By 1200 UTC 31 January, the low was found on the western border between Kentucky and Tennessee continuing to spread moderate to heavy snow into Illinois and Indiana. However, at the surface these effects can be safely neglected. Where D H is the resultant deformation, H is the horizontal divergence and is the angle measured from the axis of dilitation to the potential isotherms, theta. The magnitude of the resultant deformation can be determined from The first term represents the stretching deformation while the second term represents the shear deformation. The effects of horizontal deformation is to promote frontogenesis when the axis of dilatation lies within 45 degrees of the potential isotherms, and to promote frontolysis when the axis of dilatation lies between 45 degrees and 90 degrees of the potential isotherms.
Convergence acts frontogenetically while divergence as frontolytically.
The Q vectors must point in the direction of th elow-level ageostrophic flow towards rising air. Frontogensis by definintion increases the horizontal temperature gradient upsetting the local therm al wind balance. Symmetric instability theory combines the effects of two dynamic instabilities, inertial and convective, that act simultaneously. In the quasi-horizontal plane, the centrifugal force asct to create inertial instability, and in the vertical plane, the gravitational force acts to create convective instability. In this case the banding will orient parallel to the thermal wind.