Historical Change in Date of Last Freeze and Date of First Warm Day

This tool is excerpted from Chesapeake Bay Watershed Climate Impacts Summary and Outlook for Spring 2020.

Key Findings

  • In general, the southern portion of the Mid-Atlantic experiences the date of last freeze earlier than the northern half of the region.
  • From 2000–2019, the region has seen an increase in the number of counties with dates of last freeze in February and a decrease in the number of counties with dates of last freeze in the spring months.
  • The northern half of the region tends to see warmer temperatures later in the spring, with northern Pennsylvania and southern New York typically seeing their first warm day in March or April.
  • Between 2011–2019, nearly the entire region experienced the first warm day in February or March.

How to Use the Tool

Selecting time periods: Use the slider under each map of the region to adjust the decade used to calculate the average month displayed for each metric.
Viewing variability within a county: Hover or tap over a county of interest. A window will pop up that displays the percentage of dates for a given metric per month in each decade.

Technical Notes

These maps were generated with gridded temperature estimates from the PRISM Climate Group at Oregon State University. Parameter-elevation Regressions on Independent Slopes Model (PRISM) daily temperature data are available at a 4-km resolution for the coterminous United States. Data were processed by the Northeast Regional Climate Center to extract the annual dates of last frost, first 70°F maximum temperature, and first 80°F maximum temperature. More information on PRISM data can be found at http://www.prism.oregonstate.edu.

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