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WIND SHEAR


METEOROLOGIST JEFF HABY

VERTICAL SPEED AND DIRECTIONAL WIND SHEAR

Strong vertical wind shear is important to severe thunderstorm development. Wind shear influences a storm in potentially several ways:

VERTICAL SPEED SHEAR- Significant increase of wind speed with height

VERTICAL DIRECTIONAL SHEAR- Significant change of wind direction with height

1. A significant increase of wind speed with height will tilt a storm's updraft. This allows the updraft and downdraft to occur in separate regions of the storm the reduces water loading in the updraft. The downdraft will not cut-off the updraft and actually it will even enforce it.

2. Strong upper tropospheric winds evacuates mass from the top of the updraft. This reduces precipitation loading and allows the updraft to sustain itself.

3. Directional shear in the lower troposphere helps iniate the development of a rotating updraft. This is one component that is important to the development of a mesocyclone and the development of tornadogenesis. Strong lower tropospheric winds and directional shear together will generate high values of Helicity and thus this increases the tornado threat when severe storms develop.

4. The shear environment is important in determining the thunderstorm type. See link below:

http://www.theweatherprediction.com/habyhints/275/