Wildfire potential is a function of factors that contribute to fuel accumulation, fuel desiccation and flammability and wildfire spread, with the atmosphere playing a key role across the three components. Wildfire management in conjunction with guidance from meteorologists, ecologists and climatologists proactively try to identify geographic hotspots of potential fire activity at the seasonal, weekly and daily time scales. By prioritizing geographic areas with high and low wildfire potential, resources can be allocated to better try to control wildfire. This will be particularly important this upcoming fire season due to budget restrictions for suppression resources. While we might be able to do a fantastic job at nailing wildfire potential, what really matters is wildfire reality that is often more finicky to predict at longer forecast lead times.
Large wildfires (> 1000 acres) in the Northwest typically don’t begin their lives until mid-June to mid-July, with the main fire season in forested areas from mid-July through mid-September, with rangeland fires having a bit of a wider distribution. Remember that last year, wildfires were active into October.
Let’s take a look at current conditions and the outlooks for summer through the lens of wildfire potential.
1. The setup
The near record dry spell that has impacted much the inland Northwest since the beginning of 2013 have resulted in a precarious setup for high wildfire potential this summer. This is evident by:
(i) the proliferation of drought conditions, particularly across the southern half of the region
(ii) an earlier melt out of snow in many watersheds thereby advancing the usage of moisture and soil moisture drawdown ahead of schedule.
(iii) fuel and soil moisture conditions that are about a month ahead of schedule.
2. The outlook
The official Climate Prediction Center forecast for June-August issued May 16th called for a warmer + drier summer. This is confirmed by the latest collection of dynamical models and the last 10-runs of the Climate Predictor Center’s flagship model, the Climate Forecast System version 2.
However, unlike the atmosphere-ocean linkages that make ocean temperatures in the tropical eastern Pacific so intriguing for much of us in the western US during winter, there is rather weak long-lead seasonal predictability for summer and thus more limited predictive skill. Nonetheless, there is a decent amount of agreement for conditions that at the seasonal level look conducive to wildfire potential.
3. The hope
While the deck is stacked, there is reason for hope. May started off with extremely warm and dry conditions more typical of the apex of summer including a few early season fires in Montana and even along the west side of the Cascades in Washington State due to offshore flow that resulted in a temperature of 87F in Seattle (yes, the one in Washington state). However, the last couple weeks have brought some much-needed precipitation and cooler temperatures to the region that have stifled the trajectory towards extremely dry conditions entering June. If the situation was reversed, and the string of warm+dry weather was capping of May, it would be much worse.
After a dry spring and summer last year in the Snake River plain, fine fuel growth should be lower than in previous years and possibly limit rangeland fire.
The next two weeks call for a return to warm and dry conditions for the western US. Unfortunately that puts us around mid-June which coincides with the significant drop off in precipitation chances for much of the Northwest, and our regime shift into a summer pattern as the Pacific storm track retreats northward and weakens substantially.
While seasonal temperature and precipitation are telling of a wildfire season, the timing of precipitation during the summer can provide enough moisture to reduce flammability and the potential for large wildfires. Even if the summer is warm and dry, if we avoid 2-3 week periods without appreciable precipitation that wets fuels, wildfire potential might not be realized.
Nonetheless, the official NIFC Predictive Services outlook paints nearly all of Oregon, central Idaho and southwestern Montana red, indicating above normal wildfire potential during July + August.