Melbourne is on target for its coldest week in 19 years. Since a powerful cold front swept through Melbourne on Saturday the mercury has failed to reach 14 degrees with a very cold air mass in place. The week beginning last Saturday is likely to be the coldest week since 1996, with an average maximum of just under 12 degrees. Today and tomorrow are likely to be the coldest days, only reaching 10-11 degrees at the most. Only three times in the past 20 years has the temperature has failed to exceed 11 degrees over two days. Today is staying cold all day due to the approach of another cold front and associated low pressure system. The cloud ahead of the front is stopping the sun from providing any extra warmth. Once the front arrives, the temperature will drop further with frequent showers. Tonight skies should clear, at least for a time, allowing the mercury to fall further, with frost likely across northern suburbs. Cloud will come back in on Wednesday with a few showers likely to fall, keeping a firm lid on the temperature once again. From Thursday conditions will be milder, but each day should only scrape to 12-13 degrees for most of the rest of the week.