Autumn has begun in a warm and thundery way across much of New South Wales and it looks like lasting into the weekend. A high over the Tasman Sea and a trough in the west of the state have directed northerly winds for the past week, even bumping humidity up higher than in February in some areas. This stagnant pattern is starting to shift as cold fronts become a bit stronger. One front has just ended Broken Hill's hottest five-day March spell in six years. The far western mining town averaged a maximum of 35 degrees from Friday to Tuesday before the front brought a cooler change. Sydney has warmed past 27 degrees in each of the past five days, its longest March spell of 27-degree days in eight years. Sydney is also experiencing higher humidity so far this month than it did during February. After having reached 29 degrees today Sydney is a chance of seeing a thunderstorm, for the second time in a week, when a cold front impacts. The front is still a fairly weak one, so weak that will cool the south and east of the state but have almost no effect in the northwest. Sydney should stay below 27 degrees for the first time since last Friday. In contrast, Tibooburra should still reach at least 35 degrees this Thursday, Friday and Saturday, much the same as the previous seven days. If Tibooburra reaches 35 degrees through to Saturday it will have achieved its longest March run of 35-degree heat in six years. In March 2008 it baked through 13 consecutive days this hot. On the weekend the whole state will heat up, having at least one very warm day with a fair chance of a storms in all districts. Some areas will heat up to five-to-eight degrees above the March average before a stronger front brings a cooler change. This front is looking like the strongest since spring, leading to a temperature drop of about 10 degrees in the south of the state and also ridding some of the humidity. Given the west-to-east movement of the front, the atmosphere will stay dry for several days. Significant rain is unlikely again for at least another week.