June 3, 2020 – The official Predictive Services outlook, produced in mid May, calls for drier and warmer than average conditions in the North Ops region during June-September. The above normal cured fine fuel crop will be vulnerable to rapid spread rates of wildfires beginning in June when N-NE/Offshore wind patterns develop.
This pattern is expected more often in mid to late June. Occasional lightning will lead to new ignitions, and the threat of these fires growing to significant sizes will increase at elevations below 6000 ft from mid to late June as well. Otherwise, a gradual increase in Initial Attack can be expected in all areas during June.
In July and August the threat of wind events drops off just as lightning becomes the main threat for large wildfires at elevations above 3000 ft. The SW Desert monsoon pattern is expected to impact the North Ops region with near to below normal lightning amounts in July-August. In general, any lightning below 6000 ft elevation will pose a threat of large fires beginning in June due to very dry fuels, and the same applies to all elevations beginning in July.
A large area of the region, mainly west of the Cascade-Sierra crest and below 6000 ft, has Above Normal Potential in June, followed by most areas at 3000 ft and above in July-August.
All areas are in the Above Normal category in September.
In June “Normal” is defined as 2 or more large fires in the East Side, Sacramento Valley/Foothills, and Diablo-Santa Cruz PSAs, and 1.2 or fewer large fires in all other PSAs. In July “Normal” is 1-3 large fires per PSA. In August the Bay Area averages near 1 large fire in each PSA, while the remainder of the PSAs average between 2 and 6 large fires. In September “Normal” is defined as 1-3 large fires per PSA.
Fuels and Drought
The U. S. Drought Monitor for California shows the impact of the warmer and drier than normal rainy season. Portions of NW CA are now considered to be in Extreme Drought, and the majority of the remainder of the region is in Moderate or Severe Drought. To the west of the Cascade-Sierra crest the spring fine fuel crop came in more robust than usual. It is mostly cured below 1500 ft elevation, and well on its way to curing elsewhere. Middle and upper elevations are seeing dead fuels continue to dry, and are near seasonal normal values as June begins . The live fuel green-up phase is expected to be weaker than normal, with the drying phase commencing earlier than normal. The high elevation snow pack in the north peaked in early April at 66% of the average peak, and it has melted rapidly since then. As June begins it has almost completely melted off statewide, except above 8000 ft where more continuous cover remains. Occasional wet weather in the first half of June will temporarily slow the pace of fuel-drying and snow-melting. Early season storms came with low snow levels, leaving dry soils and dead fuels beneath the snow pack, and this has led to a lighter runoff and less moisture available for the green-up phase. In general, fuels at all elevations will reach critically dry levels about a month earlier than usual.
Low pressure systems moved through the North Ops region with rain and thunderstorms during the 2nd and 4th weeks of May, and a large portion of the region ended up with above average rainfall for the month. Most of the below average areas were in the east and south. Precipitation since the rainy season began on October 1, 2019 remains below average in all but a very small area in far NE CA. Much of the region has only received 25-70% of normal precipitation for the season as we enter the driest 4 months of the year. Temperatures were above average in most areas, with the warmest areas in the south and west. The equatorial Pacific is currently in the ENSO-neutral category, but warmer than average. It is expected to cool over the next several months, but still remain neutral. Current outlooks show some disagreement in the weather outlooks, and there are signs that a La Niña event is possible in the fall-winter.
North Ops Highlights
•Dry 2019-2020 rainy season winding down. Many areas 25-70% of ave. Light snow pack almost completely melted off, weeks ahead of usual
•Dead fuel moisture values near average as of early June
•Low elevation (< 3000 ft) grass crop -above normal fuel loading again. Mostly cured below 1500 ft. Initial Attack increasing throughout June
•Below average green up expected
•Warmer and drier than normal June-September
•N-NE/Offshore wind events will pose a bigger threat of large fires in June, Sept. Lightning will pose a bigger threat of large fires July-Aug
•Above Normal Significant Fire Potential many areas below 6000 ft elevations in June
•Most areas above 3000 ft increasing to Above Normal in July-August
•Above Normal all areas in September