A line of severe thunderstorms was marching through northern NSW on Sunday evening, bringing destructive wind gusts of over 125km/h to Narrabri and Tamworth. Narrabri recorded a wind gust of 128km/h, which was the highest recorded there in 7 years (since December 2005). Tamworth was lashed by a wind gust of 126km/h. Winds of this strength are capable of bringing down trees, power lines and even taking roofs from houses. At 9pm, the thunderstorms were forming a solid line of approximately 200-300km, stretching from Moree in the northwest to Kempsey in the southeast. It is the flow of cold, dense air out of these thunderstorms that has created the destructive wind gusts. Also, due to the length of this squall line, wind gusts of over 90km/h have been quite widespread. The line of thunderstorms is forming along a low pressure trough, which has deepened over central and northern NSW during Sunday, due to the approach of a cooler airmass from the southern states. For residents in northern NSW and southern QLD who live ahead of the squall line, it will be worth staying indoors for the remainder of Sunday evening and tidying up any loose items around the home before the storms arrival. The thunderstorms should start to weaken during the early morning hours of Monday but a threat will remain until late tonight. For those that have already experienced the wild storms, conditions should calm down significantly in the wake of the squall line.