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July 2, 2018 – The outlook for July-October is for drier than normal conditions. Warmer than normal temperatures are expected much of the summer, with a trend toward slightly below normal by the end of October. We expect a pattern of semi-persistent low pressure troughs positioned near the west coast this summer, and this pattern tends to limit the number of monsoon surges into the North Ops region, especially the west side. Eastern areas are expected to see normal to slightly below normal amounts of lightning during the typical summer thunderstorm months (July-August). The long-term precipitation and soil moisture deficit has led to robust crop of cured fine fuels at mid and lower elevations. Wildfire activity was much above normal in areas dominated by cured fine fuels in June, especially in the Sacramento Valley and surrounding foothills.
Fuels at all elevations are expected to be available for wildfire spread by mid July. Occasional lightning events, especially in eastern areas, will combine with dry fuels in July-August to produce a higher than normal potential of large fires there. As lightning diminishes late in the summer our “offshore wind season”begins, and the robust crop of cured fine fuels will once again produce a higher than normal potential of large fires in September-October.
Areas from the Sacramento Valley/Foothills and eastern Bay Area east have Above Normal Significant Fire Potential in July-August. In September-October eastern areas drop back to Normal while most western areas are added to the Above Normal category.
The normal number of large fires per Predictive Service Area is defined as:
July: 1-2 large fires, except 2-3 in the Sacramento Valley/Foothills and NW Mountains.
August: <1 Bay Area. 2-3 elsewhere, except 4-6 Northern Sierra and NW Mountains.
September: 1-3, with highest amounts in the Sacramento Valley/Foothills and NW Mountains.
The drier than normal rainy season has led to drier than normal fuels and soils across the North Ops region. The U. S. Drought Monitor product now shows a large area of “Abnormally Dry” conditions with a smaller area of “Moderate Drought” to the west of the crest. The wet spring weather was ideally timed to produce a heavier than normal crop of fine fuels at mid and lower elevations and a near to slightly above normal green-up phase among perennial live fuels.
The University of California Sierra Foothill Research and Extension Center reported that on May 1 the fine fuel crop in the foothills of the eastern Sacramento Valley had reached more than 180% of normal, higher than the 120% reading a year prior.
The longer-term precipitation and soil moisture deficit have led to a rapid curing of the fine fuel crop and a more rapid live fuel decline phase. The North Ops average 1000-hr fuel moisture chart shows that the heavier fuels are now drier than normal, and will reach the 90th percentile value during the first half of July. Heavier fuels at upper elevations will likely be available for wildfire spread nearly July, several weeks earlier than normal. There are also areas of frost kill at lower elevations that occurred when cold weather arrived late in the winter after earlier warm weather allowed the budding of trees and shrubs.