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Thunderstorms are primarily local thermal weather phenomena (usually less than 5 miles to sometimes more than 30 miles in diameter), that are caused by either local surface heating , Air Mass Thunderstorms , or by weather systems such as fronts, converging winds, or troughs aloft that force upward motion of the surrounding air. From a surface wind perspective, thunderstorms, regardless of their cause can quickly and substantially modify wind direction and speed. As shown in figure 2.3 below, the wind outflow from the base of a thunderstorm tends to hit the ground a radiate axially from the storm center. This out flow can and often does exceed 50 mph and may contain gusts in front of the storm and opposing winds aloft that create wind shear (wind flowing in opposite directions) near the surface. As thunderstorms move from their initial formation, through the mature stage (as shown) surface wind surrounding the storm changes from updrafts and inflow (at the initial stages) to down flow and outflow at the mature stage. Local thunderstorm generated winds easily overcome most synoptic surface winds as the local temperature/pressure differences often are greater than the larger scale synoptic differences.

Points to Ponder: What happens to accuracy of wind measurement at an airport with a thunderstorm sitting over the middle of airport? How do you measure wind shear?