bet from around daybreak on Friday into the day on Saturday. A SCA will be needed for Friday into Saturday for these stronger south winds. The focus is on a the potential for strong winds over Lake Michigan this weekend. The evolution of the low is the question mark at this point. How and where the low deepens and to what strength is the crux of the Saturday night through Sunday night forecast. The energy that will be responsible for this weekends potentially strong low is in the Gulf of Alaska this morning between British Columbia Canada and the state of Alaska. So, it has a long way to traverse and models are handling its evolution differently. At this point look at both operational and ensemble guidance the event has the potential to produce high in gales (to 45 knots) with some storm force gusts not out of the question (near 50 knots). This event is 4 days out so we have time to dial in the forecast based on new guidance. Bottom line, expecting a high end gale on Sunday with waves that will likely peak in the 12-15 foot range. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Duke AVIATION...Duke MARINE...Duke