Thunderstorms are set to flare up this weekend over northern parts of New South Wales and southern parts of Queensland as a trough of low pressure moves over the region. Today, thunderstorms should be focused over NSW's Northern Rivers and Northern Tablelands, although thunderstorms may extend as far south as the Hunter and as far north as QLD's Darling Downs. The slow moving nature of the storms today brings the risk of flash flooding, although storms closer to the border may contain damaging winds. On Sunday, the area of storms should spread further south, with thunderstorms possible along the ranges as far south as the Snowy Mountains. Thunderstorms again have the chance of being severe, with flash flooding the most likely phenomena, although damaging winds and large hail are also possible on the central NSW ranges. The capital cities of both states have their best chance of getting a rumble on Sunday. However, a southerly change is likely to move through Sydney early in the day, confining most storms to the western suburbs and Blue Mountains. In Brisbane, storms are likely to stay confined to the ranges. Looking ahead into the working week, the trough should move west contracting showers and storms to inland parts of both states. However, a high in the Tasman is likely to direct humid winds onto the coast, causing showers to persist until at least mid-week.