228 FXUS63 KGRR 241753 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 153 PM EDT Sun May 24 2026 .KEY MESSAGES... - Fog Likely Tonight, Locally Dense Fog Possible - Warmup into Wednesday With Low Rain Chances Mid-week - Dry and Cool Late Week && .DISCUSSION... Issued at 152 PM EDT Sun May 24 2026 - Fog Likely Tonight, Locally Dense Fog Possible Rain showers and isolated thunderstorms associated with an occluded front crossing the area should exit by early evening. Concern then develops for fog overnight given low-level moisture from today`s rain. Winds subside and skies begin to clear as high pressure moves in tonight, with a favorable environment for fog development resulting. Signals are present in guidance that pockets of locally dense fog could develop depending on the extent of clearing overnight and to what extent any sunshine today can mix. Climatology suggests that given a strong sun angle in late May, widespread dense fog is unlikely, matching the picture guidance shows. We will continue to monitor trends going into tonight. - Warmup into Wednesday With Low Rain Chances Mid-week West Michigan sets up on the periphery of a large scale ridge starting later Monday into Tuesday with the development of an omega blocking pattern over the central CONUS. 850 mb temps warm into the mid teens Celsius resulting in highs in the 80s. There are two low chances of rain for the first half of the week. First is Monday where convergence off Huron may pop an isolated shower across our northeast CWA. Confidence is low, with PoPs 10% or less. Second is Wednesday with the arrival of a backdoor cold front. Moisture quality is marginal so only light precipitation is expected. Medium range model guidance suggests enough MUCAPE will be present thunder to be in play. - Dry and Cool Late Week The post backdoor cold frontal environmnet will be slightly cooler than the first half of the week, with highs in the upper 70s likely. Comapred to yesterday, guidance has trended twoards the warmer solution with 850mb temps in the low teens. The omega blocking persists with a surface ridge in place across the region. This keeps the forecast dry for the later portions of the week. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1224 PM EDT Sun May 24 2026 Several challenges for the aviation forecast this afternoon into tonight. The confidence in timing the thunderstorm arrival into LAN and JXN is good, with occasional lightning and temporary IFR heavy rain being reported in Southwest Michigan. There is little to no lightning in the few hours of rain that will follow the up- front thunderstorm, so expecting to hold on to MVFR to tempo IFR cig/vis in the rain and remove the TS after it spends about an hour passing through the remaining aerodromes. The back edge of low clouds is crossing Lake Michigan, and mostly clear skies are present in Wisconsin and Illinois. Latest models lend less confidence in VFR late this afternoon and evening, as there may be scattered to broken cumulus on either side of 2,000 feet hanging on through sunset. Then a brief clearing is possible from sunset which should give way to fog development overnight. The timing of fog onset will be difficult to pin down as it depends on how much each location can dry out prior to sunset, but this nonetheless is a good setup for fog tonight with lingering lower atmospheric moisture, light winds, and clearing skies late in the evening. && .MARINE... Issued at 152 PM EDT Sun May 24 2026 Primary concern for marine interests is the potential development of fog across the waters tonight. Ample low-level moisture paired with a approaching high pressure system looks to calm winds enough for fog development overnight. Climatologically, the cooler waters favor fog development, which is also supported by model guidance. As a result, will be issuing a Marine Dense Fog Advisory from late this evening through mid Monday morning. As for winds and waves, Time/Height wind overviews suggest largely that light winds and sub-advisory waves are expected over the next several days. Winds in the 1-3kft range look to approach 30-35 kts later Monday into Tuesday, however the strong warm air advection in place suggests these winds won`t mix down. Other than the aforementioned Marine Dense Fog Advisory, headlines are not anticipaited over the next week. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Dense Fog Advisory from 10 PM this evening to 10 AM EDT Monday for LMZ844>849. && $$ DISCUSSION...Thomas AVIATION...CAS MARINE...Thomas

NWS GRR Office Area Forecast Discussion


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