Estimate apparent temperature with the complete NWS screening and humidity-adjustment procedure, with conservative validity handling.
01 / CALCULATION INPUTS
02 / RESULT & SUPPORTING CALCULATIONS
Assumes shade and light wind. Direct sunshine can increase heat stress (NWS notes up to 15°F); no fixed sunlight correction is applied here. Heat index alone does not determine personal safety, illness risk or safe activity duration.
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Use preliminary screening and both official humidity adjustments, with unrounded caution-band boundaries and explicit conservative withholding at extremes.
Use preliminary screening and both official humidity adjustments, with unrounded caution-band boundaries and explicit conservative withholding at extremes. Supporting calculations and limitations are shown alongside the result, with relevant local examples.
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The complete NWS procedure starts with the simplified Steadman-consistent estimate, averages it with air temperature, and applies the Rothfusz regression only when that average reaches 80°F. Applicable low- or high-humidity adjustments are then applied.
For RH below 13% and air temperature 80–112°F, the NWS square-root adjustment is subtracted. For RH above 85% and air temperature 80–87°F, the NWS high-humidity adjustment is added. The polynomial is never applied unconditionally.
The NWS equations always use Fahrenheit internally. Celsius input is converted by F = C × 9/5 + 32. Results and temperature differences are then converted consistently for both displays.
Unrounded apparent temperature is compared with continuous bands: 80–<90°F caution, 90–<103°F extreme caution, 103–<125°F danger and at least 125°F extreme danger. A lower result is not a personal safety assessment.
The NWS regression is not valid for all extreme temperature/humidity combinations. This calculator conservatively withholds air temperatures outside 40–112°F and modeled results above 140°F rather than presenting unsupported extrapolation confidently.
No. It assumes shade and light wind. NWS notes that direct sun can raise heat stress by up to 15°F, but a universal sunlight correction is not added here. Activity, health and other conditions affect risk beyond this estimate.