Mostly dry and sunny again for another week except Tuesday with mild temperatures except for impressive short-lived cold shot mid-week with widespread frost/freeze Wednesday night; warmer Friday and rain next weekend

Plain-language summary:

 

Dry weather prevails for another week, except some rain on Tuesday/Tuesday night in northern areas, possibly ending as snow showers in higher elevations. Although it turns warmer on Monday, a strong cold front will bring unseasonably chilly weather Tuesday night through Wednesday night, with a widespread frost/freeze Wednesday night except in urban areas and right next to Lake Champlain. It will warm back up by Friday, though next weekend could bring the biggest, most widespread rainfall since the beginning of May. It turns cooler for a couple of days afterward, but warmer and perhaps more humid weather will likely be dominant by the middle of the following week. 

Meteorological discussion:

 

A cold front passed through yesterday, turning the winds more northwesterly and leading to cooler temperatures today. Other than in northern Maine though, the front was dry with only some cumulus clouds in northern Vermont and New Hampshire and not even that farther south and west. This is due to a continued deep westerly to northwesterly flow of dry air from central Canada, cutting off any Gulf of Mexico or Atlantic moisture. After cooler temperatures today, the air mass will modify tomorrow, causing temperatures to rise back to near to slightly above average.

 

Source: TropicalTidbits

This general deep westerly to northwesterly flow looks to continue to another week or so, leading to more dry weather. One exception will be Tuesday, when a disturbance will pull an unseasonably strong cold front southward from Hudson Bay. This is associated with an amplification of the upper-level pattern over North America, with a record upper-level ridge and heat wave developing across western Canada and a strong trough developing over eastern Canada. Although warmth and especially moisture will be lacking ahead of the front, daytime heating from abundant sunshine and the sheer strength of the front and upper-level dynamics will lead to a little instability. This could lead to showers and even thunderstorms erupting just ahead of the front, especially south of the U.S./Canada border where the timing of the front in the afternoon will be more favorable, though interestingly, there is little signal of this from the models right now. In any case, a period of moderate rain will occur just to the north of the cold front/elongated low pressure center with the strong dynamics, with locally 20 mm in central Quebec and northern Maine. However, most other places will receive no more than 1/4” (6 mm), with close to nothing in the southern Adirondacks to southern Maine due to downsloping flow and less favorable dynamics. The rain could even change to snow showers at the end Tuesday night in higher elevations!

Source: TropicalTidbits and PivotalWeather

The strong front will push an unseasonably cold air mass in for Wednesday, accompanied by breezy northwesterly winds. Even lower elevations will struggle to reach 54F (12C), even with sunshine, and higher elevations could stay below 45F (7C). As the cold high pressure moves in Wednesday night, the combination of cold air mass, clear skies, and light winds will lead to an unusually late frost/freeze even in the Champlain and St. Lawrence Valleys away from urban areas and the immediate Lake Champlain shoreline.

Source: TropicalTidbits

The sunshine will quickly moderate the cold air mass, with temperatures rising back to slightly above average by Friday. The flow will turn to southwesterly as a low pressure approaches from the west, leading to more clouds, higher humidity, and rain next weekend. Although it is too early to tell for sure, this rain could be the most substantial since the beginning of May, given that it will have more moisture from the southwest to tap into. How much rain depends on whether the system is consolidated and stronger or split into two weaker systems that stay kind of separate.

Source: TropicalTidbits

After the storm passes, it will likely turn cooler for a couple of days, but not nearly as chilly as the middle of this week with no real cold air mass to tap into. The ridge in western Canada could make one more resurgence late this week before likely weakening into the following week, which should turn the upper-level flow more westerly or southwesterly in our area, leading to more warmth and humidity, though likely still interrupted by cold fronts given that it is still May. This flow pattern would also lead to more rain and perhaps thunderstorms when cold fronts do arrive. However, this is still somewhat uncertain as it is over a week away, and the presence of cut off upper-level lows that can occur would complicate the pattern.

Source: TropicalTidbits