Frost dates can be downscaled by applying a standard lapse rate to elevation.
This claim doesn’t hold up. Refuted A person has checked it against its sources.
The planner won’t plan around this claim. What is known instead is below.
What is actually known
On clear still nights, which are exactly the nights that produce radiative frost, cold dense air drains downhill and pools. The valley floor is colder than the slope above it. A standard lapse rate predicts the opposite and makes frost dates worse in the terrain where accuracy matters most. That is why the planner uses PRISM, whose model accounts for temperature inversions, and never a lapse rate.
The evidence
Evidence: checked against 1 source in the research-based literature.
The source
Radiation frosts occur when the heat that has been stored in the upper soil surfaces is radiated back into the atmosphere at night. Wind speeds are generally low, and an inversion usually develops with temperatures near the ground surface falling to, or below
How this rule has changed
Every change is dated, newest first. The full record, with each reason, is in the data download.
- Sources updated
- Wording made clearer
- A person read the sources and confirmed it
- Added to the rules
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Milpa Gardens. “Frost dates can be downscaled by applying a standard lapse rate to elevation.” Evidence grade: Refuted. https://milpa.garden/rules/frost-dates-can-be-downscaled-applying-standard/
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How we grade evidence
- Well established
- The rule names its mechanism and is settled, by sources a person has read and checked or by plain arithmetic and geometry.
- Promising
- The mechanism is named and the literature backs it. A few questions are still open.
- A good hunch
- Plausible by its mechanism, but field studies are thin, so treat it as a lean.
- Contested
- The evidence points both ways, or no study has tested it, so the planner does not enforce it.
- Refuted
- The claim did not survive its sources. It is kept so the folklore can be answered.