FA-71204 / Weather index computation / Member archive

K-index and Total Totals: cross totals moisture · case 04

Total Totals ignores low-level moisture.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

K = (T850 - T500) + Td850 - (T700 - Td700); VT = T850 - T500; CT = Td850 - T500; TT = VT + CT. Thunderstorm potential from K: <20 none, <=25 isolated, <=30 widely scattered, <=35 scattered, else numerous. Severe flag "severe possible" when TT >= 50 else "weak". Return [K, TT, potential, flag].

Why this case matters

Convective outlooks use K and TT as quick stability screens.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
sounding 850 18/7 700 3/2 500 -19	`[43, 74, "numerous", "severe possible"]`	`[43, 63, "numerous", "severe possible"]`	Failed

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