According to the NOAA Climate Prediction Center press release, La Niña conditions returned in August and are expected to gradually strengthen and continue into this winter. This La Niña event first appeared last summer and continued in fall, winter, and early spring. By May, it had faded away. In fact, from May to July La Niña was not present in the Pacific according to the Climate Prediction Center. Only in August did it seem to return.
While La Niña events can continue for more than one year, it is very rare for one to disappear in spring and then reappeared in late summer. In fact, there are no other case like this in the historical records that go back to 1950, according to one of the primary indices used to measure La Niña and El Niño.
If La Niña continues to redevelop, the impacts on Illinois could include a fall that is warmer and drier than average and a wet winter all along the Ohio River Valley. The next set of seasonal outlooks from the Climate Prediction Center will consider the redeveloped La Niña. The new outlooks will be released on Thursday of this week.
La Niña is the name given to abnormally cold waters along the equator in the eastern Pacific Ocean. The changing weather patterns associated with La Niña effect not only the Pacific Basin but the U.S. as well. See the Climate Prediction Center link for more information current conditions and possible impacts.
Dry Conditions Persist in Illinois
Parts of southern and eastern Illinois have struggled with dry conditions since July/August. Those conditions have expanded in recent weeks across more of Illinois. The latest U.S. Drought Monitor has slightly more than half the state in at least the “abnormally dry” category and 11 percent in “moderate drought”. Most of the impacts so far have been in agriculture and horticulture and not water supplies.
There is a strong La Niña occurring in the Pacific. Based on past events, Illinois is typically warmer and drier than normal during fall (September-November). By winter (December-February), the wetter than normal conditions typically appear in Illinois.
La Nina Returns
The NOAA Climate Prediction Center (CPC) noted earlier this month that “La Niña conditions are expected to strengthen and last through the Northern Hemisphere winter 2010-11.” A La Niña occurs when abnormally cold waters develop along the equator of the central and eastern Pacific Ocean. These changes in the ocean and atmosphere in turn influence the weather over the United States.
That feature is incorporated into the seasonal outlooks provided by the CPC. Right now they are calling for an increased chance of above normal temperatures this fall (September-November) across Illinois. Precipitation has an increased chance of being below normal in the southern two-thirds of Illinois.
For this winter (December-February), they call for an increased chance of above normal temperatures in the southern half of Illinois, with equal chances of above, below and near normal temperatures in the northern half of Illinois. They do call for an increased chance of above normal precipitation across all of Illinois and much of the Ohio River Valley. Updated official seasonal forecasts are posted mid-month here.