Forecasters call for neutral conditions, but say a La Niña is not out of the question
By Summit Voice
FRISCO — With sea surface temps cooling to near average in much of the equatorial Pacific, NOAA’s Climate Prediction Center has dropped an El Niño watch that’s been in effect for the past several months.
El Niño is part of a cyclical pattern of sea surface temperature variations that affects global weather patterns. The emerging El Niño forecast last spring and summer offered some hope for drought relief in the parched Southwest and the southern tier of states, where warmer than average Pacific Ocean temps can help boost winter and spring precipitation.
During La Niña years, when cooler-than-average sea surface temperatures prevail in the same region, the storm track often shifts northward, driving storms into the Pacific Northwest and then down across the northern Rockies and northwest Colorado.
During October, sea surface temperatures continued to reflect borderline neutral to weak El Niño conditions and even increased during the second half of the month, but atmospheric circulation — specifically the easterly trade winds — were more in line with ENSO-neutral conditions.
“While the tropical ocean and atmosphere may resemble a weak El Niño at times, it is now considered less likely that a fully coupled El Niño will develop,” NOAA experts wrote in a Nov. 8 update. “Therefore, the previous El Niño Watch has been discontinued as the chance of El Niño has decreased. While the development of El Niño, or even La Niña, cannot be ruled out during the next few months, ENSO-neutral is now favored through the Northern Hemisphere winter 2012-13.
Moderate to strong phases of El Niño or La Niña help forecasters make seasonal outlooks with more confidence. Without that signal, meteorologists rely on other cyclical ocean characteristics, including the Pacific Decadal Oscillation and the North Atlantic Oscillation. But those signals are less understood and sometimes only manifest impacts a few weeks in advance.
Under neutral Pacific Ocean conditions, the general winter outlook for much of the country is for equal chances of above-average, average, or below average precipitation. At the same time, the Climate Prediction Center is calling for a large area of above average temps across much of the Southwest up through the Rockies and eastward on to the Central Plains.