Lapse Rate & Stability Calculator
Two levels of a sounding in, the actual lapse rate out — compared with the dry and moist adiabats to read the atmosphere's stability like a forecaster.
The comparison ladder: steeper than 9.8 °C/km (dry adiabat) = absolutely unstable; between the moist (~6) and dry adiabats = conditionally unstable; shallower than moist = stable; negative = inversion. ISA's 6.5 sits — fittingly — in the conditional middle.
Formula
⚠️ For planning and education only. Weight & balance must be computed from YOUR aircraft's actual empty weight, arm and current equipment list, and verified against the POH/AFM envelope before flight.
Two levels of a sounding in, the actual lapse rate out — compared with the dry and moist adiabats to read the atmosphere's stability like a forecaster.
About Lapse Rate & Stability Calculator
Whether the afternoon brings glass-smooth haze or boiling cumulus is written in one number: how fast temperature falls with height compared to the adiabats. This calculator takes any two levels — from a METAR-plus-PIREP pair, a skew-T, or your own climb-out OAT notes — computes the environmental lapse rate, and places it on the stability ladder from inversion through absolute instability, with the flying consequences of each regime spelled out.
How to use Lapse Rate & Stability Calculator
- 1Enter — sensible defaults are pre-filled so you see a worked result immediately.
- 2Read the live results: .
- 3Check the "With your numbers" line to see the formula ELR = ΔT/Δh; compare: dry adiabat 9.8 °C/km (3 °C/1000 ft), moist ≈ 6 °C/km, ISA 6.5 °C/km substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use Lapse Rate & Stability Calculator?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula ELR = ΔT/Δh; compare: dry adiabat 9.8 °C/km (3 °C/1000 ft), moist ≈ 6 °C/km, ISA 6.5 °C/km with sources cited on the page
- ✓The comparison ladder: steeper than 9.8 °C/km (dry adiabat) = absolutely unstable; between the moist (~6) and dry adiabats = conditionally unstable; shallower than moist = stable; negative = inversion. ISA's 6.5 sits — fittingly — in the conditional middle.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
What's the physical meaning of comparing ELR to the adiabats?+
A displaced air parcel cools at the adiabatic rate (9.8 °C/km dry, ~6 moist) regardless of surroundings. If the environment cools faster with height than the parcel does, the risen parcel finds itself warmer than its neighbors — buoyant — and keeps going: instability. Cooler than neighbors, it sinks home: stability. The comparison IS the forecast.
Why is 'conditional' instability the interesting middle?+
Between the moist and dry rates, dry parcels are stable but saturated ones — cooling at the slower moist rate once condensing — are unstable. The atmosphere is then a loaded spring with moisture as the trigger: sunshine that lifts air to saturation converts fair weather into cumulus, and with enough depth, storms. Most severe-weather days start conditionally unstable.
How can a pilot measure lapse rate without a balloon?+
Note OAT against altitude during a steady climb — two readings 3,000+ ft apart give a usable ELR (this tool's inputs). Glider pilots do it habitually to predict thermal tops; IFR pilots notice inversions as the OAT rising during climb. Add the surface METAR temp and any tower/PIREP report and you have a poor-man's sounding.
What does an inversion mean for my flight?+
Smooth, stable air below a lid: haze, smoke and pollutants trapped (visibility worst right under the top), possible wind shear across the boundary where the friction-decoupled flow above slides over the calm below, and at night the radiation-inversion fog risk. Climbing through one, expect the ride to change character within a few hundred feet — both ways.
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