First Widespread Frost Possible This Weekend
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How does your garden grow? No question it was a little tough to get the local farms and yards ramped up this spring due to a late thaw and cold soil temperatures. Not very easy to prepare the fields when it's still snowing in April. But then came a record warm May, a very warm second half of summer, and the 3rd warmest September on record. On a recent trip out to Wilson Farm in Lexington it was great to see the fields still providing and the CSA shares being doled out to the after-work crowd. Only a few towns have woken up to a frost-coated lawn this fall, mainly well north and west of Boston.
ECMWF forecast for Saturday shows air just a few thousand feet above the surface well below freezing. By the way, this translates to highs in the 40s for parts of northern New England! We'll be in the 50s here across southern New England. Source: Weatherbell
All good things come to an end though, and it looks like that streak may meet its demise this weekend. The cooler blasts of air have been more frequent now that the calendar page has turned to October, and the coolest one so far is on tap for Saturday. You can't help but start thinking about cold season weather when the trusty old 850mb map (a few thousand feet up) is showing temps well below freezing. To be fair, most gardens start giving up this time of year anyway due to decreasing daylight. Saturday night may be a knockout punch for the more tender varieties.
The delivery man for this chilly air is a cold front this evening (the one causing gusty winds and scattered downpours today). Saturday's highs will stay stuck in the 50s across the region, and once the sun goes down it'll be time to fire up the furnace. High pressure crests over New England, the winds relax, and the 'heat' of the day will rapidly head back up into space. It's a good combination for radiational cooling, and the coldest readings of the season thus far. Widespread 30s are expected, although the Cape & Islands will not likely get cold enough for any frost (nor will the immediate Boston area which holds on to the heat more efficiently).
The only fly in the ointment may be some cloudiness that starts to spill over the region at night. A few models have been hinting at some high/mid-level cloudiness that could drape itself across New England. If that happens, it may provide a little bit of an insulating blanket. Good idea to be prepared either way and have the sheets ready to cover up anything you want to survive the night. Even mums, while hardy, can have their blooms bitten by the frost and they will turn brown and shrivel up if not protected. And always remember to use a sheet instead of plastic - plastic does not protect plants from the ice! The National Weather Service will issue Frost Advisories for locations they think are most at risk during the day on Saturday.
NWS forecast lows as of Thursday night. Keep in mind it doesn't have to be 32F to get frost - the coldest layer of air is right at the ground while air temperature readings are taken ~6' up. There are many times when the temp may read 35F but the lawn is covered in ice. Source: Weatherbell/NWS
Farther north it looks like the first hard freeze will take care of any and all annual plants. The valleys around northern New Hampshire, Vermont, and northern Maine should all plummet into the 20s. Goodbye mosquitoes, goodbye tomatoes, and goodbye flower boxes. On the plus side, these frosty conditions are actually coming later than average. We could easily be slammed with a heavy frost in September, but reaching temps like these in nearly mid-October is nothing unusual. For example, the record lows in Boston and Worcester on Sunday are 32F and 22F respectively. Neither city will be close, and these kind of temps are right on time.
If you can't stand to part with those flower boxes then by all means I recommend putting in the effort to cover them up or bring them indoors, because it doesn't look like we'll run another frost risk for at least another week. One more week of blooms is well worth it in my mind! Because once they're gone and the leaves fall, it's stick season. And that one lasts plenty long.
