Ag Weather Forum

Rain Pattern Still Leaves Vacancy

John Baranick
By  John Baranick , DTN Meteorologist
A compact but intense storm moving from the Black Hills to the Ozarks and then to the eastern Midwest July 29-Aug. 2 will leave a big swath of moderate to heavy rainfall. (DTN graphic)

A few days of above-normal temperatures and widespread rainfall were highly beneficial for reproductive corn, soybeans, and cotton. All three crops had increases in their good-to-excellent ratings in the USDA Crop Progress report on July 27.

However, crop stress was noted in Iowa, where dry areas of the state were bypassed by meaningful precipitation. Iowa's good-to-excellent total in both corn and soybeans slid by three points. Overall, crop ratings are third highest for corn at this point in the season and second highest for soybeans since 2011.

A ridge of high pressure remained over the southern U.S. last week. This typically brings heat and dryness. And while it did for a couple days over the weekend in the Plains and Midwest, it was supplanted by lower temperatures and a good deal of rainfall. Total accumulations over 2 inches were observed in portions of every major producing state last week. This includes a swath of more than 6 inches in southern Minnesota where flooding was observed. Other areas of flooding occurred in the Dakotas, Nebraska, Kansas, and Oklahoma and along the Gulf Coast due to the impact of Hurricane Hanna over the weekend.

The conditions have been stressful only in a few spots, while most areas remain in favorable conditions as corn, soybeans, and cotton are all in the important reproductive to early filling stages. The western half of Iowa has had rainfall deficits of 50-80% during the last 30 days, but it has not seemed to make much of a difference as both corn and soybeans have been able to take advantage of above normal subsoil moisture. This moisture is running out as subsoil moisture of short to very short has gone from 25% last week to 32% this week. The forecast for this region does not offer much in terms of meaningful rainfall.

The pattern is changing to a ridge west-trough east pattern for the next seven to 10 days. That will bring the storm track further to the south. Indeed, a disturbance between the two systems is expected to form in the Black Hills of South Dakota and Wyoming on July 29 and head southeast into the Ozarks on July 31. The system will then curve northeast and move through the eastern Midwest through Aug. 2. The system is expected to have moderate to heavy rainfall of 1-3 inches along its path and, of course, with thunderstorms there will have locally heavier amounts as well. With another disturbance and prior front over the Ozarks into the northern Delta, rainfall amounts of 4-6 inches will be possible in this area.

Northern areas will see temperatures drop below normal, reducing the amount of evapotranspiration of filling crops, but additional moisture would be welcome. Only a weak cold front with isolated to scattered light to moderate showers is expected for July 31-Aug. 2 across the northern tier; but, with soil moisture being adequate for all but western Iowa, crops should still be in good shape overall. Spring wheat, which is heading toward maturity and early harvest will benefit from the drier conditions.

The longer-range forecast indicates this general pattern could persist through at least the middle of August, though both features may be muted. If that is the case, showers would likely return to northern areas, benefiting the filling crops. For spring wheat, showers would likely hamper harvest activities.

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

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