Skew-T Log-P Reader

A real Skew-T log-P diagram plots temperature and dewpoint against pressure to trace exactly how a rising air parcel cools, and this calculator reproduces its core outputs with a lighter-weight, single-parcel thermodynamic model. It first finds the Lifting Condensation Level (LCL) — the height at which rising air cools enough for its water vapor to condense into cloud — using the Bolton (1980) approximation for LCL temperature, then converts that to pressure via the Poisson equation with Cp/Rd ≈ 3.5 for dry air. Below the LCL, the parcel cools at the dry adiabatic lapse rate (9.8°C/km); above it, once condensation is releasing latent heat, it cools more slowly at a moist adiabatic rate approximated here as a flat 6°C/km (real moist lapse rates vary with temperature and pressure, so this is a simplification). Parcel height at each pressure level comes from the standard barometric formula (44330 × (1 − (P/1013.25)^0.1903)).

CAPE is then estimated from the single temperature-excess gap between the parcel and environment at 500 mb, scaled by Rd and the log-pressure depth from the LCL — a coarser version of the layer-by-layer CAPE integration a true sounding would use. Lifted Index (environment minus parcel temperature at 500 mb) gives a standard stability read: below -6 is Extremely Unstable, -6 to -3 is Very Unstable, -3 to 0 is Unstable, 0 to 3 is Marginally Stable, and only 3 and above is labeled Stable. Because this model uses only four inputs and a single upper-air data point at 500 mb rather than a full multi-level sounding, treat its CAPE and LFC/EL estimates as rough educational approximations — a real forecast sounding integrates buoyancy continuously through the whole atmospheric column.