Lifting Condensation Level Height

Compute named Bolton LCL temperature then caller dry-adiabatic pressure/height for a surface parcel; not existing dewpoint-spread fog proxy, inferred environmental cloud base or moist-convective ascent.

Description

The lifting condensation level is the modeled point where an unsaturated air parcel becomes saturated during dry ascent.

The lifting condensation level is the modeled point where an unsaturated air parcel becomes saturated during dry ascent. Its approximate temperature, pressure and height depend on the starting temperature, dew point and pressure.^[1]

When to use Lifting Condensation Level Height

Use this tool to compute named Bolton LCL temperature then caller dry-adiabatic pressure/height for a surface parcel; not existing dewpoint-spread fog proxy, inferred environmental cloud base or moist-convective ascent.

Prepare the climate observations and any independently chosen thresholds or model parameters. Confirm units, daily coverage, time order and the intended seasonal window.

How to use Lifting Condensation Level Height and understand its results

Prepare the climate observations and any independently chosen thresholds or model parameters. Confirm units, daily coverage, time order and the intended seasonal window.
Enter parcelTemperatureK, parcelDewpointK, surfacePressureHpa, dryGasConstantJPerKgK, dryHeatCapacityJPerKgK, gravityMPerSecondSquared using the field table and calculation rules, then run the tool.
Read boltonLclTemperatureK, dryAdiabaticLclPressureHpa, dryAdiabaticLclHeightM. The explanation below defines the units, signs, ordering and any flags or placeholder values.
If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.

Input field	Meaning	Value type; see rules below	Requirement
parcelTemperatureK	Parcel temperature k	number	Required
parcelDewpointK	Parcel dewpoint k	number	Required
surfacePressureHpa	Surface pressure hPa	number	Required
dryGasConstantJPerKgK	Dry gas constant j per kg k	number	Required
dryHeatCapacityJPerKgK	Dry heat capacity j per kg k	number	Required
gravityMPerSecondSquared	Gravity m per second squared	number	Required

Enter positive temperature and dew point in kelvin, with dew point greater than 56 K and no warmer than temperature, plus positive surface pressure, gas constant, specific heat and gravity. The tool calculates the approximate LCL temperature, then pressure in the surface-pressure unit and height in m from the dry-adiabatic relations. Saturated initial air, T = Td, returns its starting temperature and pressure with height zero.

TLCL = {1/(Td−56) + ln(T/Td)/800}⁻¹ + 56; PLCL = P(TLCL/T)^(cp/Rd); zLCL = cp(T−TLCL)/g

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
boltonLclTemperatureK	Bolton lcl temperature k	number
dryAdiabaticLclPressureHpa	Dry adiabatic lcl pressure hPa	number
dryAdiabaticLclHeightM	Dry adiabatic lcl height m	number

json

{
  "input": {
    "parcelTemperatureK": 300,
    "parcelDewpointK": 300,
    "surfacePressureHpa": 1000,
    "dryGasConstantJPerKgK": 287,
    "dryHeatCapacityJPerKgK": 1004,
    "gravityMPerSecondSquared": 9.81
  },
  "output": {
    "boltonLclTemperatureK": 300,
    "dryAdiabaticLclPressureHpa": 1000,
    "dryAdiabaticLclHeightM": 0
  }
}

Limitations and assumptions

This is an approximate parcel calculation, not an observed cloud-base measurement. It assumes the supplied constants and dry ascent below saturation; it does not model entrainment, terrain, a moist ascent above the LCL or whether visible clouds form.

Numeric inputs and returned numeric values must be finite; an unrepresentable returned value produces an error. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use Showalter Index: Estimate Showalter 850-hPa-origin parcel index via explicit supplied LCL and caller piecewise dry/moist lapse approximation; differs from supplied surface-parcel lifted index, not a full pseudoadiabatic solver or validated thunder forecast. For a complementary task, use LFC Level Free Convection: Find first strict-positive buoyancy transition at/above caller LCL in supplied linear sounding, with left-censoring or explicit no-observed-LFC sentinel; touches without positive buoyancy are not free convection.

References

Lifting Condensation Level Height — tool.io

Similar or alternative tools

Showalter Index
Estimate Showalter 850-hPa-origin parcel index via explicit supplied LCL and caller piecewise dry/moist lapse approximation; differs from supplied surface-parcel lifted index, not a full pseudoadiabatic solver or validated thunder forecast.
LFC Level Free Convection
Find first strict-positive buoyancy transition at/above caller LCL in supplied linear sounding, with left-censoring or explicit no-observed-LFC sentinel; touches without positive buoyancy are not free convection.