Rural Fire Services are working hard to contain fires in the Blue Mountains and Southern Highlands, but they could get some help from above. A low pressure trough stalled over NSW this morning and is the cause of showers and thunderstorms that first developed yesterday in southern NSW. By 9am this morning parts of the Snowy Mountains had gained 30mm. But further north the only fire that may have got a splash was in Lithgow, with 0.6mm in the nearby gauge. The Blue Mountains and Southern Highlands fires are likely to get a bit of dousing today with showers and thunderstorms gradually becoming more widespread. The four fires that are out of control in this region should get at least a couple of millimetres, with the chance of getting as much as 20mm. This is both good and bad news for firefighters and those worried about their homes. Significant falls above 10mm would be very helpful for fire fighters, while light falls would only hinder back burning. The other potential downside with thunderstorms is the potential for lightning to spark new fires. The Hunter and western Sydney are also likely to see thunderstorms move through today, while further east and north the chances decrease markedly. Tomorrow will be the day to watch for the fires as temperatures soar, winds increase markedly and humidity plummets. These three factors will make any fires much more dangerous and difficult to control than in recent days. We all hope that the heavens drop buckets of water like the helicopters have been doing for days.