Incus — About

About Incus

Incus is a real-time weather intelligence tool built for motorsports racing teams. It aggregates atmospheric data, computes performance-critical metrics, and surfaces the weather metrics as a live feed — so you always have the numbers that matter.

Incus is named after the anvil-shaped crest of a cumulonimbus cloud, a striking meteorological formation that reliably signals incoming severe weather. Just as this towering cloud acts as a massive early warning for intense, rapidly-shifting conditions, this app provides precise, hyper-local forecasting data for making the best engine tuning decisions for motorsports teams across the country.

Send Feedback

Weather Metrics

All metrics are derived from three primary observations collected every 15 minutes. Calculations use precision arithmetic rounded to 6 decimal places of accuracy.

Core Inputs

T: Dry-bulb air temperature (°C)
RH: Relative humidity (%)
P: Barometric pressure (hPa)
alt: Station elevation in meters (defaults to 1m)

Saturation Vapor Pressure

The maximum amount of water vapor the air can hold at a given temperature, computed with the Magnus formula. Used as the basis for all subsequent humidity-related calculations.

$$e_s(T) = 6.112 \times \exp\!\left(\frac{17.67 \times T}{T + 243.5}\right) \quad [\text{hPa}]$$

Actual Vapor Pressure

The partial pressure exerted by water vapor in the atmosphere at the current humidity level. Higher vapor pressure means the air contains more water and is correspondingly less dense.

$$e = e_s(T) \times \frac{RH}{100} \quad [\text{hPa}]$$

Dew Point

The temperature at which the air would become saturated with moisture and condensation would begin. A high dew point relative to air temperature indicates high humidity and reduced air density. Derived by inverting the Magnus formula using the actual vapor pressure.

$$T_d = \frac{243.5 \times \ln(e\,/\,6.112)}{17.67 - \ln(e\,/\,6.112)} \quad [°\text{C}]$$

Water Vapor

Absolute moisture content expressed as grains of water per pound of dry air — the traditional unit used in engine-tuning references. The mixing ratio $r$ is first derived from the vapor and dry-air pressures, then converted to grains. Returns 0 when $(P - e) \leq 0$.

$$r = \frac{0.62198 \times e}{P - e}, \qquad \text{grains} = r \times 7000$$

Air Density

Mass of air per unit volume, accounting separately for dry-air and water-vapor contributions via the modified ideal gas law. This is the fundamental physical quantity that determines how much oxygen enters the engine per intake stroke.

$$P_d = (P - e) \times 100 \quad [\text{Pa}], \qquad P_v = e \times 100 \quad [\text{Pa}]$$ $$\rho = \frac{P_d}{R_d \cdot T_k} + \frac{P_v}{R_v \cdot T_k} \quad [\text{kg/m}^3]$$

Constants: $R_d = 287.058\ \text{J/(kg·K)}$ (dry air) · $R_v = 461.495\ \text{J/(kg·K)}$ (water vapor) · $T_k = T + 273.15\ \text{K}$

Dashboard color Green — ≥ 98 % of ISA Orange — 94 – 98 % of ISA Red — < 94 % of ISA

Relative Air Density

Air density expressed as a ratio relative to the ISA (International Standard Atmosphere) sea-level value of 1.225 kg/m³. A value of 1.00 means conditions match standard sea level. Values below 1.00 indicate thinner air and proportionally less engine power. Directly comparable across tracks and weather conditions.

$$\rho_{\text{rel}} = \frac{\rho}{1.225}$$

Reference: $\rho_0 = 1.225\ \text{kg/m}^3$ — ISA sea-level air density at 15 °C, 1013.25 hPa

Pressure Altitude

The altitude in the US Standard Atmosphere that corresponds to the current barometric pressure, regardless of actual elevation or temperature. Pressure altitude rises as pressure drops — a lower-pressure day at a sea-level track behaves like a higher-elevation track.

$$PA = 44307.69 \times \left(1 - \left(\frac{P}{1013.25}\right)^{0.190284}\right) \quad [\text{m}]$$

Reference: NWS Pressure Altitude calculator

Density Altitude

Density Altitude is the altitude in a standard atmosphere that has the same air density as the current conditions. It combines the effects of temperature, pressure, and humidity into one number. Higher density altitude means thinner air, less oxygen, and less engine power — requiring a leaner jet or different tune. Lower density altitude means denser air and potentially more power.

$$DA = 44307.69 \times \left(1 - \left(\frac{\rho}{1.225}\right)^{0.234963}\right) \quad [\text{m}]$$

While pressure altitude accounts only for barometric pressure, density altitude factors in humidity and temperature as well — making it the preferred reference for carburetor jetting, fuel mapping, and performance prediction.

Dashboard color Green — < 700 ft Orange — 700 – 2,100 ft Red — > 2,100 ft