Nor'west Arch - Storm over the mountains

In Christchurch we have a fohn weather pattern where the wind comes in off the Tasman Sea, rises over the Southern alps dropping heavy rain, and then blows across the plains, usually bringing warm dry weather to Christchurch,

When the cloud rolls in we get a nor'west arch when the rest of the sky is cloudy, and there is a strip between that cloud and the mountains that is blue. We often get nice sunsets then too.

Today it looked really stormy with rain streamers below the cloud, and it is quite dark.