Significant Weather Blog: Friday, December 12, 2025 5 PM

Light Accumulation of Snow Likely for Southeast New England this Sunday

A rather fast-moving storm will pass south of New England Sunday and bring a period of light snow or flurries to southern New England.  This event is expected to fall well below normal blog criteria but is likely to yield the first accumulating snowfall, albeit light, for the southern New England coastal plain.  Will first discuss some of the key factors in this weather set-up followed by a forecast of timing and amounts.

Discussion

The upper-level trough that will spawn a surface low pressure center off the mid-Atlantic coast fills the criteria for a passing short wave upper trough with moderately significant amplitude.  It reaches the east coast as a positively tilted trough (i.e., its axis runs southwest to northeast) but transitions into a neutral north-south orientation as it passes offshore and eventually a more negative tilt orientation (southeast to northwest axis) much farther offshore and over the Maritime Canada.  The positive tilt orientation usually supports weaker and faster surface systems which in turn limits the amount and duration of precipitation.  As the upper trough becomes more neutrally oriented offshore, the surface low center is expected to intensify and gain more latitude.  Thus, a major or long duration snowfall is very unlikely for southern New England.  This upper trough, however, has enough amplitude to bring mid to upper moisture northward and at least some uplift to enable most areas to experience a period or two of light snow with the higher amounts closer to the south coast where the moisture will be more abundant and the atmospheric uplift (the process that causes water vapor to condense and fall out as precipitation) stronger.  Looking at jet dynamics, the southern part of southern New England should lie under the right entrance region of an upper-level jet, a favored area for upward motion.

Another factor is that there could be some ocean effect enhancement over the Cape as well as possibly the Plymouth County coast south of Boston.  The physics behind ocean effect snow is analogous to lake effect snow.  Cold air moving over significantly warmer water (be it lake or ocean water) causes low level instability and subsequently intense upward motion (albeit over a shallow layer of the atmosphere) which wrings moisture out of the air and bands of snow showers or squalls.  Typically (although not always) the ocean effect snowfall is considerably less robust than its lake effect counterpart.  Anyway, snowfall on Sunday could be locally a little heavier along the Plymouth County coast and Cape Cod as well as cause snow showers to linger longer into Sunday night, especially over the Cape unless this system is just suppressed too far south with dry and subsiding arctic air dominating.

There remains variability in the computer model output with respect to track and intensity of the surface low center.  Most of the models depict light snow overspreading southern New England at least as far north as the I-90 corridor with at least a few inches accumulating along the south coast.  A notable exception, however, is the GFS model that has consistently depicted a very suppressed and weak system far south of New England with very little or no snow accumulation in most of southern New England.

The cold temperatures typically support higher snow to liquid ratios.  However, upward motion in the best dendrite growth zone is relatively weak and results in small snow to liquid ratios and less efficient snow accumulation.  A shift toward the north in the track could increase dendrite production.

With these somewhat competing factors under consideration, the forecast has not changed appreciably from yesterday’s blog.

Forecast

Light snow will spread rapidly west to east across southern New England during Sunday’s early morning hours (after midnight and before dawn).  Light snow will end west to east across most of southern New England Sunday afternoon.  The snow may persist a while longer along the Plymouth County coast south of Boston into the early evening and possibly well into Sunday night over the Cape and Nantucket due to ocean effect snow showers.

Snowfall totals of a dusting to around an inch anticipated along the I-90 corridor increasing to 1 to 3 inches along and south of the I-95 corridor in MA, RI, and CT (extending west to New York City).  A band of 2 to 4 inches is possible across the Cape and Islands.

Will continue to monitor this weather development and provide an update over the weekend if there are any significant changes.  Will provide an outlook for any potential significant weather for the week ahead on Monday.

About this Blog and Disclaimer

The National Weather Service monitors the weather 24/7 and updates forecasts, watches, and warnings as necessary.  For most of southern New England, refer to your local Weather Forecast Office for the latest forecast/warning information at weather.gov/box.  For information from other Weather Forecast Offices, go to weather.gov and click on the location of interest on the map.

A blog is issued when there is a potential risk of hazardous weather to southern New England and serves to provide background information regarding the significant weather with somewhat of an educational slant.  In the case of hurricanes, the author will attempt to issue a message when any portion of the United States coastline may be seriously impacted.  It’s intended to complement and not serve as an alternative to official forecasts issued by the National Weather Service.  Readers are urged to check National Weather Service forecasts and warnings for the most timely and updated weather information.  This weather message is solely produced by the listed author and does not constitute an official product of the Blue Hill Observatory and Science Center (BHOSC).

The frequency of this blog will depend upon the nature of the weather threat and availability of the author.  Thus, for the latest information on weather forecasts and warnings, refer to the National Weather Service, which monitors and forecasts the weather 24/7.

Blue Hill Observatory and Science Center (BHOSC)

The BHOSC maintains a continuous daily observation record that dates from February 1, 1885 without interruption and provides educational information on weather and climate to area students and the community at large.  Your support of BHOSC is much appreciated and enables this nonprofit organization to maintain the long-term climate record at the Blue Hill Observatory (longest continuous record in North America) and provide valuable educational resources on weather and climate via outreach to schools, site visits/tours, webinars, and conferences.  For more information on the Blue Hill Observatory and Science Center, explore bluehill.org.

Message issued December 12, 2025 by:
Bob Thompson
Retired National Weather Service Meteorologist
Blue Hill Observatory and Science Center Board member