Cloud Base Height from Spread (quick field rule)

Inspectable records

Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Area

Earth & Space (astronomy, orbital mechanics, meteorology, geology, geodesy, oceanography)

Tranche

tranche-5

Evidence ID

t5-170

Ledger rows

1

No ledger note is attached.

Review findings

The existing honest label 'rule-of-thumb approximation' is appropriate, but the computes description must not state that this is exactly the LCL. Require temperature and dew point in the same unit and require temperature to be at least as high as dew point.

Formula and scope findings

• The formula h(ft) ≈ 400 × (T−Td in °F) is a standard rule-of-thumb estimate for cloud-base height above ground level, but it is not exactly the same as the thermodynamic LCL calculation. The claim 'same as LCL' is therefore potentially misleading and should be changed to 'rough LCL/cloud-base approximation.'
• The formula does not state the required physical constraint T ≥ Td; when Td > T it produces a negative, physically invalid cloud-base height.

Unit assumptions

• T and Td are both actual temperatures in °F; the difference must be calculated in Fahrenheit degrees.
• The output is an approximate height in feet above ground level (AGL), not feet above mean sea level.
• The 400 ft/°F coefficient assumes near-surface atmospheric mixing and typical conditions; it is not a universal exact LCL coefficient.

Boundary hardening

BREAK_CLAIMED · SELF_FLAGGED

The formula produces a negative raw height when dew point exceeds temperature and overflows to Infinity for opposite extreme finite inputs. Both cases should be rejected or explicitly flagged rather than silently returned as ordinary estimates.

Errata and corrections

No applied erratum is attached to this unique-name record.

Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

{
  "inputs": {
    "temperature_f": 70,
    "dew_point_f": 60
  },
  "expected_outputs": {
    "estimated_cloud_base_ft_agl": 4000
  },
  "working": "Spread = T − Td = 70 − 60 = 10 °F. Height ≈ 400 × 10 = 4,000 ft AGL."
}

Related workflows

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json · VERIFIED_CLEAN
• evidence-tranche5/tranche5-results.json
• BOUNDARY_HAZARD_CATALOG.json