FA-71228 / Weather index computation / Member archive

Antecedent precipitation index: chronological ordering · case 03

Backfilled late reports make the API grow instead of decay.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

obs are [day, precip_mm] in any order; process in ascending day order (stable for equal days). Between observations API decays by k^(day gap); several reports on the same day accumulate without decay; negative precipitation is a sensor glitch treated as 0. Return API after each observation, rounded to 0.01.

Why this case matters

Flash-flood guidance and soil wetness models use API as a moisture state.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
basin 15	`[5.0, 35.0, 48.01, 64.27, 59.35, 55.77]`	`[5.0, 4.05, 16.14, 18.08, 48.08, 55.77]`	Failed

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