Met Eireann has issued an unusual weather warning for six counties.
Ireland is used to seeing alerts for rain and wind, but a fog warning will be in place overnight.
The Status Yellow alert is for Dublin, Kildare, Longford, Meath, Offaly and Westmeath.
It is in place from 9pm on Saturday until 12 noon on Sunday.
Forecasters say it could lead to hazardous travelling conditions.
Met Eireann say: “Areas of dense fog will form tonight in near calm conditions and will be slow to lift on Sunday morning.
“Poor visibility will lead to hazardous travelling conditions.”
It comes as high pressure continues to bring settled conditions for Ireland, which is due to last until the early days of next week.
However the weather is due to become unsettled mid-week with the possibility of colder weather hitting for Christmas.
Some weather models - which are subject to change - show heavy snow blanketing parts of Ireland on December 25.
