Hazards associated with Pulse and Multicell Storms
Severe convective hazards produced by storm-scale multicells are less likely to occur than with their supercell counterparts. Given that the deep layer shear is low, the amount of CAPE available to individual updrafts becomes one of the primary predictors for the likelihood and strength of convective hazards. Individual updrafts have relatively short lifetimes which, probabilistically, puts limits on hail growth potential as well as the production of other convective hazards. In particular, the threat of supercell tornadoes in low shear environments is nearly nonexistent.
Damaging Winds
Especially in a strong CAPE environment containing dry layers of ambient air, stronger pulse updrafts can transport a sufficient amount of moisture to higher levels so that, through evaporation into ambient dry air, a cold dense downdraft can lead to damaging winds on the surface. Alternatively, damaging winds are also more likely with multicells that move embedded in uniformly strong but weakly sheared flow by transporting elevated higher-momentum air to the surface in isolated downdrafts. The likelihood and areal extent of damaging winds also increases as multicells grow upscale and develop stronger, larger cold pools.
Large Hail
Hail can grow to large sizes if hail embryos are exposed to supercooled water, especially in the -10°C to -30°C layer, and if the residence time in such a layer is sufficient. In weak shear and high CAPE environments, updrafts can briefly become quite strong and supply the hail growth layer with plenty of supercooled liquid water, but the pulse nature of those updrafts limits the hail residence time, and therefore the hail size. In a probabilistic sense, it is quite unusual to encounter any hail larger than golf balls with pulse severe storms.
Flash Flooding
The rainfall amount received at a point location is driven by the rain rate and the exposure time to that rain rate. While low-shear multicells (pulse storms) can produce bursts of very intense rain, especially in high CAPE environments, the lack of updraft longevity and size limits the flash flood potential. High CAPE environments with weak steering flow (slow moving cells) or ongoing updraft redevelopment over the same locations provides the optimal setup for flash flood generation. More details can be found in Doswell et al. (1996).
Tornadoes
Supercell tornadoes are very unlikely to occur with multicells embedded in weak deep-layer shear. Non-supercell tornadoes, however, are possible in association with weak shear storm-scale multicells. In the early stages of a growing updraft, vertical vorticity embedded in a boundary below can be vertically stretched to create a ground circulation of tornadic strength if the updraft is growing very vigorously and resides over the boundary for some period of time. This requires very steep lapse rates and weak boundary-relative deep layer flow.