Indicator: High Air Temperature Extremes (1948-2017)

Access the Indicator Materials: - Analysis & Methods - Data File - Map Service This metric is based on temperature data collected from land-based weather stations and compiled in NOAA’s Global Historical Climatology Network, Daily edition (GHCN-Daily) dataset. Using stations with sufficient long-term records, the Indicator calculates daily maximum temperature percentiles, identifies exceedances that represent unusually hot days, and then measures how the frequency of those unusually hot days changes over time. Note: This Indicator supported progress tracking toward the Monitoring and Assessment Outcome in the original Chesapeake Bay Watershed Agreement, adopted in 2014. The Watershed Agreement and Adapting to Changing Environmental Conditions Outcome were revised in 2025.