**WHAT ARE THUNDERSTORM WINDS?** Thunderstorm winds are winds that occur during thunderstorms and that can/may cause possible damage depending on the severity. Thunderstorm winds cause more damage and are more frequent than what tornadoes are. The winds can exceed 160km/h (100mp/h). The winds come in many forms, such as squall lines of thunderstorms or in the form of downburst winds but the most frequent is called straight-line wind which is associated with the leading edge of a rain cooled out-flow, called a gust front (usually what the awesome pictures of storms sweeping in) The strong winds are simply air in motion, flowing from high atmospheric pressure to low pressures. Many factors contribute to damaging surface winds - as precipitation begins to fall it drags air with it, this precipitation drag initiates a downdraft - which is intensified by evaporative cooling as dry air from the storms edge can mix with the cloudy air in a storm, which can make it hazardous to air craft. Some other strong winds that are aloft are carried down with the downdraft by a process called momentum transfer which leads to rapid downward rush of air that impacts the ground and is forced to spread out causing gusty to damaging winds. There is a wind force scale known as the Beaufort scale which provides a description of wind speed based on sea conditions. There are 17 levels in the Beaufort scale that are calculated over a 10-minute sustained wind speed (knots) (Knots > Kmph = 1 knot = 1.85km/ph) Beaufort Scale (General wind classifications) 0 (120 knots) - Cyclonic/Hurricane Australian Cyclone Classifications using Beaufort Scale (Australian Region/South Pacific) Level 0 to 7 [Tropical Low/Tropical Depression] Level 8 & 9 [Tropical Cyclone 1) Level 10 & 11 [Tropical Cyclone 2] Level 12 & 13 [Severe Tropical Cyclone 3] Level 14 to 16 [Severe Tropical Cyclone 4] Level 17 [Severe Tropical Cyclone 5] There is also another scale, called the Enhanced Fujita Scale (EF scale) which relate to tornadoes. EF0 - (105-137kmph) - Minor to no damage. [Possible damage to gutters - branches broken off trees, etc] EF1 - (138-178kmph) - Moderate damage. [Roofs severely stripped, loss of exterior doors, broken windows/glass] EF2 - (179-218kmph) - Considerable damage. [Roofs torn off well constructed homes, trees up rooted, cars lifted off ground] EF3 - (219-266kmph) - Severe damage. [Stories of well constructed homes destroyed, severe damage to large buildings, trains overturned.] EF4 - (267-322kmph) - Extreme damage. [Well constructed homes completely leveled, cars and other large objects thrown about.] EF5 - (>322kmph) - Total destruction. [Well built homes destroyed/leveled, steel reinforced concrete structures critically damage, tall buildings collapse or severe damage.] **How to stay safe in thunderstorms with strong/extreme winds** --- You should maintain an emergency pack with a battery powered torch and radio, and tools for emergency repair and food supplies, first aid, blankets and extra clothing, keep your car fuel tank full in case petrol stations close down after a storm. If a building:- Stay inside with doors and windows shut and stay away from windows and doors and exterior walls. Go to a small interior room or stairwell on the lowest floor of the building (bathrooms are usually best choice) If possible crouch under heavy furniture and protect your head with a cushion or mattress. If outside:- Seek shelter in a building (not a car or caravan) immediately. If no shelter is available, lie flat in low dry spot (ravine or ditch) or under a low bridge. Keep alert for flash floods. Protect your head. As a last resort, hang on tightly to the base of a shrub or small tree.
Posted on: Thu, 27 Nov 2014 11:13:27 +0000
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