


Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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572 FXUS63 KGRR 180542 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 142 AM EDT Sat Oct 18 2025 .KEY MESSAGES... - Wet and Stormy Saturday/Saturday night, and Wet and Windy Sunday - Another Wet and Windy System Monday Night-Tuesday - Unsettled and Cool Weather Wednesday-Friday && .DISCUSSION... Issued at 318 PM EDT Fri Oct 17 2025 - Wet and Stormy Saturday/Saturday night, and Wet and Windy Sunday A lot of weather to impact Southern Lower Michigan through the weekend, especially given the quiet late summer and fall over the past few weeks. We are in the relative calm before the storm this afternoon, that will continue through most of the night after a few early morning showers that moved across Central Lower. We are in a warm sector in the wake of the elevated warm front that moved through earlier, with the cold front still well west of the area over MN and IA this afternoon. In addition, Gulf moisture is just starting to be drawn northward into the system. Sfc dew points in the 40s and a lack of moisture below 7-9k ft are keeping the area dry. This will continue through much of tonight. We will see showers and some isolated storms arrive across the NW corner of the forecast area toward/after midnight, and then further south and east Saturday morning. The arrival of the showers and few storms will be with the 850 mb jet axis nosing over the area. This looks to bring a line of showers and embedded storms toward the lakeshore toward 12z Saturday. These showers and storms will initially be quite benign as they will be elevated in nature, with just a little instability to support weak updrafts. We do see a decent potential for the line of showers and isolated storms to strengthen a bit through the afternoon for the SE portion of the area. HREF mean MU CAPEs are forecast to increase to over 500 J/kg. This is likely due to low level dew points increasing into the low to mid 60s, and some diurnal heating ahead of the line of rain. If the instability of 500-1000 J/kg can be realized, we could see some strong to maybe even marginally severe storms for a few hours Saturday afternoon. Deep layer effective shear of 40-50 knots is quite favorable for some organization. If the instability can not be realized, the shear would likely overcome the instability, and not much would be expected. Mid level lapse rates are good around 6.5- 7.0 C/km to support some hail. The low level jet over the SE corner of the area will provide for some decent low level shear for some wind, and maybe even rotating storms. This will have to be monitored. The heavy rain potential really looks to be centered on Saturday night, especially from around 03-09z. This will be the result of the deepening sfc low to our east with the long wave trough supporting it, and strong short wave energy currently over AZ lifting NE ahead of the long wave trough. This short wave and jet energy will help to provide a fairly strong FGEN signature just NW of the low in the TROWAL/deformation zone. This will wring out the very moist air mass (250% of normal pwats for date) that will move in. Thankfully with the lack of rain and drought conditions over the past few months, we have some room for it to go. Please see the Hydrology section below for more detail. Finally, the sfc low will move by the area on Sunday, but we will see additional showers likely, while adding some strong winds to the mix. We will see the strong gradient on the backside of the strengthening low move over the area just before daybreak on Sunday along the lakeshore. This will then spread across the entire area through Sunday. The highest winds look to be just inland from the lakeshore where 40-50 mph winds are likely. Inland areas will be a little less with more friction from the ground, and the better gradient being over the lake. Showers will continue all day as the upper trough will be slowly approaching all day, with additional short wave energy rotating through. - Another Wet and Windy System Monday Night-Tuesday After a brief respite Sunday night and Monday, we will see more windy and wet weather move in over the area by Tuesday morning. High pressure between the strong departing system, and the next one moving in from the NW will be short lived. Stronger winds from the SW will arrive late Monday, and rain will arrive ahead of the system Monday night. This system will not be in the process of strengthening like the weekend system. It will be a fairly strong upper low however, leading to strong dynamics. Moisture will not be nearly as rich with this system, but it will eventually be pulling some moisture northward from the Gulf. - Unsettled and Cool Weather Wednesday-Friday More widespread rain will give way to instability showers on Wednesday under the cold pool and cyclonic flow aloft. We could even see some heavier lake effect rain showers develop along the lakeshore as 850 mb temps drop to as low as -2C, giving delta t`s mid to upper teens C with water temps still 16-18C. The Tuesday/Wednesday upper low will set the stage for general long wave troughing to persist over the area through the end of the week. We will see some short wave ridging build in centered around Thursday, but another short wave dives in by Friday giving the area another round of showers, and keeping the air mass cool. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 142 AM EDT Sat Oct 18 2025 This forecast period is starting out with mainly high clouds in place at all of the terminals. Showers are starting to form over Lake Michigan and are ongoing over Wisconsin. This axis of shower activity with some isolated storms will arrive at KMKG by 11z or so, and will continue to move across most of the rest of the forecast terminals, except maybe staying north of KJXN. MVFR conditions are likely, and there may be some periods of IFR with the heavier showers/storms. This first batch will move out by about 18z. A few showers may linger, but there will be a relative lull in the more widespread shower activity. Later in the afternoon and into the evening, the I-94 corridor is likely to see additional scattered showers and isolated storms develop. Then beginning around 03z, widespread rain will move over the I-94 corridor and spread north through 05-06z. IFR conditions are forecast to develop in this widespread rain. Some isolated storms will remain possible. && .MARINE... Issued at 318 PM EDT Fri Oct 17 2025 Small Craft Advisory conditions through Saturday evening. Gales likely on Sunday. Gales possible late Monday through Tuesday. Hazards to small craft will be frequent through at least Wednesday next week. Winds 10 to 25 knots from the south-southwest are expected over the water through Saturday, slowly subsiding into a temporary lull Saturday night. Today and tonight, those winds will build 5 to 8 ft waves from Grand Haven toward Manistee. Strengthening low-pressure system tracking from SW to NE across Lower Michigan early Sunday will have strong winds on the back side of it along with cooler air flowing in amid northwest winds. Ensemble models, particularly the European ensemble system, continue to indicate about 75 percent of solutions favor gale force gusts over the southern half of Lake Michigan aimed at the Michigan shore. A gale watch has been posted for Sunday morning through evening. Somewhat relaxed winds within a high pressure ridge Monday morning will be fairly short-lived also, as another developing low-pressure system appropriate for the season consolidates over the western Great Lakes. Any lull in hazardous conditions for small craft Monday morning will be temporary. Depending on the strength and track of the center of the low, there is a chance of southwest gales Monday night, but west-northwest gales are more probable on Tuesday. The European ensemble system, though potentially underdispersed this far out (giving us overconfidence), have about 70 percent of members favoring gales over Lake Michigan during Tuesday. && .HYDROLOGY... Issued at 318 PM EDT Fri Oct 17 2025 Significant rainfall is expected over the next several days across much of Lower Michigan. The total amount of rain we are expecting continues to slowly nudge upwards as forecast details come into focus. The rain will be spread out over several rounds, primarily spanning Saturday and Sunday, with the heaviest rain currently expected before/during sunrise on Sunday. Overall averages across much of the area will probably end up in the 1 to 2 inch range, with some multi-county streaks of 2-3"+. The good news is that because we`re in a drought, the rivers have plenty of room to put this water. Some of the midsize rivers in the area like Sycamore Creek (Holt), Buck Creek (Grandville), and the Looking Glass River (Eagle) are the most likely to see rises close to bankfull, but no river flooding is expected unless this storm seriously overperforms our expectations. It would probably take 4"+ over a fairly large area to begin flooding the midsize tributaries mentioned above. Nevertheless, with water levels currently running lower than normal due to the drought, notable within-bank rises are expected across most of the area. Anyone with personal property near the waters edge leftover from the summer should prepare for rising water. While river flooding isn`t a big concern, if some slow-moving heavy rain bands park over some of our urban areas we could see some localized minor flooding develop in the classic low spots and other poor drainage areas. It`s hard to pin down which urban areas would be most at risk of this happening, but recent model trends suggest the eastern edges of our area are most at-risk, which would include Lansing and Jackson areas. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for LMZ844>849. Gale Watch from Sunday morning through Sunday evening for LMZ844>849. && $$ DISCUSSION...NJJ AVIATION...NJJ MARINE...CAS HYDROLOGY...AMD