The long-awaited change of air is on New England’s doorstep, as a well-defined cold front separating the long-standing warmth and humidity in the Northeast from cooler and less humid air marching through Eastern Canada is poised to cross New England.  Ahead of the cold front, a few morning showers in Northern and Central New England didn’t amount to much, but as breaks of sun between clouds allow temperatures to rise into the 90s in the southern half of New England, the afternoon arrival of the cold front will mean scattered thunderstorms, increasing from midday through the afternoon and continuing through the evening.  The storms erupt as an indicator of an overturning air and, fueled by the abundant humidity with dew point temperatures in the 70s, will produce torrential rain at times along with frequent lightning, while some of the stronger storms will be capable of producing localized damaging gusts of wind.  As always, “when thunder roars, go indoors” – if you can hear thunder, the storm is close enough for lightning to be a danger.  Although flash flooding isn’t likely for most, it’s not impossible that the combination of heavy rain rates with a dry and hard ground resistant to absorbing water may lead to enough water in a short enough time to overwhelm drainage and result in spots of flooding.  Overnight Tuesday night the cold front will ease toward the South Coast and swing the wind to blow from the north and northeast, opening the flow of new, cooler and less humid air that will take hold of New England for days on end.  At first, the change in air isn’t a clean one through all levels of the sky, with some warmth and moisture still battling against the cool air aloft, resulting in times of clouds and a few showers Wednesday, and some pockets of showers Thursday, with both days reaching near 80 degrees as a high temperature.  A second, reinforcing shot of cooler, drier air arrives Thursday evening with one last round of showers before opening the pathway for delightful, pleasant air with a fair sky to take hold Friday through Sunday, and even into the start of next week!  By the middle of next week, warmth and humidity builds back enough for an increased chance of showers and thunder to re-enter the forecast, but not to the extremes we just experienced!