|CAPE stands for Convective Available Potential Energy. It is a measurement of the amount of engery available to a buoyant parcel of air during the process of convection. CAPE is measured in joules per kilogram (J/kg) The higher the amount the more productive the atmosphere to severe weather i.e. the higher the figure the more unstable the atmosphere is.|
STORM MOTION is the average wind speed in knots a storm will move and the direction the storm will move from. The storm moves slower than the ambient wind speed since a storm has a large mass of water that has to be pushed along. The turbulence within a storm also makes it more difficult to push along. Storms will move more quickly in cases where there is speed shear with height (wind speed increases with height).
The storm motion is given as the compass direction from which the storm will move from. The meteorological compass has 90 degrees being a wind from the east, 180 degrees being a wind from the south, 270 degrees being a wind from the west and 0 degrees / 360 degrees being a wind from the north..
Strong storms will veer (move to the right of the original path of motion) due to storm dynamics.
Storm motion gives insight into which direction supercells and tornadoes will move from on days in which supercell thunderstorms are favorable.
This information was taken in parts from the website of METEOROLOGIST JEFF HABY
|Relative vorticity is a measure of the rotation of fluids about a vertical axis relative to the earth's surface. Colors indicate the strength of relative vorticity, red for positive (counterclockwise rotation) and blue for negative (clockwise rotation) vorticity, respectively.|
|Positive vorticity at the 500 hPa level are often associated with cyclones and troughs in the 500 hPa topography (see right-hand picture).|
Positive Vorticity develops in a wind field with counterclockwise curvature and/or due to shear with higher velocities on the right, as seen in flow direction.
|Negative Vorticity develops in a wind field with clockwise curvature and/or due to shear with higher velocities on the left, as seen in flow direction.|
Negative vorticity at the 500 hPa level is often associated with fair weather and ridges in the 500 hPa topography.
Vorticity is an important measure and used to locate dynamically active zones and fronts. The omega-equation, an equation used to diagnose vertical motion (or the so called omega, in pressure units) links vorticity and vertical motion. It says that:
greater upward velocity occurs where there is greater advection of positive vorticity by the thermal wind
The geostrophic vorticity at the 700 hPa level is often used as a representative value for the omega equation. Now the thermal wind is only a mathematical construct (vector difference between geostrophic winds at two different heights or pressures) and not an actual wind. To examine the thermal wind, thickness maps are needed:
A thickness map between two different pressures (e.g 1000 and 500 hPa) is a measure of the average virtual potential temperature within that layer, where blue is cold and red is warm. As can be seen the thermal wind is parallel to the thickness contours, with cold air to the left in the northern hemisphere. Closer packing of thickness colors indicates a stronger horizontal temperature gradient and thus a stronger thermal wind. By the thermal wind relationship, the horizontal temperature gradient causes the geostrophic wind to change with altitude (how much is shown by a thermal wind vector).
Note that if thickness lines (layer temperature) cross pressure lines, there is a temperature advection (a transport of temperature by the wind. The wind is parallel to pressure lines and stronger if isobars [lines of constant pressure] are closer together). In the thickness map shown above, there is cold air advection over Great Britain.
Greater upward velocity favors clouds and heavier precipitation and that's another good reason to look for vorticity. It may be complicated to evaluate vertical motion from vorticity, but this has historical reasons. If you like it simple examine the plots of vertical velocity.