Snow showers this afternoon, then cold through Tuesday; snow changing to rain Tuesday night into Wednesday; uncertain weather pattern afterwards, but looks mostly cold with more chances of wintry precipitation next weekend and perhaps beyond

Plain-language summary:

Scattered snow showers will occur along and northwest of the Appalachians through this evening, with minimal snow accumulation in lower elevations. The coldest day of the fall so far will occur tomorrow. The weather pattern later in the week, which was very uncertain a few days ago, is now clearer. An elongated storm Tuesday night into Wednesday will bring a snow to rain setup, though it could stay as all snow in the Laurentians and northern Maine, where the heaviest accumulations are expected. It will turn colder again afterward, but not exceptionally cold, with most of the cold air aiming to the west. Another winter storm is possible next weekend, but that is dependent on a lot of details with the various disturbances and overall flow configuration that are not known yet. Afterward, cold appears to be dominant through the end of November, though it could be more moisture-starved depending on how the broad the cold air masses and upper-level troughs are and their ability to suppress moisture to the south.

Meteorological discussion:

A moisture-starved disturbance passing through southern Quebec today in the deep west to northwest flow is producing scattered snow showers, especially north of the U.S./Canada border along and northwest of the Appalachians and in higher terrain, with downsloping leading to drying to the southeast. Snow accumulation will be minimal (<1” or 2.5 cm) in lower elevations. A cold high pressure follows for tonight through Tuesday, leading to highs in most areas along and northwest of the Appalachians staying below freezing for the first time this fall on Monday, and widespread low temperatures of 10-20F (-12C to -7C) Monday night, with some cold hollows getting even colder than that. Initially, with the uniform cold north-northwest flow along the long axis of the still warm Lake Champlain waters, a small area of light lake-effect snow accumulation is possible near the southern tip of Lake Champlain tonight.

 

Source: RadarScope

 

 

Source: TropicalTidbits

 

 

As the cold high pressure slides eastward and modifies, a two-piece storm system will be approaching from the west. The strength of the two systems and the interaction between them has led to major uncertainty in the weather pattern for the middle to later part of the week. A few days ago, many but not all models showed a very amplified northern disturbance that would bring a lot of warm air into the region, making precipitation all rain, but then advect very cold Arctic air behind it deep into the U.S. However, models have come into much better agreement over the last 1-2 days on a northern disturbance that will be somewhat weaker and not dig as far south, staying more separate from the southern disturbance. Therefore, the two disturbances will not phase into a big storm, but instead produce an elongated area of precipitation from the southeast U.S. all the way to Hudson Bay and central/northern Quebec. There will be enough cold air at the start for precipitation to start as snow Tuesday night, especially from the Adirondacks on northeastward, and it could be briefly heavy. Given the strong southerly flow, areas of less precipitation or quicker changeover to rain will occur in the downsloped areas of the Champlain and southern St. Lawrence valleys. Meanwhile, the same flow will lead to upslope enhancement of snow in Laurentians, where it could stay cold enough through the entire storm for all snow, and the eastern Green and White Mountains, where a heavy burst of snow is likely before it changes over to rain or stops. Although the initial primary low will move north into northwestern Quebec, a secondary low pressure will develop in southern New England and become the dominant system, keeping the cold air in Maine, keeping it all snow in central and northern Maine as well. Other areas will have precipitation changed to a light rain by Wednesday morning before ending entirely by Wednesday evening.

Source: TropicalTidbits

Source: TropicalTidbits

 

 

Behind the storm, it will turn colder again, but not as cold as originally expected due to the weaker, less amplified nature of the northern disturbance. A trough will dig into the western U.S. while the southeast U.S. ridge remains to some extent. This is very reminiscent of the weather pattern last winter and is more typical of a La Niña than the moderate to strong El Niño we are currently in. This pattern tends to favor a storm track into the Great Lakes and then New England or Quebec, which combined with the plentiful supply of cold air in Canada, would lead to snow near and north of the U.S./Canada border and rain south of there, but this really depends on the strength of disturbances and troughs ejecting from the Rockies and the downstream ridge/trough pattern. One such potential storm could strike next weekend.

 

Source: TropicalTidbits

The weather pattern becomes quite uncertain next weekend. After the potential storm, there is ensemble support for cold air and upper-level troughing to be more dominant in eastern North America, with the southeast U.S. ridge weakened and pushed southward, at least for a few days. However, the cold high pressure appears to set up over the Plains or Midwest U.S., instead of over southern Canada, leading to more westerly flow in our area that would promote some modification of cold air masses over the Great Lakes and bare ground over southern Canada. As such, the coldest temperatures will likely stay to the west, which is pretty common for late fall and early winter. Still, below-average temperatures will likely dominate for the rest of November. The broad upper-level troughing could also make it difficult for moisture-rich disturbances to come out of the southern U.S. and come up the East Coast to form Nor’easters and dump snow in the cold air. However, I certainly wouldn’t rule out coastal storms completely given the temperature contrast between the cold continental air and the warm Gulf Stream waters; we just need the pattern to become a bit sharper and more amplified than is currently projected, with a southern stream disturbance to come in at the right time to take advantage of the pattern. Without that, snow would come from moisture-starved northern disturbances. It wouldn’t take much for most of the area to have a snowier than average November; typically, the lack of cold air, not moisture, is the main limiting factor for snow this early in the season.

Source: TropicalTidbits