La Nina spurs SOUTHWEST US DROUGHT 2005

Link to image of SOUTHWEST US DROUGHT OCT 05-JAN 06

LA NIÑA SPURS DROUGHT CONDITIONS, WILDFIRES ACROSS THE SOUTHERN US The anomalous pattern of cooler than average sea surface temperatures (SSTs) across the central and eastern Pacific and warmer than average SSTs over the West Pacific, better known as La Niña, is ultimately responsible for the widespread drought conditions and wildfires that have ravaged much of the southern US, including the southern and central Plains, the Southwest, and southern and central Florida. So far, 11 fatalities have been linked to fires in Texas where it is estimated that 3.5 million acres of land, about 2 percent of the state, have burned. The Texas panhandle has been especially hard hit, particularly near the town of Borger where 3 people died and over 400,000 acres have burned. In neighboring Oklahoma, there were large grass fires in the southwestern portion of the state. In New Mexico, there was a large grass fire in the northeastern part of the state, but the biggest blaze was near McDonald in southeastern New Mexico, which consumed 92,000 acres. The drought has also affected parts of the Florida Peninsula. Conditions are dry over central and southern Florida where a few isolated wildfires have been reported in conjunction with the start of the springtime wildfire season.

Coincident with the SST anomalies associated with La Niña, there are corresponding anomalies in the atmospheric circulation pattern. During La Niña, stronger-than-average trade winds blow from east to west across the Pacific. Coupled with the warmer-than-normal waters in the West Pacific and cooler-than-normal waters over the East and central Pacific, precipitation is enhanced over the West Pacific, including Indonesia, the Philippines and northern Australia, and suppressed over the central and eastern Pacific. During northern hemisphere winter, this pattern leads to a northward shift in the mean position of the jet stream over the eastern North Pacific, resulting in above-average precipitation over the Pacific northwest and below-normal rainfall over much of the southern tier, including the Southwest, the southern Plains, the northern Gulf Coast, and Florida.

The Tropical Rainfall Measuring Mission satellite (known as TRMM) was launched into service in November of 1997. It was designed to measure rainfall over the global Tropics using both passive and active sensors, including the first and only precipitation radar in space. The TRMM-based, near-real time Multi- satellite Precipitation Analysis (MPA) at the NASA Goddard Space Flight Center monitors rainfall over the global Tropics. Based on an 8 year MPA rainfall climatology, rainfall anomalies were constructed for the period October 2005 through January 2006 for the continental US. The resulting pattern of wet and dry anomalies closely resembles a classic La Niña pattern. It shows higher-than-average precipitation over the Northwest (green and blue areas), especially along the coast and over the coastal ranges of Northern California, Oregon, and Washington State (blue areas) where storm systems have been steered in by the jet stream. Almost the entire rest of the country, except for New England, has below normal rainfall. The strongest dry anomalies or rainfall deficits (orange areas) extend from Texas up through the central Plains into the upper Midwest and across the northern Gulf Coast and over peninsular Florida. Significant deficits also occur over portions of the Midatlantic region. However, in the Southwest, which already receives very little rain, the impact is far greater than for a similar anomaly in the southeast, which receives a lot more rain on average. As a result, most of Arizona, New Mexico, West Texas, and central Oklahoma have received less than 25% of their normal rainfall for the period. The current La Niña is expected to persist for the next several months.

TRMM is a joint mission between NASA and the Japanese space agency JAXA.

Image produced by Hal Pierce (SSAI/NASA GSFC) and caption by Steve Lang (SSAI/NASA GSFC).