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Published February 13, 2012, 10:51 AM

Weather patterns

A chunk of the Midwest (especially west of the Mississippi River) is dry all the way to the Canadian border. What a change from last year, when it was so wet in North Dakota and northern Minnesota that farmers who had intended to plant corn had to switch to soybeans. What will this spring and summer be like?

A chunk of the Midwest (especially west of the Mississippi River) is dry all the way to the Canadian border. What a change from last year, when it was so wet in North Dakota and northern Minnesota that farmers who had intended to plant corn had to switch to soybeans.

What will this spring and summer be like?

According to several meteorologists/weather experts, the La Nina influences that have been affecting agriculture production for the past few years are once again effecting this current winter. However, this winter’s effect is different from what we would normally expect in the U.S. One factor in how the La Nina played out this winter was the volcano eruption of Mt. Grímsvötn in Iceland in May. There was also a major eruption at Shiveluch in Russia. This has added to the cooling of the polar air mass and caused unusually warm winter temperatures in the Central and Western U.S. This is the first time since 1783 and ’84 that there have been large eruptions in the North Pacific and North Atlantic in the same year. An eruption in either area produces a cold North American winter 80 percent of the time.

Iceland is home of the Icelandic low, which determines how many winter storms will enter the lands around the Atlantic Ocean and is a factor for shaping wind directions in the North Atlantic — especially the polar jet stream. Last year, the Icelandic low was warped by the huge eruption of the Icelandic volcano. The cooler, denser air altered air pressure and the Icelandic low strengthened.

We could see weather fluctuate in 2012 because of the North Atlantic oscillation (NAO) and the Arctic oscillation (AO). The NAO goes back and forth from positive to negative and back again and is shaped by the Icelandic low and a high pressure system over the Azores, the Azores high. When there is a strong difference between the Icelandic low and the Azores high, the two channel the path of the middle-latitude westerly winds blowing across the Atlantic, driving marine air and moisture deep into Europe, North Africa and the Middle East.

The volcanic strengthening of the Icelandic low is encouraging the AO to return to neutral. Normally, with a La Nina and last year’s eruption of Russia’s Mt. Sheveluch, the AO would be severely negative, but the eruption of Mt. Grímsvötn in Iceland changed things. The AO should continue to be variable the rest of the winter. Now, any cold front that enters North America is not blocked because the NAO is wavering between neutral and positive.

Currently, 58 percent of the contiguous U.S. is said to be dry and 36.21 percent is in actual drought. The area of greatest concern is in the West. December was the driest on record for most of California. However, because of an abundance of water from last year’s snowpack, the reservoirs are fairly full. Some places in the Southern Plains have enjoyed 150 to 300 percent of normal precipitation. Still, Texas only has changed the territory in drought from 100 percent to 99.4 percent dry and 95.1 percent is still in drought.

Large portions of Alberta, Saskatchewan, and Manitoba have received 40 percent less of normal precipitation. Unless rains pick up before April and May, they will be planting in dry conditions.

La Nina appears to have peaked and remains moderate at the beginning of February. Experts think the phenomenon will fade through late winter and into early spring. The Pacific should be neutral by mid- to late-spring. Here is where experts are split. Some think the ocean waters will be warm, some say neutral or cool again into autumn. Regardless, the AO and NAO will be pressured to retreat to neutral territory and back to positive. This should cause winter to have a speedy retreat.

Sue Martin of Ag & Investment Services Inc. in Webster City, Iowa, can be reached at (800) 527-0051, e-mail ag_invst@wmtel.net.

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