Western Montana Fire Season, Month by Month

When is fire season in western Montana?

Legally, Montana's wildfire season runs from May 1 through September 30, inclusive; that is the definition in Montana Code Annotated 76-13-102. Ravalli County's 2024 wildfire protection plan describes the practical season as typically May to October, with most fire activity in the summer months when fuels are driest, and says late-season fires are typically put out by fall precipitation.

Missoula County's 2018 wildfire protection plan gives the clearest numbers. From 1998 to 2017, about 65 percent of wildfires in the county occurred in July and August and another 10 percent in September; most of the remaining quarter occurred in April, May, June and October. The county averaged about 150 fires a year, most of them very small: 72 percent were under a quarter acre.

How does risk build through a typical summer?

The Missoula County plan tracks seasonal dryness with the Energy Release Component, an index fire managers use for how much energy a fire could release in heavy fuels. Using 20 years of data from the Ninemile Ranger Station, it describes a typical pattern: low values in spring, a dip in June because June is usually the wettest month, a steady rise once dry summer conditions arrive in July, and conditions favorable for wildfire spread in an average year from mid-July through late August. As moisture returns in September and October and the sun weakens, the index falls.

The extremes matter as much as the average. The plan notes that in a wet summer the index may never reach fire-favorable levels, but in a dry year it can reach them as early as May and stay there into October. In 2017, after a big snowpack and a wet spring, precipitation stopped in mid-June and western Montana slid into what meteorologists called a flash drought; the index was above the 97th percentile on most days between late July and early September. That year more than 230,000 acres burned in Missoula County.

What happens in winter, December to February?

Winter is the quiet season for fire and the best season for some kinds of fuel work. Deciduous shrubs are leafless so it is easy to see what you are cutting, and with snow on the ground the chance of a saw or chipper starting a fire is low. Removing hazard trees and thinning around a house can usually go ahead whenever access allows.

Burning slash piles in winter requires extra steps. Montana DEQ says that during the winter burn season, December 1 to February 28, burning needs a permit from your local fire control authority plus DEQ approval, granted case by case based on dispersion forecasts. In Missoula County, burning in that window falls under a separate Essential Prescribed Wildland permit with an application and a winter burning certification exam. Our guide to burning slash piles covers how it works.

What happens in March and April?

Snow goes off the valley floor and the south-facing slopes, and last year's dead grass is exposed before new growth greens up. An older Colorado State University fact sheet on defensible space says keeping grass short is extremely critical in the spring after the snow is gone but before plants green up, and in the fall when grasses cure. Early spring grass fires, often from debris burning, are a real part of the year: Missoula County's plan lists debris burning as the cause of 14 percent of fires.

This is the time to clean up what winter left behind: needles in gutters and against foundations, branches down from snow load, and dead grass in the 30 feet around the house. Montana DEQ lists the spring and summer open burning season as March 1 to August 31, with a permit from the county fire control authority activated on the day of the burn. Our spring wildfire prep checklist has the full list.

What happens in May and June?

Green-up and rain. The Missoula County plan's weather table shows May and June as the wettest months at the Missoula airport, about two inches each on average, and Ravalli County's plan lists May, June and November as the wettest months at Hamilton. Fire starts are possible but usually limited, and spring growth makes this the season when the fuel for later fires is grown.

Pine work needs care in this window. The extension guide Reducing Fire Risk on Your Forest Property warns that green pine slash over three inches in diameter created from winter through mid-July can breed Ips bark beetles that then attack healthy trees, so pine thinning in spring should be followed by prompt slash cleanup or deferred to later in the year. See our guide to pine engraver beetles and slash.

What happens in July and August?

Peak season. Missoula County's data put about 65 percent of fires in these two months, and the energy release index typically sits in the fire-favorable range from mid-July through late August. The plan's weather data show daytime summer humidity of 30 to 40 percent on average, dropping to an average of 19 percent in August in the severe seasons of 1994 and 2000. In 2000, dry lightning on July 31 started about 100 fires in the Bitterroot, according to the Northern Rockies Fire Science Network.

This is a maintenance season, not a project season. Keep grass mowed short in the inner zone, keep needles off the roof and out of Zone 0, keep irrigation running where it protects the house, and avoid starting anything. Watch for Red Flag Warnings, which the National Weather Service issues when critical fire weather is occurring or imminent, and for state and county fire restrictions, explained in our guide to Montana fire restrictions. Our guide to keeping defensible space up through fire season covers the routine.

What happens in September and October?

Risk tapers but does not end. About 10 percent of Missoula County's fires were in September, and the county's data show the index can stay high into October in a dry year. Statutory wildfire season ends September 30. Montana DEQ lists a fall open burning season of September 1 to November 30, during which it issues county-wide restrictions based on the dispersion forecast; Missoula County's own season for prescribed wildland burning permits runs March 1 to November 30.

Fall is also when needles come down. Montana State University Extension says seasonal needle drop occurs in late summer to early fall, so gutters and roof valleys filled in October will be full again by spring. Once the weather turns, fall is one of the best windows for thinning and ladder fuel work, for reasons set out in our guide to why fall and winter are the best time for fuel reduction.

What happens in November?

Snow comes to the mountains and usually to the valleys, and the fire year is effectively over. It is a good month to stack firewood well away from the house for the winter, finish fall cleanups, and plan next year's work while the problems are still fresh in your mind. Trees and shrubs that looked fine in summer but sit too close to the house are easier to judge once leaves are down.

It is also a good month to book. Lining up a walkthrough in late fall or winter leaves time for the work to be finished well before the grass cures next summer. Our defensible space maintenance schedule shows how the annual and multi-year tasks fit together.

Does fire season start earlier than it used to?

The county plans say conditions are changing. Ravalli County's 2024 plan states that changing climatic conditions and high fuel loading are leading to longer fire seasons and higher fire intensity, and that wildfires in the county are increasing in size and intensity, with over 500,000 acres burned from 2000 to 2019. Montana DNRC's west-central landowner guide says the increased frequency of large, severe fires has been associated with warmer and drier weather trends.

For planning purposes, assume the fire-favorable window can open in May in a low-snow year and stay open into October in a dry fall. That is the practical reason to finish fuel work before summer rather than during it.

When should you schedule fire mitigation work?

The short version: tree work and thinning in fall and winter, cleanup and mowing in spring, maintenance only in midsummer, and needle cleanup again in fall. HJ Property Care's fire mitigation service follows that calendar across Missoula and Ravalli counties, with seasonal cleanups, fall cleanup and leaf and needle removal on the maintenance side.

This calendar is part of our Montana Wildfire Guide. Burn seasons and permit rules change, so confirm current dates with Montana DEQ and your county before burning anything.

Call HJ Property Care & Tree Service at (406) 215-7319 or request a free estimate and we will walk the property with you.

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