Steven Williams was down in Timaru for Christmas 2004, while there a thunderstorm developed on Boxing Day just north of the town. Here is what he had to say:
“An interesting convergence line developed to the north of Timaru from about 5.30pm on boxing day with a dry northwest land breeze converging with a cool moist easterly sea breeze near the coast. An upper cold pool supplied sufficient instability for cb’s to form in what was quite a dry atmosphere. Funnel clouds, hail and lightning (CG’s) were observed within the line. This Canterbury storm would have produced large hail, though much of it would have fallen just off the coast. It was a dry low precip type storm, a classic hail maker”
It looks to of been quite a site with a series of such lovely isolated cumulonimbus clouds in Steven’s photographs. The first formed around 5.30pm as Steven says while a second higher based cell developed around 8pm in the same spot, both storms moving east offshore due to the upper westerly winds. Two funnels developed on the first cell which can be seen in the first and fourth photo below.
A shot here of the higher based cell, Steven saw lightning from it and suggests the precipitation seen falling will be hail.