While Thursday and Friday promise to be pleasant and sunny, there is a chance that we could experience snow or rain during the weekend. The large scale flow over New England will be southwesterly over the coming days, and Boston will be on the edge between the cold inland air and the warmer ocean air during the weekend. The precipitation will occur in this transition region, and whether or not we get snow and/or rain will depend on which side we end up on. One extreme is cold temperatures (low 30s) and clear skies, while the other is warm temperatures (high 40s) and lots of precipitation. We will most likely end up somewhere between the two, with temperatures around 40°F and intermittent rain during the day or snow during the evening.
We have experienced unseasonably warm weather this week, and Wednesday's high of 86°F was the highest September 27 temperature ever recorded in Boston. However, the temperatures started dropping after a cold front from the northwest passed over us on Thursday. Tropical storm (formerly hurricane) Maria will be passing to our southeast during Thursday and Friday, but the storm will be too far away to affect us with any strong winds or rain. The rain that we can expect on Saturday is instead coming from the northwest, where another incoming cold front will bring along a minor low pressure system. Expect light showers on Friday night and during Saturday. After the passage of this low pressure system we can expect several days of mostly clear skies, when we will be under a large high pressure system ranging from Maine to the Carolinas in latitude and from the coast to the Great Lakes in longitude. This will likely bring temperatures around 70°F and plenty of sun during Monday through Wednesday.
Southwesterly flow will advect unseasonably warm air toward New England on Wednesday and Thursday. A low pressure system will pass to the west of Massachusetts on Thursday, and even though most of its associated precipitation will fall inland, there is a high chance of rain on Thursday morning and early afternoon. The winds will be strong at around 15 mph.
A cold front swept through the area on Wednesday, and it will be followed by high pressure and mostly clear skies on Thursday. The high pressure system over Montana and low pressure system over southern Hudson Bay will both shift east during Veterans Day, and the cyclonic flow from the low pressure system will bring us cold air from the northwest. This cold front is expected to pass through the area on Friday evening and give us temperatures close to freezing on Friday night, and low temperatures on Saturday. The southeastward-moving high pressure system will build up during its passage over the Great Lakes early Saturday, and the westerly flow caused by it will bring dry, warmer air into the area on Sunday. Expect mostly clear skies throughout the weekend. The dry air and clear skies are expected to persist through Tuesday. Except for Friday night and Saturday, the temperatures are normal for this time of year: climatological mean high and low temperatures are 53°F and 40°F, respectively. While we experienced more rain than usual in October, the yearly accumulation is significantly lower than climatology: 27 compared to 37 inches. This is still far from the lowest recorded precipitation accumulation at this time of year, which was 20.27 inches in 1965.
Two low pressure systems will bring rainy weather to the Boston area for the rest of the week. The first system has moved northeast from the central parts of the U.S. over the past few days, and should bring intermittent rain from Thursday night through Friday night. This low pressure system will cause strong southwesterly winds over the same time period. High temperatures will be in the mid- to high-60s during both Thursday and Friday, and Thursday night’s low temperature will likely be around 55°F. This is well above the climatological mean high (50°F) and low (36°F) temperatures of this time of year.