A major Pacific moisture plume is delivering the most significant rainfall event for the Treasure Valley since spring, bringing much-needed relief to an exhausted fire season while potentially impacting outdoor events and holiday weekend plans.
Significant rain headed to Idaho in Scott Dorval's video forecast
How Much Rain Can the Treasure Valley Expect?
This is shaping up to be a meaningful precipitation event for the Treasure Valley. Here is a breakdown of expected rainfall through Friday:
| Location | Expected Rainfall Tonight Through Friday |
|---|---|
| Treasure Valley (Boise area) | 0.25 to 0.50 inches |
| West-Central Idaho Mountains | 1.00 to 1.50 inches |
| East Central Idaho Mountains | 0.75 to 1.00 inches |
| Western Magic Valley / Camas Prairie | Less than 0.10 inches |
| Southeast Oregon | 0.50 to 0.75 inches |
For context, Boise's average September rainfall is about 0.47 inches for the entire month. This single event could deliver more than half of that in just a few days, making it the most significant rainfall event since spring.
Spirit of Boise Balloon Classic: Weather Impact
The Spirit of Boise Balloon Classic, one of the Treasure Valley's most beloved late-summer events, could be impacted by this week's weather. Hot air balloon flights require calm winds and clear skies, and the current forecast presents challenges:
- Thursday morning: Showers likely with a 60 percent chance of precipitation and cloudy skies. Balloon flights will likely be impacted and possibly cancelled.
- Friday morning: Patchy fog before 10 a.m. and a 50 percent chance of showers. Conditions will be marginal for balloon operations.
- Saturday morning: Patchy fog between 7 and 10 a.m. before mostly sunny skies develop. This could be the best morning of the week for balloon flights, though fog could delay early morning launches.
- Sunday morning: Mostly sunny with a 20 percent chance of showers before noon. Another potentially good morning for balloon flights.
Balloon Classic organizers and attendees should monitor the official Spirit of Boise Balloon Classic website and social media channels for the latest flight status updates, as conditions can change rapidly.
Fire Season Relief: A Significant Development
This rainfall event could not come at a better time for firefighters and fire managers across the West. The central Idaho mountains, which have seen some of the most active fire behavior this summer following weeks of record heat, stand to receive 1 to 1.5 inches of rainfall through Friday. This level of precipitation represents a significant development for fire suppression efforts:
- Moisture levels in fuels will increase dramatically, reducing fire behavior and spread rates
- Fire danger ratings will drop from critical to moderate across much of the region
- Firefighters will gain a significant tactical advantage as fire activity diminishes
- Air quality across the Treasure Valley and central Idaho will improve
- The risk of new fire starts from lightning will be greatly reduced
Southeast Oregon, which has also seen significant fire activity this summer, will receive 0.50 to 0.75 inches of rainfall, providing additional relief to fire operations in that area.
Labor Day Weekend Day-by-Day Outdoor Guide
Saturday: The best day of the holiday weekend for outdoor activities. Mostly sunny skies with a high near 74 degrees after morning fog clears. Excellent conditions for hiking, camping, and outdoor events. A 20 percent chance of showers and thunderstorms develops after midnight.
Sunday: Mostly sunny with a high near 76 degrees and a 20 percent chance of showers before noon. A good day for outdoor activities in the morning and early afternoon. Shower and thunderstorm chances increase Sunday night with a 50 percent chance of precipitation as the upper low begins steering east.
Labor Day: A 50 percent chance of showers with patchy morning fog and a high near 71 degrees. Keep outdoor plans flexible and have a backup plan. Conditions will be cooler and wetter than a typical Labor Day in the Treasure Valley.
Central Idaho Mountains: Significant Rainfall and Possible High Elevation Snow
The central Idaho mountains will see the most significant rainfall totals of the event, with 1 to 1.5 inches expected through Friday. Embedded thunderstorms capable of producing locally heavier amounts remain possible Thursday and Friday afternoons, which could cause localized flash flooding near recent burn scars. A Flash Flood Watch remains in effect for these areas.
Looking ahead to Sunday night and Monday, the upper low will begin steering east while capturing abundant Pacific moisture from the southwest. This pattern shift will bring heightened chances for heavy rainfall over south-central Idaho late Sunday through most of Monday. Snow levels may lower enough to bring light snow or mixed precipitation to the highest peaks, signaling the first hints of the approaching fall season.
Extended Outlook
By Tuesday and Wednesday, ensemble models favor a transition to drier conditions and a subtle warming trend as an upper-level ridge attempts to build inland from the Pacific coast. Temperatures throughout the extended period will remain generally near or slightly below seasonal averages, a welcome change from the record heat of recent weeks.
Tonight
Showers, mainly before 4am. Low around 54. Northwest wind 6 to 11 mph becoming light and variable. Winds could gust as high as 21 mph. Chance of precipitation is 80%. New precipitation amounts between a tenth and quarter of an inch possible.
Thursday
Showers likely before 2pm, then a chance of showers after 3pm. Cloudy, with a high near 69. East southeast wind 5 to 7 mph becoming calm in the afternoon. Chance of precipitation is 60%.
Thursday Night
Showers likely, mainly after 5am. Patchy fog after 4am. Otherwise, mostly cloudy, with a low around 52. Northwest wind 5 to 8 mph becoming calm after midnight. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.
Friday
A 50 percent chance of showers. Patchy fog before 10am. Otherwise, partly sunny, with a high near 66. Calm wind.
Friday Night
A 30 percent chance of showers before midnight. Partly cloudy, with a low around 49. Calm wind.
Saturday
Patchy fog between 7am and 10am. Otherwise, mostly sunny, with a high near 74.
Saturday Night
A 20 percent chance of showers and thunderstorms after midnight. Partly cloudy, with a low around 52.
Sunday
A 20 percent chance of showers before noon. Mostly sunny, with a high near 76.
Sunday Night
A chance of showers and thunderstorms. Mostly cloudy, with a low around 54. Chance of precipitation is 50%.
Labor Day
A 50 percent chance of showers. Patchy fog between 8am and 10am. Otherwise, partly sunny, with a high near 71.
Monday Night
A 20 percent chance of showers. Partly cloudy, with a low around 51.
Tuesday
Patchy fog. Otherwise, sunny, with a high near 74.
Tuesday Night
Partly cloudy, with a low around 53.
Wednesday
Mostly sunny, with a high near 78.
