Conceptual Model
Strong storm top divergence is used as one of many signatures suggesting a severe thunderstorm. The presence of a significant Storm Top Divergence signature indicates a strong updraft, as the upward velocity in a strong updraft is simply evacuated as outflow at the top of the thunderstorm. The intensity of the divergence is therefore positively correlated to the intensity of the updraft (Witt & Nelson, 1990).
A strong updraft increases the chances of all four severe weather types, especially large hail and damaging winds. A study by Witt and Nelson (1990) derived a useful relationship between maximum storm top divergence and probabilities of maximum hail size (for more see diagnosis tab). Damaging winds are included, as a strong updraft is likely to produce a strong downdraft, especially if large hail is expected.
Determining Thunderstorm Classification
Storm Top Divergence signatures can be found in all three of the storm types listed here. To help determine the classification of the thunderstorm you are observing, use the following flow chart to help diagnose which thunderstorm conceptual model you should consider more closely.
