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5. Compose a question

Concept

Separate conditions before combining them. Where was a day both at or below freezing and in the coldest fifth of the observed period? Run the shared setup.

Tiny example

cold = (pipe(cube) | v.threshold_state(threshold=0, direction="below")).unwrap()
unusual = (pipe(cube) | v.quantile_state(quantile=0.2, direction="below")).unwrap()
coincidence = (pipe(cold) | v.overlap(unusual)).unwrap()

Explanation

overlap requires exactly aligned coordinates; it does not silently reproject or resample. The relative threshold is local to each cell and this short period, not a definition of an extreme climate event.

Try it / worked example

frequency = (pipe(coincidence) | v.mean(dim="time", keep_dim=False)).unwrap()
frequency.plot()
plt.show()

Read this as the fraction of observed days satisfying both conditions. Do not infer damage or risk from co-occurrence alone.

What to learn next

6. Inspect the result · quantile_state · Working lands vignette