New England will have two more waves of precipitation coming through to continue this rather unsettled stretch. The first of these two will enter into western New England Monday afternoon and continue to move east through Tuesday. The second, much more organized system, will move into the region Tuesday night and continue through much of Wednesday.
MONDAY & TUESDAY
After a mainly dry start to Monday, The first of the two storms this week will move into the region. This system will involve a primary low pressure system near the Great Lakes with a secondary low forming along a warm front near New England. This front will provide the basis for precipitation to break out across New England.
Initially, the system will likely either be rain (to the south) and snow (to the north). In between the plain rain and snow will likely be an area with wet snow and freezing rain mixing with plain rain. This area would most likely be across the Berkshires and Worcester Hills along with southern Vermont and New Hampshire. The lower elevations of southern New England will be plain rain and the northern tier of New England will see snow showers.
Below: HRRR showing potential weather this evening:
As the evening and night go on, a warm nose from warm air advection will rise through the mid-levels across northern New England, allowing temperatures to spike above freezing. At the same time, cold air will likely get trapped at the surface across the mountain valleys as surface high pressure sits over Quebec, allowing the surface to remain cold.
This setup will allow for either sleet or freezing rain to develop, depending on how deep the warm layer of air can become. A deeper layer of warmer air will allow for freezing rain while a shallow layer will allow for sleet. At this point, freezing rain is more favored over sleet due to continuing warming of the mid-levels.
Around (or just after) midnight, drier air looks to work into the system, allowing the widespread, steadier precipitation to end. At the same time, colder air dammed across the surface of the mountain valleys may filter southward toward Massachusetts. This will happen as the surface low pressure system moves just south of New England, preventing the warm front from moving through the region. This would allow for freezing rain, however, with the drying of the mid-levels, it's likely to be more by way of patchy freezing drizzle.
Below: Diagram of cold air damming, which will likely be taking place along New England's mountains with this system:
With all of that said, New England will be looking at a mixed bag of precipitation from Monday afternoon through Tuesday. Precipitation will be the most widespread and steadiest from Monday afternoon through midnight before breaking up and becoming more isolated and lighter. Snow showers will likely continue across Maine through Tuesday morning. A winter weather advisory has been issued for a large swath of New England (seen below) for the chances of minor snow and ice accumulations.
When all is said is done, minor wintry accumulations are expected, with a couple inches of snow possible across interior New Hampshire and Maine along with the Green Mountains. Freezing rain accumulations will likely be minor as much of it will come down as periodic freezing drizzle through Tuesday. Areas that stay rain the whole time (lower elevations of southern New England) will pick up a quarter to half inch of rain.
New England will be between storms for the day Tuesday. New England will likely remain socked in under a thick cloud cover. With colder air streaming down from the north, it will be a cold day and temperatures are unlikely to move too much through the day. Much of the region should stall out in the upper 20s to mid 30s. Patchy drizzle and freezing drizzle (where it's below freezing) will be possible through the day.
WEDNESDAY & THURSDAY
A strengthening cold front will approach New England ahead of a trough over the Great Lakes. A surface low pressure system will likely form along this front to the south of New England and move northward through New England during the day Thursday. The storm system will be strengthening as it moves through the region.
The storm will be an inside-runner as it passes through western New England. This will allow Tuesday's cold air dam to erode across New England as mild air from the south surges northward ahead of the system. Guidance continues to favor a winter washout storm for most, with rain dominating precipitation type for many. With that said, a flip snow on the backside remains possible for western New England, though snowfall will not be the primary precipitation type anywhere in New England.
Scattered showers are currently favored to begin to fill back in Tuesday night into Wednesday morning. Widespread rain, which will be moderate to heavy at times, will continue through the daylight hours Wednesday. The day will likely be fully washed out for New England.
Below: Euro showing potential weather Wednesday afternoon/evening:
A widespread 1-3 inches of rain will be possible across New England. Exactly where the heaviest rain falls is still uncertain. The big question will be if the heaviest amounts end up favoring western New England or eastern New England. Regardless, a widespread inch or two of rain is likely across New England, with the Weather Prediction Center placing all of New England within 1-2 inches of precipitation.
Below: Weather Prediction precipitation forecast from Wednesday morning to Thursday morning:
While the region remains in a drought, this system could produce heavy enough rainfall rates to create excessive rain in the short term despite the ongoing drought conditions. It will be a drought-denter in the long term. So, while this rainfall will help the drought in the long-term, the short-term impacts of excessive rainfall combined with snowmelt can't be ignored. These concerns will be higher across northern New England.
Below: Weather Prediction Center excessive rainfall outlook for Wednesday and Wednesday night:
The storm will also likely produce a period of strong wind gusts. Exactly where the strongest winds set up will come down to the exact track of the low pressure system. The strongest winds will be on the east side of the storm. The westward shift in guidance will put much of Maine and Eastern Massachusetts in the zone for the strongest winds gusts. A low -level jet with the magnitude of 60-80+ knots is possible across eastern areas. This could result in wind gusts of 50+mph for coastal areas. The area with the highest threat level for these winds is Downeast Maine, though this could still shift.
Below: Winds at the 850mb level (about 4,700 feet above sea level) Wednesday night. This strong jet will likely bring strong winds to the surface:
As the system moves away, the cold front will get pulled through the region, resulting in a sharp temperature drop, though a flash freeze is not expected. The storm is expected to be wrapped up by Thursday morning. Some snow is possible on the backside, but accumulations are expected to be minimal across western New England.
FRIDAY
Typical cold air that gets wrapped around the backside of a departing storm will peak on Friday, with highs in the 20s north to 30s south. A rather strong area of high pressure will build to the west, bringing calm conditions, though typical upslope snow showers are likely in the mountains.
WEEKEND
High pressure continues to build into New England on Saturday with moderating temperatures. Sunday may see a weaker system begin to approach.
Below: Current weather map for Saturday morning (December 14):
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