Update Friday 11am: Bureau senior forecaster Tom Delamottesays a low pressure system moving over Victoria will bring thunderstorm activity to the state's north and west from Friday afternoon.
"It looks like it will persist right across the weekend once it extends across the state, so particularly on Saturday we will see fairly showery conditions," he said.
"Some isolated thunderstorms could produce some hail, and we are probably most likely to see any storm activity on Saturday afternoon."
Mr Delamotte said rainfall would be hit and miss, but the state's west could receive up to five millimetres on Friday and Saturday.
Thursday: It wasn't quite the record-breaking low maximums experienced in the Mallee, but Horsham's temperature on Wednesday was significantly cold.
The city reached a top of 9.3 degrees.
It Hopetoun, the temperature only reached 6.1 degrees on the same day.
It marked the first time since July 12, 2016 - when the top was 8.7 - that Horsham's mercury didn't rise above 10 degrees at any time in the day.
In Ararat and Stawell, temperatures reached 12.7 and 13.1 degrees respectively.
On Thursday, Bureau of Meteorology senior forecaster Michael Efron said: "Across the northwest we saw extensive fog developing overnight Tuesday into Wednesday. And then without any strong winds the fog and low cloud persisted through the Mallee and Wimmera as well. That actually prevented any sunlight getting through, keeping conditions chilly across the region."
Mr Efron said more cold air and rain was forecast for the weekend, with all Victorian weather districts at risk of storms.
The bureau is predicting two to five millimetres to fall in Horsham on Saturday, with the chance of a thunderstorm in the afternoon and evening.