Storm and thunderstorm communication is an art that requires moderation

At the beginning of August, weather forecasts showed a chain of events that, if realised, would have been very rare. Thunderstorm-susceptible air mass, in which the moisture content of the air was almost record-breaking, was arriving in Finland. At the same time, airstreams in the lower atmosphere were forecasted to be very strong, which made thunderclouds potentially dangerous.

As the weather condition was so rare, the on-call meteorologists of the Finnish Meteorological Institute issued their warnings exceptionally early.

It was known that forecasts covering multiple days would have significant uncertainty, and various uncertainty factors were also highlighted in media communications and interviews. In severe thunderstorm conditions, the location, intensity and extent of thunderstorms may change in a 6–24-hour forecast even if the overall situation remains the same.

When the actual weather conditions differ even slightly from the forecast, the experience of a failed forecast is emphasised due to the small size of thunderclouds. At the beginning of August, anticipated phenomena such as large hail, damaging squalls and flash floods occurred, but they were occurring just outside Finland’s borders, mainly in Estonia and Sweden.

Warning colour guides preparedness

A general challenge in meteorological communications is how to relay information about dangerous weather in such a way that the uncertainty is also communicated in the message. The increasingly common practice is to mark weather and condition warnings in the colours of traffic lights from green to red and present probability information in words or numbers at the same time. The Finnish Meteorological Institute has been applying this principle for about ten years. However, according to our observations, users of the warning service do not always pay sufficient attention to the coloir of the warning.

The increasingly common practice is to mark weather and condition warnings in the colours of traffic lights from green to red.

The particular challenge of storm and thunderstorm communication is to avoid a situation in which ‘the boy cries wolf’ too often and, when the wolf actually appears, no one believes this has happened. This trend could be avoided by making better use of the warnings’ colours.

If a person monitoring the weather starts their own preparedness measures based on orange and red weather warnings, the number of weather conditions requiring preparedness will hardly become a problem. For example, the Finnish Meteorological Institute has issued an orange or red thunderstorm warning to Uusimaa only in three situations in the last five summers. In the Central Finland and Northern Ostrobothnia regions, a similar warning has been issued about ten times. In these situations, an average of 11,000 cloud-to-ground discharges have been observed in Finland per day, which is a significant amount in the Finnish thunderstorm climate.

Yellow warnings are issued significantly more, but in these cases a more accurate monitoring of forecasts and warnings is usually a sufficient measure.

Successful communication and preparedness require cooperation

The sharing of probability and uncertainty information between safety-critical actors has been the norm for a long time, and many intensive users of weather data use weather safety products versatilely in their preparedness processes. In public debate, however, the setting is more complicated.

The Finnish Meteorological Institute formulates warnings and communications to the best of its abilities—naturally with varying degree of success. However, the interest of the general public may be captured by something else than a meteorologist’s uncertainty speculations.

In Finland, the public is generally interested in weather news, and many people want to experience exceptional weather themselves by, for example, taking photographs and videos. Forecasts and warnings are easily interpreted as too certain, and rare weather can be outright expected. Even though it is ultimately good that your own observation site is safe from damages and extreme weather, the situation may still be disappointing.

In Finland, the public is generally interested in weather news.

All in all, successful storm and thunderstorm communication requires skill and moderation from all parties. The source of the message, that is, the Finnish Meteorological Institute, is heavily responsible for producing press releases and warnings as clearly as possible and keeping information about uncertainties as part of the communication. In the future, we must invest even more in the visibility of this information and explaining the uncertainty in the days preceding the storm or thunderstorm. It is also our duty to provide advice and information on how to interpret warnings and how to prepare for future weather.

Whoever interprets this information should pay attention to uncertainties and warning colours, and interpret forecasts and warnings with caution. The core requirement for successful preparedness is a general interest in weather and conditions, and this is something that we are doing excellently with in Finland.

Ari-Juhani Punkka & Anssi Vähämäki

The writers are the head of preparedness and the head of the weather and safety centre at the Finnish Meteorological Institute