Hyperlocal Wet-Bulb Temp, Rain/Snow Freezing Level & Alert Lab (2026)

When snowflakes fall from cold clouds into a dry, above-freezing surface air layer (for example, `+2.5°C` at `35%` relative humidity), moisture sublimates and evaporates off the surface of the snowflake. That evaporation absorbs latent heat from the flake itself, keeping the snowflake's internal temperature at the **Wet-Bulb Temperature** (`-1.4°C` in that scenario)—well below freezing!

Meteorologist Roland Stull published an empirical closed-form equation in the *Journal of Applied Meteorology and Climatology* (2011) that computes Wet-Bulb Temperature (`Tw`) directly from air temperature (`T` in °C) and relative humidity (`RH%`) using four `atan()` terms with an accuracy within `±0.3°C` across standard atmospheric pressures.

Commercial fan and lance snow guns require a Wet-Bulb Temperature of `-2.0°C` (`28.4°F`) or colder (`-1.5°C` with nucleating additives). At `28°F` Dry-Bulb and `90%` humidity, the wet-bulb is `-2.7°C` (marginal), whereas at `34°F` Dry-Bulb and `25%` humidity, the wet-bulb is `-3.1°C` (excellent snowmaking despite above-freezing air).

The human body cools itself primarily through the evaporation of sweat from skin maintained near `35°C` (`95°F`) while core temperature stays at `37°C` (`98.6°F`). When the ambient Wet-Bulb Temperature reaches `35°C` (or `~31°C` in empirical Penn State human trials), sweat can no longer evaporate into the air, leading to uncompensable hyperthermia even in shade with unlimited water.

The classic `10:1` rule (10 inches of snow per 1 inch of liquid water equivalent) only holds near `-1°C` to `-3°C` (`27°F–30°F`). In cold dendritic growth zones (`-12°C` to `-18°C`), SLR climbs to `15:1` or `20:1` ('Champagne Powder'), whereas near `0°C` (`32°F`) wet cement snow drops to `5:1` or `7:1`.