006 FXUS63 KGRR 151921 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 321 PM EDT Wed Jul 15 2026 .KEY MESSAGES... - Heat Risk Decreasing Next Few Days - Slight Chance of Shower or Storm Late in the Day - Unhealthy Smoke on Thursday - Chance of Thunderstorms Friday-Saturday && .DISCUSSION... Issued at 321 PM EDT Wed Jul 15 2026 - Heat Risk Decreasing Next Few Days Dew points higher than yesterday, now in the lower to mid 70s, and temperatures in the lower to mid 90s, are pushing the heat index to its highest values of this current heat wave, about 100-105. Planning to let go of the heat advisory at 8 PM. Temperatures may reach the lower 90s again on Thursday, but dew points should be comfortably lower behind the weak cold front which is coming down from the north tonight. Ensembles favor a couple more cold fronts Saturday and then on Tuesday as synoptic scale troughs dig into Ontario. - Slight Chance of Shower or Storm Late in the Day For areas between Lansing and Jackson, can`t rule out a shower or thunderstorm popping up later today and moving southeast, but it`s about a 10-20 percent chance. This will be where surface wind confluence/convergence will be relatively greater, while the cap lifts and weakens with falling upper-level heights. The 12z HREF models have not been on board with deep convection, however. There will be about 2,000 J/kg of MLCAPE and 25 knots of 0-6 km shear, but any potential updrafts should be hindered by the remnant CINH layer and substantial dry air entrainment. Gusty winds are possible if any well developed shower or isolated thunderstorm does occur. - Unhealthy Smoke on Thursday Satellite and AWOS visibility observations have the smoke front around Ludington to Clare as of mid-afternoon Wed, moving south. AWOS visibility in north-central Lwr MI has been 1/2 mile to 3 miles today with Unhealthy AQI measurements. Surface PM2.5 concentrations from the HRRR and Canadian models suggest smoke will blanket all of Michigan on Thursday. Michigan EGLE will be the official source for air quality forecasts. However, there is hope that weak southwest flow on Friday may provide some relief to Southwest Michigan. - Chance of Thunderstorms Friday-Saturday Upper-level shortwave trough and surface low moving across the northern Great Lakes will provide some thunderstorm chances late in the week. Friday`s potential looks pretty spotty with relatively thin CAPE, weaker low-level shear, but moderate deep- layer shear. Saturday`s CAPE will be greater, and wind fields and shear parameters will be stronger, though the greater potential for storm coverage will be over northern to eastern Lwr MI, given relatively stronger capping over our area and surface flow off Lake Michigan. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 139 PM EDT Wed Jul 15 2026 Smoke (FU) remains the main focus for the forecasts over the next 24 hours. The leading edge can be seen along the U.S.-10 corridor as of 1730z on visible satellite imagery. This is advancing southward slowly through tonight. Generally followed the HRRR- Smoke model visibilities for trends. It shows the leading edge dissipating as it sinks south, with another batch of smoke then coming down. We have high confidence that this smoke will gradually reduce visibilities to MVFR, later at the I-94 terminals. There is a chance that some brief periods of IFR will be possible in some more dense pockets. No reason to believe it will change much on Thursday as the winds bring more smoke down. && .MARINE... Issued at 321 PM EDT Wed Jul 15 2026 Smoke over Lake Michigan with visibilities below one mile are possible later today near Ludington, and everywhere on Thursday. There is a chance of an isolated thunderstorm developing over the lake from Friday morning through Saturday. Saturday is likely to be a hazardous day for small craft and swimmers with west to north winds building up 3 to 5 ft waves. && .CLIMATE... Issued at 240 AM EDT Wed Jul 15 2026 Here are the high temperature records for July 14 and 15. Location July 15 Grand Rapids 95 (2013) Lansing 99 (1977) Muskegon 93 (1995) Kalamazoo 103 (1936) Battle Creek 100 (1977) Holland 98 (1932) && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Heat Advisory until 8 PM EDT this evening for MIZ037>040-043>046- 050>052-056>059-064>067-071>074. Air Quality Alert until midnight EDT Thursday night for MIZ037>040-043>046-050>052-056>059-064>067-071>074. MARINE...None. && $$ DISCUSSION...CAS AVIATION...NJJ MARINE...CAS CLIMATE...RAH

NWS GRR Office Area Forecast Discussion