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Historical Records Show Weather Patterns Influence First and Last Frost More Than Temperature Trends


You might think that a cold spring would mean a late frost, but in fact regional spring temperatures and the last day with frost are unrelated.  

The frost-free season in North America is approximately 10 days longer than it was a century ago and University of Utah scientist Court Strong wanted to find how frost across the U.S. was influenced by regional and global weather circulation patterns. He found that weather systems, for example El Nino, better predict when the first and last frost will occur compared to just mean temperature.  

“It seems logical that a longer growing season should be in some way tied to global warming and it’s not entirely separate, but it turns out that over the past century circulations has been more important in explaining the variations that we’ve seen.”

While phenomena like El Nino are well monitored and therefore used in many climate studies, this analysis included data from a broad array of atmospheric circulation patterns. This all-encompassing approach allowed for the data to indicate which circulation patterns were important to include in the study as opposed to scientists choosing only well-understood weather patterns. 

“If we think about long-term potential for agriculture in the state and we are interested in knowing what the likely time period is available between the spring and the fall frosts, we need to look at global climate models to get that information.  The most effective way to do that is to look at models that get these circulation patterns in the historical record correct. Now that we have the study we know which circulation patterns we need to examine” said Strong.

Greg McCune from the U.S. Geological Survey, a co-author on the paper, also stressed the need to consider the interacting effects of cyclical weather patterns together with rising global temperatures when making long-term environmental and economic planning decisions.