NAPERVILLE, Illinois, June 29 (Reuters) - It is common for June to deliver many ups and downs for Chicago corn and soybean futures, but those swings have been especially strong this year with expanding U.S. drought up against forecasts for a wetter July pattern.

June markets have one final test with the U.S. Department of Agriculture’s acres and stocks reports on Friday. This set of reports is associated with the largest average CBOT corn and soy moves of the 15 major USDA report days per year.

Directionally, corn and soy futures on June 30 tend to react to acres far more often than stocks, though U.S. weather forecasts often add to the chaos. That has been the case in the last couple years, and the market is entering Friday’s report fresh off a steep weather-driven sell-off.

In the six sessions ended Thursday, CBOT December corn futures plunged 15.9%, June’s biggest six-session loss in at least three decades. Corn had surged 14.5% in the prior six trading days, the month’s largest six-day gains since 2012.

November soybeans ended fractionally higher on Thursday, though they shed 8.1% in the five prior sessions, among the month’s largest-ever five-day declines. That was slightly stronger than the late June 2022 losing streak but nowhere near June 2021’s unmatched five-session dive of 14.2%.

In mid-June, November beans had gained as much as 11.5% over five sessions, their biggest five-day winning streak for the month in over 30 years.

REPORT-DAY ACTION

June 30 has been more eventful in recent years for corn prices than those for soybeans, as December corn has moved an average 5.4% on this day over the past four years with a low of 4.3%. That compares with an average of 2.9% for soybeans and a low of 1.2%.

But sometimes the day’s price action goes against the USDA report outcomes. That happened for both corn and beans last year, as U.S. crop weather was improving and prices were correcting from historically elevated levels.

Analysts basically nailed both corn acres and June 1 corn stocks last year, which was unprecedented, but December futures fell more than 5% on report day. Soybean acres in June 2022 landed below all trade estimates for the third time in four years and stocks were slightly bearish, and November futures lost 1.4%.

Corn would fall another 6.7% and beans nearly 10% in the two sessions that followed last year's report day, spanning July 4 holiday trade, a particularly vulnerable time for U.S. weather markets.

One big difference between this year and last is that commodity funds still held sizable net long positions in both corn and soybeans heading into June 30, 2022. But as of Thursday, funds may have been back in bear territory on corn and closer to flat in soybeans.

Karen Braun is a market analyst for Reuters. Views expressed above are her own.

(Reporting by Karen Braun Editing by Matthew Lewis)