Rainy and chilly today with clearing late in the day into tonight; turning much warmer through Tuesday, with first severe t-storms of season possible Tuesday evening; cooler and dry Wednesday and Thursday, then brief warmup Friday, then perhaps more persistent cooler and unsettled weather but with higher uncertainty

Plain-language summary:

 

A storm bringing a soaking rain to the entire region and chilly conditions today will move out later today into tonight with clearing skies. It rapidly warms up on Monday and Tuesday, with even some severe thunderstorms possible Tuesday evening before turning cooler but not particularly chilly and dry Wednesday and Thursday. It turns briefly warmer on Friday, especially in southern areas, before turning cooler again next weekend and perhaps also early the following week. The weather pattern then slows down, likely leading to several cool and/or unsettled days in early May, but it is unclear if there will also still be warmer, sunnier days mixed in.

 

Meteorological discussion:

 

Rainy and chilly today with clearing in afternoon in Ontario and Quebec, tonight in northern New England

 

It's a rainy weekend for just about the entire region as a low-pressure system somewhat slowly moves eastward into Maine this afternoon. A pool of cold air on the back side of the storm, combined with thick clouds and precipitation, is leading to unseasonably cool temperatures across northern New England today, with even snow falling in areas of heavier precipitation, though with little or no accumulation except at higher elevations. However, to the northwest, where clouds are clearing, allowing the strong late April sunshine to warm up the ground and air, it is much warmer. The storm will move off to the east tonight, with clear skies almost everywhere.

 

Rapidly warming up through Tuesday, which will be warmest day of year so far, before possible severe thunderstorms Tuesday evening

 

A rapid warming trend will take place Monday into Tuesday as a surface high-pressure system moving into the western Atlantic, combined with a surface low-pressure system moving into central and northern Quebec, promotes a southwesterly flow of warm and increasingly humid air from the U.S. Plains. Tuesday will be the warmest day of the year so far for most of the region, especially in northern areas that missed the almost summerlike warmth last week. Many lower elevation areas south of Montreal will reach or exceed 77F (25C) with at least partial sunshine boosting temperatures, quite a change from the cold rain and snow of today! A strong cold front will follow Tuesday night and could trigger isolated to scattered severe thunderstorms for the first time this year for our region. The highest chance of this is eastern Ontario, southern Quebec, and northern New York, where the cold front passes in the evening, when warmth and instability is maximized. The storms will then quickly move eastward and weaken overnight, eventually reaching Maine by late Tuesday night if they haven't already dissipated by then. Given the quick passage of any storms, total rainfall will be relatively light and far less than the current weekend storm.

 

Source: TropicalTidbits

 

Source: Storm Prediction Center

 

Cooler and dry Wednesday and Thursday, warmer Friday especially in southern and western areas, while it turns cloudier and rainier to the north and east

 

A cooler but not particularly chilly surface high-pressure system follows for Wednesday and Thursday, with mostly clear skies and slightly cool temperatures, with Wednesday being the cooler day. With clear skies, dry air, and light winds due to the surface high-pressure system right over our region Wednesday night, a widespread frost and/or freeze is expected then away from large bodies of water and urban areas. Another surface low-pressure system will move northeastward into the Great Lakes and then Quebec on Friday, promoting southwesterly flow of warm air from the U.S. Plains again, though clouds and rain could temper the warmup, especially north of the U.S./Canada border, and in Maine due to cold air damming and flow off the still cold western Atlantic Ocean, depending on the exact storm track.

 

Source: TropicalTidbits

 

Slow-moving weather pattern starting next weekend, likely several cool and/or unsettled days in early May but considerable uncertainty remains

 

After the storm passes through Quebec and then moves eastward by Saturday, it turns cooler behind it, but it might not just be the quick hitting cool shot like most recent cool shots. The North American weather pattern is likely to become at least somewhat blocked, with high-latitude ridging over Nunavut and Greenland (associated with a slightly negative NAO) connecting to a developing upper-level ridge over the northern Rockies and central Canada. This pattern is conducive for disturbances and upper-level troughs moving eastward from the western U.S. to cut off and slow down underneath the high-latitude ridging. This could lead to persistent upper-level troughing resulting in cool and showery conditions for several days in early May and blocking any surge of warmth and humidity from the southwest. It would also lead to a slower-moving weather pattern, with low and high-pressure systems moving slowly or possibly even remaining stationary at times, but these patterns always lead to highly uncertain timing of weather systems and the associated sensible weather in the long-range. This kind of slow-moving, blocked weather pattern climatologically becomes more common as we progress later into the spring, since the weakening temperature gradient leads to the polar jet stream weakening and retreating farther north, making it easier for weather systems to tunnel underneath the polar jet stream and get stuck. 

 

Source: TropicalTidbits

 

For now, there is considerable model disagreement in just how strong the -NAO and blocking effect will be, as well as the exact placement of the persistent features. This means that models disagree on whether the slow-moving weather pattern will set up such that we experience the core of the cool, unsettled weather, or if the cool, unsettled weather is mostly to the east, with upper-level ridging in central Canada able to nose eastward often enough for frequent still rather warm, dry, and sunny days.

 

Source: TropicalTidbits

 

Source: Climate Prediction Center