AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1206 AM EST Sat Jan 31 2026 .WHAT HAS CHANGED... - Cold Weather Advisories have been extended into Friday night and Saturday morning for hazardous wind chills. - A winter storm watch continues for Cape Cod and the islands, with the risk of accumulating snow and strong winds Sunday confined to this area, from a powerful offshore winter storm. - The potential for widespread moderate coastal flooding has decreased due to a more offshore storm track. - Gale Warnings have been issued for the nearshore waters including Boston Harbor and Narragansett Bay. - Dry, chilly start to next week with chances for another round or two of snow in the second half of the week. && .KEY MESSAGES... - Frigid temperatures tonight into Saturday morning. - A powerful ocean storm looks more likely to pass farther offshore of southern New England Sunday into Sunday night. Greatest overall impacts from accumulating snow and strong winds will be across southeast coastal Plymouth county, Cape Cod and the Islands Sunday and Sunday night. Much lighter accumulating snow with lesser overall impact further inland into southeast MA, with little if any impact into the Boston- Providence corridor Sunday. - Minor to perhaps moderate coastal flooding Sunday into Monday along the eastern Massachusetts coast. - Dry, chilly start to next week with chances for another round or two of snow in the second half of the week. && .DISCUSSION... Key Message 1...Frigid temperatures once again tonight into Saturday morning. Cold Weather Advisories have been extended into tonight and Saturday morning, with actual air temps falling to zero to minus 10 across the region! These temps were derived from the NBM and the colder MOS guidance, given light winds tonight. However, a sufficient light WNW breeze at 5-10 mph to generate colder wind chills from minus 10 to minus 15, which meets our extreme cold advisory criteria. Hence, we extended the cold weather advisory into tonight/early Sat morning for most of RI/MA/CT. We excluded the south coast as wind chills there are more in the zero to minus 5 range. Still very cold, but shy of criteria. Nonetheless, dangerous cold for anyone outdoors tonight/early Saturday. Key Message 2...12z models continue the trend from the overnight guidance, tracking a powerful vertically stacked low (sub 970 mb) a fairly good distance southeast of the 40N/70W benchmark. However, given its very large circulation and precip shield, combined with ocean effect snow (OES) bands, along with possible 850-700 mb Fgen snow bands clipping the Cape and islands, we decided to hold with the winter storm watch for this region. Sufficient guidance supporting 0.3 to 0.6 inches of qpf over this area, which includes the 3km NAM, Canadian, Icon, AI models and some ensemble members. Therefore this supports a risk of 4-7" across the Cape and Islands, with highest totals over ACK and the outer Cape given OES enhancement. As we know, northwest of the mid level Fgen bands, there is strong subsidence. Thus, a sharp cutoff in accumulating snow northwest of the Cape Cod canal. Hence, we lowered snow totals over southeast MA to 1-2", up to 3" southeast coastal Plymouth county give OES. Then an inch or less in the Boston-Providence corridor, with a shutout westward into CT/western-central MA. Snow will advance south to north early Sunday morning and continuing through the day and into Sunday night. Regarding winds, despite the low tracking well southeast of the 40N/70W benchmark, the sub 970 mb low and its low level NNE jet will scrap Cape Cod and the islands with 50-55 kt at 925 mb Sunday afternoon. Model soundings indicate NNE winds gusting up to 45 kt/50 mph are possible across the Cape and islands, with less wind northwest of the canal, with diminishing wind field aloft combined with a more northerly wind trajectory there. These wind speeds are covered in the winter storm watch. Key Message 3...Minor to perhaps moderate coastal flooding Sunday into Monday along the eastern Massachusetts coast. The potential for moderate coastal flooding continues to decrease as guidance continues to take this system furthur offshore, but areas of moderate flooding should be limited to locations south of Boston, especially on Cape Cod (Bay side), Martha`s Vineyard, and Nantucket, and is more likely during the Sunday evening and midday Monday high tides. Ensemble guidance still shows large ranges in possible water levels for Nantucket and Dennis, which is tied to uncertainty in storm track and timing of the highest surge. Farther north, these forecast ranges are much smaller which indicates higher confidence in minor flooding impacts from Boston to the Merrimack River. Since we still have a good amount of uncertainty, we decided to maintain the Coastal Flood Watch. If the storm trends even farther offshore, water levels and impacts would be lower than currently forecast, and would likely result in minor impacts for much of the coastline. Additionally, the timing of the highest surge appears to be near low tide Sunday afternoon, but if it is delayed (or arrives sooner) it would coincide closer to high tide and would lead to higher water levels and greater impacts, although a reasonable high- end scenario would still be within the moderate flood category. As a reminder: Minor flooding refers to shallow flooding up to 1 foot deep and can result in temporary road closures on more vulnerable coastal roads. Moderate flooding refers to flooding 1 to 3 feet deep and can cause more widespread road closures, damage to shorefront property, and debris on coastal roads from large waves. Vehicles left in flood prone areas can also be flooded. KEY MESSAGE 4...Dry, chilly start to next week with chances for another round or two of snow in the second half of the week. As this weekend`s storm wraps up Sunday night and moves out Monday, high pressure begins to build in over the Great Lakes and southern Ontario. This will bring a drying out period to southern New England for the start of next week along with easing winds as the pressure gradient relaxes. Afternoon highs Monday and Tuesday are likely to hover right around 32F, allowing for a little bit of melting of snow. However, given the clear skies and light winds, temperatures plummet overnight and range from single digits to mid teens across southern New England, refreezing any snowmelt and creating slick spots on untreated surfaces. Leading into the second half of next week, we`re starting to keep an eye on a couple of systems with possible impacts to southern New England. The first is a coastal low developing somewhere off the coast of NC/SC and moving northeast, possibly bringing a quick round of snow showers to the region Thursday/Friday. The second is a low sweeping out of the Canadian Rockies and across the Great Lakes late Friday into Saturday, possibly bringing gusty winds, colder temperatures, and another round of snow. Model guidance shows a large amount of uncertainty given these events are still 6-7 days away, but something to be aware of over the next week or so. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 06z update... Through Saturday...High confidence. VFR. Light WNW winds under 10 knots today Saturday night...moderate confidence. VFR and dry weather, but MVFR/VFR cigs arrive toward morning in eastern MA. Sunday/Sun night...moderate confidence. Periods of light snow/flurries this period with a combination of MVFR/VFR conditions. North winds 15-25 kt Sunday, become NNW Sun night. KBOS Terminal...High Confidence in TAF thru Saturday. Light WNW winds today around 10 knots KBDL Terminal...High Confidence in TAF through Saturday. VFR. Light WNW winds today under 10 knots. Outlook /Sunday Night through Wednesday/... Sunday: Mainly VFR, with local MVFR possible. Strong winds with gusts up to 45 kt. Chance SN. Sunday Night: VFR. Strong winds with areas of gusts up to 45 kt. Slight chance SN. Monday through Monday Night: VFR. Breezy. Tuesday through Tuesday Night: VFR. Wednesday: VFR. Slight chance SN. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Diminishing winds and seas today as high pressure builds in. A powerful ocean storm which tracks well south and east of the waters on Sunday. Potential for high end gales to low end storm force NE gusts to 40-50 kt over the waters starting Sunday morning. Seas expected to build to 15-20 ft on the waters east of Cape Cod resulting in dangerous conditions for mariners. In additions, areas of light to moderate freezing spray will develop Sat night/Sun morning and again Sun night. Outlook /Sunday Night through Wednesday/... Monday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 16 ft. Freezing spray likely. Monday Night: Winds less than 25 kt. Areas of rough seas. Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Tuesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Wednesday: Winds less than 25 kt. Slight chance of snow. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Cold Weather Advisory until 10 AM EST Saturday for CTZ002>004. MA...Cold Weather Advisory until 10 AM EST Saturday for MAZ002>019- 026. Coastal Flood Watch from Sunday morning through Monday afternoon for MAZ007-015-016-019-022>024. Winter Weather Advisory from 4 AM Sunday to 4 AM EST Monday for MAZ019-022>024. RI...Cold Weather Advisory until 10 AM EST Saturday for RIZ001>004. MARINE...Gale Warning from 7 AM Sunday to 1 AM EST Monday for ANZ230. Freezing Spray Advisory until 1 AM EST Saturday for ANZ231-235- 237-250-251-254-256. Gale Warning from 4 AM Sunday to 4 AM EST Monday for ANZ231- 232. Heavy Freezing Spray Warning until 1 AM EST Saturday for ANZ232>234-255. Freezing Spray Advisory from 4 AM to 1 PM EST Sunday for ANZ233>237-251-256. Gale Warning from 6 AM Sunday to 1 AM EST Monday for ANZ233- 234. Gale Warning from 3 AM Sunday to 1 AM EST Monday for ANZ235- 237. Gale Warning from 5 AM to 11 PM EST Sunday for ANZ236. Small Craft Advisory until 1 AM EST Saturday for ANZ250- 254>256. Gale Warning from 7 AM Sunday to 4 AM EST Monday for ANZ250. Gale Warning from 6 AM Sunday to 4 AM EST Monday for ANZ251. Storm Warning from 7 AM Sunday to 4 AM EST Monday for ANZ254- 255. Gale Warning from 4 AM Sunday to 1 AM EST Monday for ANZ256. && $$