![]() Thirdly, a series of thunderstorms may sometimes travel or regenerate along a single line, resulting in large amounts of rain in repeated downpours over the same area. Weaker or less organised thunderstorms may also induce flash flooding if they are moving very slowly. An intense thunderstorm can cause flash flooding if the core passes directly overhead. It depends on soil type, presence of vegetation, land slope, saturation from previous rains, and the rainfall rate. The downdraught may be further enhanced by the frictional drag of the precipitation and by strong mid-level winds.įlash flooding is the least predictable thunderstorm event. This cools adjacent air which becomes denser and plummets toward the ground in the downdraught. Inflow of drier air into the mid-levels of the cloud leads to evaporation of precipitation and cloud particles. ![]() These wind squalls are generated as follows. Ragged low clouds often accompany the on-rushing gust front, which usually pushes out ahead of the core region by several kilometres before weakening. These downdraughts will spread out as gusts as they reach the ground, usually inside or along the edge of the rain curtain. Hail is also more common in relatively cooler conditions aloft (less melting on descent) so the tropics rarely experience severe hail.ĭamaging wind gusts will almost always originate from downdraughts originating in the core. Large hail depends directly on updraught strength (and thunderstorm regeneration), which is indicated by a steep back side structure with boiling tops that overshoot the anvil. Once the hail has grown too large to be supported by the updraughts, it falls to the ground. Small stones form and grow as they are swept up and held aloft by the strong air currents. Alternating clear and frosted rings inside the hailstone bring us back a crystalline time capsule from a long, turbulent ride on updraughts and downdraughts reaching speeds of 160 km/h. Hailstones are fascinating ice sculptures which form in the strong updraughts within thunderstorms. There is no absolute relationship between these events and visible thunderstorm features, but a few pointers are relevant. Severe thunderstorms produce large hail, damaging wind, very heavy rainfall and tornadoes. If thunderstorms are forecast for your area, stay alert for severe thunderstorm warnings which may be issued and updated later in the day and, of course, keep a lookout on the sky! What Severe Thunderstorm Events Require Regularly check the radio and the Bureau's website (for local and regional weather forecasts and reports, and monitor the radar and satellite images. Severe weather events may not be common in some areas of Australia but a long history of 'surprises' demonstrates that we cannot take the weather for granted.
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