surface temperature is projected to rise throughout the 21st century under all assessed emission scenarios [2]. Such global warming directly affects precipitations because the water holding capacity of air increases by about 7% per degree C [3] that leads to more water vapor being retained in the atmosphere. Storms, thunderstorms, extra-tropical rains, snow, are therefore supplied with more moisture and produce more extreme precipitation events. Such events are observed to be widely occurring, even where total precipitation is decreasing, and, in combination with rapid snow melting, they increases the risk of flooding. Given that floods are usually weather-induced, meteorological services provide local authorities with a periodical weather and flood hazard forecast that contains an encoded alert level on a predetermined set of geographical areas. The alert level is used to trigger actions according to a predefined
Prevailing road surface conditions, the grip between tyres and the road surface, strongly correlate with traffic accident rate. Surface friction is reduced especially during snowfall or icing. Friction observations derived from Vaisala's optical DSC111 sensors, operated during two winter seasons (2007/2008, 2008/2009) at several Finnish roadside stations have been used. The devices measure the depth of water, snow and ice on the road surface and also produce an estimate of prevailing friction. The observations have been used to develop statistical equations to model road surface friction. The model has been evaluated against an independent dataset from winter 2009/2010. The goal thereafter was to integrate the scheme into the road weather service of the Finnish Meteorological Institute by combining background information from a road weather model with the derived statistical equations.
During the morning rush hours of 17 March 2005, a band of intense snowfall affected the Helsinki metropolitan area in southern Finland. The event caused severe pile-ups on the highways, with almost 300 crashed cars, the deaths of three people and more than 60 people injured. The snowfall was soon followed by freezing drizzle. Some of the media later blamed this as being responsible for the unprecedented number and severity of the accidents that had occurred. However, the official inquiry came to the conclusion that the pile-ups had been caused by the very poor visibility due to intense snowfall and excessive driving speeds combined with reduced road surface friction. In this study, these two viewpoints are investigated, by using high time-resolution dual-polarization radar observations to analyse the changes in intensity and form of the precipitation leading to the event. The radar data were particularly useful in supplementing weather observations.
A total of 13 commercial airplanes were struck by lightning in October (10 in 1 day) and December (3 on 3 separate days) 2011 in the main Finnish Helsinki–Vantaa airport. The number of lightning-struck airplanes is extremely large, considering the time of year and the small number of flashes by the storms. This paper indicates the characteristics of these cases regarding the synoptic situation as well as their forecasting. There were remarkable differences in the operational models; the high-resolution nonhydrostatic model was superior in predicting the convective nature of the event compared to the coarser-resolution hydrostatic model. The interview of the pilots of the struck airplanes shows that the pilots did not receive detailed information to avoid the situation; also, the lightning strike affected the pilots, even causing temporary loss of sight and hearing. Luckily, no fatalities or severe damage to the airplanes occurred. The most interesting case is 19 October 2011; during this single day, a total of 10 airplanes were struck. The analysis suggests that a major cause for the large number of struck airplanes is that the planes took off directly into the convective core of the storm and the planes initialized the flashes themselves. However, the time of the year, the near position of the storm area relative to the takeoff path, and the necessity to use only a certain takeoff path because of the direction of wind makes the convective scenario difficult to predict and avoid. The pilots have expressed interest in receiving training for these cold-season thunderstorms.
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