343 FXUS63 KGRR 270802 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 402 AM EDT Mon Apr 27 2026 .KEY MESSAGES... - Showers and Thunderstorms expected this afternoon into tonight - Rain showers possible Wednesday and Thursday - Drier and cooler Friday and Saturday && .DISCUSSION... Issued at 401 AM EDT Mon Apr 27 2026 - Showers and Thunderstorms expected this afternoon into tonight Forecast parameters have not changed much with regard to the system moving in tonight. We still have strong wind fields in place with 60 knots forecast at 850mb and 60-70 knots in the mid levels at 500mb. So, deep layer shear remains high at 50-60 knots. Our issue remains the lack of stronger instability. The HREF continues to show 500 to 1,000 j/kg of MUCAPE which is not overly impressive. Another negative factor that is related to the lower CAPE is the fact that we may see some rain move in this afternoon associated with the robust upstream convection. The rain would obviously hinder chances at better destabilization. The SPC outlook for us has not changed much over the past 3 days which is indicative of the steadiness of the system in the models. We are mainly looking at a wind threat given the magnitude of the wind fields and that is contingent on seeing some better instability move in. HREF and machine learning tools like Nadocast support at least the threat of strong winds across western and southern portions of the forecast area. HREF has a signal in the max gusts that Lake Michigan may play a role in some of the stronger wind gusts at least in the lakeshore counties. So, while the threat of severe weather tonight is somewhat low the wind fields have our interest and we will be monitoring closely. Rivers have been steadily falling now for days which is good. We will see rain on the order of a half inch to an inch in a quarter in some heavier swaths. At this point we are not expected major issue with this rain. There may be a delay in the fall or slight rises, but nothing like we saw the past couple of weeks. - Rain showers possible Wednesday and Thursday Much lighter rain showers are possible Wednesday and Thursday. The showers look to be diurnally driven with the upper trough nearby/overhead. Wednesday the showers may be aided by a low passing by to our south. Thursday`s chances looks to be aided by thermally driven forcing with heat of the day producing troughing at the surface over the Lower Peninsula. - Drier and cooler Friday and Saturday We look to be drier and cooler for the end of the week. Frost and freezing temperatures will once again come into play. Wednesday night through Saturday night (4 nights in a row) we could be dealing with frost/freeze related headlines. The fruit crop is in full swing at most locations so once we get by the thunder chances tonight our focus will pivot to the cold and its affects on early season fruit and flowers. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 219 AM EDT Mon Apr 27 2026 A low pressure system will take aim on the Great Lakes today from the Central Plains. We will see ceiling lower through the day from high clouds this morning with bases at or above 20,000 feet dropping into the 5,000 to 10,000 foot range this afternoon. Some scattered showers are possible this afternoon in advance of a warm front, but the bulk of the heavier precipitation should hold off until after 00Z. In the 00Z to 06Z time frame we will see showers and thunderstorms affect the TAF sites. Ceilings will also lower further into the MVFR category and by the end of the period towards 06Z even IFR conditions are possible. Bottom line, VFR today with conditions trending worse tonight as a low pressure system moves through the Great Lakes. Wind will be noticeable and a concern for aviation today. Winds will be southeast increasing into the 15-30 knot range this afternoon and evening. Winds will veer to the south overnight. && .MARINE... Issued at 401 AM EDT Mon Apr 27 2026 Conditions will get rough on the big lake this afternoon and evening as winds steadily increase. Winds will be southeast and offshore this morning, but speeds will increase into the 15 to 25 knot range. This afternoon, winds will veer just a bit to south- southeast and increase to 20 to 30 knots. This evening, we are concerned that we will hit gale force out of the south. Coordinated with surrounding offices and consensus was to stick with the Small Craft Advisory for now given this is a warm air advection wind and its hard to mix into the cold air near the lake surface this time of year. The day shift will re-evaluate, but there is 40 knots in the mixed layer. Winds will decrease into Tuesday as the low pulls away. As for waves...3 to 5 footers are likely in the nearshore waters towards sunset. Waves will peak around midnight at 6 to 10 feet north of Grand Haven and 3 to 6 feet to the south. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Small Craft Advisory from 8 AM this morning to 6 PM EDT Tuesday for LMZ844>849. && $$ DISCUSSION...Duke AVIATION...Duke MARINE...Duke

NWS GRR Office Area Forecast Discussion