Predicting the Movement of Mesoscale Convective Complexes

Abstract

A procedure for operationally predicting the movement of the mesobeta-scale convective elements responsible for the heavy rain in mesoscale convective complexes is presented. The procedure is based on the well-known concepts that the motion of convective systems can be considered the sum of an advective component, given by the mean motion of the cells composing the system, and a propagation component, defined by the rate and location of new cell formation relative to existing cells. These concepts and the forecast procedure are examined using 103 mesoscale convective systems, 99 of which are mesoscale convective complexes. It is found that the advective component of the convective systems is well correlated to the mean flow in the cloud layer. Similarly, the propagation component is shown to be directly proportional (but opposite in sign) and well correlated to the speed and direction of the low-level jet. Correlation coefficients between forecast and observed values for the speed and direction of the mesobeta-scale convective elements are 0.80 and 0.78, respectively. Mean absolute errors of the speed and direction are 2.0 m s 01 and 17Њ. These errors are sufficiently small so that the forecast path of the centroid of the mesobeta-scale elements would be well within the heavy rain swath of the typical mesoscale convective complex.

Characteristics of mesoscale-convective-system-produced extreme rainfall over southeastern South Korea: 7 July 2009

“…11), while the mid-level mean wind direction is approximately 229 • (16 m s −1 ) between 3 and 7 km. This is consistent with the results from previous studies (Corfidi et al, 1996;Corfidi, 2003). The propagation vector (forward 225 • , 7 m s −1 ) was generally oriented opposite to the mean wind and cell motion.…”

“…Strong shear reversal has been documented in back-building MCS events by Schumacher and Johnson (2008). Corfidi et al (1996) and Corfidi (2003) developed a simple vector technique to predict MCS motion using advection and propagation. The propagation component is defined as the rate of change of location of new cell development relative to existing cells (Chappell, 1986;Doswell et al, 1996).…”

The Effects of an Active Phase of the Madden-Julian Oscillation on the Extreme Precipitation Event over Western Java Island in January 2013

“…Java Island. It has been reported that the propagation of mesoscale convective complexes (MCSs) is basically determined by the mean flow of the cloudlayer (850−300 hPa) and development of new convective cells (Corfidi et al 1996). In the midlatitude MCSs, new cell formation is usually opposite in direction to that in the lowlevel (850 hPa) jet but equal in magnitude.…”

Belgium´s record rainfall event: a look back at the Eupen flash flood of 1953

“…A fast low-level supply of very moist air, such as can be provided by a low-level jet, may also focus heavy convective rainfall across a particular area for a longer time by offsetting the motion of the cells due to upwind propagation, as described in Corfidi et al (1996). Thus, a moist and sufficiently unstable environment exhibiting high values of mean relative humidity, very large values of PW, relatively weak steering flow and the potential for training or upwindpropagating cells tends to be associated with a higher likelihood of flash flood events.…”