2 months from now it wouldn’t, though. Climatology is factored in.
For instance, the first hot pattern of summer is often harder on the general population, since people aren’t acclimated yet.
It was 61 at SEA today which is normal. Dewpoint was in the 30s and there was decent north wind. Probably felt a little chilly there. Its show mid to upper 60s tomorrow. If that qualifies for heat risk then the map will be bright red everywhere all summer.
I’ve also heard that a heavier emphasis will be placed on WBGT (wet bulb globe temperature) w/rt heat headlines in the future. It is a better measure than heat index.
Thresholds will vary by region, of course. Criteria in SE US/Desert SW will be different than the PNW, for instance.
Yeah basically it’s calculated with respect to each locations’ climatology (in addition to factors such as duration, diurnal cycle, and parameterization to extrapolate dewpoint, etc.