Thursday marks a transition from warmth and humidity to cool, fall air. But that transition will be heralded by showers, downpours and thunderstorms.
It was clear Thursday morning that the air in southern New England is significantly more humid than in the north, even though the approaching cold front was still chugging along through Ontario and Quebec.
This subtle difference in air will likely become important as even more moisture moves into New England from the south. Infused with that moisture, developing showers, downpours and thunderstorms are likely to produce high rainfall rates.
The combination of dense morning fog with downpours will impact travel, particularly in the afternoon and evening commute for the southern half of New England. That's why our weather team issued a First Alert declaration Thursday. Downpours are expected to continue cropping up while slowly drifting southeast through the evening into Thursday night.
Get Boston local news, weather forecasts, lifestyle and entertainment stories to your inbox. Sign up for NBC Boston’s newsletters.
By Friday morning, the incoming cold front will have swooped up not only the downpours but also the humidity, shipping both out to sea to be replaced by cool, new air from Canada.
An onshore wind will probably mean at least some clouds continue to bubble up Friday morning in eastern Massachusetts. As the day wears on, drier air will take hold for a trend toward sunshine with temperatures holding just shy of 70 degrees at the coast and 70 to 75 degrees inland.
Dry and cool air will stick around Saturday into the first part of Sunday. Rain is set to return sometime Sunday as warmth and humidity attempts, unsuccessfully, to push back into New England. The clash between cool air in place and approaching warmth will spread rain showers and eventually a period of rain over New England Sunday.
The start time will be crucial because once it arrives, it’s not going to stop quickly. At this point, it looks like the showers will arrive Sunday afternoon and be gone by Monday morning for a dry, fall-feeling week of weather in our exclusive First Alert 10-day forecast until a chance of showers returns next weekend.
