What the comparison measures.

NASA satellite-and-model climate data give regional estimates near the US Census Bureau’s 2020 county centers of population. Reanalysis combines observations with a model. These are regional grid-cell estimates, not direct station observations, county averages or property findings.

Two decades, five measures

Each year, we count days with maximum temperature ≥35°C, humid heat as described below, minimum temperature ≥24°C, and precipitation ≥50 mm. We also take the largest daily precipitation total. Each annual measure is averaged over 1991–2000 and 2016–2025. Change is the later mean minus the earlier mean. All days, including leap days, are required. Missing inputs fail the build. The NASA series cover 12,784 complete days per county, 1991–2025. Intervening years are retained but excluded from the decade means.

35°C is 95°F; 24°C is 75.2°F (about 75°F); 50 mm is 1.97 inches (about 2 inches). The Celsius and millimeter thresholds are exact. They are descriptive thresholds, not local warnings or FEMA definitions. Daily minimum is a proxy for warm nights. Precipitation includes the liquid-water equivalent of frozen precipitation. Grid averaging can suppress extremes. A zero does not mean no station events occurred.

Humid heat

Dry heat counts miss humidity. Miami-Dade has no days at or above 35°C in the NASA series, yet humid summers can be dangerous. Humid-heat days have a maximum hourly NOAA heat index of at least 103°F (39.4°C), the shade-based “Danger” band. We apply NOAA’s heat-index calculation and its adjustments to hourly temperature and dew point from Copernicus (ECMWF) reanalysis. Relative humidity is derived from temperature and dew point. This covers 1991–2000 and 2016–2025.

Humid heat uses a different regional grid and local clock days. The NASA measures use local solar days. Daily means cannot recover hourly extremes. An earlier daily estimate was about 1.7 times an hourly comparison for Harris County and was dropped. The available NASA hourly record begins in 2001, so it cannot supply a matching 1991–2000 hourly count. NOAA’s chart assumes shade; full sun can add up to 15°F. Reanalysis can understate humid extremes. A zero is a regional grid-cell count.

NOAA cross-check

The same ≥35°C test was applied to NOAA county climate records for all 20 comparison years. NOAA’s estimates interpolate station observations and average them across each county. NASA and NOAA differ in geography, method and daily boundaries. Los Angeles, Denver, Harris and Chittenden increase in both series, by different amounts. Miami-Dade stays at zero in NASA but rises from 2.2 to 5.7 days/year in NOAA. Warm nights and precipitation were not independently cross-checked. Agreement does not validate either count.

Interpretation

Ten-year samples are not 30-year climate normals. No significance test, causal attribution or future projection was made. Regional daily precipitation extremes are unsuitable for drainage design, flood zones or station record claims. Climate metrics are separate from the FEMA sample. Original labels, non-rating states and observation windows remain unchanged. FEMA identity and redistribution issues remain unresolved.

Sources

NASA supplies regional climate estimates. NOAA supplies the county cross-check and heat-index guidance. The US Census Bureau supplies population context. Copernicus (ECMWF) supplies humid-heat inputs. No agency endorsement is implied.

Download the climate values, including annual measures and comparison results. Data credits.