Near record La Niña conditions continue

One of the strongest La Niña’s ever has contributed to wildfires in Colorado and is very likely to impact U.S. weather into the spring

Check out this outstanding time-lapse video of the Dome Fire shot by Mikey Pounds in Boulder, and posted on Vimeo. Whipped by high winds possibly related to La Niña, it forced evacuation of 1,800 people.

In September, I reported that by one of the measures used to monitor what scientists call the ENSO cycle, the tropical Pacific Ocean had plunged into La Niña conditions at a record pace. Now, Klaus Wolter of NOAA’s Earth System’s Research Laboratory is is reporting that in September and October, the La Niña was the second strongest on record for that time of year.

For an explantion of the ENSO cycle, please see my earlier post about the developing La Niña and its impacts. That article also includes an explanation of how Wolter’s method for tracking La Niña differs from NOAA’s official ENSO advisory.

According to Wolter, La Niña typically brings dry and windy conditions to the Northern Front Range of Colorado during late summer and fall, raising the risk of wildfires. And that’s what we’ve experienced during the last two months: dry, windy conditions — and three wildfires.

The first two, the Fourmile Canyon and Reservoir Road fires, occurred in September. The third, the Dome fire, occurred just one week ago. Like the Fourmile blaze, it ignited just west of Boulder. Within a few hours it forced the evacuation of 1,800 people and crept to within several hundred yards of the city. Luckily, firefighters were able to contain it quickly. No homes burned, and no one was hurt. (A fourth blaze, the Cow Creek Fire, was sparked by lightning in Rocky Mountain National Park back in June, and continued into October in a rugged, densely-wooded area that had not burned for 370 years.)

Whipped by very high winds reaching more than 60 miles per hour, the Fourmile Canyon Fire developed into the most destructive blaze in Colorado history, destroying 169 homes. But the Dome Fire had an even greater potential to blow into the City of Boulder itself, since it was closer. Luckily, although it was windy that day, conditions weren’t quite as bad as those on Labor Day weekend, which is when the Fourmile fire blew up. In an email message this morning, Wolter said that “if we had had the Labor Day wind conditions with the Dome fire, we would have seen much worse impacts – those winds did not get nearly as strong, nor last as long, as on Labor Day.”

El Niño, the other side of the ENSO, also played a role in the fires we’ve been experiencing. It brought a wet spring and early summer to Colorado, resulting in more plant growth. When that vegetation dried out later in the season, it provided more fuels for the wildfires.

This has been “sort of the ‘perfect’ set-up for fires now (wet first then dry and windy),” Wolter said. At the same time, there were fewer thunderstorms and thus less lightning this late summer and fall, “so the ‘chaotic’/unpredictable component has been the ‘ignition source’, i.e., humans rather than lightning.”

What can the United States as a whole expect going forward? According to NOAA:

Expected impacts in the United States include an enhanced chance of above-average precipitation in the Pacific Northwest, Northern Rockies (along with a concomitant increase in snowfall), and Ohio Valley, while below-average precipitation is most likely across the south-central and southeastern states. An increased chance of below-average temperatures is predicted for coastal and near-coastal regions of the northern West Coast, and a higher possibility of above-average temperatures is expected for much of the southern and central U.S. (see 3-month seasonal outlook released on October 21st, 2010).