Early melting of the snowpack, and quick drying of grasses and other fine fuels will boost the risk of significant wildfires in parts of the West, the National Interagency Fire Center reports.
The overall risk will be around normal across the region. Anticipated normal temperatures or lower should keep snowmelt rates around average, which could result in a delayed start to fire season in areas with abundant snowpack, NIFC said.
An early start is possible along the Canadian border in areas with below-average snowpack.
Abundant winter and spring moisture at middle and low elevations should result in a heavy crop of fine fuels that become increasingly conducive to fire across the West, from south to north, in May and beyond.
Bryan Henry, acting fire weather program manager for NIFC Predictive Services, said the grass fire season could be fairly active at low and middle elevations in the northern Great Basin including southwestern Idaho and part of eastern Oregon. Already wet soils, and the anticipated green-up of grasses and other fine fuels, are factors.
Midsummer grass fires could be fast-moving if they are wind-driven, but forecast temperatures are closer to normal in contrast to the past two years, which were hot, he said. A fire’s growth rates in the absence of wind would be more closely tied to humidity.
Summer storms could have a slightly greater chance of including precipitation — rather than the more typical dry thunderstorms — possibly delaying fine fuels’ usual schedule for drying, Henry said.
NIFC said the risk is normal in the Northwest but higher in Washington and northwestern Oregon west of the Cascade Range. Above-normal risk should expand into southwest Oregon in July.
The states’ snowpack is near or above normal, but most accumulation has been on the east side of the Cascades. Much of Washington and northwest Oregon have accumulated significantly below-average rainfall since the first of the year, while southwestern and eastern Oregon have been wetter than average.
Large-fire potential is normal in the Northern Rockies, but dry conditions persist in northern Idaho and western Montana. Projected above-average precipitation during the summer convective-weather season suggests thunderstorms, lightning strikes and wind outflow could increase, NIFC said.
Drying fuels in western areas could see slightly faster snowmelt in April and May due to above-average temperatures, offset by near-average precipitation.
The northern Idaho panhandle and northwestern Montana have dry-soil anomalies that warrant close monitoring. Risk in southwestern Idaho and eastern is normal, aided by above-normal snowpack.
In Northern California, foothills and lower mountains around the Sacramento Valley and San Francisco Bay Area, above-normal significant large-fire risk is expected in June and July. Strong snowpack and above-average recent precipitation should aid brush and grass growth, NIFC said. Conditions are expected to be warmer and drier than average starting late this month.
Heavy snow in the northern Sacramento Valley in mid-February caused extensive damage to plants and trees, increasing dead and down fuels that boost potential for significant wildfires starting in June.