Some U.S. restaurants have been warning customers of a “national pickle shortage,” and it turns out that those warnings have some merit. According to Fox Weather, heat and drought across Mexico brought on by the El Niño climate cycle has led to a shortage of pickling cucumbers in the country. When you consider that the U.S. imports about three-quarters of its fresh cucumbers — including those used for pickling — from south of the border, it’s easy to see how problems in Mexico could lead to a shortage in the U.S. According to a report from the Department of Agriculture, cucumber imports were…