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Feels-Like Metrics Explained

The thermometer says 30 °C, but it feels like 38 °C. Or it's 5 °C outside and the wind makes it feel closer to -2 °C. SmartMixin shows up to five different "feels-like" metrics that capture what the air actually feels like to your body, combining temperature with humidity, wind and sometimes sunlight.

This article explains what each metric means, where the value comes from, and why your station may show some but not others.

The Five Metrics

Heat Index

Heat Index combines temperature and humidity to describe how hot it really feels in warm, humid weather. Above roughly 27 °C, humidity prevents sweat from evaporating efficiently, so the body cools down less and the air feels hotter than the thermometer reads.

Rule of thumb: most relevant in summer, when both temperature and humidity are high.

Humidex

Humidex is the Canadian counterpart to Heat Index. It uses a different formula but has the same goal: capture the discomfort of heat combined with humidity. You may see it quoted in weather forecasts in Québec and parts of Europe.

Note: Heat Index and Humidex measure the same idea with different formulas. The two values are usually close but not identical.

Wind Chill

Wind Chill combines temperature and wind speed to describe how cold it feels when wind strips heat away from exposed skin. It is only meaningful in cold weather — typically below about 10 °C — and only when there is measurable wind.

Rule of thumb: most relevant in winter. Wind Chill is not computed above ~10 °C because the formula is no longer physically meaningful.

THW (Temperature-Humidity-Wind)

THW is a Davis-specific apparent-temperature index that combines all three factors — temperature, humidity and wind — into a single "what it feels like outside" reading that works year-round.

Available on Davis stations only.

THSW (Temperature-Humidity-Sun-Wind)

THSW adds solar radiation to THW. It captures the difference between standing in the shade and standing in direct sun on an otherwise calm summer day — a difference everyone notices but no other index accounts for.

Available on Davis stations only, and only on Davis models that include a solar radiation sensor.

Where Does the Value Come From?

Some stations compute feels-like values on the device and transmit them to SmartMixin. Others send only raw measurements (temperature, humidity, wind), and SmartMixin computes the feels-like values on its servers from those raw readings.

Provider	Heat Index	Humidex	Wind Chill	THW	THSW
Davis	native	computed	native	native	native
WeatherFlow	native	computed	native	—	—
Ecowitt	computed	computed	computed	—	—
Ambient Weather	computed	computed	computed	—	—
Weather Underground	computed	computed	computed	—	—
MyAcuRite	computed	computed	computed	—	—
Netatmo Weather	computed	computed	computed	—	—
Public stations (SYNOP)	computed	computed	computed	—	—

Native means your station calculates the value itself and sends it to SmartMixin.
Computed means SmartMixin calculates the value on its servers from your station's raw temperature, humidity and wind readings.
— means the metric is not available for this provider.

Why does Humidex always say "computed"? No weather-station manufacturer transmits Humidex natively — it's a regional index. SmartMixin always derives it from temperature and humidity.

Why a Metric May Not Appear on Your Station

The most common question we hear is "why don't I see Heat Index (or Wind Chill, or THW) on my station?" There are a few simple rules:

Wind Chill needs wind

A station without an anemometer cannot produce a Wind Chill value, native or computed. For example, a basic Netatmo indoor + outdoor setup without the wind module will never show Wind Chill, and neither will a Davis Vantage Vue indoor head used on its own.

Heat Index and Humidex need humidity

If your station does not measure humidity, or its humidity sensor is faulty and reporting zero, Heat Index and Humidex cannot be calculated. This is rare in practice — almost every weather station with a thermometer also has a humidity sensor.

Wind Chill disappears in warm weather

Wind Chill is only physically meaningful below about 10 °C. Above that threshold the formula doesn't apply, so you will not see a Wind Chill value on summer days even if your station has a working anemometer.

THW and THSW are Davis-only

If you have an Ecowitt, Ambient Weather, WeatherFlow or other non-Davis station and you're wondering why THW or THSW don't appear, the answer is that these are proprietary Davis indices. Other manufacturers don't transmit them, and SmartMixin doesn't synthesise them — THSW in particular requires a solar radiation sensor that most non-Davis stations don't have.

Where to Find These Metrics in SmartMixin

Feels-like values appear in several places throughout the app and webapp:

Live tile on your station's home view — when a value is available
Analysis report — the "Feels like" section is shown whenever your station provides temperature and humidity
Charts — feels-like metrics appear as additional lines alongside temperature on temperature charts
Alerts — the mobile app has a dedicated Feels like alert category. When you create an alert in that category, SmartMixin only shows the sub-metrics that your station actually emits. Alert thresholds respect your temperature unit preference (°C, °F or K).

Frequently Asked Questions

Why is the Heat Index on my Davis station slightly different from the value I see on a nearby public station?

Different sources use slightly different formulas. Davis stations transmit their own Heat Index calculated on the device, while public stations don't transmit a Heat Index at all — SmartMixin computes one on the server using a standard formula. The two values should be close but rarely identical.

Why doesn't my Netatmo station show THW or THSW?

THW and THSW are proprietary Davis indices. They are only available on Davis stations, and THSW additionally requires a solar radiation sensor.

Why does Wind Chill disappear in summer?

Wind Chill is only meaningful in cold weather (below about 10 °C). Above that threshold the index is hidden because it would not reflect real physical conditions.

Can I set alerts on feels-like metrics?

Yes. The mobile app has a Feels like alert category. The sub-metrics it offers depend on what your station provides. See Setting Up Weather Alerts for the alert workflow.

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