At 4:21 AM on Wednesday morning, the fall equinox marked the start of autumn. In the world of meteorology, we consider the fall season to be September, October and November, but this year our weather certainly seems to have matched the calendar's definition of the seasons better than the usual weather patterns. Summer's extension into mid-September has given way to a somewhat cooler pattern, but daily high temperatures are still averaging significantly warmer than normal and our exclusive NECN 10-day forecast shows no change to that theme through the end of September, which should ensure the month ranks among some of the warmest Septembers on record for New England (currently, Boston, for example, is on pace for the warmest September).
The autumnal equinox marks a time of the year - as does the vernal (spring) equinox - when the sun shines directly on the equator, marking nearly equal amounts of daylight and night. This graphic shared by the National Weather Service Forecast Office in Albany, NY, illustrates this well:
Of course, there are two questions that most of us New Englanders have: when will cooler temperatures set in, and when will it rain again? The answer to both of these questions hinges on a change in the jet stream pattern aloft - the fast winds high in the sky that steer our storm systems and separate cold air to the north from warm to the south. For the time-being, these jet stream winds have locked deep moisture for significant rainfall to our south, over the ocean, and in the Rockies. There is one window for this pattern to change in the first week of October, allowing some periods of moisture to stream northward into New England, but right now it seems more likely that moisture will remain south. Interestingly, the air forecast to move into New England will be both cool and dry in nature, but dry air tends to warm quickly with sunshine, so if we maintain a rain-free pattern, we maintain warm daytime high temperatures relative to what we'd normally expect. There are some signals that cooler air will make more firm inroads to New England in the second week of October, but no signs, at this time, that a cooler-than-normal pattern will take hold anytime soon. In fact, the signals are the opposite - warmer-than-normal air may reign supreme in the Northeast, overall, through the fall.