Thunderstorm is a shawl in the shape of a right angle isosceles triangle of 100 x 200 cm (altitude x hypothenuse).
It is all over featuring stockinette slip stitch patterns (mosaic) from or inspired by Barbara Walker’s Mosaic Knitting.
The shawl is worked in 2 colours. Be sure to have enough contrast between the chosen colours for the mosaic designs to arise effectively.
This pattern is appropriate for knitters with some experience with slip stitch patterns as well as basic knitting knowledge of k, p, k1tbl, yo.
The instructions are written in detail in five sections and also contain charts for the first three sections of the project.

Many thanks to the testers for their wonderful knits and their useful hints:

Jenipurr
u-wind
woolitron