California fires could reach record levels in 2008

An unusually early and dangerous fire season has hit California, where at least 33 fires burning over a total of 190,000 acres are active, according to the Interagency Fire Center. The fires were sparked over the weekend when an unusually far southward-moving storm system brought numerous thunderstorms to central and northern California. Over 8,000 lightning strikes hit the region. Most of these strikes were not accompanied by rain, since a very dry atmosphere at low levels caused much of the thunderstorm rain to evaporate before reaching the surface. The lightning strikes ignited an unusual number of fires, due to exceptionally dry vegetation in California. This year, the state experienced its driest spring season (March-April-May) since record keeping began in 1895, and much of the state is in moderate to severe drought.


Figure 1. Visible satellite image from NASA's Aqua spacecraft on Monday, June 23, 2008, showing smoke from hundreds of wildfires sparked by lightning in California. The red regions show where the satellite's sensor detected fires burning. The smoke has created air pollution levels in excess of the federal standards for fine particulate matter (PM2.5) over much of California's Central Valley. Image credit: NASA.

The forecast
With the dry season only beginning, it could be a record fire year in California. Even before last weekend's lightning storms, California had already seen an unusually large number of destructive wildfires, according to CalFire--90,000 acres had burned, compared to 42,000 acres during the same period last year. It is not unusual for large portions of the state to receive no rain at all in July and August, such as occurred last year (Figure 2). The jet stream typically moves far enough north in summer that the migrating low pressure systems that bring California most of its rain only hit the northernmost portions of the state. With high fuel levels due to a century of misguided fire suppression efforts, moderate to severe drought gripping the state, no rain in sight for months to come, and an above-normal chance of warmer than average temperatures forecast this summer for the state by NOAA's Climate Prediction Center, expect a record fire season in California.


Figure 2. Observed precipitation over California during 2007. Much of the state received no rain at all during July and August, which is a common occurrence. A little bit of thunderstorm activity did make it into the easternmost portion of the state, thanks to moisture flowing north-westward from the Arizona Monsoon. However, the Sierra Mountains block this moisture from reaching the central and western portions of the state. Image credit: NOAA.

Tropics
It's quiet in the tropical Atlantic. There are no threat areas to discuss, and none of the models are forecasting tropical storm formation in the next seven days. Beyond a week from now, the GFS is hinting that the region off the coast of Africa could see some development, but it is still probably too early for this too occur, despite warmer than average sea surface temperatures in the region.

Jeff Masters