Chilly and showery through tonight; warming with increasing sunshine Monday and Tuesday; turning cooler for rest of the week with scattered showers but heavy rainfall is unlikely; uncertain warmup afterward but high confidence in continued dryness

Plain-language summary:

 

After being chilly and showery through tonight, even through tomorrow morning for Maine, it will warm up and dry out with increasing sunshine Monday and Tuesday. After a brief line of showers and possibly a few thunderstorms Tuesday night, it turns modestly cooler but still with sunshine except possible isolated showers Wednesday through Friday. Then, it turns much cooler and cloudier with showers Friday night into Saturday, but with heavy rainfall very unlikely. It then dries out and turns sunnier, possibly turning warm to hot for the following week, though that is uncertain given the blocked and slow-moving nature of the weather pattern. Humidity will be rather low by early summer standards even if it warms up after next weekend, with rainfall likely remaining scant, potentially leading to drought and wildfire concerns at least temporarily.

 

Meteorological discussion:

Chilly and showery today into tonight, even through tomorrow morning for Maine, then warming and drying with increasing sunshine Monday and Tuesday

 

It is a chilly and showery day with widespread thick cloud cover for much of the region as a weak low-pressure system tracks through the Northeast U.S., leaving our region on the cool side with low-level easterly flow out of Atlantic Canada underneath the relatively warm temperatures aloft. Many areas will struggle to reach above 50F (10C)! This is more like a cool-season storm with only light stratiform precipitation due to the lack of strong dynamics or deep Gulf of Mexico or western Atlantic moisture involved, yet with widespread cloudiness. The exception is Maine, which is still partly sunny and dry ahead of the system, though the rain will arrive there later this evening. The earlier area has mostly collapsed at this moment, but another area of rain over the Great Lakes will expand as it moves eastward and lead to a steadier rain for several hours this evening for most of the region, though persisting into Monday morning for Maine. The rain and clouds will move out from west to east tomorrow, with a warmer air mass from the west also entering the region. The clouds may not move out in time in southeastern Quebec and eastern New England for a true warmup, but areas to the west will see afternoon sunshine and rising temperatures. Sunshine and continued warm advection from the west and southwest ahead of a cold front will lead to Tuesday being the warmest day of the week. The cold front will bring a line of scattered showers and possibly even thunderstorms Tuesday evening and Tuesday night given the warmer air mass, though the westerly flow and lack of Gulf of Mexico or western Atlantic moisture will limit humidity and instability needed for truly strong to severe thunderstorms.

 

Source: TropicalTidbits

 

Gradually turning cooler for rest of the week with scattered showers, Friday night into Saturday, but no steady or heavy rainfall 

 

After Tuesday, the outlook is looking cooler than it did a week ago, starting with the cold frontal passage Tuesday night. An upper-level ridge will still develop over central Canada downstream of an upper-level trough extending from the northeastern Pacific to western Canada (-PNA). However, it is poised to be sharper and extend farther north than earlier expected, even becoming an omega block stretching into Nunavut. This block is not captured well by the near-neutral NAO and AO indices given that it isn't associated with high-latitude or Greenland blocking, revealing a limitation with those indices. This means that instead of the upper-level ridge broadening and spreading eastward into our region with warm, dry weather as earlier expected, a likely closed-off upper-level low will instead push directly southward into our region Friday evening into Saturday, especially over southeastern Quebec and eastern New England, on the eastern side of the ridge. Before that, Tuesday night's cold front will have already cooled it down to near or slightly below average temperatures for Wednesday through Friday, with a slight bit of upper-level ridging leading to decent sunshine though perhaps with isolated showers given still relatively cool air aloft and strong May sunshine leading to some instability.

 

Then, the truly cold upper-level low arrives Friday night into Saturday, while the unseasonable heat gets shunted farther and farther west toward the Canadian Prairies where the core of the upper-level ridge is. If the upper-level low is strong enough and far enough west, it will also spark widespread rain and incredibly cool temperatures for late May throughout the region, but it could also be weaker and farther east, leading to a somewhat drier and not as cool scenario, especially in western areas which would see more sunshine in this scenario. However, given the flow directly from the north or north-northwest, moisture will be sparse, limiting rainfall amounts for most even with a stronger upper-level low. It will also push any large organized systems with the subtropical jet stream and semblance of summer humidity far to the south of our region. Even without much rainfall, abundant daytime cumulus clouds could occur given the cold air aloft and strong May sun angle. It should gradually dry and clear out Sunday and following Monday as the upper-level low pushes to the southeast of our region, though the residual cold air aloft could still promote daytime cumulus clouds and even isolated afternoon showers.

 

Source: TropicalTidbits

 

Potentially turning warm to hot following week, but with high uncertainty, but greater confidence in dryness 

 

It is likely that the omega block pattern will gradually flatten for the following week as we enter June, allowing some of the upper-level ridging to eventually reach our region, in which case some of the anomalous warmth building in central Canada will be able to push into our region. However, this would be beyond 1 week from now, and it is notoriously difficult to predict when these omega block patterns will break down in the medium to long range. A more persistent block or an upper-level ridge that is farther west would lead to more repeated cold fronts and upper-level lows pushing from the west or northwest and less warmth for our region. It is amazing how consistently the models have backed off the eventual warmup and keeping our region more in the influence of upper-level lows or troughs in the medium to long-range. In either case, there is strong agreement on it being much drier than average for this time of year extending from the Upper Midwest all the way to Atlantic Canada, with the deep and broad west-northwesterly flow cutting off any Gulf of Mexico or western Atlantic moisture, and our region being in the synoptically-favored region for descent east of the upper-level ridge and west of the upper-level trough. This means that rainfall will be scant and there will likely be many relatively sunny days with low humidity, even if it turns warm. If it lasts long enough, drought and wildfires could become an issue at least temporarily.

 

Source: TropicalTidbits

 

Source: Climate Prediction Center