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Tuesday, January 10, 2012

NIFC SEASONAL OUTLOOK: Weather and Fuels Discussion

For Southern and Central California
Issued: January 2nd, 2012
Valid for: February 2012 –April 2012
Weather Discussion
After a relatively cool and wet autumn, the weather pattern quickly changed to a much drier one during December 2011. Several locations reported record, or near-record low December rainfall, especially over central California where winter snowfall has been largely absent in the Sierras.
 Most of the Sierra Nevada’s saw little if any precipitation, leading to the one of the latest seasonal closures of high elevation roadways in recent memory.
 The severe precipitation deficit in December left snowpack at a paltry 10% of average by the end of the month.
 This low precipitation amount stands in stark contrast to December 2010 when an “atmospheric river” of moisture brought steady precipitation for much of the month.
Last winter, the Eastern Pacific was in a moderate to strong La Niña condition.
 This season, the current ENSO index shows the La Niña conditions are in the weak category. Long range models indicate the La Niña may slowly strengthen this spring before dissipating during the summer.

While the weak La Niña may partially explain the lack of rainfall this year, other atmospheric factors may be responsible for the unseasonably dry weather. Last winter, the circulation across the northern hemisphere was largely influenced by a negative or cold phase, Arctic Oscillation and Northern Atlantic Oscillation.
 This resulted in a large area of low pressure in the Gulf of Alaska which was able to spawn several impressive storms in late 2010. This season, the low in the Pacific has been replaced by strong high pressure which has kept the storm track well to the north of the district. This shift may be the result of a strongly positive oscillation in the Arctic and Northern Atlantic Oscillation.
This oscillation generally lasts for a few weeks and it is reasonable to expect this oscillation to de-amplify or switch to a negative oscillation in coming weeks.
 However, the underlying La Niña condition will likely continue through the rest of the “rainy season.” Weak La Niña’s tend to result in below average precipitation for the region, especially over Southern California.
 Therefore below average precipitation can be expected through the rest of the winter and into the early spring months.

• Temperatures near to slightly above normal.
• Precipitation below normal, especially over Southern California.
• Near normal large fire potential through March, then above normal potential over several areas by the beginning of April.

Fuels Discussion
Early fall precipitation allowed for substantial grass greenup to occur. However, at the start of the calendar year, most of this new grass crop is on the verge of returning to dormancy. Widespread curing of south aspect seasonal grasses is likely to occur in January with most fine fuels finishing curing earlier than usual this year.

Higher elevation and heavier vegetation will likely begin to dry out earlier than normal this year, given the lack of snowpack at higher elevations. In addition, ladder fuels and brush and shrubs will be more vunerable to ignition by the early spring.

Due to these factors, large fire potential will likely be above normal over many areas away from the ocean and its moderating maritime influence. Inland regions and areas from 3,000 to 8,000 feet may be the most vulnerable to new ignitions by the end of winter into early spring. If late winter snows do not arrive, expect the high risk areas to migrate to higher elevations in the Sierras. The lack of winter snow may also lead to the possibility of drought returning to a large portion of the area by the beginning to middle part of spring.

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    ****REMINDER**** Every fire has the ability to be catastrophic. The wildland fire management environment has profoundly changed. Growing numbers of communities, across the nation, are experiencing longer fire seasons; more frequent, bigger, and more severe, fires are a real threat. Be careful with all campfires and equipment.
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