Ag Weather Forum

Though extremely cold air was present over much of the country east of the Rockies in late August and early September, it has been very warm since then and is forecast to continue through October, if not longer.

The upper-level pattern that has supported the higher temperatures, generally a ridge across Canada, has been tough to move out of the country. And on the occasion that it has moved, it has been quickly replaced.

The ridge provides the warm air to the surface, but also blocks the cold air farther north toward the North Pole. Any disruptions to this ridge have come from the Pacific, a source of mild air, not cold air. What will be the kicker to a change in this pattern? We will have to look at the tropics, but probably not the side you expect.

For now, above-normal temperatures are favored for most of the United States for quite some time. There is a slight exception for those across the South and possibly the East. Underneath the upper-level ridge in Canada lies a trough that will be tough to eliminate in the Southeast. That will keep temperatures down a few degrees, making for mild but seasonable conditions. Disturbances that go through Canada may also bring some milder air into the Northeast and possibly bring a day or two of below-normal temperatures before springing back up above normal. But in general, the country is favored to be warm.

To go along with the higher temperatures, precipitation will be limited for a lot of the country. Though the West could see some inundation of disturbances from the Pacific and thus areas of rain, the middle of the country will be hard-pressed to see much precipitation. The disturbances from the West are likely to be deflected northward through Canada while their fronts sweep through the U.S. Some rain is bound to occur, and favors the Northern Plains, but many areas of the country are going to remain dry -- except those exposed to tropical influences.

Indeed, the tropics are coming alive again in the Atlantic as we have Hurricane Gabrielle in the middle of the Atlantic heading toward Spain this weekend, Tropical Storm Humberto in the central Atlantic heading toward or west of Bermuda, and yet another tropical wave north of Hispaniola heading toward the Bahamas for this weekend. This one is expected to form into a tropical storm and head north toward the Carolinas. There is a lot of uncertainty regarding the track of this system. It could remain offshore or move far enough north to sit over the Carolinas for a couple of days next week. Should it do that, it would likely produce a massive amount of heavy rainfall that would likely cause flooding, even for areas that are currently in drought.

But that is not the tropical feature we are watching for a pattern change in October. Instead, we will be focused on the western Pacific for development there. There are already tropical storms and typhoons in the basin, but these are not the ones we will monitor.

Instead, at the end of next week, there is potential for one or more additional storms to develop. Where they go could significantly affect the pattern across the U.S. for the second and third week of October. If a typhoon is strong enough and moves northward toward the Aleutians in the North Pacific, it would add energy to the jet stream, amplifying the pattern and causing it to shift significantly across the U.S. That could move the ridge out of Canada and bring through a burst of colder air to the Central U.S. But being so far out in time, it is only a suggestion by a few model runs. If there is no significant typhoon that curves up into the North Pacific, then the overall warm and dry pattern will continue for some time.

This is the overall pattern that is most likely during a developing La Nina in the central Pacific Ocean as we are currently experiencing. Even if a disruption to the pattern occurs, it will likely be brief and we would return to the warmer situation, possibly through much or all of November. For some areas, it will feel like an extension of summer at times. For others, it will only be holding off the coming winter, which is forecast to be more harsh in terms of cold bursts.

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John Baranick can be reached at john.baranick@dtn.com

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