Overnight Wednesday night a huge and very proficient rain producing MCS (Mesoscale Convective System) moved across parts of the corn belt. Copious amounts of rain (too much in a lot of locations) was observed in parts of Iowa, Illinois, Indiana, and Missouri. Across the central High Plains it continued to be dry. (click for a larger version)
This MCS should impact a large part of the High Plains. Some areas will receive a pretty good soaking (1 to 2 inches of rain) while others may see on the order of 1/4 to 1/2 inch. There likely will be quite a bit of wind with the system, but not much if any hail.
Once that system moves by, the majority of Friday will be dry and almost certainly dry over the weekend (with the exception of the Rockies and adjacent foothills).
Other than the storms tonight, it should be mainly dry (and cooler over the weekend). It will be warming during the first of the week and this favorable harvest weather will last until about mid-week next week. But, as I have stressed in the previous posts here, that favorable window of opportunity to get the harvest completed and other field week accomplished, will be closing fast.
It is starting to look more and more likely that MCS's will begin to impact the plains almost nightly beginning as early as Wednesday night (July 1). Not everyone will get rain, but a large percentage will. These nightly occurrences could last through the weekend.
Then, it looks like MUCH cooler temperatures (higher humidity too) and wetness will arrive, most likely after the 4th.
One observation I've made over the years is the trend of what is called the Southern Oscillation Index. It is a value that is calculated based on surface pressures between Darwin and Tahiti. It is one measure of an El Nino or La Nina. I've noted that when the index value crashes (decreases rapidly) it typically is followed by a colder regime across the central part of the country. I'm not totally confident of a summer-time response, but all indications point to significant cooling. There is also some tropical weather trying to form across the western Pacific and this would also lead to downstream energy propagation and would support significant cooling.
Here is a chart of the SOI index (click for larger version)....
The two previous SOI "crashes" were followed by much colder weather!
The cooling may last several weeks (on average). Any additional rains would also act as a feedback mechanism in keeping temperatures down that could even last into August! One of the longer range forecast models has consistently pointed to a colder than average July. The latest run continues to support that notion. In that output denoted below, the gray areas are ranges of possibilities based on ensembles. The black line is the average. If this was to verify, it would have a negative impact on Plains corn growth as the growing degree days will be significantly less than normal.
Next update - probably June 29.