588 FXUS63 KGRR 221830 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 230 PM EDT Mon Jun 22 2026 .KEY MESSAGES... - Midweek Rain Chances - Pattern Change Late Weekend into Next Week && .DISCUSSION... Issued at 230 PM EDT Mon Jun 22 2026 - Midweek Rain Chances A 90-100 kt upper jet streak moves into the Great Lakes by Wednesday and an upper trough with a 40-50 kt mid level jet core is shown at 500 mb Wednesday evening. A LLJ of 20-30 kts is shown to impact Lower Michigan Wednesday morning through late Wednesday night or Thursday morning. At the surface, a weak cold front is slated to move through Wednesday night. Ahead of this front is where showers and some thunderstorms are likely to develop. The question is how much we destabilize ahead of this front. Better MLCAPE is shown Wednesday across WI/IL where 1000-2000 J/kg is suggested by the Nam3km whereas less than 1000 J/kg is shown here. A round of morning to midday showers is possible Wednesday which could put a damper on instability later in the day and also lead to a high temperature bust as well (currently forecasting mid 70s, but if rain starts earlier then highs may not get out of the 60s given that is where wet bulb temperatures would be). If we get a window to destabilize later in the day and storms try to develop, they will have some decent shear to work with per Nam3km soundings at GRR showing 0-6 km deep layer shear of 45 knots at 00z Thursday and 0-3 km shear of 30 knots. DCAPE is projected to reach 1000 J/kg. While we are in SPC`s Day 3 General Thunderstorm outlook, given these parameters we`ll need to watch instability trends to see if any storms can develop and take advantage of an environment that could lead to organized activity and perhaps some scattered strong wind gusts given downdraft potential. Showers and a few embedded thunderstorms will press east on Thursday and mainly impact areas near and east of US 127. The rest of the area will gradually begin drying out. - Pattern Change Late Weekend into Next Week Ensemble guidance is favoring a pattern change that will bring warmer temperatures as well as considerable humidity back to the region. This will be courtesy of upper ridging trying to build into the area, which the ECE/GEFS/CMC all show to similar degrees (~590 dm average) starting as early as Sunday or Monday. The warm air advection in association with this building ridge should press a warm front through the region sometime Sunday into Monday. The passage of this front will quickly and decisively advect high dew points and PW values into Lower Michigan and the change will be noticeable. The front should bring a risk for some showers and thunderstorms but it is a bit early to pin that down. Post front, highs will climb well into the 80s with some ensemble members supporting 90 or higher and some hazardous heat index readings as well. Whether the ridge builds strong enough to push convective chances north of the region is unclear. Ensemble guidance has a notoriously hard time with summertime ridge strengths in our region and sometimes as you get closer to "the event" the rain chances look much higher than previously indicated and temperatures not as hot as originally thought (eg. we are in the CPC Heavy Precipitation Outlook from June 29-July 1). Still, at this range there is a growing signal for heat and humidity to build into next week and hopefully ensemble guidance will better capture where the more active storm track will set up and whether that will include our region or not. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 127 PM EDT Mon Jun 22 2026 Low pressure to the south is creating a northeast wind flow across the terminals this afternoon. SCT to bkn cu was noted across the region. Expecting VFR conditions through the period. However, a couple hours of MVFR cu near BTL is possible early this afternoon. && .MARINE... Issued at 230 PM EDT Mon Jun 22 2026 As of early afternoon waves have generally been 1 to 2 feet but they will continue building through the afternoon with increasing NW flow. We have already noticed some whitecaps on the South Haven beach cam. Expect hazardous swimming conditions especially north of piers through this evening and that is why a Beach Hazards Statement is in effect from Oceana County south to Van Buren. After tonight, we may be able to avoid hazardous wind and wave activity that would warrant headlines for the remainder of the week. Two periods to watch that may be close calls are Tuesday afternoon and then again Wednesday afternoon when waves will likely get into the 2 to 3 foot range. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement until midnight EDT tonight for MIZ043- 050-056-064-071. MARINE...Small Craft Advisory until midnight EDT tonight for LMZ844>848. && $$ DISCUSSION...Hoving AVIATION...04 MARINE...Hoving

NWS GRR Office Area Forecast Discussion