The southwest U.S. ridge strengthened late last week, the last few days of June. This ridge then pushed well to the north over the western U.S. during the weekend and during the first couple of days of July. This is the reason for the extreme heat that developed in the southwest and eventually pushed all the way northward through the Pacific Northwest and into southwest Canada earlier this week. This ridge has been weakening somewhat since early this week, enough to allow a weak cold front to push through the Pacific Northwest and into the northern plains at the end of the week. This trough will continue east across the northern plains to the Upper Midwest and then to the Great Lakes region during the weekend and early next week. The hot weather advances east ahead of this trough but not the same degree of heat that was seen through the west coast states, it should retreat was a little once the trough reaches the northern Midwest and the Great Lakes region.
The Atlantic ridge had been relatively weak early this week when the western ridge was strong but it was strong enough hold an old cold front over the southeast and middle Atlantic region for much of the week. This lead to numerous rain showers as moisture streamed north out of the eastern Gulf of Mexico and through the area. The Atlantic ridge strengthened late in the week and is now fairly strong and located just off the east coast. This has allowed hot, dry weather to cover the Middle Atlantic and the northeast states while also forcing the frontal boundary a little to the west and bringing more rain to the southeast Midwest region.
The outlook for next week shows the Atlantic ridge weakening again while the western ridge strengthens again. However, the western ridge does not look to become has strong as it was earlier this week. It also does not look to move as far north as it did in the western US early this week. This ridge appears to set up somewhere in the region from the central and south Rockies through the central and southern plains to the southwest Midwest. This would be further to the east, and thus closer to, the US corn growing areas. It does not appear that the ridge wants to move into the Midwest and bring exended periods of heat and dryness but there is some uncertainty in this outlook. If the ridge sets up on the eastern edge of the regions mentioned it would be hotter and drier than if it were to set up on the western side of the range. This pattern will need to be watch during the next 2-3 weeks as the corn crop moves through pollination.