Frost in Manitoba in May?

Can you believe we would be covering the tomatoes this late in May? Well if we hadnt they would be black.. even with covers the tips of some of the leaves are nipped with frost.. usually after the full moon which was May 17 we do not hav to worry about frost but 2011 is going to be another year to remember I am thinkn. 5:30 am frost was thick enough to scrape with scrapper..