A Status Yellow snow and ice warning has been issued for 11 counties.
The alert for all of Connacht, as well as Cavan, Monaghan, Donegal, Dublin, Louth and Wicklow will become valid from 8pm tonight.
It will last until 10am tomorrow morning.
Met Éireann says it will be icy across all 11 counties, with some outbreaks of snow expected to fall before morning.
Level Yellow.— Met Éireann (@MetEireann) February 12, 2020
There could be further status orange weather warnings on the way as Storm Dennis heads towards Ireland.
Met Éireann says we are in for wet and windy weather from Friday with the worst of the conditions on Sunday.
Counties in the south, west and north west will be hardest hit.
Forecaster Siobhan Ryan says the storm is expected to bring very unsettled weather.
"As of Friday we are going to see a deterioration in our weather and a marked one over this weekend.
"Particularly on Sunday with the highest winds at that point and right through the weekend will be spells of wet weather too."
Met Éireann reckons Storm Dennis could bring similar conditions to Storm Ciara, which battered the country over the last few days.
"At the moment, I would anticipate warnings coming into effect across Ireland.
"It is hard to say just how high the warnings will be but certainly there will be yellows out and possibly some orange in play.
"Really the peak winds will be during Sunday and right throughout there will be sustained winds.
Our Atlantic chart shows precipitation and pressure forecast in 6 hour intervals for the next 7 days.https://t.co/9Giuj4CR5mFebruary 12, 2020
"So another very windy episode on the way later this week and possibly into the beginning of next week too."
Currently, Met Éireann are forecasting a very wet and very windy start to Saturday as Storm Dennis makes its way to Ireland.
There will be rain in all areas with the west getting the heaviest.
Another band of heavy rain will come in on Saturday night accompanied by strong to gale force winds.
Sunday looks to be wet and windy once again with showers turning wintry over high ground.
The west coasts will experience gales to strong gales.
The unsettled weather will continue into next week with Monday and Tuesday remaining wet and windy.
Dennis is the fourth named storm of the 2019-20 season.