# SunSoak & the science · SunScope
How the SunSoak index works — built on the UTCI standard with a rain and snow penalty, a Solar Model for your surroundings (forest, alpine, beach, river, desert, open water), and full mean radiant temperature.

# SunSoak & the science

The honest felt-temperature number, and what goes into it.

## What is SunSoak?

Standard UTCI is calculated assuming open, unshaded conditions with no precipitation — it tells you how the wind and sun affect your body, but not the full picture of where you actually are or what the weather is actively doing to you. SunSoak fills those gaps with three layers of original calculation stacked on top of the UTCI foundation.

## The precipitation penalty

Rain and snow are not in UTCI. The soak-factor formula adds an original penalty based on rain intensity, snowfall rate, and wind speed — reflecting the extra chill of wet clothing and skin. Light drizzle (under 1 mm/hr) reduces the felt temperature by roughly 1–2 °C. Heavy rain combined with strong wind can push it down by 7–8 °C. Snowfall carries an additional penalty on top.

## The Solar Model

UTCI assumes you are standing in the open. SunScope's Solar Model adjusts the solar radiation load and air temperature for the place you actually are, selectable from a dropdown on the SunSoak column. There are eight models:

Solar Model | What it does to the felt temperature
--- | ---
Grass / Open Field | The UTCI default — full sun exposure over natural ground, no adjustment.
Town / City | Urban heat island raises air temp ~2–3 °C; building canyons cut direct and diffuse solar, with reflections partly offsetting the reduced sky view.
Beach / Lakeside | Water and sand reflect extra radiation back at you, increasing the effective solar load and UV dose.
River / Riverbank | Canopy and valley walls cut direct sun; evaporative cooling from the water lowers apparent air temperature.
Forest / Woodland | Canopy reduces direct radiation by around 85%; air temperature is adjusted down for evapotranspiration cooling.
Open Water | Full solar exposure with additional reflection off the water surface, no shade or shelter, and no ground-heat contribution.
High Altitude / Alpine | Thinner atmosphere at ~2,000 m enhances radiation by around 15%, adjusted for exposed ridge conditions.
Desert / Arid | Extreme radiation load from high-albedo sand and bare ground, with ground-level heat significantly raising the felt temperature.

Selecting a Place, Activity, or Work profile automatically sets the most appropriate Solar Model for that context — but you can always override it manually. The chosen model also drives the Shade Air column, which estimates the air temperature sitting in that model's typical shade (see the column reference).

## Mean radiant temperature

The full radiant heat load from surrounding surfaces — ground, walls, sky, and direct sun — is calculated as Mean Radiant Temperature (Tmrt) and fed into the UTCI polynomial. On a sunny day this alone can add 20–30 °C to the felt temperature compared to a shaded reading. It is why stepping into shade feels so much cooler even though the air temperature hasn't changed.

## Reading the result

The combined SunSoak value is colour-coded into thermal stress bands so you can read conditions at a glance — see reading the stress bands. For a plain-language description of every column that feeds into or sits alongside SunSoak, see the column reference.