Ask retired ag climatologist Jim Newman, West Lafayette, Ind., about the upcoming fall in the Midwest, and he leans heavily toward a warmer, drier than usual fall. He sees those conditions prevailing throughout October and likely into early November, covering the early fall period.
Listen to Iowa State ag climatologist Elwynn Taylor at the recent 2006 Farm Progress Show, Amana, Iowa, and you would have come away with a different impression. Taylor leaned more toward cool and wet across much of the Corn Belt, saying Indiana might be in a transition zone that would be tougher to call.
Why do two noted ag climatologists disagree? The difference seems to stem from varying views on the status of the current El Nino cycle. That's the phenomenon that involves warming of tropical Pacific Ocean waters. Warming or cooling of sea surface waters is linked to changes in atmospheric pressure, which in turn affect global air circulation patterns aloft around the globe. Shifts in these circulation patterns can directly impact long-term, seasonal weather shifts.
Taylor contends that an El Nino, or warm phase event, has already begun, probably starting in August. He credits it with being responsible for the cooler, wetter weather in late August and early September, and implied that the wet conditions that hampered the opening of the Farm Progress Show were the first signs of the change.
Newman counters that the cycle was still in neutral phase, and is only now beginning to show signs of moving toward a warm phase event. Who's right?
That may be for ag climatologists to debate. Newman says that Pacific Ocean waters are warming, but so far only at deep depths. Sea surface temperatures to date have shown very little increase in temperature. He contends that it is the variation at sea surface level and resulting impact on circulation patterns that cause global change, not what happens at levels deeper within the ocean.
Newman also contends that there is typically lag time once an El Nino event begins before weather changes are detected. Often that lag time is up to three months or more. Put another way, if an El Nino warm phase event began in October, large impacts on global seasonal weather patterns might not show up until either mid-or late-winter.
Newman believes other factors besides El Nino will play a large role in weather patterns this fall. Look for that to remain true until the warm phase event becomes fully formed, he concludes.