Windy, mild rainstorm to affect the region Monday; snow showers and colder for Tuesday; chilly mid-week, then milder with likely extended dryness without much wind; perhaps finally stormier and somewhat colder after Christmas

Plain-language summary:

 

After a mild and mostly dry day with increasing clouds today, a strengthening but quick-moving storm will bring heavy rain, strong winds, and unseasonably warm temperatures on Monday. Much colder air and some snow showers, especially in Vermont on northwestward, will occur on Tuesday. Chilly and dry weather takes over for mid-week before turning milder but still dry for the rest of the week and even through Christmas. It could turn stormier, snowier, and somewhat colder between Christmas and New Year’s Day.

 

Meteorological discussion:

 

A strong high pressure has moved offshore the East Coast today, while a strong low pressure with a lot of Gulf of Mexico and western Atlantic moisture is strengthening over Florida. The low pressure is being steered northward by an upper-level trough to the northwest, and strengthening southeasterly winds on its eastern side will pull warm, moist Atlantic air into our region as it continues to strengthen and move into Quebec by Monday, after a mild and dry day today with increasing clouds. This somewhat inland Nor’easter type track normally would produce an area of heavy snow on the storm’s northwest side in winter, but with no cold air anywhere near the storm, the precipitation will fall only as rain with freezing levels reaching 10,000’ (3000 m), with it being heavy at times for many areas given how moist the air is. The rain will be the heaviest just to the northwest of the surface low pressure track, in the comma head of the storm, from northwestern New York into the Laurentians, while the Champlain Valley and Eastern Townships of Quebec will get slightly less due to downsloping off the Green and White Mountains initially. Southeastern facing slopes of the mountains in Vermont, New Hampshire, and western Maine will receive enhanced rainfall due to upslope. Most of the region will receive 1-3” (25-75 mm) of rain. Areas in New Hampshire and Maine east of the surface low track will also get very warm for 6-12 hours, briefly getting as high as 60F (16C). Given the strength of the low pressure system, widespread strong winds will occur east of the low pressure track, especially over mountain summits, in coastal areas, and northwestern slopes of the Appalachians where downsloping will enhanced the winds. Coastal Maine could see the strongest winds of all. The windiest areas will see wind gusts of 60+ mph (100+ kph). However, given the fast movement of the storm, the most intense weather will already be out of the region by later Monday night.

 

Cold air finally arrives from central Canada by Monday night, accompanied by a closed though elongated upper-level low that doesn’t quite phase with the Nor’easter that would already be in northeastern Quebec by this time. The upper-level low will dig into the Ohio Valley before moving into northern New England and quickly weaken, bringing snow showers along and to the north of its path. This area includes eastern Ontario, northern New York, northern Vermont, and southern/central Quebec, with less farther east as the upper-level low weakens and opens up into a trough. With the northerly low-level flow, the northern Adirondacks and Green Mountains will get some terrain enhancement. With most of the moisture whisked away by the preceding Nor’easter, snow accumulations will be light, being <2” (5 cm) for almost everyone. Areas southeast of the Appalachians likely will not see any snow at all.

 

Source: TropicalTidbits

Source: TropicalTidbits, PivotalWeather, and NOAA

 

After that, it looks rather quiet for at least several days, as strong upper-level ridging overhead in Canada and an unusually weak temperature and height gradient lead to an unusually slow movement of storms, with the nearest storm still being over the western U.S. Initially, it will be a bit chilly mid-week with the surface high pressure over Quebec promoting wind straight out of the north into our region, but the air mass isn’t particularly cold, and whatever chill will erode as the high pressure moves to the east, turning whatever wind to the east or southeast. The strongly positive AO and NAO indices will keep the true Arctic air well to the north for the foreseeable future, though the slight ridging in western North America associated with a positive PNA will also prevent a strong ridge in eastern North America from pumping record warmth into our region. Other than a weak disturbance or two that could bring a few rain or snow showers and a brief cooldown in northern areas, it looks dry and increasingly mild later in the week and even into Christmas.

 

Source: TropicalTidbits

 

It likely becomes more active after Christmas. A parade of storms will enter California starting late this week, and they will slowly move across the southern and central U.S. and likely eventually reach the mid-Atlantic U.S. coast just after Christmas. There’s still a glaring lack of true cold air, though there appears to be a little more cold air sneaking from Quebec, perhaps helped by the NAO and AO falling from very positive to slightly positive. Also, climatology dictates that it will likely be at least marginally cold for snow by the end of December if the storm track is favorable or to our south. A lack of southeast U.S. ridge that has been prominent in many recent winters will also help. Any storm strengthening along the coast would also generate its own cold air, helping any rain or mixed precipitation change to snow. There could be 2 slow-moving storms between Christmas and New Year’s Day, and with some luck, there might be just enough cold air to produce snowstorms in our region, especially over higher terrain, though it could still be too warm as well.

 

Source: TropicalTidbits

 

Source: Climate Prediction Center