The kind fo weather we have often is the deciding factor for crop yields in Iowa. Moisture is the most important factor. That used by crops comes from rainfall during the season plus soil reserves. Here's how we stand for 1962.
Shaw, R. H. and Duncan, E. R.
"Crop Yield Prospects for 1962,"
Iowa Farm Science: Vol. 16
, Article 7.
Available at: https://lib.dr.iastate.edu/farmscience/vol16/iss7/7