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Surface-Spread Cloud-Base Approximation

Estimate surface-parcel condensation height from temperature and liquid-water dew point using the FAA convergence method and explicit limits.

Use this result well

Inputs that matter
Surface air temperature (°C), Liquid-water dew point (°C), Sources and assumptions
Output to expect
Surface-spread convective-base estimate
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Surface-spread convective-base estimate

Estimate the lifting-condensation height of a surface parcel from a liquid-water temperature/dew-point spread. Saturation permits zero height. This approximation neither measures an observed cloud ceiling nor handles elevated cloud layers.

Approximate base = 1000 × 1.8 × (T − Td) / 4.4 ft above the parcel starting level, with temperatures in °C; FAA convergence approximation.

Updated: September 2026

Example Scenarios

Inspect the example and its input basis, then substitute your own documented measurements or matched cases.

Surface air temperature (°C): 25Liquid-water dew point (°C): 15

→ 4,090.909091 ft approximate parcel condensation height

Common Mistakes to Avoid

Mixing observation and model inputs

Use the exact units, timestamp, level and measurement or model basis stated by the selected mode. A similar quantity from another instrument or product is not automatically interchangeable.

Treating an illustrative case as a measurement

Replace the example with your own sourced inputs. Retain missing values and method limits, and keep raw source data alongside a saved calculation.

FAQ

Estimate the lifting-condensation height of a surface parcel from a liquid-water temperature/dew-point spread. Saturation permits zero height. This approximation neither measures an observed cloud ceiling nor handles elevated cloud layers.

Retain the station or profile identity, observation or issue/valid time, measurement units, quality flags, source and stated method. Missing values, trace precipitation and known zeros have different meanings.

Save weather case keeps an explicit local record. Copy MD includes current inputs and notes; Download CSV includes the current result breakdown. Keep portable copies separately and retain raw source data.

About Surface-Spread Cloud-Base Approximation

Estimate the lifting-condensation height of a surface parcel from a liquid-water temperature/dew-point spread. Saturation permits zero height. This approximation neither measures an observed cloud ceiling nor handles elevated cloud layers.