Fire forecasters are keeping their eyes on the annual “green-up” of grasses and other low-to-the-ground plant material that could turn into fuel in the West as the weather warms, thanks to significant late-winter precipitation in spots.
“March is a transition month. Pre-greenup grassfire activity is not uncommon along and east of the Rocky Mountain Front,” the National Interagency Fire Center’s predictive-services unit said in a forecast for March through June. “At least average activity is expected until green-up takes hold.”
Subsequently, impacts from above-average precipitation in late winter and early spring “could translate into another above-average grass crop that could prove to be problematic in June.”
In the Northwest, the risk of naturally ignited wildfires is generally low through June due to recent and anticipated cool, wet conditions, the report said. But dry spells could increase fire danger enough to raise the risk that prescribed fires escape their project boundaries during strong wind events accompanied by low humidity.
Forecasters identified above-normal potential for significant fires in parts of Northern California.
“Due to down and dead fuel loading in the northern Sacramento Valley and the expected curing of a robust fine fuel and brush crop at lower elevations, the Bay Area, Sacramento Valley and Mid Coast areas, except the Mendocino National Forest, will have above-normal significant fire potential in June,” the report said.
In the Rocky Mountains, normal potential for significant fires is expected through June. But forecasters in recent years have seen more large fires as pre-green conditions coincide with climate warming trends, and occasionally windy periods, across eastern plains areas in March and April, NIFC reported.
Mixed conditions are expected in the Northern Rockies, including above-average temperatures and faster snowmelt in the west, and nearly normal conditions in the east.
If near-average temperatures and precipitation persist during green-up in May and June in plains areas, fuel moistures would remain nearly normal, the report said.
In western areas, slightly faster snowmelt in April and May — from possibly above-normal temperatures — “would be offset by near-average precipitation, in terms of producing very low dead-fuel moisture values.”