Hazards Associated with MCSs
Damaging Winds
As deep convection grows upscale and its cold pool strengthens over time, the threat of damaging winds becomes the primary convective hazard to consider. In particular, bow echoes and derechoes can be responsible for damaging and destructive straight line winds. Preferred locations for strong surface winds are:
- Along the axis of a descending rear-inflow jet (often the apex of a bowing echo)
- Near stronger reflectivity cores along the leading line of active convection especially if the gust front stays close to that core
Tornadoes
Tornadoes are possible with MCSs, either in the form of supercell tornadoes associated with individual embedded supercells within an MCS, or in the form of mesovortices along the leading edge of a convective line. Preferred location for such mesovortices are near the apex of a bowing core segment and along the poleward side of that apex.
Hail
The hail threat diminishes as deep convection grows upscale and as ambient instability is more quickly consumed by the larger number of updrafts present in an MCS. Embedded severe cells, often found at the end of a convective line or near gaps within that line, are the likeliest places for marginally severe hail to fall.
Flooding
MCSs can be very potent flash flood producers, especially in the following circumstances:
- Slow-moving
- Large in size
- Moving across the same locations for an extended period of time
- When backbuilding
Rather than the instantaneous rainfall rate, it is the exposure time to moderately heavy rain that ultimately drives the flash flood threat. It is advisable in these situations to closely monitor the rainfall accumulations at those locations that have been experiencing rainfall over an extended period of time.