In a stormy murky night, out of nowhere an intense flash pierces through the sky, swiftly meandering and splitting into innumerable graceful branches, with tips forming over tips, to paint a magnificent drawing. A short while later comes a deafening blast. Rumble! Rumble! Sleeping beauties are all but awakened. This is lightning. This is thunderstorm.

Lightning is a natural wonder, but is also a fast gunman who kills in seconds. Occasionally somebody in Hong Kong gets injured due to lightning strokes. The most effective preventive measure is to seek shelter indoors. It is thus imperative for those who work or have activities outdoor to know when thunderstorm may strike.

In addition to looking out for Thunderstorm Warning and using Location-Specific Lightning Alert Webpage,you may now also refer to the Observatory's new "Hong Kong Lightning Nowcast" service to keep track of thunderstorm development. It makes use of the direction and speed of areas of thundery showers derived from "Short-range Warning of Intense Rainstorms in Localized System (SWIRLS)" along with real-time lightning location data collected by "Lightning Location Information System (LLIS)" to predict where lightning strikes. Through blending observations with forecasts, this service provides lightning nowcast up to one hour ahead at user's actual or selected location, enabling the public to get hold of the development and movement of thundery showers for better precaution.

With the launch of this service, those engaging in outdoor activities are encouraged to refer more often to the Observatory's location specific lightning nowcast. For instance, before hiking one may first draw up a contingency plan with exit routes, then watch out for weather changes and regularly review the chance of thunderstorms in the next couple of hours during the trip. If necessary, he/she may alter the route or cancel the trip immediately to avoid accidents.

To use "Hong Kong Lightning Nowcast" service, one can access the Observatory's mobile website, and then choose "Hong Kong Lightning Nowcast" under "Weather at Your Location" (Figure 1). Alternatively, one may also choose "Automatic Regional Weather Forecast" on the Observatory's website and click on the "lightning" icon (Figure 2). Lightning icons indicate whether there will be lightning within the designated 30-minute period of forecast. A red lightning icon indicates lightning within 10 km, while an amber icon indicates lightning within 15 km. Icons in the second 30-minute forecast period are depicted in hollow shapes to indicate lower certainty of forecast. You may also watch the related "Cool Met Stuff" episode (Chinese only) to better understand the usage of this product.