(The Colby Fire as seen from satellite. Image source: NASA)

Major wildfires in winter? It may sound odd, but that’s what’s happening in a California suffering under a climate-change spurred drought that is currently its 9th worst on record.

Yesterday, beneath a dry dome of high pressure and spurred by Santa Ana winds, the Colby fire sparked in a populated suburb of Los Angeles amid a deepening California drought. Today, the fires exploded into a nearly 2,000 acre monstrosity. The blaze, fueled by 30 to 50 mph winds was proving difficult to contain as over 500 firefighters rushed to the scene in an effort to keep it from leaping down into nearby population centers. Mandatory evacuations were in place for hundreds of residents as the fire aggressively advanced toward homes and places of work.

(Colby Fire threatens local businesses. Image credit: Julie Palagyi)

Red flag warnings are now in place for many LA counties, which are expected to experience continued strong winds, above average temperatures, and single-digit humidity over the next 24 hours. Such conditions are conducive for the further spread of the Colby fire as well as for the sparking of additional blazes throughout the LA region.

Abnormally Warm, Abnormally Dry

Wildfires are rare in California this time of year. During winter, the region typically experiences wetter, rainier  and cooler conditions as storms flow in off the Pacific Ocean. But this year, a powerful blocking pattern has forced warmer, drier air over the region. It is the other side of the same blocking pattern that is flooding the Arctic with above average temperatures while disrupting the polar vortex and resulting in episodes of extreme weather over the eastern and central US.

(Jet Stream Pattern for Thursday and Friday. Image source: University of Washington.)

Note the very high amplitude ridge pushing up from California all the way into central Alaska and the corresponding trough digging down into the eastern US and pushing all the way to the Gulf of Mexico. This image is just a snap shot of the same blocking pattern that has persisted since late March of last year, resulting in wet, stormy conditions for the Eastern US and dry, hot, drought and fire conditions for the western US.

Blocking patterns of this kind have occurred in the past. But it is extraordinarily rare for such events to persist for ten months running. It is also the kind of event that climate experts such as Dr. Jennifer Francis warn is currently caused by a massive loss of sea ice cover in the Arctic and will become more common as sea ice continues its warming-induced retreat resulting in further Jet Stream weakening, meandering and retrenchment.

Weather Pattern Part of Trend Produced by Human-Caused Climate Change

This fixed weather pattern led to very severe conditions in California for December that, according to Dr. Jeff Masters at Weather Underground, resulted in a -4.67 reading on the Palmer drought severity index. This makes December of 2013 the 9th worst drought month on record for California (although anecdotal evidence coming in through January indicate that current conditions may be even worse). It is also worth noting that of the top ten worst drought months to occur since 1880 in California, five have now occurred since 1991 — a climate record that shows an increasing number of dry and record dry periods. Such increasingly extreme drying was predicted by numerous climate models for the US southwest as human warming continued to intensify and advance into the 21rst century.

Though such changes were anticipated by scientists, if not by politicians, business leaders, or the media, it was not clear that a strong fire hazard would emerge in even winter months. But this year has seen numerous intense west coast fires during winter time. Such new conditions are quite anomalous. And should the blocking pattern continue to persist, expect extreme heat, drought and fires to ramp up through spring and summer.

Links:

Plumes of Smoke Waft Through Colby Skies as Wildfire Rages

Historic Drought Intensifies in California

University of Washington

NASA