####018004931#### 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 ####018004212#### FXUS65 KPIH 151922 AFDPIH Area Forecast Discussion National Weather Service Pocatello ID 122 PM MDT Wed Jul 15 2026 .KEY MESSAGES... - Monsoon moisture remains in place through early next week for more showers and thunderstorms. Friday looks to be the day with the most widespread activity this week. - Some storms COULD produce decent downpours and gusty winds - Temperatures SHOULD continue ABOVE AVERAGE but may fluctuate based on early day cloud cover && .DISCUSSION... Issued at 106 PM MDT Wed Jul 15 2026 Main impact is southerly flow aloft is continuing to pump monsoonal moisture into southeast and central Idaho. There will be a threat daily for the next week. As of now activity Thursday looks to be slightly more widespread than today with Friday even more active and a pretty high chance for everyone. Sunday will be the day with the best chance of the least convective activity at this point with an increase again early next week. Humidity will be fairly high for Idaho with dewpoints in the 40s and 50s through the next 7 or 8 days. It will remain above normal with highs expected to remain in the 90s in lower elevations with days with minimal cloud cover hitting the upper 90s and lower 90s in higher cloud cover and thunderstorm coverage. Lows generally upper 50s and 60s in low elevations and mid 40s to mid 50s mountains. Winds not expected to be impactful with generally light speeds other than near any thunderstorm outflows. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1154 AM MDT Wed Jul 15 2026 VFR conditions expected through the forecast period. Monsoonal moisture continues to bring BKN/OVC CIGs to IDA and DIJ for a few more hours before we should begin to see some clearing. Not expecting much precip chance today as hi-res models show a bit of a break this evening and overnight. Still a low-end chance for a stray shower/storm but not high enough to include mention in the forecast. Things look to stay dry through the period but some isolated precip chances will be possible just beyond the current 18Z period into Thursday afternoon/evening. Winds should be light, around 10 kts or less, through the period. && .FIRE WEATHER... Issued at 1226 AM MDT Wed Jul 15 2026 Our monsoon pattern keeps hold over Idaho heading into next week. We have a deeper surge moving through this morning, shifting east of us by this evening. For today, thunderstorms will likely remain isolated with a few pockets where scattered coverage exists...but that is not looking to be widespread at the moment. The chance of outflow winds over 35 mph is lower today, nothing higher than 30%. On the flip side, like yesterday we may see some spots with locally heavy downpours with over 0.20" with any given storm. The next surge of monsoon moisture arrives during the day tomorrow, but looks "dry" enough for lighter rainfall amounts even where we get thunderstorms to develop. Tomorrow may be an interesting day due as lack of earlier day cloud cover MAY produce more instability, and increased lightning coverage across higher elevations. That will be a trend that needs to be monitored for any potential critical fire weather concerns. There is higher chance of gusts of 35-55 mph (20-60%) with even higher chances across southwest and far western Idaho. The ridge shift backs to the northwest a bit through the weekend, pushing deeper monsoon moisture back across central and eastern Idaho. This should bring a higher potential of wetting rains areawide, with lightning coverage highly dependent on where we get cloud breaks and better instability each day. This overall pattern remains in place into next week, with some expected shifting east or west of the main plume of moisture as low pressure well to the northwest tries to nudge the ridge east once again...even if briefly. Temperatures should remain ABOVE AVERAGE in the 80s and 90s.. && .PIH WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...GK AVIATION...McKaughan FIRE WEATHER...Keyes