The Easter long weekend will commence with an outbreak of dangerous weather, with two separate thunderstorm bands set to pummel much of eastern Australia.
Good Friday will have the feel of summer as warm and humid northerly winds create the perfect environment for thunderstorms, which should form in a broad region from about Rockhampton down to Victoria, including around Sydney, Brisbane, and Canberra.
Melbourne can also expect wet weather, but without the risk of severe storms.
Current indications show two lines of storms will develop.
The first will form early in the morning west of the ranges then sweep towards the coast by midday.
The second, more intense band, will follow through the afternoon and is likely to include the two most severe storm types; supercells and squall lines.
Supercells are long-lasting, rotating cells responsible for the majority of damage from thunderstorms.
They are capable of producing large hail stones, winds in excess of 125 kilometres per hour which can fell trees and cause property damage, and, flash flooding.
They are also capable of causing tornadoes, although Australia only averages about 10 to 20 tornadoes per year, well below the US's 1,200.
Squall lines are less powerful than supercells but often impact a larger region.
They occur when multiple storm cells develop in a line and merge together to form an advancing storm front hundreds of kilometres long.
Supercells and squall lines are both likely on Friday due to a powerful jetstream kilometres over eastern Australia, which is carrying winds up to 200kph.
A jetstream is a rapid river of wind about 10 kilometres above the ground and is one the major drivers of weather patterns around the globe.
For thunderstorms a jetstream acts to tilt the vertical storm cloud, keeping updrafts away from the downdrafts.
This separation is critical in allowing storms to grow to an intensity where they can bring dangerous weather.
The jetstream will be at its peak above northern NSW and south-east Queensland, although a suitable environment exits for severe weather right down to northern Victoria.
The Bureau of Meteorology is already flagging the threat, tweeting this morning the risk of destructive winds and giant hail in south-east Queensland.
Sydney, Brisbane and Canberra in the firing line
All three capitals could see showers and storms on Friday morning, but the more likely time for severe weather is the afternoon and evening.
Canberra, being further inland, has an earlier storm window and the first half of the afternoon is the favoured period on Friday for severe weather.
For Brisbane and Sydney, the later afternoon and early evening is the most likely time for severe weather, although Brisbane storms could rage long into the night
Drier and cooler westerly winds will clear storms off the east coast on Friday night, setting up drier and more autumnal weather for the east coast through the remainder of the long weekend, although Sunday will be cold enough for snow on the Alps.
