Weather: 'Dirty ridge' shrouds New Zealand with cloud

A "dirty ridge" of high pressure is creating overcast and cloudy conditions over New Zealand this week.

While the high helps keep things calm and dry, MetService says it also brings plenty of cloud for many western and inland areas - as well as some possible fog too.

"You could say this high is keeping many parts of Aotearoa cloudy, with a blanket of cloud at night keeping temperatures from dropping even lower than the already chilly forecast temperatures," meteorologist Tui McInnes says.

"Meteorologists often refer to this situation as a 'dirty ridge'. The anticyclone effectively traps moisture beneath it, restricting how it can move around in the atmosphere.

"The end result is more persistent cloudy conditions, especially during the morning and evening."

Although New Zealand can expect a mild Autumn week of weather overall, McInnes warns we can expect a few "nippy mornings", with some frosts possible.