Seasonal climate prediction requires mechanisms in the Earth's climate system that are deterministic, and thus potentially predictable, over interseasonal time scales. The El Nino/Southern Oscillation (ENSO) is one climate mechanism that evolves predictably from season to season, and recent work (Montroy (1996); Bunkers et.al (1996); Carlson et.al (1996)) suggests ENSO related climate impacts over agriculturally important regions of the United States. Using U.S. Climate Division data from 1895 to the present and the SST Index of Wright (1989), the effects of both El Nino and La Nina ENSO phases on seasonal climate over the central U.S. is investigated, with focus given to potential agricultural effects.
Preliminary results indicate a significant tendency toward above/below median summer (JAS) rainfall/temperature over portions of the Missouri River drainage basin during El Nino periods. During El Nino winter-spring periods (DJF-FMA) a significant tendency for above median and 4th quartile rainfall is indicated over Texas, Oklahoma, Kansas, and Nebraska. Northern Plains temperature is significantly skewed above seasonal medians and into the 4th quartile during El Nino winters, while seasonal temperatures over the Southern Plains and Texas gulf coast are skewed below normal. During summer periods consistent with extreme La Nina conditions, a consistent tendency towards 4th quartile seasonal temperatures is indicated over the corn belt region of eastern Nebraska, Iowa, and northern Illinois. La Nina winter periods also show a significant incidence of extreme dryness and warmth over Texas and portions of Oklahoma, Arkansas, and Louisiana, while a higher than normal incidence of extreme cold conditions is indicated over the Northern Plains during NDJ.