Fifty-five percent of the continental U.S. was in a moderate to extreme drought by the end of June, NOAA’s National Climactic Data Center in Asheville, N.C., said in its monthly State of the Climate drought report. That’s the largest percentage since December 1956, when 58 percent of the country was covered by drought.

This summer, 80 percent of the U.S. is abnormally dry, and the report said the drought expanded in the West, Great Plains and Midwest last month with the 14th warmest and 10th driest June on record.

The nation’s corn and soybean belt has been especially hard hit over the past three months, the report said. That region has experienced its seventh warmest and 10th driest April-to-June period.

“Topsoil has dried out and crops, pastures and rangeland have deteriorated at a rate rarely seen in the last 18 years,” the report said.

The report is based on a data set going back to 1895 called the Palmer Drought Index, which feeds into the widely watched and more detailed U.S. Drought Monitor. It reported last week that 61 percent of the continental U.S. was in a moderate to exceptional drought. However, the weekly Drought Monitor goes back only 12 years, so climatologists use the Palmer Drought Index for comparing droughts before 2000.