Risk management is so important for project success that the Project Management Body of Knowledge uses an entire chapter to cover the topic. Construction work must often be performed under the influence of external factors, including the weather. Contractors must suspend any activity that cannot be completed safely when weather conditions are unfavorable.

The weather cannot be predicted with 100% accuracy, and conditions can change in seconds. There are also site-specific conditions that create microclimates, such as terrain features and surrounding constructions. Weather risks can only be managed effectively with the direct measurement of meteorological conditions.

Understanding the Limitations of Weather Forecasts

There are three types of weather data that must be considered in construction management:

• Historical data, which is useful when planning projects that will be built over several months or years;
• Weather forecasts, which are suitable for short-term planning, such as scheduling weekly activities; and
• Direct measurements from a weather monitoring system, to detect sudden changes and take quick decisions.

Some projects are managed based on weather forecasts, which is much better than ignoring the weather completely. However, forecasts have an important limitation: they describe the overall conditions that can be expected for a region, but they cannot predict short-term changes and microclimates. These are precisely the two most dangerous factors in a construction project.

• Sending materials and other objects flying at high speed;
• Causing construction workers to lose their balance;
• Damaging building elements that are still a work in progress; and
• Gusts are particularly dangerous when tower cranes are involved. Lifting operations should be suspended if the weather becomes unfavorable since gusts can easily destabilize a crane.

Weather forecasts provide the maximum wind speed that can be expected, but there is no way to tell exactly when a gust will occur. The only solution is monitoring the wind speed continuously, and reacting quickly when it starts to increase.

A common rule of thumb to anticipate dangerous winds is assuming that gusts have twice the average wind speed. For instance, if the anemometer measures 15 mph, gusts will have a speed of around 30 mph. In projects that use tower cranes, the maximum wind speed for safe operation should be checked with the manufacturer. However, lifts are normally suspended when the wind speed approaches 20 mph, to avoid 40 mph gusts.

Importance of Wind Direction and Turbulence

Measuring wind direction is also very important since risks change depending on the direction from which the wind blows. In the case of tower cranes, the mechanical loading effects of the wind are determined by speed and direction. For example, wind blowing from behind a crane tends to push the load away. This increases the swing radius, causing a higher bending load on the boom.

Another metric that is commonly overlooked is wind turbulence, which is commonly confused with speed. Turbulence describes if the wind is steady or constantly changing: higher turbulence means that the wind is more chaotic. Even if the average wind speed has remained constant, an increase in turbulence can create additional risks.

Additional Weather Factors to Consider in Construction

Most weather risks in construction are related to the wind, but there are other factors that must be kept under watch. Extreme temperatures are dangerous for workers, and they can limit the ability to concentrate. Very low temperature also threatens equipment, since it reduces the loading capacity of many components.

Fog, rain and any other factors that limit visibility should also be considered. Construction workers must be fully aware of their surroundings to work safely, and low visibility makes accidents more likely. When strong winds occur along with low visibility, the risks are increased.

To be useful in construction management, a weather monitoring system must have remote connectivity. Weather monitoring is also useful if a missed deadline must be justified with the client: the data gathered provides evidence that construction could not proceed faster.