The famous “Bridgewater Jerry” made an appearance on Thursday morning, a spectacular fog phenomenon the Bureau of Meteorology says is most common from late autumn through winter.
BOM meteorologist Matthew Thomas said the Jerry forms when moist air from the Upper Derwent Valley and the Jordan River converge at Bridgewater
Driven by cool overnight katabatic winds (a type of wind which flows downhill with gravity), this combined moisture travels down the Derwent River and moves into Hobart.
According to Mr Thomas, the fog is most common from late autumn through winter, as windier spring conditions usually disrupt its formation
While the upper Derwent regularly experiences fog, it takes specific atmospheric conditions – like the recent high relative humidity over northern Tasmania spilling into the Jordan Valley – for the fog to successfully reach Hobart
Predicting the Jerry’s exact movements remains challenging for meteorologists due to a lack of automatic weather stations in the Jordan Valley to monitor surface conditions, Mr Thomas said.
The Jerry’s formation relies heavily on overnight cloud cover, which acts as a blanket that traps surface heat and inhibits fog.
If skies clear overnight on Thursday the Upper Derwent will likely see fog again on Friday, though there is a significantly lower chance of it extending all the way into Hobart, Mr Thomas said.
Looking ahead at the broader forecast, the state’s South will remain dry in the short term. Showers will primarily affect the North on Friday, before building in the West and North West throughout Saturday.
By Sunday afternoon and evening, a weather trough will push over the state, finally bringing showers to Hobart and the South East.