The met office has issued a yellow alert warning that thunderstorms, probably accompanied by hail will affect the area.
Locally, the accumulated precipitation may exceed 35 millimetres per hour it said.
The alert is in force from 6 pm on Sunday to 11 am on Monday.
Temperatures tonight will drop to 10 C inland, 12 C on the coasts and 3 C in the higher peaks where ice may form.
Monday and Tuesday will be cloudy at intervals, with scattered showers and isolated thunderstorms that may be accompanied by hail.
On Tuesday there may also be snow in the mountains.
Wednesday will be partly cloudy with possible scattered showers and thunderstorms. Snow or sleet is expected in the higher peaks.
Temperatures will be at the same levels on Monday and Tuesday which is close to average for the time of year, but will drop on Tuesday night and on Wednesday.