Frontal Boundaries; Troughing to Rule New England's Upcoming Weather

Another unsettled weekend is on tap for New England, though it won’t be nearly as impactful as last weekend. On Saturday, the stationary frontal boundary that brought significant flooding to Arkansas through southern Ohio will slowly shift eastward as an area of low pressure rises to New England's north. This will bring widespread, steady precipitation from west to east Saturday afternoon through Saturday night.

Precipitation will move into western New England by late morning and steadily spread east through the afternoon. The system will need to eat away at some dry air over New England when it first arrives. Heavy rain is not expected, but a widespread light to moderate rain will occur. The bulk of this initial wave will begin to end by Saturday evening, however, generally unsettled weather will continue through Saturday night and into Sunday.

Below: HRRR showing potential weather around mid-afternoon today:

High temperatures will likely be reached around midday on Saturday. Once precipitation begins to arrive, evaporational cooling will begin to take place. Evaporational cooling is the process of an air mass cooling as water evaporates within it (as water changes from a liquid to vapor, it absorbs heat). Since the precipitation will be arriving in a very dry air mass, initial rainfall will evaporate, allowing temperatures to cool through the afternoon and evening.

This will set up a very raw afternoon with a chilly rain for most. Across the northern tier, enough cooling will likely take place that precipitation will quickly become a wintry mix or snowfall. This is most likely across northern New Hampshire and interior Maine, where a winter weather advisory is in effect.

At this point, only an inch or two of snow is expected across the northern tier, mostly over Maine. Some icing will once again be likely as a warm nose pushes northward with cold air locked at the surface (the theme of this spring so far). It’s looking like a glaze to a tenth of an inch for most across areas that will see freezing rain. A worst-case scenario is looking like a quarter inch at this time.

Below: Probability of at least a glaze of ice through Sunday morning:

On Sunday, the advancing warm front will likely push into southern New England by morning, but the cold front will follow quickly behind. With that, temperatures have trended down a bit for Sunday with the chance for 60+° highs now pretty low everywhere in New England. Regardless of the exact timing of the warm and cold fronts, it will be a milder day than Saturday.

Below: HRRR showing potential temperatures Sunday afternoon:

As far as precipitation goes, scattered showers will continue ahead of and along the cold front Saturday night into Sunday morning. Any wintry precipitation across the north will gradually switch to plain rain through this time. As the cold front sweeps through, it will lead to gradually drying air with showers becoming more and more isolated as the day goes on. Sunday afternoon will likely end up mainly dry for a majority of the region.

This frontal boundary will likely end up stalling to the south of New England later Sunday through Monday. Sunday night into Monday morning, a wave of low pressure will ride along this stalled front and bring another round of precipitation to the region. This would likely enter New England overnight Sunday to Monday morning.

Below: RGEM showing potential weather early Monday morning:

With this arriving overnight when temperatures are at their coldest, some light snowfall will be possible across central New England with rain showers farther south. Both snow and rain will likely be light. This system will slide south of New England, so the northern third of New England will likely miss out. There remains some spread in just how far south the front sinks Sunday night. The farther south the front makes it, the farther south precipitation will be pulled Sunday night and Monday.

This frontal boundary will begin to push away by Monday night and Tuesday morning. Just as it does, another robust trough will push eastward from the Great Lakes and track through northern New England. This will drag a rather strong cold front across the region. This will bring colder temperatures and another round of precipitation.

The northern and southern streams will come close to phasing over New England, but recent trends have been toward the northern stream system mainly staying on its own. This would lead to lighter snow showers for the north with lesser rain and snow showers along the cold front for southern New England. With that said, there's still enough spread with ensembles to continue to watch trends for the potential of a coastal low developing. This would bring more widespread snow to the north and rain/snow to the south.

It does appear that phasing will happen once the system gets beyond New England, so eastern Maine will have the best chance for the highest impacts from this system. Trends will continue to be watched over the next couple days as winter weather impacts will be possible across much of interior northern New England (not just Maine).

Looking beyond, the overall pattern does look to flip from where it has been for the first week of April. Despite this, the flip is not one to warmer and calmer weather for New England. The current pattern has involved a trough over the west with the jet stream moving straight through New England. This has led to an active pattern with changeable temperatures. Heading into next week, a ridge-in-the-west-trough-in-the-east pattern looks to develop. This will promote generally cooler weather continuing for the first half of April. This could also promote a continuation of more unsettled weather.