With drought continuing to intensify across Oklahoma, the state received unwelcome news from the eastern equatorial pacific region: La Niña conditions have returned, and are expected by NOAA’s Climate Prediction Center (CPC) to continue through the first half of 2009. While these cooler-than-normal pacific waters may be thousands of miles away, climate studies have shown the phenomena can still impact the weather in Oklahoma.

La Niña influences weather across the world, but it influences Oklahoma’s weather by altering the jet stream’s path over the U.S., pushing it farther to the north. The Pacific Northwest would then see increased stormy conditions while the southern sections of the U.S., to the south of the altered storm track, would experience precipitation deficits. Warmer weather is also a possible implication for Oklahoma during La Niña conditions.

The combination of warmer and drier conditions for Oklahoma would not bode well for the upcoming fire season, which generally peaks in February and March. There are currently 18 counties with burn bans issued by local County Commissioners in Oklahoma. These burn bans coincide with the worst drought-stricken areas of the state.

Drought conditions in south central Oklahoma are currently labeled “severe” by the U.S. Drought Monitor, with “moderate” drought and abnormally dry conditions in other areas. Much of the southeastern half of the state has had 20-40 percent of normal precipitation over the last 120 days (mid-September through mid-January). In fact, the Oklahoma Mesonet sites at Burneyville and Ardmore have recorded a meager 2.1 inches of precipitation since September 16, 2008. Similar amounts are indicated by the Oklahoma Mesonet across southern and eastern Oklahoma.

CPC considers cooler-than-normal ocean temperatures in the equatorial pacific region La Niña “conditions” if they are forecasted to persist for three consecutive months. A full-fledged La Niña “episode” has not occurred unless those conditions exist for at least five consecutive overlapping three-month seasons. The last La Niña episode occurred from August 2007 through July 2008.