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.

Description

The level of free convection is the first transition into positive parcel buoyancy above a chosen condensation level.

The level of free convection is the first transition into positive parcel buoyancy above a chosen condensation level. A profile already positive at the search boundary cannot locate the lower transition from those observations.^[1]

When to use LFC Level Free Convection

Use this tool to 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.

Prepare the observed sounding, cloud records or forecast verification data. Check pressure and height coordinates, wind conventions and the stated units.

How to use LFC Level Free Convection and understand its results

Prepare the observed sounding, cloud records or forecast verification data. Check pressure and height coordinates, wind conventions and the stated units.
Enter heightsM, suppliedBuoyancyMPerSecond2, suppliedLclHeightM using the field table and calculation rules, then run the tool.
Read observedLfcFound, observedLfcHeightM, lfcLeftCensored. 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
heightsM	Heights m	list of number	Required
suppliedBuoyancyMPerSecond2	Supplied buoyancy m per second2	list of number	Required
suppliedLclHeightM	Supplied lcl height m	number	Required

Provide increasing heights, aligned buoyancies and an LCL inside coverage and below the profile top. Interpolate the boundary. Positive buoyancy there returns that height with left-censoring true; otherwise find the first strict-positive transition. No observed LFC returns −1 and false; a zero touch alone does not qualify.

LFC = first linearly interpolated crossing from buoyancy ≤0 to buoyancy >0 above LCL

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

Output field	Meaning	Value type
observedLfcFound	Observed lfc found	boolean
observedLfcHeightM	Observed lfc height m	number
lfcLeftCensored	Lfc left censored	boolean

json

{
  "input": {
    "heightsM": [
      0,
      1000,
      2000
    ],
    "suppliedBuoyancyMPerSecond2": [
      -1,
      0,
      1
    ],
    "suppliedLclHeightM": 0
  },
  "output": {
    "observedLfcFound": true,
    "observedLfcHeightM": 1000,
    "lfcLeftCensored": false
  }
}

Limitations and assumptions

Buoyancy and LCL are supplied. There is no profile extrapolation or hidden parcel ascent calculation.

Numeric inputs and returned numeric values must be finite; an unrepresentable returned value produces an error. Numeric lists are limited to 100,000 entries; the rules above may require smaller limits. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors. A successfully returned false flag is an evaluated outcome; its meaning is explained above.

Alternative or Complementary methods

Use EL Equilibrium Level: Locate first upper zero crossing terminating observed positive-buoyancy layer after caller LFC search boundary; retain unobserved EL/right-censored positive layer rather than extrapolating sounding top. For a complementary task, use CAPE Convective Available Potential Energy: Integrate positive portions of caller precomputed virtual parcel/environment buoyancy in observed height window, resolving each linear zero crossing; no hidden parcel lift, full sounding CAPE outside coverage or storm safety.

References

LFC Level Free Convection — tool.io

Similar or alternative tools

EL Equilibrium Level
Locate first upper zero crossing terminating observed positive-buoyancy layer after caller LFC search boundary; retain unobserved EL/right-censored positive layer rather than extrapolating sounding top.
CAPE Convective Available Potential Energy
Integrate positive portions of caller precomputed virtual parcel/environment buoyancy in observed height window, resolving each linear zero crossing; no hidden parcel lift, full sounding CAPE outside coverage or storm safety.