Rain continues to be moderate to heavy this afternoon and will continue through the evening hours as a cold front marches slowly eastward crossing New England.
There is a flood advisory posted for eastern Massachusetts in areas in light green. Red areas to the north have a flood warning. Remember, this is as of about 5PM. Things will change over the next few hours.
The heaviest of the rain will occur through the first half of the night. The radar image below shows the flow of the rain up from the south this evening.
The latest hi-resolution models ends the rain during the middle of the evening, but also brings a quick period of leftover showers back to Cape Cod and perhaps as far north as Boston around midnight.
The simple explanation for the rain today is colder drier air to the west of New England lifting the warm and humid air over us now and bringing showers, possible thunder and copious amounts of rain. Much of the moisture is flowing northward from areas just west of Bermuda. This type of air is loaded with moisture. This evening there may a small connection to the moisture near Hurricane Gonzalo to enhance the rain. The picture below is from the water vapor channel of the GOES satellite. The white shading represents high levels of moisture while darker colors are dry. Note the dark eye (drier) in the center of hurricane Gonzalo.
The map below is from the GFS model. I put a circle around Gonzalo and a rectangle around the tropical moisture plume ahead of the cold front affecting our region. There appears to be some interaction between the two which will likely enhance the rainfall. This would mean that some areas could see final totals near or over 2 inches of rain.
Even without the connection to Gonzalo’s moisture this is a very juicy weather system.
Humidity levels will run high into the evening and temperatures mild. The homebound commute will be a wet one with some areas seeing big puddles. We haven’t had a lot of rain this fall, so the upside of this precipitation is that we do need rain as we head into winter. The map below shows how much rain may fall in selected areas by the time the rain ends. Notice the heaviest rain is in eastern Massachusetts and likely over areas that have been the driest this fall.
After the system passes a return to sunshine happens Friday. It’s still going to be quite mild with highs 65-70. It won’t be as humid. Friday night is also a mild night with low temperatures remaining in the lower 50s for much of the night.
A cold front crosses the area late Saturday and ushers in the coldest air of the season so far. This change will be dramatic and noticeable. Highs on Sunday, in spite of abundant sunshine will struggle to reach 40F in the mountains and only in the lower 50s along the coast. It’s really going to feel like late fall come Monday morning with a hard freeze over the far interior and perhaps a frost along the coast. Monday through Wednesday mornings could see frost anywhere so use the weekend to move plants inside or at least be prepared to cover them up next week.
Another weather system may bring a period of cold and damp weather at the tail end of next week prior to another warm-up next weekend. Of course this is getting to the edge of the reliability of a forecast so expect some changes to this part of the prediction in the coming days.