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 TERMINOLOGY FOR THE STORM OF THE MONTH PAGES

Here are a few general definitions in nontechnical terms that you might read about while viewing our Storm of the Month selections:


Algorithm - a computer program analysis that helps interpret the raw radar data more efficiently.

Cape - a measure of available potential bouyancy energy from a given vertical temperature/dewpoint profile(balloon sounding data) in Joules/kg units

Composite Reflectivity - a plane view of the maximum intensity reflectivity returns in the column of air directly above a particular location on the ground.

Cross Section(Reflectivity)- a vertical slice of reflectivity returns taken through a section of a storm used for detecting certain characteristics.

Decibels(dBz) - a measure of the energy returned to the radar by precipitation particles after they are hit with electromagnetic radiation.

Doppler Velocity(Base) - a measure of the frequency shift between pulses of electromagnetic radiation after the pulses impact precipitation particles and the energy returns to the radar. Normal interpretation allows 'to' and 'from' speeds(knots) to be determined along each radial extending out from the radar(Greens usually toward the radar, and Reds are away from the radar).

Echo Tops - a plane view of the maximum height at which reflectivity energy returns were received back to the radar for each point on the ground.

EHI - an Energy Helicity Index combining Capes with low level Helicities(usually in a range of 1 to 6 units, 6 being more intense).

Helicity - a measure of the wind shear factor due to speed and directional differences through a defined layer in a vertical wind profile(usually in a range of 0 to 600 m*m/s*s, 600 being stronger).

MSI - a Mesocyclone Strength Index algorithm that gauges the intensity and overall organization of a radar-identified Mesocyclone(normally 0-6000, 6000 being more intense). Along with the Meso Rank factor(normally 1-15, 15 being more intense), these two indexes give us a good idea how threatening the rotating thunderstorm might be.

Storm Relative Velocity - a measure of the Base Velocity data with the Storm motion speed and direction added to each data point. This image greatly enhances the detection of velocity couplets and other shears.

Vertically Integrated Liquid (VIL) - a measure of liquid water content in each column of data above a certain location(grid-based) or in association with a certain identified storm(cell-based) that contains reflectivity returns and expressed in kilograms per square meter. Higher values usually mean that hail is occurring in the storm. These values have variable meaning based on the environmental airmass in which they occur(daily & seasonally affected). Normally, the more significant values vary from 40kg/m*m in winter to 65kg/m*m in summer.

For more detailed information on theF-Scale.

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