New England Weather This Week: Trough-Dominated

It'll be a generally active week with troughing dominating. Frontal systems will cross the region today and Wednesday, making those days the wettest ones. Troughing will help keep things cooler later in the week as well.

MONDAY

A strong frontal system will cross New England through the day today. The center of this system will remain just to the north of Vermont today, with its cold/occluded front pushing through the region from southwest to northeast. This will support a line of rain and downpours, with a few embedded rumbles of thunder crossing the region through the morning and likely lingering into the afternoon. A triple-point low will fail to form over New England, keeping this a rather quick punch instead of a long-duration rain event.

A line of potent downpours will cross the region through the morning. Once the downpours pass, showers will likely linger for at least a little while afterward. By this afternoon, the leading line of downpours will likely begin to weaken somewhat as it enters Maine. Showers will gradually wind down from southwest to northeast through the afternoon and evening as a dry slot works into the region.

Below: HRRR showing potential weather late this morning (1st image) and around mid-afternoon (2nd image):

Rainfall rates of 1-2 inches an hour will be possible within the line of rain and downpours. Despite this, the progressive nature of the system as well as preceding dry conditions will limit any flash flooding potential to localized street ponding. The fast nature of the system will also limit how much rain falls across the region. A widespread half inch to inch of rain is expected, with upslope enhancement in the mountains allowing for 1-2 inches of rain total. The fronts will lose their steam as they push into eastern and northern Maine, allowing for less rainfall there.

The upper-level wind field with this system will be rather strong, with winds even down to 2,000 feet above sea level around 45-60mph. Despite this, there remains uncertainty with how much of this wind can mix down to the surface during the downpours. The low levels (from the surface to 2,000 feet above sea level) is likely to see a subtle inversion, which could lock the highest winds gusts away from the surface. Gusts of 30-40mph are likely with much more isolated instances of 40-60mph.

Below: winds at the 850mb level (about 4,700 feet above sea level),showing a rather strong low-level jet. How much of this can mix to the surface during the fine line is a big question:

Once a dry slot moves in behind the showers, rapid drying will likely ensue. The center of the trough and a cold pool aloft will remain just north of Vermont. This could spark some wrap-around showers, mainly for western New England, moving into this evening and during the overnight hours. Showers tonight will be most likely across northern Vermont and New Hampshire, who will be closest to the center of the system.

Below: HRRR showing hourly weather from this evening through Tuesday morning:

TUESDAY

A narrow short-wave ridge will build into most of New England on Tuesday. This ridge will build between the departing low pressure system and another quickly approaching from the Great Lakes. This will give New England a one-day break from the active weather (for the most part). Skies will see variable clouds, with more generally building later in the day as the next system approaches. That system may send its first showers into westernmost New England by the evening.

Despite the passage of a strong cold front on Monday, temperatures will remain on the milder side, with 60s generally dominating. This will come as brief ridging ahead of the next system will result in a quick switch back to a more southerly flow. Southerly flow almost always precedes a cold frontal passage, and with cold front quickly following Monday's, a southerly flow will re-develop instead of a northwesterly flow that normally follows a strong cold front.

Below: 500mb height anomaly showing Monday's system weakening over Maine, with next trough set to arrive from the Great Lakes:

WEDNESDAY

For Wednesday, a very similar setup to Monday looks to play out. This will come as another rather strong frontal system moves just to New England's north, dragging a cold/occluded front across the region. Similar to Monday, a secondary low is currently not expected to form, which will keep this system from becoming a longer duration storm. At this point, even the timing looks similar, with a line of showers moving from west to east from Tuesday night through Wednesday afternoon.

This system doesn't look quite as potent as today's system. Rainfall rates look to be lower and the wind currently doesn't look nearly as strong. At this point, a widespread quarter to half inch of rain across the region looks likely. In a flip from Monday, the highest rainfall totals will likely set up across interior Maine, with totals dropping gradually moving south and west in the region.

Below: Current rainfall outlook for Wednesday:

THURSDAY & FRIDAY

A ridge-in-the-west-trough-in-the-east pattern looks to set up for late this week. This will keep New England under broad cyclonic flow and troughing. Thursday and Friday. This will allow for cooler than average weather for late-October along with partly to mostly cloudy skies. There won't be any organized systems during this time, but a few subtle waves will likely pass, allowing for the potential for some spot showers. Much of this time will be dry and precipitation will be most likely within the mountains.

Below: 500mb height anomaly, showing broad troughing remaining over the northeast late this week:

The deep trough and its cold pool allow for some rather dreary days and chilly weather. The freezing level may drop below 3,000 feet above sea level. This would allow for some snowflakes across the mountains, especially later Thursday and into Friday. As stated before, the steady precipitation will have exited the region by this time, but a few spot showers will certainly be possible.

Below: Potential freezing altitude Friday morning:

WEEKEND

The main question for this weekend will be whether or not the upper-level low will lift into the Canadian Maritimes by Saturday, or if it continues to hang around. Should it lift away, a drier and slightly warmer weekend could be on tap. If it lingers, another cool day with spot shower chances will occur for Saturday. For Sunday, guidance is split between dry weather and ridging and the potential for another system to approach, bringing showers. The main question for Sunday will be whether or not ridging is strong enough to hold back showers.

Below: Current weather map for Sunday (October 26), showing high pressure in place and the potential for some showers. This is due to uncertainty surrounding whether or not the ridge will be strong enough to hold back showers: