Quite mild through Thursday with slow-moving storm to bring widespread rain mid-week before likely changing to snow showers late week; turns colder and drier for weekend and early the following week, then perhaps finally more snow?

Plain-language summary:

After an increasingly mild, dry, but rather cloudy period today through Tuesday, a slow-moving storm will bring widespread light to moderate rain across the region Wednesday with unseasonably mild temperatures. Rainfall will be far less than last Monday’s storm. Precipitation will lighten and likely change to intermittent snow by Friday before it dries out by late in the weekend and early the following week. No major storms are expected for a while afterward, but the colder air and northerly or northwesterly flow could bring moisture-starved clippers that bring light snow, especially along and west or northwest of the Appalachians. It is likely that eventually, the El Niño-enhanced subtropical jet will bring storms with more moisture into our region.

 

Meteorological discussion:

 

With ridging dominating eastern North America, it will be dry today through Tuesday and getting increasingly mild. As is often the case at this time of year when it is mild with broad ridging, there will be rather light winds with moisture trapped underneath an inversion, leading to low clouds that don’t break up easily due to the very low sun angle. During this time, a storm will slowly move east across the central U.S. and get occluded and cut-off, with the slow movement being due to it being cut off from the polar jet stream way to the north. The lack of the polar jet stream also means that there will be no cold air ahead of the storm, and as the storm arrives on Wednesday, it will be unseasonably mild in the whole lower troposphere, and precipitation type will be rain, even in higher elevations, except possibly from central Quebec to northern Maine. Since the storm will already have occluded and is no longer strengthening, rainfall amounts will be no more than moderate for most, unlike this past Monday’s storm. 

 

Source: TropicalTidbits

 

 

However, this is a tricky setup, with a broad cut-off low but multiple vorticity maxima rotating around and interacting with each other. It is not clear how slowly the whole system will move eastward. It could be already moving out by Friday if the polar jet stream pushes into the storm by then, or if it remains removed from the storm, and the storm strengthens a bit more and is more cut-off, it might not move out until Sunday. It might also get buried to our south and leave us with dry high pressure as early as Friday, as some recent model runs have hinted at. The GFS model run yesterday morning (top) vs this morning (bottom) illustrates this complexity and uncertainty. In either case, colder air will gradually move in from the north and also will be manufactured in the upper-level low via ascent and precipitation. The combination of these two should lead to most areas changing over to snow by Friday, especially from the Appalachians on northwestward, as it gradually gets colder, assuming that the upper-level low doesn’t get buried too far south and dry it out completely. By the time the precipitation changes over to snow, most of the moisture and strongest ascent will likely have passed to the east, meaning that snow will be more intermittent and accumulations will likely be light except in higher elevations. However, it is still possible that one of the vorticity maxima spawns coastal low development that enhances precipitation and snowfall in certain areas.

 

Source: TropicalTidbits

 

 

Source: TropicalTidbits

 

 

After the storm slowly pulls out, it will dry out with broad deep-layer northerly flow across the region, but it won’t be particularly cold, with no real arctic air and strong ridging and anomalous warmth persisting in western and central Canada. However, this ridging associated with a +PNA will also prevent any more surges of warmth into our area, and NAO and AO flipping sign to negative will help to pull colder air down from higher latitudes, though given how warm Canada is now with an unprecedented lack of snow cover in many areas, it will take a while before it turns bitterly cold. Moisture-starved clippers could dive down from central Canada and bring snows to our region later the following week, with western or northwestern slopes getting upslope enhancement and areas southeast of the Appalachians likely receiving little or no snow. With the broad deep-layer north to northwest flow, there is no indication yet of a juicy storm associated with the subtropical jet stream being able to move into our area and bring a real snowstorm, with it instead remaining mostly modestly cold and dry. However, the cold air should make it feel more like winter, and occasional disturbances will bring at least light snows to our region, and eventually, some of the subtropical jet fueled storms could make it up to our region and bring more substantial snows, especially given the strong El Niño we are in. There also does not appear to be very cold arctic air that would suppress all the moisture and subtropical jet fueled systems to the south.

 

Source: TropicalTidbits

 

Source: Climate Prediction Center