Compare forecast windows by placing the forecast for each candidate crossing period side by side and checking the same four details: wind direction and force, weather, visibility and sea state. Treat the comparison as a planning snapshot rather than a guarantee, because conditions can change quickly and an earlier check may no longer describe the crossing.
Make the comparison like-for-like
Use the same inshore forecast reference for every candidate period and record the following:
| Field | What to record |
|---|---|
| Crossing period | The specific period being considered |
| Wind | Forecast wind direction and force |
| Weather | Forecast weather conditions |
| Visibility | Forecast visibility |
| Sea state | Forecast sea state |
| Changes | Any difference since the previous check |
Keeping the same fields makes the windows easier to compare. A forecast for one area should not be mixed with a forecast for another without making that difference clear.
Compare changes across all four fields
Read across each row instead of relying on one apparently favourable detail. A different wind forecast cannot be cancelled out by clearer visibility, and a change in sea state should remain visible even if the weather entry is unchanged.
If a later forecast check changes any field, update the comparison and repeat the full review. Conditions can change quickly, so an older reading should not be presented as the current one.
What the traveller must still confirm
The cited guidance does not state a universal wind, visibility or sea-state threshold for calling a forecast window acceptable. It also does not promise that conditions will remain unchanged.
Before relying on a window, the traveller should:
- check the current inshore forecast for the intended crossing area and period;
- review any applicable local notices or instructions; and
- repeat the comparison if a forecast detail has changed or is unclear.
The four forecast fields help organise the decision, but they do not replace current information or applicable instructions.