Developing La Nina conditions -- the cooling of ocean surface temperatures off the western coast of South America, which have been found to disrupt normal weather patterns in the United States -- are likely to continue into spring, according to the National Oceanic and Atmospheric Administration (NOAA).
This will potentially bring below-average temperatures to the Pacific Northwest and above-average temperatures across much of the South, at least until March, NOAA said in a monthly update. Above-average precipitation in the Ohio and Tennessee valleys and below-average precipitation across the South, particularly the Southwest and Southeast, can also be expected, according to NOAA.
In December negative equatorial sea surface temperature anomalies strengthened across the central and east-central Pacific Ocean, average subsurface oceanic temperatures fell; convection remained suppressed near the International Date Line, and both low-level easterly winds and upper-level westerly winds strengthened across the equatorial Pacific, NOAA said.
"Collectively, these oceanic and atmospheric anomalies reflect the development of La Nina," NOAA said.
NOAA's temperature forecast for the Northwest and South was generally in agreement with one issued last month by WSI Corp. of Andover, MA (see NGI, Jan. 5). In its three-month forecast, WSI called for colder-than-normal temperatures to dominate the Northwest through March. WSI said warmer-than-normal temperatures are expected in the Southeast and South Central regions in January and February but, unlike NOAA, predicted that colder-than-normal temperatures would move into the south-central region in March and be in effect across the Southwest throughout the three-month period.
NOAA previously attributed 2008's above-normal hurricane season to an ongoing multi-decadal combination of ocean and atmospheric conditions, lingering La Nina effects and warmer tropical Atlantic Ocean temperatures (see NGI, Dec. 1, 2008).
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