After a beautiful weekend for New England, much of next week will likely be dominated by troughing in the jet stream over the east coast. This will keep the east coast cooler while the west heats up (the northwest will be seeing some big time heat for this time of year). This pattern is similar to what New England was in at the end of April and the beginning of May, although not quite as extreme.
This set up will allow multiple frontal boundaries to cross New England over this upcoming week. These boundaries can lead to cool, cloudy and wet weather. This isn't the case this time as there doesn't appear to be much by way of rain crossing the boundaries. Temperatures will be seasonable to warm on Monday and Tuesday. Tuesday afternoon through Wednesday could be unsettled, with scattered showers around, although much of the time will likely be dry with peaks of sunshine.
A "sharp" cold front is looking to cross the region sometime on Tuesday or Wednesday. This front will knock temperatures down below average for Wednesday. While the entire region will have noticeably cooler weather, it will be more pronounced in certain areas. For instance, Boston is looking at the low 60s on Wednesday for a high with a Thursday morning low in the low 40s. That's cooler, but not notably cool for mid May. The Upper 60s are average for May 17th for the city.
Northern New England, particularly Vermont, is currently looking at a more notable cool down for Wednesday through Thursday morning. Thursday morning lows are looking to drop to around the freezing mark for much of northern New England (away from coastal areas). After highs on Wednesday are currently looking to top out a good 10-15 degrees below average for many areas.
This is all being set up by the cold front that will be dropping through the region. This front is looking to be rather potent for mid May. Since New England will be in a trough, it allows temperatures to drop like a stone. A trough in the east already sets up cooler conditions, so when a cold front drops in, it can pack a punch. This cool down isn't looking to be all that crazy or historic, but it is notable enough to warrant this article.
The National Weather Service of Burlington states that the air in place at elevation on Wednesday will be more indicative of mid-March than mid-May. There is a chance for snow showers at elevation on Wednesday night in Vermont. These snow showers will likely remain above 2,000 feet.
It's looking likely that Thursday morning will feature a frost for much of northern New England with some freezes possible. These patterns are the reason New Englanders are advised to wait until Memorial weekend to plant their gardens.