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June 1, 2019 – The majority of the North Ops region received well above average precipitation in May. Only portions of the far northern end of the region were drier than normal. Since January 1st the entire region has received above average precipitation, with a large portion at 150% or more of normal. Average temperatures were below normal from January through the first half of April. After a warm and dry stretch from mid April through early May, cooler then normal weather returned to much of the region through late May, in addition to the above normal rainfall. The high elevation snow pack snow water content remains well above average for the date as we enter June.
The annual grass crop has mostly cured below 3000 ft in the Sacramento Valley and foothills, the Bay Area and in the southern end of the Mid Coast PSA. Many other live fuels are still in green-up due to the cool, wet weather in May. Above 3000 ft and in northwestern areas grasses are earlier in their curing phase, and live fuels have yet to see their peak fuel moisture. The ongoing weak El Niño pattern in the equatorial Pacific is expected to continue into the fall/winter months. The North Ops multi-station average 1000-hr fuel moisture had reached slightly drier than normal in early May, but cool wet weather since then has brought readings well above normal. Drought conditions currently do not exist in California.
The North Ops region has another robust fine fuel and brush crop that will be vulnerable to above normal fire behavior and spread potential in many lower elevation areas in June and July, with middle elevations (3000-6000 ft) joining in August and September. Also, a rare heavy snow event in the northern Sacramento Valley has led to lots of dead and down trees and limbs. Finally, there has been an increase in tree mortality in the past year, as shown in the Tree Mortality Task Force density map. These fuels issues may contribute to another active fire season this year.
The first half of June is expected to trend from mild with occasional rain to warmer than average and dry, but occasional low pressure troughs and cold fronts are expected to bring brief periods of showers and thunderstorms to the northern and eastern mountains into the middle and possibly the latter portion of June. However, these same system could produce dry windy weather to the west of the Cascade-Sierra crest in lower elevation areas with cured fine fuels, elevating significant fire potential at times. Overall, the longer-term Predictive Service outlook calls for near normal temperatures and precipitation through September. In the absence of strong heat waves, the high elevation snow pack will gradually melt through July, continuing high fuel and soil moisture readings.
Little to no significant fire activity is expected through July at elevations above 6000′, and fire activity there will likely be on the quiet side of the normal range in Aug-Sep. Lower elevations (below 3000′) will see increasing grass fire occurrence in June, especially in the central and southwestern portions of the region. Middle elevations (3000-6000 ft) will gradually dry out a normal to slightly slower than normal rate, reaching Above Normal Significant Fire Potential in many areas by late July or August. El Niño patterns during summer months tend to correlate with a prevailing SW-W flow aloft, leading to fewer monsoon surges into the North Ops region, and therefore, less lightning occurrence than usual. Due to the expected moist conditions, lightning strikes at upper elevations through July will not be as likely to produce large fires, compared to 2018 when the snow pack was below normal.
Normal large fire occurrence in June is defined as 2-3 large fires in the Sacramento Valley and Foothills and Far Eastside PSAs, and fewer than 2 large fires in all other PSAs. In July normal is defined as 2-3 large fires in the Sacramento Valley and NW Mtns and 1-2 large fires in all other PSAs. In August normal is defined as 3-6 large fires in the NW Mtns, NE CA, and Northern Sierra PSAs and 1-3 large fires in all other areas. Significant fire occurrence drops of most notable east of the crest in September.
June – September 2019 Highlights
– Near normal temperatures and precipitation through September.
– Above normal snow pack gradually melting through July.
– Weak El Niño continuing throughout the summer.
– Heavy fine fuel crop, completely cured at lower elevations in June. Above normal brush growth.
– Below normal amount of summer lightning due to prevailing SW-W flow.
– Above Normal Significant Fire Potential at lower elevations Sacramento Valley/foothills and fine fuel-dominated areas of Mid Coast and Bay Area June through September, spreading north and including most middle elevations in August/September.
– Significant Fire Potential remaining quiet at high elevations.