May 1, 2018 – The outlook for the North Ops region for May-August is for warmer and drier than normal conditions. A semi-persistent low pressure trough may set up along the west coast this summer, and that may lead to less than normal lightning in our western areas, while active monsoon conditions in NV may be close enough to our eastern areas to produce quite a bit of lightning. The wet spring has led to a fairly normal live fuel green-up phase. Overall, though, the region has experienced a significant snow pack and precipitation deficit this year. The fuel moisture decline phase is expected to be steeper than normal, and we expect fuels to be available for wildfire at all elevations earlier than normal. May will likely be quiet with live fuels and soils still fairly moist. The Large Fire Potential for May is Normal.
It is expected that fire activity will ramp up in June at lower elevations and east of the crest, and this represents an earlier start than normal by a few weeks. The Above Normal Large Fire Potential areas in June are the Far East Side, the foothills of the Sacramento Valley, and the Diablo portion of the eastern Bay Area. In July-August the Northeast California and Northern Sierra PSAs are added to the Above Normal areas due to the possible combination of dry fuels, a bit more wind, and occasional lightning events.
The majority of the North Ops region received above normal precipitation in April, continuing a wet, unsettled weather pattern that began in late February. However, the vast majority of April precipitation fell in the first week of the month. So far the spring has been a bit wetter than normal. Temperatures throughout the region were slightly warmer than normal. The snow pack water content reached its peak on March 26th at only 48% of normal in the north. Warmer and drier weather since the first week in April has led to a rapid decline in snow water content values. The snow pack will likely dissipate much earlier than normal this year, perhaps as early as late May or early June for some areas. The total rainy season precipitation remains well below normal with around a third of the region below 70% of normal.
The wet weather since late February pushed dead fuel moisture readings well above normal. The recent warmer and drier than normal weather is leading to a decline in heavy fuel moisture values. Anticipated warmer and drier than normal weather could lead to a fairly steep fuel moisture decline in the upcoming months. The overall deficit in precipitation produced “Abnormally Dry” conditions in the North Ops region in January, but this area has become smaller lately due to the precipitation received since late February. A normal green-up phase is now expected, but the seasonal precipitation and snow pack deficit will likely lead to a steeper declining fuel moisture phase in both dead and live fuels and an earlier curing of annual grasses with fuels reaching critical values for wildfire activity earlier than normal. There are also areas of frost kill at lower elevations that occurred when cold weather arrived after the budding of trees and shrubs.
May through August is expected to be drier and warmer than normal conditions. In fact, the west coast is expected to receive well below normal precipitation in July and August. This is due the expectation of semi-persistent low pressure troughing along the west coast, which would tend to limit the number of monsoon surges into our western areas. Our eastern areas may still see a normal amount of monsoon surges and lightning, however. Overall, the precipitation and snow pack deficit will lead to fuels becoming available to wildfire earlier than normal at all elevations. The wet spring will ensure a normal green-up among live fuels, and perhaps a bit heavier loading of fine fuels, and the fine fuels will likely cure a bit earlier than normal. With some of last year’s robust fine fuel crop still present and add to the fine fuel loading in the late summer and fall.
Typically, little to no large fires occur in May. Normal large activity in just is 1-2 large fires in most PSAs, except in the Sacramento Valley/Foothills and Far Eastside PSAs, which average 2-2.5 large fires. In July, normal is 1-2 large fires in most PSAs, except the Sacramento Valley/Foothills and NW Mountains, which average 2-3 large fires. These numbers continue to increase in August, with the highest numbers being 4.8 large fires in the Northern Sierra and 5.6 in the NW Mountains.
All of the North Ops region has Normal Significant Fire Potential for May. In June, the Far East Side, Sacramento Valley Foothills, and Diablo Mountain portion of the Bay Area are Above Normal. The remainder of eastern areas are added to the Above Normal area in July and Aug.