Can one annual wind rose hide a seasonal siting problem?

The short answer

Yes. An annual wind rose combines different periods, so it can conceal a seasonal change in wind direction that matters to a turbine position. The annual plot remains useful, but a site with seasonal obstacles, seasonal demand or changing flow patterns should also examine the relevant periods separately.

Define the decision-relevant seasons

Choose periods that relate to the site's question: irrigation months, winter operation, tourist occupancy or a vegetation change. Use consistent direction conventions and identify the hours represented by each plot. A season with sparse valid data should not look as well established as one with strong coverage.

Distinguish a rose showing frequency from one showing an energy-related contribution. The direction occurring most often need not provide the greatest useful generation during the period of interest.

Overlay the actual exposure

Place the seasonal directions on the candidate-position plan. A position open to one prevailing sector may be sheltered when the seasonal flow reverses. Examine the relevant obstacles and terrain without assuming that a single annual direction describes every operating month.

If vegetation changes with the season, record the corresponding condition. A correction inferred from a bare-tree photograph should not silently represent leaf-on exposure. Where the effect is material, ask the assessor how the seasonal interpretation is supported.

Use seasonal evidence without overclaiming it

Compare the seasonal resource with demand and practical operating constraints. The preferred position might maximize useful energy in the critical season rather than maximize an unsupported annual headline. Keep that objective explicit when comparing alternatives.

The deliverable should include the annual plot, relevant seasonal plots, their data coverage and the reason each affects the decision. These plots support siting and energy assessment; they do not by themselves verify turbine performance, safe operation or electrical compatibility for the selected system.