If you planted things like tomatoes and basil and peppers, it’s highly advisable that you get a sheet or light cloth over them tonight as unusually cold air has arrived. Plastic is not recommended.
Temperatures well away from the coastline are likely to go down into the low to mid-30s and there could even be pockets of 20s. This will damage tender vegetation.
You may not actually see any frost on Thursday morning because the air is so dry that there’s not enough moisture for frost to form. Nevertheless, when temperatures get into the 20s there can definitely be damage to plants.
In terms of the apple crop, temperatures would have to go down under 30 degrees for there to be damaged to the apples. It’s not impossible but I think the odds are we stay just above that critical mark for most of the orchards.
Hummingbirds and other species that have arrived will definitely be cold overnight, but this will not be catastrophic. Just be sure your feeders are full of some new sugar water as they will likely need all the fuel they can get tonight.
If Boston goes below 40 degrees overnight it will be only the fourth time that has happened on the 18th of May. It is fairly unusual for the city to get this cold this late in the season.
The key to just how cold it will get will be how much wind keeps up overnight. Wind mixes the air and prevents the worst of the cold, but if it dies out and goes calm, more extensive 20s could occur.
With the July-strength sunshine, readings will quickly rebound on Thursday, getting into the lower 60s in the afternoon, and this will be the end of any frost chances for the season. Sunshine will continue Friday with temperatures 65 to 70 in the afternoon fairly typical.
Our eyes then turn towards some rainfall potential on Saturday. Clouds will thicken and there should be a period of showers and perhaps even steadier rain arriving during the afternoon.
The exact timing of this still needs to be tweaked but it’s likely that the back half of Saturday will be wet. On Sunday, the rain and murkiness should clear out fairly early in the morning, leaving us with a partly to mostly sunny afternoon. It will be warmer with temperatures in the mid to upper 70s.
This looks like the only chance of rain through much of next week in our much drier than average pattern.