480 FXUS63 KGRR 280123 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 923 PM EDT Mon Apr 27 2026 .KEY MESSAGES... - A Period of Strong Winds Likely This Afternoon and Evening - Turning Progressively Colder This Week; Frosts & Freezes Coming && .DISCUSSION... Issued at 235 PM EDT Mon Apr 27 2026 - A Period of Strong Winds Likely This Afternoon and Evening A deepening springtime low will be moving from IA toward the western U.P. tonight as a shortwave trough swings through the region. Periods of showers and a few thunderstorms will accompany this system. Strong deep layer shear moves in after 20z but with an absence of CAPE. Very little MLCAPE is indicated by the 12z HRRR for the remainder of today and tonight, with perhaps 500+ J/kg of MUCAPE moving in prior to FROPA overnight. While instability will be our main limiting factor for organized convection, the very strong wind fields just off the surface are concerning with 50-60 kts indicated from 925-850mb this afternoon and evening. What we`ve seen with the 12z CAM guidance is a signal for wake low wind gusts in the post-stratiform rain region on the north side of a convective complex moving across IL/MO and that has certainly bore out in reality. Several sites across IA and now IL have gusted in the 45-55 mph range behind the stratiform precip region moving through metro Chicago. This is coincident with 3 hour pressure drops around 8-10 mb. We feel the best way to handle this is with a Wind Advisory as opposed to the less visible SPS. If a small area of higher gusts materialize then perhaps SVRs will be needed, or if a larger scale, a High Wind Warning may be considered. The Advisory will be in place through 8pm but could be extended if the threat goes longer than anticipated. Any additional showers and storms that develop late tonight and into the overnight hours will likely be fairly tame but could put down some swaths of 0.50" or more of rain creating brief ponding of water on roads overnight before that threat diminishes. - Turning Progressively Colder This Week; Frosts & Freezes Coming Ensemble guidance is in good agreement regarding upper troughing settling in this week and below normal temperatures moving in. Mean 850mb temperatures are shown to dip to around -5C by late week. Several nights of frosts and freezes are likely to materialize across most of the region starting Wednesday night and lasting through Saturday night. The worst conditions are anticipated Thursday night and Friday night. Both of those look to be radiational events. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 922 PM EDT Mon Apr 27 2026 Ceilings trended VFR to MVFR outside of the recent shower and thunderstorm round. A wake low progressed through the region behind the organized storm cluster and brought gusts up to 49 kts through the terminals. Chances for showers and thunderstorms continue tonight. Another round of strong showers with embedded thunderstorms will exit the lake over the region near 2-3Z, and a secondary burst of strong winds is possible with it. MVFR to possible IFR conditions can be expected with the showers and thunderstorms. Vicinity showers will remain as the bulk of the activity pushes east out of the forecast area near 9z, while ceilings trend more solidly MVFR to eventually VFR. Winds will remain an aviation concern tonight as gusty southeast wind veer to a more southwesterly direction, and then westerly early Tuesday morning. Outside of a brief lull in winds Tuesday morning, gusts up to 30 kts are likely for most of the terminals through Tuesday afternoon. Winds will then ease Tuesday evening. && .MARINE... Issued at 235 PM EDT Mon Apr 27 2026 A short duration Gale Warning is being issued to cover gusty winds behind an area of showers and embedded thunderstorms moving over Lake Michigan. These wind gusts are already observed to be in excess of 50 mph across northern IL and would last longer than a typical thunderstorm wind gust would. The wind direction would be from the E/SE. Following the Gale, a Small Craft Advisory goes into effect to cover building waves and elevated winds over the lake into Tuesday. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Small Craft Advisory until 6 PM EDT Tuesday for LMZ844>849. && $$ DISCUSSION...Hoving AVIATION...EAK MARINE...Hoving

NWS GRR Office Area Forecast Discussion