A splitting storm is a phenomenon when a convective

thunderstorm A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustics, acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorm ...

will separate into two

supercell A supercell is a thunderstorm characterized by the presence of a mesocyclone, a deep, persistently rotating updraft. Due to this, these storms are sometimes referred to as rotating thunderstorms. Of the four classifications of thunderstorms (su ...

s, with one propagating towards the left (the left mover) and the other to the right (the right mover) of the mean

wind shear Wind shear (; also written windshear), sometimes referred to as wind gradient, is a difference in wind speed and/or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical ...

direction across a deep layer of the

troposphere The troposphere is the lowest layer of the atmosphere of Earth. It contains 80% of the total mass of the Atmosphere, planetary atmosphere and 99% of the total mass of water vapor and aerosols, and is where most weather phenomena occur. From the ...

. In most cases, this mean wind shear direction is roughly coincident with the direction of the mean wind. Each resulting cell bears an

updraft In meteorology, an updraft (British English: ''up-draught'') is a small-scale air current, current of rising air, often within a cloud. Overview Vertical drafts, known as updrafts or downdrafts, are localized regions of warm or cool air that mov ...

that rotates opposite of the updraft in the other cell, with the left mover exhibiting a clockwise-rotating updraft and the right mover exhibiting a counterclockwise-rotating updraft. Storm splitting, if it occurs, tends to occur within an hour of the storm's formation. Storm splitting in the presence of large amounts of ambient crosswise

vorticity In continuum mechanics, vorticity is a pseudovector (or axial vector) field that describes the local spinning motion of a continuum near some point (the tendency of something to rotate), as would be seen by an observer located at that point an ...

, as characterized by a straight

hodograph A hodograph is a diagram that gives a vectorial visual representation of the movement of a body or a fluid. It is the locus of one end of a variable vector, with the other end fixed. The position of any plotted data on such a diagram is proporti ...

, produces similarly strong left and right movers. Storm splits also occur in environments where streamwise vorticity is present, as characterized by a more curved hodograph. However in this situation one updraft is highly favored over the other, with the weaker split quickly dissipating; in this case, the lesser favored split may be so weak that the process is not noticeable on

radar imagery Imaging radar is an application of radar which is used to create two-dimensional images, typically of landscapes. Imaging radar provides its light to illuminate an area on the ground and take a picture at radio wavelengths. It uses an antenna and ...

. In the Northern Hemisphere, where hodograph curvature tends to be clockwise, right-moving cells tend to be stronger and more persistent; the opposite is true in the Southern Hemisphere where hodograph curvature tends to be counterclockwise.

Characteristics

Storm splitting was discovered via weather radar in the 1960s. Storm splitting is most favored when the direction of

is aligned with the motion of the storm, a condition known as ''crosswise

'' (via the

right hand rule In mathematics and physics, the right-hand rule is a convention and a mnemonic, utilized to define the orientation of axes in three-dimensional space and to determine the direction of the cross product of two vectors, as well as to establish th ...

, the direction of ambient rotation associated with this vorticity would be perpendicular to the storm motion). Such conditions can be quantified by having low

storm-relative helicity {{Short pages monitor