Updated: 646 PM EST Fri Jan 17 2025
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An approaching cold front will result in a southerly flow of even milder air for Saturday with a period of rain showers Saturday afternoon into early evening. Dry weather should prevail for the first part of Sunday behind this cold front. A wave of low pressure moving in later Sunday through early Monday is likely to bring accumulating, plowable snowfall to Southern New England, though the exact forecast accumulations will hinge on the system's track near or through Southern New England. This will be followed by an arctic outbreak later Monday into Wednesday with Wind Chills likely dropping to between 10 and 15 below zero.
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UNTIL 6 AM SATURDAY MORNING
Key Messages:
* Near to above normal temperatures
High pressure moves off the Mid Atlantic coast tonight, shifting winds to the S to SW across southern New England. Not especially strong for this time of year. Increasing clouds expected, which will temper the impact of radiational cooling. Anticipating low temperatures to be near to above normal..
6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT
Key Messages:
* Above normal temperatures with breezy conditions Saturday.
* Rain showers developing in the afternoon, becoming more widespread during the evening.
A cold front is expected to cross southern New England Saturday night. Showers becoming more widespread by evening, then tapering off from west to east behind this front as it moves offshore.
Saturday:
A weak shortwave trough and cold front approaches the region Saturday. Moisture gradually increases into the afternoon with precipitable water values around 150-200% of normal by early evening. This wave will bring a broad area of ascent supporting our next chance of precipitation. Showers begin to develop in the afternoon from west to east, becoming more widespread mid- afternoon to early evening.
Expecting mainly rainfall for this event given the increasing warm air advection.
There is a slight risk for some freezing rain or light snow at the onset Saturday morning across the higher terrain towards the Berkshires. At this point, thinking up to an inch of snowfall is possible before rain mixes in or all precipitation transitions to all rain.
Temperature-wise, thinking the significantly colder air starts to arrive late Saturday night. This will not be enough time to bring low temperatures even to near normal levels..
SUNDAY THROUGH FRIDAY
Key Messages:
* Plowable snowfall likely late Sun/Sun night, with potential for half-foot or more of snow in interior Southern New England. Winter Storm Watches issued for Sunday into early Monday for Northern CT and western/central MA.
* Below normal temps and low wind chills for early to mid next week associated with coldest airmass to this point in winter. Highs may struggle to reach the mid teens in interior CT and MA.
Details:
Sunday and Monday:
We continue to monitor developments regarding the potential for accumulating snowfall centered during the Sunday afternoon to early Monday morning timeframe. This is in association with a wave of low pressure which moves northeast from the central Appalachians/mid- Atlantic region.
There is still a considerable spread in potential outcomes specific to this system, due to a still-uncertain low pressure track either through Southern New England or offshore. In particular, an offshore pass through Southern New England closer to the 12z ECMWF and more of its ensemble members would favor an offshore, colder, less-liquid- equivalent QPF scenario and would likely lean to a widespread accumulating snowfall, if of the fluffier variety given the cold temps. Another potential outcome at play is a camp favored by the GFS, Canadian GEM and their ensemble members, which are closer or even through eastern portions of Southern New England such that warmer air aloft may favor portions of the eastern New England coastal plain to initially see plain rain (or, rain mixing in with snow) before the colder air flips precipitation over to all- snow; with the steadiest and even potentially areas of banded snow occurs in interior Southern New England along and northwest of the 925-850 mb thermal gradient.
Because of a continued uptick in model-forecast QPF across all global ensembles, and after coordination with WPC and NWS offices, we opted to hoist Winter Storm Watches for interior portions of Southern New England (northern CT, western/central MA) for Sunday afternoon into early on Monday. For the areas in the winter storm watch, we felt the potential for 4-8" with locally embedded higher amts (especially if banding materializes) was conceivable for those areas. Due to the potential for warmer air cutting in and reducing accums for eastern MA and RI, we opted for around a 2 to 5 inch accumulation for these locations; a colder/more offshore storm track certainly could push those totals upward and possibly force winter storm watches eastward in later updates were that to be the case.
But it is still too uncertain to make that decision given the current model-forecast situation.
Precip still looks to begin Sunday afternoon, and with the peak occurring Sunday evening into early Monday, snow should easily accumulate on all surfaces when it does develop. With it being a holiday weekend, the adverse impact on travel should be at least attentuated some than it would otherwise.
Early to Mid Next Week:
One of the coldest airmasses to this point in the winter season takes hold through at least midweek. Below normal temps and wind chills in the single digits above to single digits below zero are forecast, with potential for lower wind chills pending wind speeds. Tue and Wed look to be the coldest days, and it is possible that Cold Weather Advisories could be needed.
Depending on how much snow falls Sun night/Mon, low temps could be colder than forecast given a fresh snowpack.
Late-Week:
Mostly stuck with NBM output given a rather busy weekend to midweek forecast timeframe. But it appears as though we start to gradually thaw out of the truly deep cold as we move into late in the week. Drier weather and temps returning back into the 20s..
Forecast Confidence Levels:
Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.
00z TAF Update:
Through Tonight: High confidence.
Mainly VFR, though there is a chance at VFR/MVFR cloudiness near southeast MA, Cape and Islands by daybreak. Light S/SW winds.
Saturday...High Confidence in trends. Moderate Confidence in timing.
VFR conditions through mid morning or so, gradually becoming MVFR in the afternoon and early evening. Localized IFR conditions possible by early evening. Rain showers will also overspread the region during the afternoon hours from west to east. A few scattered showers are possible after 15z.
Saturday Night...High Confidence in trends. Moderate Confidence in timing.
MVFR trending to VFR. Areas of IFR could linger across RI and southeast MA until after midnight, before improving late.
KBOS TAF...High Confidence in TAF.
KBDL TAF...High Confidence in TAF.
Outlook /Sunday through Wednesday/...
Sunday: Mainly VFR, with local IFR possible. SN likely, chance RA.
Sunday Night: Mainly IFR, with local MVFR possible. Breezy. Chance SN.
Martin Luther King Jr Day: VFR. Breezy. Slight chance SN.
Monday Night through Tuesday: VFR. Breezy.
Tuesday Night: VFR.
Wednesday: VFR. Breezy. Slight chance SN.
Forecaster Confidence Levels:
Low - less than 30 percent. Medium - 30 to 60 percent. High- greater than 60 percent.
High confidence.
High pressure moves across the waters tonight, keeping light winds and seas. S to SW winds increase Saturday ahead of an approaching cold front. Building seas across the outer coastal waters. Small Craft Advisories will be issued for the outer coastal waters for a period from late Saturday morning into Sunday morning. This advisory could be extended with later forecasts.
Outlook /Sunday through Wednesday/...
Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain.
Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 9 ft. Rain, chance of snow. Areas of visibility 1 to 3 nm.
Martin Luther King Jr Day: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 9 ft. Chance of freezing spray, slight chance of snow.
Monday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Chance of freezing spray, slight chance of snow.
Tuesday: Winds less than 25 kt. Seas up to 5 ft.
Tuesday Night through Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of snow.