# Filter 5: 90 °F+ heat-index days

**Status:** Not started.

**Data keys:** `humidHeatDays`, with the audit columns `humidHeatSourceFips`
and `humidHeatFipsAdjustment`. Calculation:
[filter-calculations.md](../filter-calculations.md) §5.

## Findings

**7. Heat Index days are a daily-extrema proxy.** Daily Tmax and daily minimum
relative humidity are paired even though their observation times may differ.
The result should not be described as an observed hourly maximum Heat Index.

**8. Heat-year completeness is permissive.** Any year with at least one valid
Tmax/RH pair is included in the equal-year average. A minimum valid-day rule
would reduce low-biased partial-year counts.

Cross-filter findings that affect this filter, in
[00-cross-filter.md](00-cross-filter.md): 12 (Alaska and Hawaii not covered),
13 (Lexington, VA uses Rockbridge County as a proxy), and 24 (no gridMET
section in the data-sources doc).

## Decisions

None yet.

## Tasks

Not started; follow the per-filter review checklist in
[pipeline-plan.md](../pipeline-plan.md) §5.