Ag Weather Forum

Upper-Air Outlook for Summer

Bryce Anderson
By  Bryce Anderson , DTN Senior Ag Meteorologist
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Near-stationary high pressure along the Western Canada coastline, and a standing low-pressure area over the northeastern U.S., appear to be well-established as controlling features for the 2018 summer season. (DTN graphic)

Meteorologist Nate Hamblin, who is in our DTN long-range forecast group, is contributing his comments in this blog item. I asked Nate to offer comment on the upper-atmosphere features which are dominating our spring weather pattern and how they might play into the summer forecast. Here are his comments. -- Bryce

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High-latitude atmospheric blocking (high pressure) has had a large influence over the weather pattern across North America throughout 2018. When this happens, the pattern tends to become stagnant, with persistent temperature and precipitation anomalies in many locations.

DTN has analyzed the upcoming summer pattern carefully, using analogs from similar years based on the shift from a weak La Nina to a weak El Nino. In addition, various computer model guidance solutions were factored in.

Both the models and the analogs strongly suggest that high-latitude blocking will remain a significant feature through the summer months. Although the blocking regime can change or even disappear for short periods of time, the features that will be prevalent in the means will be the western North America ridge and the eastern Canada trough. When these features are in place, there are common reactions that take place, noted below.

During this summer, hot and dry weather will be persistent across the Southern Plains through the Mississippi Delta. Drought conditions will likely be maintained or even intensify across the High Plains areas. In the Mississippi Delta and eastern Texas, drought development is possible by later this summer. Sometimes, tropical systems can bring relief to areas adjacent to the Gulf Coast and this is certainly possible later this summer. However, prevailing conditions will be less favorable than normal across the western Gulf of Mexico. This will lower the risks overall for tropical storm development. In addition, thunderstorm complexes can set up, even in an otherwise dry pattern, to bring localized heavy rains to portions of the region. This is possible, especially early in the summer season. However, any such instances will only help in sporadic areas and this will not be enough to save the region from increasing dryness overall.

Farther north, dry weather will likely develop and be maintained across portions of the Northern Plains, the Upper Midwest, and most of the Canadian Prairies this summer. Heat will show up closer to the Canadian Rockies through the northern Rockies of the U.S., but the heat should be muted significantly by refreshing polar air masses across the lower sections of the Plains and into the Upper Midwest.

But, while temperatures may be cooler, these impulses will likely move too quickly to allow much moisture build-up. Thus, precipitation will be light. This cycle should be prevalent through the summer season. As a result, dryness and drought could become an issue as the summer progresses. In the central Plains and Midwest, limited moisture could flow in, but precipitation is likely to be sporadic.

This is likely to lead to regional dryness with localized areas of heavier rainfall. This should be more prevalent early in the summer, with lesser chances by later July and August. Temperatures in the Central Plains through portions of the Midwest will finish up somewhat above normal with short stretches of intense summer heat possible, followed by brief refreshing cool shots.

Farther west, hot and dry weather is expected across the West Coast of the U.S. and into southwestern Canada. Drought conditions are likely to intensify in these areas. Meanwhile, the Desert Southwest is likely to experience a very hot and dry start to the summer season. The model guidance and DTN analogs suggest that the summer monsoon season will pick up beginning later July and continuing into the early fall season. This is likely to improve severe drought conditions in localized areas that see abundant rainfall. However, given the very dry start, confidence is not high that the monsoon rains will be abundant enough to bring widespread improvement.

In the eastern U.S., on the other hand, ample moisture is expected to occur across the Ohio and Tennessee Valleys through the Northeast this summer. This should occur because the eastern Canada trough should allow fronts to frequently push southeastward into these areas, and these fronts are likely to interact with Gulf moisture. This wet pattern will lead to largely seasonable temperatures in these areas.

Finally, the trough position over eastern Canada is likely to bring a chilly summer overall to portions of this region, especially areas near and east of Hudson Bay. Precipitation should not be too far from normal, but regional dryness could show up in northeastern Canada.

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Thanks again to Nate for his comments. A summary of the effect on crop prospects is this: both northern and southern crop areas could have some dryness concerns during this season, especially in the Southern Plains, where drought conditions are already established. Don’t lose track of the Delta and Southeast drier prospects. Central crop areas, including the western Midwest, will likely have crops drawing on soil moisture reserves during the summer, similar to what we saw a year ago.

A final note: Analogs that DTN looked at for reference in the analysis are the years 1951, 1963, 2006 and 2009. Corn production in those years shaped up this way: 1951, above average; 1963, record for the time period; 2006, third-largest on record; and 2009, record for the time period.

Bryce Anderson can be reached at bryce.anderson@dtn.com

Follow Bryce Anderson on Twitter @BAndersonDTN

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