Regional Daily 95 Percentiles for Heatwave Detection

Introduction: This portal provides a detailed view of the 95th percentile of maximum and minimum surface air temperatures for Maryland as a whole, its counties and climate divisions at daily resolution from NCEI's nClimGrid-Daily area-averaged dataset. These calculations are critical for understanding extreme temperatures and heatwaves (ESTOC 2023). There is not an universal definition of a heatwave, so in this instance, the 95th percentile is used to define extreme heatwaves. If the daily surface air temperature maxima and minima are above the 95th percentile of the daily values, for at least three days, they define an extreme heatwave. However, because temperatures vary naturally from day to day, taking data from just a single calendar day across 30 baseline years provides a sample size that is too small and noisy. To smooth out this daily noise, a 5-day window centered on the target day is used to generate a sample of 150 values centered around a particular day.