Early-summer warmth this week but no extreme heat; dry at first but scattered showers and thunderstorms return later in week; gradual cool down with showers next weekend; likely staying a bit cool and possibly unsettled next week

Plain-language summary:

After an extended period of unsettled weather, it is finally dry and sunny today. It will be cool tonight, but only the coldest hollows will experience a frost or freeze. It will turn much warmer, with temperatures resembling early summer for several days this week. It will be mostly sunny and dry for a few days, but then it will turn more humid and somewhat cloudier with a lesser day-to-night temperature difference and the chance of afternoon and evening showers and thunderstorms. It will likely turn wetter on Friday or next weekend, though the timing and duration of rain is uncertain. It will likely turn cooler and perhaps unsettled with showery weather at times for a while afterward, with unusually consistent temperatures likely, characteristic of most of this spring,

Meteorological discussion:

Dry and sunny today, cool tonight with isolated frost and freeze in cold hollows

 

After a series of slow-moving, cut-off lows brought an extended period of showery to very wet weather, especially south of the U.S./Canada border, it is finally dry and sunny across the region today with surface high pressure in control. For some areas, this will be the first completely dry day in more than 10 days. The surface high pressure is moving in behind a modest cold front, so it will be cooler than average for mid-May. Relatively clear skies tonight will lead to good radiational cooling, though the lack of a truly cold air mass and all the wet ground adding moisture to the boundary layer will preclude a frost or freeze except in the normally coldest hollows, like in particularly protected valleys.

 

Source: TropicalTidbits

 

Weather pattern remains blocked, but this time, with early summer weather for upcoming week, dry early on before afternoon and evening scattered showers and thunderstorms later in week

 

Like the past 2 weeks, the North American weather pattern will continue to be rather blocked, with several slow-moving blocking ridges and cut-off lows. However, the system will be configured somewhat differently this week, with upper-level ridging building and nosing into northern Ontario and western Quebec, helped by a digging upper-level trough in western North America associated with a negative PNA. This is a reversal from model guidance a week ago, when I wrote that most models had backed off on summer warmth for our region, but that turned out to be a misleading trend. Meanwhile, a cut-off low will meander south of the upper-level ridge, way to our south across the southern U.S. This will lead to warming trend with mostly sunny skies through mid-week in our region, with early summerlike temperatures, though the wet ground and lack of strong westerly flow to bring hot, dry air directly from the west will limit how hot it gets. Also, by Wednesday evening, the cut-off low in the southern U.S. will have moved slightly northeastward into the central Appalachians, close enough to bring more clouds and moisture from the south, with increasing dew points. As such, the hottest weather will actually be in northern areas into central Quebec. This will bring potentially several days of dew points of 59F (15C) or higher, unseasonably high for mid-May, with warm nighttime temperatures and the chance of afternoon and evening showers and thunderstorms, especially in higher terrain. However, there appears to be a lack of a strong trigger for widespread thunderstorms or anything severe.

 

Source: TropicalTidbits

 

Likely rainy Friday and/or next weekend, then cooler and possibly unsettled without much temperature swings

 

The warm and relatively humid air (for mid-May) will continue through Friday. However, another cut-off low will approach the Great Lakes by Friday, and disturbances rotating around the cut-off low will likely bring periods of rain at some point later on Friday or next weekend, though the exact timing is uncertain given the slow-moving nature of cut-off lows. The cut-off low will be weakening as it approaches our region next weekend, with the surface low-pressure system likely going to the northwest of our region, perhaps keeping the steadiest rain and coolest temperatures to the northwest, with gradual cool advection instead of a strong cold front in our region. There is still the possibility of the system redeveloping along the Maine coast and re-strengthening the following Monday, allowing for a more extended period of rain and chilly temperatures in our region, especially in Maine, though they appears relatively unlikely for now. 

 

Source: TropicalTidbits

 

Afterward, pronounced high-latitude blocking will promote general surface low-pressure and upper-level troughing in our region, even with a generally negative PNA continuing. This will likely lead to most days being near to slightly cooler than average, with cooler temperatures being more due to some cold air aloft, clouds, and showers rather than a true low-level arctic cold air mass. The cold air aloft will also lead to instability at times with any daytime heating given the strong May sun angle. Without access to truly cold or hot air, and clouds tempering any diurnal temperature swings, temperatures could be once again unusually constant, like most of this spring.

 

Source: TropicalTidbits

 

Source: Climate Prediction Center