Horticulture, glasshouse and polytunnel growers: the wind call, at your height

As a grower or production manager, you regularly decide on opening or closing vents and side-rolls. You also secure polythene covers, especially before gales. This decision-making happens daily, often several times a day during the autumn gale season from October to March.

Making the wrong call can lead to significant issues. If polythene is lifted or a tunnel is lost, you face crop loss within the structure. This also leads to downtime, impacting your production schedule. There is also the risk of staff injury when re-covering structures in high winds.

Your decisions are based on the gust speed at tunnel height and the wind direction relative to your tunnel orientation. Your limit for these actions is typically set by the structure manufacturer's rating and your own experience as a grower. The instrument helps you make these calls by providing relevant wind data.

While the instrument provides data and probabilities, the final decision remains yours. It supports your judgment, but it does not approve or certify any action. Your own document, your limit, and the competent person on site always make the call.

For horticulture, glasshouse, and polytunnel operations, the critical wind measurement is the gust speed at your tunnel height. This is often around 4 metres, but you can set the working height in the instrument to match your specific structure. The instrument interpolates wind data to your exact working height, showing gusts alongside the mean wind speed.

Knowing the gust speed at your working height is more important than general wind forecasts. A sustained mean wind might be manageable, but a sudden gust can lift covers or damage structures. The instrument provides wind data at 10, 80, 120, and 180 metres, and then interpolates to your specified height.

Your operational limit for wind speed is not a fixed, universal figure. It is set by your structure manufacturer's specifications and your practical experience. This limit is what you enter into the instrument to tailor its alerts and probabilities to your specific needs. The instrument does not set this limit for you.

Heights below 10 metres are extrapolated below the lowest model level. This means the data for heights like 4 metres is derived from higher-level models. This extrapolation is clearly badged in the instrument.

The instrument shows the probability of wind gust exceeding your set limit for each hour. This is expressed as P(above your limit) and is computed from ensemble members. An ensemble forecast runs the weather model multiple times with slightly different starting conditions, giving a range of possible outcomes.

If the instrument shows a 20 per cent chance of exceeding your limit, it means two out of ten ensemble members predict winds above your limit. At this level, you might monitor the situation more closely but not necessarily take immediate action, depending on the cost of a wrong call for your operation.

When the probability reaches 50 per cent, five out of ten ensemble members predict winds above your limit. This suggests a higher risk, and you might start preparing to secure structures, such as checking tie-downs or ensuring staff are ready for action. This is a point where models show significant disagreement.

An 80 per cent probability means eight out of ten ensemble members predict winds above your limit. At this stage, the models largely agree on strong gusts, and you would likely implement your full securing procedures, such as closing vents, lowering side-rolls, and ensuring all polythene is firmly battened down to prevent damage or crop loss. The Agreement Spine feature shows where the models agree and disagree.

This is an example of how you might use the instrument during a typical day, especially during the autumn gale season:

• 06:00: Your morning brief (Pro plan) arrives, showing a 20 per cent chance of gusts above your 4 m limit by 18:00. You note this but continue with your planned morning tasks.
• 09:00: You check the instrument. The P(above your limit) has risen to 40 per cent for 18:00. The Agreement Spine shows some models are now predicting stronger gusts. You decide to have your team check all polythene fastenings during their morning rounds.
• 12:00: Another check shows the P(above your limit) is now 60 per cent for 18:00, with more ensemble members predicting high gusts. You issue a directive to prepare for securing the polytunnels, ensuring all side-rolls are ready to be lowered.
• 15:00: The probability for 18:00 is now 80 per cent. The models largely agree on strong gusts. You make the call to fully secure all polytunnels, closing vents and lowering side-rolls. You ensure all staff are aware of the increased wind risk.
• 18:00: Gusts reach near your limit, as forecast. Your structures are secured, and no damage occurs. You record the forecast, your limit, and your decision for future reference.

Your operational limit for wind speed is a critical factor in protecting your horticultural structures. This limit is not set by the instrument; it comes directly from your own documentation. This could be the manufacturer's specifications for your glasshouses or polytunnels, or it might be a limit you have established based on years of experience on your site.

The instrument allows you to input this specific limit. For example, if your polytunnel manufacturer states a maximum gust speed of 80 km/h, you would enter 80 into the instrument. This personalises the alerts and probability calculations to your exact operational requirements.

When you set up the instrument, you specify your working height. For growers, this is typically the height of your tunnel, often around 4 metres. The instrument then provides interpolated wind data at this specific height, showing gusts beside the mean wind speed.

By using your own documented limit and working height, the instrument provides relevant information for your decisions on opening or closing vents, securing polythene, or managing other wind-sensitive tasks. It ensures the data you see is directly applicable to your specific structures and operations.

The instrument maintains a dated record page of what was forecast, what was observed, the limit you used, and the call you made. This record is important for several reasons in horticulture.

Firstly, it provides a clear log of your decision-making process. If a structure is damaged during a high-wind event, you have a record of the forecast you received and the actions you took based on that information. This can be useful for internal reviews or discussions with insurers.

Secondly, this historical data helps you refine your operational limits and responses over time. By comparing past forecasts with actual observed conditions and the outcomes on your site, you can gain a better understanding of how different wind speeds impact your specific structures. This allows you to adjust your limits or protocols for future events.

Finally, the record serves as a learning tool. You can review past events, especially during the challenging autumn gale season, to identify patterns or improve your preparedness for similar conditions. It allows you to prove against past events, such as specific storm gusts at your site, how your decisions were informed by the available data.

Horticulture in Ireland faces particular challenges due to its Atlantic exposure, especially during the storm season from October to March. This period brings frequent gales, making wind management a daily concern for growers with glasshouses and polytunnels.

Met Éireann, as the national forecaster, provides general weather forecasts, but the instrument offers site-specific wind data at your working height. This level of detail is necessary for managing structures that are highly susceptible to wind damage.

Decisions on opening or closing vents, securing polythene, and planning operations like spraying or pollination need to account for sudden changes in wind speed and direction. The instrument helps you anticipate these conditions, particularly the critical gust figures at tunnel height.

Spring is also a key time for tunnel erection, and accurate wind data is essential for planning these activities efficiently. The instrument supports these seasonal demands by providing detailed, localised wind information, helping growers protect their investments and maintain production.