Temperatures in Sydney have hit 30C but there are likely to be showers in the afternoon and possibily severe thunderstorms in parts of NSW and Canberra as a cold front moves through.
The Bureau of Meteorology says the areas at greatest risk of severe thunderstorms include Bourke, Dubbo, Parkes, Wagga Wagga, Albury, Griffith and Canberra.
Other areas that may be affected include Condobolin, Nyngan, West Wyalong, Narrandera, Cobar, Wanaaring, Brewarrina and Enngonia.
The storms could include destructive winds gusting to 120km/h - strong enough to bring down trees or powerlines - as well as large hailstones and heavy rain.
A severe thunderstorm warning has been issued and further warnings are likely as the storms move east.
The 30 degree temperatures in Sydney on Monday are about 8-10 degrees above average for this time of year.
Thunderstorms are likely to continue on Tuesday and could impact parts of north eastern NSW.