Fire Season 2025 in western North America: Distinctly unusual, and still evolving

Daniel Swain PhD

Key Points

• Most destructive wildfire event of 2025 likely occurred at an unusual time of year–in the Los Angeles region in January
• A weak and delayed summer rains and anomalously hot temperatures across the interior allowed for numerous large and long-burning fires later than usual in season 
• A late-season surge in anomalous heat and lightning along Pacific Coast has reinvigorated fire season in early September
• Above-average wildfire activity remains possible until onset of sustained seasonal rainfall, especially during strong wind events and in southern California

An anomalous winter firestorm: the Los Angeles fires of January 2025

While by many definitions the traditional “fire season” does not begin until spring, it would be a major omission to not at least briefly discuss the catastrophic wildland-urban interface firestorm that unfolded in the Los Angeles region in January 2025. Even now, in September, thousands of Californians are still grappling with mass displacement and insurers are still managing what have been in some cases record-breaking losses. And that this event occurred at a seemingly unusual time of year highlights a subtle but important reality: in some locations, major wildfire activity can occur well outside the warmest months of the year. 

Though winter fires may be less common in most settings, they can still be highly consequential if they do occur (especially as preparedness may be lower this time of year due to the perceived lower risk level). This is exemplified by the December 2021 Marshall Fire–a primarily grass and brush fire on the high plains just east of the Rocky Mountain Front Range that destroyed over 1,000 structures in the suburbs between Denver and Boulder, Colorado amid an extreme wind event following record-breaking antecedent warmth and dryness.

Such winter fires, while still relatively uncommon, are perhaps less so than previously believed–and may be occurring more often as the climate warms and as strong winter wind events become increasingly likely to coincide with dry vegetation conditions. Recent experience, therefore, suggests a growing need for an expanded definition of what constitutes “fire season” in western North American (and perhaps also elsewhere). 

Figure 1: Between spring 2024 and early winter 2025, southern California experienced an extreme wet-to-dry “hydroclimate whiplash” event. This temporal sequence, which initially allowed for prodigious growth of grass and brush that subsequently dried out to record-breaking levels, set the stage for an extreme wind event in January 2025 to drive catastrophic fires in the wildland-urban interface. Illustrated here is the magnitude of the wet-to-dry swing, quantified in units of change of the 6-month Standardized Precipitation-Evaporation Index, with the black rectangular box highlighting the region where the fires occurred. (Adapted from Swain et al. 2025: “Increasing Hydroclimatic Whiplash Can Amplify Wildfire Risk in a Warming Climate” in Global Change Biology, Feb. 2025)

While these devastating events in early 2025 may have set the tone for the more traditional fire season months that followed, subsequent wildfire-related losses in the United States as of early September have been, thankfully, relatively modest. Despite a rather active fire season overall, a large majority of the largest and fastest moving fires with greatest destructive potential have occurred in remote areas away from population centers. As is further discussed below, however, fire season is not over yet and there is reason to believe that some regions in the Western U.S. may yet face the potential for additional destructive fires in 2025 before all is said and done.

A weak monsoon leads to extreme heat away from Pacific coast–and major fires

The North American Monsoon–a seasonal reversal of the prevailing (dry) westerly winds to (moister) easterly winds–typically brings much-needed seasonal rains in the form of afternoon and evening thunderstorms to much of the Desert Southwest, Great Basin, and southern Rocky mountain states beginning in August and continuing through August or sometimes September. Accordingly, the hottest temperatures of the year often occur in the Southwest U.S. deserts in May or June–before cooling clouds and downpours arrive. This year, however, the monsoon was largely a “no-show” in July and even into mid-August–allowing peak summer temperatures to persist into August and setting new extreme heat records in cities like Phoenix. One notable exception to the elevated heat this summer was the Pacific Coast of California–which, due to stronger-than-expected oceanic upwelling of cold ocean waters, remained substantially cooler than the long-term average (despite unusually warm conditions across California’s mountains and deserts).

Figure 2: Summer 2025 temperature across the western United States as represented by percentile rankings. Across nearly all of the U.S. West, June-July was among the top-10 hottest on record (and locally the hottest on record in portions of Arizona as well as western New Mexico and western Colorado). Notably, however, the Pacific Coast of California was actually cooler than the long-term average despite much warmer than average conditions in California’s mountain and desert regions. Via Western Regional Climate Center.

This combination of widespread near-record heat and a delayed monsoon onset allowed fire season in Arizona, Utah, Nevada, and western Colorado to continue at an elevated level of intensity for much longer than is typical–and numerous large fires burned across the region for nearly the entire summer. Perhaps the most notable and largest of these fires was the Dragon Bravo Fire, which occurred along the North Rim of Grand Canyon National Park. The fire, which was ignited by a lightning strike amid historic vegetation dryness, ultimately went on to burn nearly 60,000 hectares (~146,000 acres, becoming the seventh largest in Arizona history) and over 100 structures–including the historic Grand Canyon Lodge and most of the North Rim park infrastructure (and also led to a toxic chlorine gas leak from a burned water treatment plan, requiring evacuation of firefighters and visitors alike). Meanwhile, in western Colorado, the Lee Fire went on to become the fifth largest in state history after burning around 56,000 hectares (~138,00 acres), though it only destroyed a handful of structures due to its relatively remote location.

Figure 3: Summer 2025 precipitation across the western United States as represented by percentile rankings. Across portions of the Pacific Northwest and Desert Southwest/Four Corners region, June-July was among the top-10 driest on record. Via Western Regional Climate Center.

Another year of intense “pyroconvection” in the West

During July and August, multiple strong “pyrovortices”–essentially wildfire-generated tornadoes akin to their severe thunderstorm-derived counterparts and similar in strength–occured on various interior Western North American fires. These types of events, which are distinct from lesser “fire whirls” that occur on fires of all sizes and intensities, form when the extreme but localized heating generated by an intense fire combines with ambient wind shear to cause the ascending column of air atop the fire to rotate rapidly, and sometimes violently. Remarkable footage of these well-documented events highlights the risk such phenomena pose to firefighters and even to nearby structures. Fortunately, during the North American fire season of 2025, there were no serious injuries associated with these vortices due to a combination of luck and increased firefighter awareness.

Research into wildfire-generated pyrovortices is in its relative infancy, though there has been an anecdotal increase in the documented occurrence of such events in recent years. Some of this increase likely stems from the increased ease of documentation of this relatively rare phenomenon in the smartphone video recording era. But recent experience with intensifying wildfires in multiple regions globally (including the western United States and western Canada, southern Europe, and southeastern Australia) suggests that various “pyroconvection”-related hazards–i.e., those related to fire-generated thunderstorm or thunderstorm-like clouds reaching well over 10km in height, including tornado-strength vortices–may be a growing hazard as wildfire burn environments become more volatile. Indeed, among researchers globally, there has been growing convergence between the fire weather and severe convective weather communities amid increased recognition that many of the most extreme wildfire events share striking similarities with, and can even cause, severe thunderstorms.

Record heat in late August/early September, plus widespread lightning, initiates a late-season reinvigoration of fire season

As of this writing in early September, a substantial escalation in wildfire activity from central California well northward into British Columbia and even the Northwestern Territories of Canada was underway. This late-season wildfire outbreak was facilitated by a number of factors–most prominently including a major heatwave (which set new all-time September monthly temperature records at its peak in western Canada) and hundreds of new fire ignitions from recurrent waves of thunderstorms. Some of these thunderstorms were “dry,” meaning they generated lightning but little to no co-occurring rainfall (something that recent research suggests may be a growing challenge in a warming Western U.S.). In some cases, strong and erratic outflow and downburst winds from thunderstorms pushed lightning-ignited fires in unexpected directions. Amid such conditions, much of the small and historic community of Chinese Camp in the Sierra Nevada foothills of California was destroyed by fast-advancing flames on September 2nd. 

Remarkably, over 142,000 lightning strikes occurred in California alone between August 1 and September 4. Fortuitously, however, most of these struck in regions not presently affected by drought in northern portions of the state–limiting both the total number of lightning fire ignitions and the intensity of subsequent fires compared to what would most likely have transpired under severe drought conditions (as occurred during the 2020 August lightning “fire siege”).

Figure 4: Snapshot of a high-resolution weather model (HRRR) depiction of vertically integrated smoke density over the United States of September 4th, 2025. A dense and broad plume of wildfire smoke extended thousands of kilometers eastward from the Pacific Northwest states of Washington and Oregon as well as British Columbia in western Canada to cities as far eastward as Chicago and St. Louis.

The effect of this recent heat and lighting was compounded by a widespread swath of moderate to extreme drought in the Pacific Northwest states of Washington and Oregon as well as western Canada, especially British Columbia. Here, fire season typically fades by early autumn but this year remains at near-historic levels of activity as of early September, with numerous high-intensity fires burning in forested regions. Widespread and locally severe smoke pollution have resulted, triggering air quality warnings and public health alerts, with vast plumes of smoke extending eastward thousands of kilometers and across much of the North American continent. Some beneficial rain is expected across much of the region in coming days–especially across Oregon and northwestern California–but likely not enough to end fire season in most locations. Should another heatwave or major dry wind event occur thereafter, fire activity will likely increase substantially once again.

Wildfire risk will remain above typical levels across portions of western U.S. & Canada until seasonal rains arrive (especially southern California)

Figure 5: Drought conditions across the United States as depicted by the U.S. Drought Monitor as of early September, 2025. Widespread severe to extreme drought continues across most of the Western U.S. except for northern and central California, where no severely anomalous dryness is present this year.

Severe to extreme drought has persisted since the spring for a broad portion of the interior U.S. West, extending from southern California eastward across Arizona and Utah to western portions of Colorado, Wyoming, and New Mexico. While the onset of seasonal rains in the Pacific Northwest and northern Rocky Mountain states will likely end fire season in the coming weeks, much of the interior West as well as central and southern California will remain primed for elevated wildfire activity well into the autumn, and potentially into the early winter months–especially during periods of strong winds. Across central and southern California, strong and dry downslope winds tend to occur most often from September through January–often in alignment with very dry vegetation conditions. Across the Rocky Mountains, strong winds in autumn can also occur but cooler and moister conditions are often a limiting factor. 

In autumn 2025, given pre-existing drought and seasonal predictions of pointing to greater-than-average odds of further anomalous West-wide warmth and possibly dryness in the interior, elevated late-season wildfire activity may occur across a wider than usual region (i.e., not only in coastal central/southern California but perhaps also in portions of the interior Rocky Mountain region). Additionally, elevated wildfire risk in coastal southern California may linger well into autumn or even beyond–a consideration that is top of mind for many in the region following January 2025’s devastating Los Angeles fires.

Figure 6: The most recent (10 Sep 2025) Copernicus C3S seasonal forecast, which comprises the ensemble average prediction across a wide range of international predictive modeling systems, suggests high odds of much warmer than average conditions (top panel) continuing across the American West between October and December, with a modest tilt in the odds toward drier than average conditions (bottom panel) as well across central/southern California as well as the southwestern interior. As predicted, these conditions would allow fire season to remain active well into autumn or even early winter in some more southerly locations.

Many wildfires, but comparatively few acres and structures burned: Some lessons from an unusual fire season

Figure 7: Area burned by wildfire in California since 1987. Exceptional fire seasons between 2016 and 2021 have been followed by comparatively less active ones 2022-2025 as the extent of severe to historic drought in forested regions has lessened. Data via Cal Fire plus provisional sources for 2025; 2025 data are year-to-date through Sep 4.

Fire Season 2025 has been an unusual one in multiple respects across the Western United States. First, it is highly likely that the most destructive fire events of the entire year (by a wide margin) will have occurred in January–a month not historically considered to be a likely contender for what may ultimately become the single costliest wildfire disaster in history. Second, wildfire activity in western North America experienced a lull from mid to late summer before roaring back by early September–with indications that above average activity might continue much later into the autumn than has historically been typical in some regions.

Also notable has been the divergence between the above-average number of wildfires this year yet below-recent-average area burned in the United States–and, contrarily, the near-average number of fires in Canada but dramatically greater than average area burned. 

In the western United States, this pattern appears to be due to several opposing influences. Widespread drought and elevated lightning activity yielded a landscape receptive to ignitions and a ready source of ignitions, respectively–contributing to the elevated number of fires. Yet episodes of elevated fire activity this summer were not strongly clustered in time (allowing time for firefighting crews to move from fire to fire without substantially depleting resources), and also generally did not coincide with major large-scale windstorms (thus avoiding sustained periods of rapid fire spread). Thus, despite a historically hot and dry summer in some parts of the interior West, historic wildfire conditions were fortuitously not observed through the end of August.

Figure 8: Area burned by wildfire in Canada since 2000. Recent years have experienced exceptional wildfire outbreaks across broad swaths of Canadian boreal forest. Following the record-shattering 2023 fire season, 2025 (as of early September) has already experienced the second-greatest area burned on record. Data via the Canadian Wildfire Information System; 2025 data are provisional and year-to-date through Sep 4.

In western and central Canada, however, the situation has been very different. Despite a near-average number of known ignitions, fires have burned an extremely large area, primarily in boreal forests–and as in recent severe fire seasons, there have been mass displacements from remote communities and voluminous long-range smoke transport that has affected cities as distant as New York and Washington, D.C.. In fact, were it not for the record-shattering Canadian fire season of 2023 before it, 2025 would already have set a new record for area burned in the country. The effects of a warming climate on Canadian wildfires has rapidly become more apparent in recent decades, as the influence of an increasingly “thirsty” atmosphere tends to exert the strongest influence in densely forested environments (such as those that cover much of Canada’s land area).

Final Thoughts

Ultimately, these observations about the unusual and still-unfolding fire season of 2025 emphasize a couple of broader lessons. First, neither the number of ignitions nor the area burned by wildfire tell us what we need to know about the societal and ecological impacts of those fires. Despite being relatively modest in size, the Los Angeles fires in January were the most destructive on record; although the United States has experienced an elevated number of fire ignitions so far this year, the area burned has thus far remained below the recent average (whereas in Canada the opposite has been the case). And finally: seasonal predictions can only tell us about the fires to come. Antecedent conditions and long-term climate trends are indeed quite important, but the number, location, and timing of ignitions as well as the occurrence of strong wind events are also critical–yet only the former are potentially predictable at seasonal scale. 2025 has already brought some surprises, and there may yet be a couple more in store before the season is over.