FA-71291 / Weather index computation / Open access

Pasquill-Gifford stability class: overcast neutral override · case 01

Overcast days receive unstable daytime classes.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The overcast neutral override is applied only at night.

THE FAILURE

The overcast neutral override is applied only at night.

Unsuccessful approach: Applying the override from 7 octas neutralises broken-cloud nights.

Case contract

Wind class: <2, <3, <5, <6, >=6 (index 0..4). 8 octas returns "D" day or night. Day: tables by insolation strong [A,A-B,B,C,C], moderate [A-B,B,B-C,C-D,D], slight [B,C,C,D,D]; unknown insolation returns None. Night: >=4 octas [E,E,D,D,D], <=3 octas [F,F,E,D,D].

Why this case matters

Air-dispersion screening models choose plume spread from the stability class.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(wind_ms, is_day, insolation, octas):
    day = {"strong": ["A", "A-B", "B", "C", "C"],
           "moderate": ["A-B", "B", "B-C", "C-D", "D"],
           "slight": ["B", "C", "C", "D", "D"]}
    thin = ["E", "E", "D", "D", "D"]
    clear = ["F", "F", "E", "D", "D"]
    if octas == 8 and not is_day:
        return "D"
    i = 0 if wind_ms < 2 else 1 if wind_ms < 3 else 2 if wind_ms < 5 else 3 if wind_ms < 6 else 4
    if is_day:
        if insolation not in day:
            return None
        return day[insolation][i]
    return (thin if octas >= 4 else clear)[i]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['wind 1.0 day strong 2 octas', [1.0, True, 'strong', 2], 'A'], ['wind 1.0 day moderate 5 octas', [1.0, True, 'moderate', 5], 'A-B'], ['wind 1.0 day slight 8 octas', [1.0, True, 'slight', 8], 'D'], ['wind 1.0 day slight 3 octas', [1.0, True, 'slight', 3], 'B'], ['wind 1.0 night None 3 octas', [1.0, False, None, 3], 'F'], ['wind 1.0 night None 4 octas', [1.0, False, None, 4], 'E'], ['wind 1.0 night None 8 octas', [1.0, False, None, 8], 'D'], ['wind 1.0 day strong 7 octas', [1.0, True, 'strong', 7], 'A']], [['wind 1.0 day overcast-ish 4 octas', [1.0, True, 'overcast-ish', 4], None], ['wind 1.0 night None 7 octas', [1.0, False, None, 7], 'E'], ['wind 1.0 day strong 7 octas', [1.0, True, 'strong', 7], 'A'], ['wind 1.9 day strong 2 octas', [1.9, True, 'strong', 2], 'A'], ['wind 1.9 day moderate 5 octas', [1.9, True, 'moderate', 5], 'A-B'], ['wind 1.9 day slight 8 octas', [1.9, True, 'slight', 8], 'D'], ['wind 2.9 day slight 8 octas', [2.9, True, 'slight', 8], 'D'], ['wind 2.9 night None 7 octas', [2.9, False, None, 7], 'E']], [['wind 1.0 day slight 8 octas', [1.0, True, 'slight', 8], 'D'], ['wind 1.9 night None 3 octas', [1.9, False, None, 3], 'F'], ['wind 1.9 night None 4 octas', [1.9, False, None, 4], 'E'], ['wind 1.9 night None 8 octas', [1.9, False, None, 8], 'D'], ['wind 1.9 day overcast-ish 4 octas', [1.9, True, 'overcast-ish', 4], None], ['wind 1.9 night None 7 octas', [1.9, False, None, 7], 'E'], ['wind 1.9 day strong 7 octas', [1.9, True, 'strong', 7], 'A'], ['wind 5.9 day strong 7 octas', [5.9, True, 'strong', 7], 'C']], [['wind 1.9 night None 7 octas', [1.9, False, None, 7], 'E'], ['wind 2.0 day moderate 5 octas', [2.0, True, 'moderate', 5], 'B'], ['wind 2.0 day slight 8 octas', [2.0, True, 'slight', 8], 'D'], ['wind 2.0 day slight 3 octas', [2.0, True, 'slight', 3], 'C'], ['wind 2.0 night None 3 octas', [2.0, False, None, 3], 'F'], ['wind 2.0 night None 4 octas', [2.0, False, None, 4], 'E'], ['wind 2.0 night None 8 octas', [2.0, False, None, 8], 'D'], ['wind 2.9 day slight 8 octas', [2.9, True, 'slight', 8], 'D']], [['wind 1.0 day slight 8 octas', [1.0, True, 'slight', 8], 'D'], ['wind 2.0 night None 7 octas', [2.0, False, None, 7], 'E'], ['wind 2.0 day strong 7 octas', [2.0, True, 'strong', 7], 'A-B'], ['wind 2.9 day strong 2 octas', [2.9, True, 'strong', 2], 'A-B'], ['wind 2.9 day moderate 5 octas', [2.9, True, 'moderate', 5], 'B'], ['wind 2.9 day slight 8 octas', [2.9, True, 'slight', 8], 'D'], ['wind 2.9 day slight 3 octas', [2.9, True, 'slight', 3], 'C'], ['wind 2.9 day strong 7 octas', [2.9, True, 'strong', 7], 'A-B']]]
for label, args, expected in fixtures[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
wind 1.0 day strong 2 octas	`A`	`A`	Passed
wind 1.0 day moderate 5 octas	`A-B`	`A-B`	Passed
wind 1.0 day slight 8 octas	`B`	`D`	Failed
wind 1.0 day slight 3 octas	`B`	`B`	Passed
wind 1.0 night None 3 octas	`F`	`F`	Passed
wind 1.0 night None 4 octas	`E`	`E`	Passed
wind 1.0 night None 8 octas	`D`	`D`	Passed
wind 1.0 day strong 7 octas	`A`	`A`	Passed

SHA-256 / 679a70cca1cb748e3829d07015305075a2d4afc9868eb508d0c3e4d2ee495e10

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(wind_ms, is_day, insolation, octas):
    day = {"strong": ["A", "A-B", "B", "C", "C"],
           "moderate": ["A-B", "B", "B-C", "C-D", "D"],
           "slight": ["B", "C", "C", "D", "D"]}
    thin = ["E", "E", "D", "D", "D"]
    clear = ["F", "F", "E", "D", "D"]
    if octas >= 7:
        return "D"
    i = 0 if wind_ms < 2 else 1 if wind_ms < 3 else 2 if wind_ms < 5 else 3 if wind_ms < 6 else 4
    if is_day:
        if insolation not in day:
            return None
        return day[insolation][i]
    return (thin if octas >= 4 else clear)[i]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['wind 1.0 day strong 2 octas', [1.0, True, 'strong', 2], 'A'], ['wind 1.0 day moderate 5 octas', [1.0, True, 'moderate', 5], 'A-B'], ['wind 1.0 day slight 8 octas', [1.0, True, 'slight', 8], 'D'], ['wind 1.0 day slight 3 octas', [1.0, True, 'slight', 3], 'B'], ['wind 1.0 night None 3 octas', [1.0, False, None, 3], 'F'], ['wind 1.0 night None 4 octas', [1.0, False, None, 4], 'E'], ['wind 1.0 night None 8 octas', [1.0, False, None, 8], 'D'], ['wind 1.0 day strong 7 octas', [1.0, True, 'strong', 7], 'A']], [['wind 1.0 day overcast-ish 4 octas', [1.0, True, 'overcast-ish', 4], None], ['wind 1.0 night None 7 octas', [1.0, False, None, 7], 'E'], ['wind 1.0 day strong 7 octas', [1.0, True, 'strong', 7], 'A'], ['wind 1.9 day strong 2 octas', [1.9, True, 'strong', 2], 'A'], ['wind 1.9 day moderate 5 octas', [1.9, True, 'moderate', 5], 'A-B'], ['wind 1.9 day slight 8 octas', [1.9, True, 'slight', 8], 'D'], ['wind 2.9 day slight 8 octas', [2.9, True, 'slight', 8], 'D'], ['wind 2.9 night None 7 octas', [2.9, False, None, 7], 'E']], [['wind 1.0 day slight 8 octas', [1.0, True, 'slight', 8], 'D'], ['wind 1.9 night None 3 octas', [1.9, False, None, 3], 'F'], ['wind 1.9 night None 4 octas', [1.9, False, None, 4], 'E'], ['wind 1.9 night None 8 octas', [1.9, False, None, 8], 'D'], ['wind 1.9 day overcast-ish 4 octas', [1.9, True, 'overcast-ish', 4], None], ['wind 1.9 night None 7 octas', [1.9, False, None, 7], 'E'], ['wind 1.9 day strong 7 octas', [1.9, True, 'strong', 7], 'A'], ['wind 5.9 day strong 7 octas', [5.9, True, 'strong', 7], 'C']], [['wind 1.9 night None 7 octas', [1.9, False, None, 7], 'E'], ['wind 2.0 day moderate 5 octas', [2.0, True, 'moderate', 5], 'B'], ['wind 2.0 day slight 8 octas', [2.0, True, 'slight', 8], 'D'], ['wind 2.0 day slight 3 octas', [2.0, True, 'slight', 3], 'C'], ['wind 2.0 night None 3 octas', [2.0, False, None, 3], 'F'], ['wind 2.0 night None 4 octas', [2.0, False, None, 4], 'E'], ['wind 2.0 night None 8 octas', [2.0, False, None, 8], 'D'], ['wind 2.9 day slight 8 octas', [2.9, True, 'slight', 8], 'D']], [['wind 1.0 day slight 8 octas', [1.0, True, 'slight', 8], 'D'], ['wind 2.0 night None 7 octas', [2.0, False, None, 7], 'E'], ['wind 2.0 day strong 7 octas', [2.0, True, 'strong', 7], 'A-B'], ['wind 2.9 day strong 2 octas', [2.9, True, 'strong', 2], 'A-B'], ['wind 2.9 day moderate 5 octas', [2.9, True, 'moderate', 5], 'B'], ['wind 2.9 day slight 8 octas', [2.9, True, 'slight', 8], 'D'], ['wind 2.9 day slight 3 octas', [2.9, True, 'slight', 3], 'C'], ['wind 2.9 day strong 7 octas', [2.9, True, 'strong', 7], 'A-B']]]
for label, args, expected in fixtures[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
wind 1.0 day strong 2 octas	`A`	`A`	Passed
wind 1.0 day moderate 5 octas	`A-B`	`A-B`	Passed
wind 1.0 day slight 8 octas	`D`	`D`	Passed
wind 1.0 day slight 3 octas	`B`	`B`	Passed
wind 1.0 night None 3 octas	`F`	`F`	Passed
wind 1.0 night None 4 octas	`E`	`E`	Passed
wind 1.0 night None 8 octas	`D`	`D`	Passed
wind 1.0 day strong 7 octas	`D`	`A`	Failed

SHA-256 / a7c4a6b23e3935de3e36b1effe3d8be5d2674a2f68fd4073e8a88d6c887589d0

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 8 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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Verification & scope

Stipulated deterministic teaching model of an operational weather index; coefficients and thresholds are fixed by the contract and no claim of standards conformance is made. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:48:28.420588+00:00.

Case digest / 141b72124cfd2d17deff6da834fc3fdc45cdcd3239c408c03fd21cd4ee02bb59