Weather Events

Significant weather events are related to the occurrence of mesoscale convective systems. In Southeastern South America (SESA), where these systems are related to the presence of SALLJs, the principal weather events are heavy precipitation, gusts, hail, lightning, and tornadoes.


Parameter Description
Precipitation
  • Heavy rain showers in the convective part of the MCS and local flash floods.
  • Hail showers accompanied by heavy rain episodes.
  • Extended precipitation from stratiform clouds behind the leading region of an elongated MCS. This can produce floods if the convective system moves slowly.
Temperature
  • Sharp drop possible associated with the passage of outflow boundaries
Wind (incl. gusts)
  • Severe wind gusts (> 25 m/s) and downbursts or microbursts
  • Tornadoes
  • Strong shear in the middle and upper troposphere near jetstreams and resulting aviation turbulence issues. This is shown in the above diagram in the case of a sharp upper trough.
Lightning
  • High flash rate in the convective part of the MCS.
Other relevant information
  • The most intense weather events (heavy rain, dangerous winds and hail) occur to the north and northwest of the MCS's center during its early stages of development.
  • Extended precipitation from stratiform clouds dominates the center region of mature MCSs.


The following schemes show the main three types of MCS in SESA and the location of the significant weather events:


Squall line
10 January 2001/05.25 UTC - TRMM/VIRS IR 10.8 image, LIS lightning location (black dots) and TMI rain rate (blue contours).


Symmetric System
21 December 2003/08.22 UTC - TRMM/VIRS IR 10.8 image, LIS lightning location (black dots) and TMI rain rate (blue contours).


MCS with embedded supercells
15 November 2006/23.36 UTC - TRMM/VIRS IR 10.8 image, LIS lightning location (black dots) and TMI rain rate (blue contours).