The fall in temperature is expected to hit Ireland in the coming days as flooding and rain gives way to severe frost.
When the icy blast hits, AA Roadwatch are warning drivers to allow plenty of time to reach their destination and to de-ice their windscreen -- but not with hot water.
The AA's Arwen Foley told the Herald today that the key to good driving in icy weather are gentle manoeuvres and not braking or accelerating quickly.
Earlier today, motorists were confronted with impassable routes following prolonged heavy rain overnight.
Traffic was reduced to a crawl on a number of main routes in Dublin including the M1 motorway at the Donabate junction, the N32 and at Blake's Cross.
While the rain cleared, strong winds made it feel colder than the temperatures suggested.
"The whole of this week will be cold, with temperatures dropping a degree or so each day," Met Eireann's John Eagleton said today.
"By Thursday, which will be the coldest day, there will only be about three or four degrees during the middle part of the day," he added.
Sub-zero night temperatures will cause severe frost, which will linger through the day.
The overnight flooding caused problems for DART services which only operated between Greystones and Dalkey and Dun Laoghaire and Howth/Malahide because of severe flooding at Sandycove.
Gorey and Rosslare rail services were also affected.
The conditions led to heavy traffic throughout the city, particularly inbound on the Swords Road from before the Whitehall flyover to Drumcondra, on the Phibsborough Road and inbound from Con Colbert Road through to Heuston Station.
Gardai said there was severe flooding from Ballyboughal to Oldtown in North Co Dublin.
AA Roadwatch told drivers to exercise extreme caution, drive with lights on, slow down and increase braking distance.
Meanwhile, England continues to be battered by storms, with two deaths, 800 homes flooded and thousands of motorists rescued.
Forecasters have warned there may be worse to come as bad weather moves northwards.
A 21-year-old woman was killed in Devon after being crushed by a tree and a man died on Thursday after his car became wedged under a bridge in Somerset.