Live feels-like from wind or humidity - with an air→feels Δ strip, formula domain gate, and NWS-style caution bands.
Apparent temperature only. Not medical advice, occupational heat stress, or a full-sun WBGT tool.
By Ahmet C. Toplutaş·Site owner & editor · Science & weather tools
Last updated May 21, 2026 · Reviewed May 21, 2026 · Planning estimates only - not tax, medical, or investment advice
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Air temperature answers one question: what does a sheltered thermometer read? Wind chill and heat index answer a different one: how wind or humidity change heat loss or heat stress on exposed skin. Forecasts say “feels like” because people dress and pace outdoor time for the second number, not the first.
Wind chill models convective heat loss from a bare face at walking height — not wind chill on a parked car or a wall thermometer in still air. Heat index models shade conditions with relative humidity — full sun, pavement radiating heat, and exertion can feel worse than the index alone.
This page keeps both visible. The panel’s air → feels Δ strip is the unique job — show the gap, not another cost ladder or anniversary table.
Decision framing: “How far is exposure from the air reading?” - not “the weather is exactly this many degrees.”
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North American wind chill is defined for air ≤ 10°C and wind ≥ 4.8 km/h (~3 mph). Below that wind speed, the formula treats calm air as invalid — light breeze still matters to comfort, but the official index is quiet.
The Rothfusz heat index is defined for air ≈ ≥ 27°C (80°F) and relative humidity ≥ 40%. Cool, dry afternoons and humid mornings below 27°C often sit outside both formulas — that silence is honesty, not a broken calculator.
When inputs fail the gate, the panel reports air temperature and labels the regime inactive instead of inventing a dramatic feels-like. Tap Mild gap day to see that behavior on purpose — a teaching case for “why did the forecast not show heat index today?”
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A feels-like of −8°C when air is 0°C is a different story from −8°C when air is already −8°C. The Δ strip places air at center and moves a marker left (colder feel from wind) or right (hotter feel from humidity). Large Δ days are when clothing and exposure decisions diverge from the raw thermometer.
Commuting by bike at 25 km/h adds effective wind even when the ambient forecast says 10 km/h — your relative wind can push a marginal day into wind-chill territory. On the hot side, humidity can add 6–8°C to perceived stress while the dry-bulb reading barely moves; the strip makes that asymmetry visible at a glance.
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Bands echo National Weather Service wind-chill frostbite timing and heat-index caution charts. They ignore sun load, wet clothes, exertion, age, acclimatization, and medication. Use them as planning cues, then check official forecasts and local guidance for warnings.
Frostbite timing shrinks fast as wind chill drops below −27°C (−17°F class). Heat caution escalates when index crosses ~32°C (90°F) into extreme caution and danger zones — the panel’s band text summarizes that ladder without replacing NWS products.
Heat index assumes shade. Full sun can feel worse than the index — treat the number as a floor outdoors at noon.
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Wind chill (°C, wind in km/h), valid for T ≤ 10°C and V ≥ 4.8 km/h:
Heat index uses the Rothfusz regression on °F inputs (with NWS humidity adjustments), then converts back to your display unit. Other countries use different wind-chill or humidex formulations — this panel follows North American NWS-style definitions for consistency with US forecasts.
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Example A — winter bike. 0°C air, 25 km/h wind (panel preset).
Wind chill ≈ −5.9°C → Δ ≈ 5.9°C colder than air. Thermometer says “around freezing”; exposed skin loses heat like a still day near −6°C. Tap Winter bike and watch the marker slide left.
Example B — sticky patio. 32°C air, 70% RH.
Heat index ≈ 40.4°C → Δ ≈ +8.4°C vs air. Dry reading feels “hot”; humidity pushes caution bands toward extreme caution while guests still quote “only 32.” Tap Sticky patio.
Example C — deep freeze. −15°C air, 40 km/h wind.
Wind chill ≈ −27.4°C → Δ ≈ 12.4°C. Frostbite timing tightens sharply in this band — limit exposed skin minutes, not “it’s only −15.” Tap Deep freeze.
Example D — mild gap day. 18°C, light breeze — both formulas inactive. Air = feels; Δ ≈ 0. Apparent-temperature tools target extremes, not every afternoon.
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No. Air temperature is what a sheltered thermometer measures. Wind chill and heat index estimate how wind or humidity change heat loss or heat stress on exposed skin. The panel’s Δ strip shows that gap on purpose - a small Δ is mild weather; a large Δ is when forecasts talk about “feels like,” not just the air number.
The North American wind-chill equation is defined for air ≤ 10°C and wind ≥ 4.8 km/h. The Rothfusz heat-index equation is defined for air ≥ about 27°C (80°F) and relative humidity ≥ 40%. Outside those domains the index is not what NWS charts use - the panel reports air temperature and marks the domain gate instead of inventing a fake feels-like.
Cold, windy days use wind chill. Hot, humid days use heat index. Mild mid-range air (roughly 10–27°C) often sits outside both formula domains - that is expected, not a bug. Scene presets jump to typical winter-commute and sticky-patio cases so you can see each regime honestly.
They are planning labels inspired by National Weather Service wind-chill frostbite timing and heat-index caution charts. They are not a medical diagnosis, and they ignore sun, clothing, wet skin, and exertion. Treat a “danger” band as a cue to check official forecasts and local guidance, not as a treatment plan.
Standard heat index assumes shade and a light wind. Full sun can push perceived stress higher than the index. If you are in direct sun, treat the panel’s number as a floor, not a ceiling.
No. It is an educational NWS-style calculator for understanding apparent temperature. Workplaces, athletics, and medical decisions need official thresholds, wet-bulb globe temperature, or clinician guidance - not this page alone.
LIVE FEELS-LIKE
Thermometer ≠ feels ↓Scene presets
Domain needs ≥ 4.8 km/h (≈ 3 mph).
Updates live. Thermometer ≠ feels-like. Not medical advice.
Wind chill
-5.9°C
Air 0.0°C · Δ −5.9°C colder feel
AIR → FEELS Δ
Wind pulls the marker left of air — skin loses heat faster than still air at the same thermometer reading.
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