Cold air in the wake of a front will lead to rapid cooling tonight across the southwest of the state. A ridge of high pressure is building across the region, leading to clear skies. However, the positioning of the ridge will also play an important part in producing a cold morning, as it will lead to a weak offshore wind circulation along the southwest coastline. This significantly limits the moderating effect of the relatively warm ocean, with cold dry air from the interior spreading out to sea. The minimum temperatures tomorrow morning will be several degrees below the August average for coastal towns and cities, including Perth, Geraldton and Albany.