AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 224 PM EST Sat Dec 20 2025 .WHAT HAS CHANGED... Small Craft Advisories and Gale Watches upgraded to Gale Warnings. Small Craft Advisories hoisted for Narraganset Bay and Boston Harbor. Confidence in minor snow accumulations has increased on Tuesday...particularly across interior southern New England. High uncertainty on temperatures Friday into next weekend. && .KEY MESSAGES... - Gusty southwest winds overnight especially at higher elevations and near the coast. - Turning much colder Sunday night into Monday with gusty northwest winds. - Minor accumulating snow expected Tue especially across the interior where 1-3" seems reasonable with localized 4" amounts possible in the higher terrain. - Dry with highs in the 30s to lower 40s follow Wed & Thu /Christmas Day/ but will be quite blustery Wed with less wind Thu /Christmas/. - Low confidence forecast Fri into next weekend with unseasonably mild temps to our southwest and very cold air just to our north. Shallow cold air and wintry mix possible at times in our region. && .DISCUSSION... KEY MESSAGE 1...Period of gusty southwest winds overnight tonight. High pressure will be slow to move offshore overnight. At the same time an area of low pressure over southern Canada moves towards northern New England. The resulting pressure gradient will bring a period of gusty SW winds tonight especially over higher terrain and along immediate coast where SW gusts to 25-35 mph expected. 15-25 mph gusts elsewhere. Clouds increase tonight but dry weather will prevail with steady or slowly rising temps overnight as winds increase. KEY MESSAGE 2...Turning colder and blustery late Sun into Sun night Strong cold front swings through from west to east between 15-18z. Dry FROPA expected with a bone dry column and PWATS around 0.10 inches. Thus, went with the NBM with near-zero POPs for the region tomorrow. Expecting a gusty SW wind ahead of the front, namely for coastal locations where better mixing is present. Will likely see gusts around 25-35 mph. Increasing PBL heights and a 45kt LLJ behind the front will bring similar winds later Sunday into Monday morning. Winds gradually diminish through Monday as the pressure gradient weakens. Seasonable temps Sun ahead of the front then falling temps behind the front Sun afternoon, especially interior and turning much colder Sun night as 850 mb temps bottom out at -12 to -15C. Wind chills by Mon morning will drop to 5-10F and near zero in the Berkshires. Temps will be several degrees below normal Mon with highs upper 20s and lower 30s and plentiful sunshine in very dry airmass. KEY MESSAGE 3...Minor accumulating snow expected Tue especially across the interior where 1-3" seems reasonable with perhaps localized 4" amounts possible across the higher terrain. A ridge of high pressure moves off the coast as a fast moving low pressure system approaches from the west on Tue. This combination will result in WAA developing across southern New England. An initially cold boundary layer should allow for snow to develop in most locations near daybreak Tue. Given that there is not a surface high pressure system in eastern Canada and assuming that the surface low tracks to our north...would expect Ptype issues to develop near and especially southeast of I-95 Tue afternoon. Regardless...this looks to be a minor snow event with the greatest risk across the interior where boundary layer issues are less of a concern. Currently...thinking 1-3" of snow seems reasonable especially across interior southern New England with perhaps some localized 4" amounts in the higher terrain. That being said...there is still uncertainty given this is a Day 3 forecast. The 12z GFS operational run is a big outlier that is further south with the low pressure system than the rest of the guidance...this results in colder thermal profiles. It also indicates additional QPF Tue night with an inverted trough setup. We think this is a very low probability because it does not even have support from most of its individual ensembles...but would bring the potential of several inches of snow right to the I-95 corridor. KEY MESSAGE 4...Dry with highs in the 30s to lower 40s follow Wed & Thu /Christmas Day/ but will be quite blustery Wed with less wind Thu /Christmas/. Low pressure will intensify significantly as it moves east and away from the region. This combined with high pressure over the Great Lakes will result in dry/blustery conditions with chilly temps Wed. A ridge of high pressure builds to our south Thu resulting in dry/seasonable chilly temperatures but with less wind. High temps Wed and Thu /Christmas/ will be in the 30s to the lower 40s with Christmas being the milder day. KEY MESSAGE 5...Low confidence forecast Fri into next weekend with unseasonably mild temps to our southwest and very cold air just to our north. Shallow cold air and wintry mix possible at times. A very difficult forecast Friday into next weekend given our region may end up in the battle zone. Unseasonably mild weather just to our southwest with very cold/below normal winter-like temperatures just to our north and northeast. We may be dealing with shallow cold air at times and perhaps a bit of rain/ice and/or snow at times. Not much more we can say at this point...but appears we may not share in the unseasonably mild temps much of the time impacting most of the lower 48. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 18z TAF Update...no significant changes. Tonight through Saturday...High Confidence in trends VFR conditions expected. SW winds through this afternoon and tonight. SW gusts 25-30 kts resume late tonight into Sunday morning, mainly along the immediate coast and Islands and higher terrain. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Monday Night through Thursday/... Monday Night: VFR. Breezy. Tuesday: Mainly IFR, with areas MVFR possible. Breezy. SN, RA. Tuesday Night: Mainly VFR, with local IFR possible. Windy with gusts up to 35 kt. Chance SHRA, slight chance SHSN. Wednesday: VFR. Windy with gusts up to 35 kt. Wednesday Night: VFR. Breezy. Christmas Day: VFR. Breezy. Slight chance SHRA. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through Monday...High Confidence. Southwesterly gales develop tonight ahead of a cold front. Winds of 25-35 kts expected with gusts as high as 40 kts. Gale warnings for the inner and outer coastal waters go into effect at 06z tonight and go through 12z Monday morning. Elsewhere, Small Craft Advisories for Narragansett Bay and Boston Harbor. Gradual improvements on Monday. Outlook /Monday Night through Thursday/... Monday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Tuesday: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Local rough seas. Rain likely, snow likely. Local visibility 1 to 3 nm. Tuesday Night: Low risk for gale force winds with local gusts up to 45 kt. Areas of rough seas. Chance of rain showers. Wednesday: Moderate risk for gale force winds with local gusts up to 45 kt. Areas of rough seas. Slight chance of rain showers. Wednesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Christmas Day: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 1 AM Sunday to 7 AM EST Monday for ANZ230-236. Gale Warning from 1 AM Sunday to 7 AM EST Monday for ANZ231>235-237-250-251-254>256. && $$