AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 415 AM EST Sat Feb 21 2026 .WHAT HAS CHANGED... Winter Weather Advisories canceled for this morning. Little to no additional snow accumulation today. Given increased confidence in a high-impact storm, Winter Storm Watch expanded to include all of southern New England. Thinking that the highest snow totals will be along and SE of the I-95 corridor with slightly lower amounts farther inland. Blizzard conditions are possible near the coast, as well as RI and southeast MA. High Wind Watch consolidated into the Winter Storm Watch with a mention of possible blizzard conditions. && .KEY MESSAGES... - Light snow showers continue today with little additional accumulation expected. - A strong coastal storm likely brings a period of significant impacts to much of the region Sunday afternoon into Monday night. The area of highest snowfall and greatest impacts is still somewhat uncertain, but a widespread high-impact event appears more likely with the latest forecast cycle. && .DISCUSSION... KEY MESSAGE 1...Light snow showers continue today with little additional accumulation expected. Light snow showers are expected to continue through mid-morning today as an inverted trough remains over New England. However, the dendritic growth zone will dry out through this morning, leading to poor snow growth potential. Expecting very minor accumulations, if any, this morning, with northeastern MA most likely to see highest additional totals. KEY MESSAGE 2...A strong coastal storm likely brings a period of significant impacts to much of the region Sunday afternoon into Monday night. The area of highest snowfall and greatest impacts is still somewhat uncertain, but a widespread high-impact event appears more likely with the latest forecast cycle. Deterministic and ensemble models have come into better agreement with the powerful coastal low slated to impact our region Sunday afternoon into Monday night. The increasingly amplified trends of the last few model cycles have been driven by a much stronger downstream ridge. This change resulted in a quicker evolution of the upper level trough for Sunday afternoon from a neutral/positive tilt over the Ohio Valley on previous runs, to more of a negative tilt transposed several hundred miles east over the Mid Atlantic on more recent runs. With these changes to the upper air pattern, models have advertised solutions much closer to the coast. Consensus in guidance shows a more classic Nor`easter track with low pressure emerging off Cape Hatteras Sunday evening, then rapidly deepening as it passes near the 40N/70W benchmark Monday afternoon. Some guidance even shows this surface low getting captured by a deep upper level low Monday morning, which would result in a track inside the benchmark. Fortunately, these trends have helped to greatly reduce track variability amongst the deterministic guidance and ensembles. The GFS and NAM continue to show the most extreme solutions with a track inside the 40N/70W benchmark, while the ECMWF and Canadian have a track closer to the benchmark itself. So, while it is great to see better agreement in the synoptic details, the next forecast hurdle will be determining where the heaviest snow will fall. Given that we are still 2-3 days away, we aren`t quite in the range to start nailing down mesoscale features like banding or the location of heaviest snowfall. However, there are several synoptic clues that hint at a dynamic short term forecast ahead. As with most deep cyclones, this powerful coastal storm will feature a trough of warm air aloft (TROWAL). TROWALs help to increase frontogenesis and create banded precipitation patterns. Temperatures in this layer will rise to above 0C, helping to drive what will likely be some heavy bands of snow. The exact placement of these bands will depend on subtle differences in the track of the low center. Here, a change of even 25-50 miles could mean significant adjustments to the location of any one mesoscale band. A look at model soundings confirms the risk for areas of heavy snow with a deep dendritic growth zone collocated with -strong vertical motion. Snow ratios will suffer somewhat with the combination of a strong low level jet (LLJ) fracturing dendrites and marginal temperatures at the coast Monday afternoon. Another facet of this storm will be a period of strong to damaging winds Monday. Storms of this magnitude usually have a strong LLJ but it is less common to have also have a thermodynamic environment that allows winds aloft to readily mix to the surface. Looking at a 70-80 kt LLJ Monday that will pair with steep low level lapse rates to bring widespread strong to damaging winds. Confidence is highest across coastal zones where the NBM has a 50-70% chance for wind gusts over 50 mph for much of southern Rhode Island and coastal/SE Massachusetts. Given the trends and increased confidence we expanded the Winter Storm Watch to include the rest of the CWA. The latest NBM has a 50% chance of greater than 6 inches of snow all the way up to the NH border. Also mentioned the chance for blizzard conditions for much of S RI, SE MA, and the Cape/Islands where there is higher confidence in 3+ hours of blizzard conditions. Consolidated the High Wind Watch headline into the Winter Storm Watch with the mention of the blizzard conditions. Onset of the snow looks to be sometime Sunday afternoon into the evening hours, with the peak of the snowfall rates later Sunday night into Monday, before snow tapers off Monday evening. It`s possible dry air at onset could cause snow to hold off until Monday, something depicted toward end of 12km NAM run, so it`s also not out of the question that the bulk of the snow could fall during the day Monday. Finally, high astronomical tides Monday into Tuesday brings the potential for minor to moderate coastal flooding along eastern MA coast, depending upon timing of highest surge. Surge guidance and pattern recognition suggests a 3 foot surge around high tide early Monday morning and again early Tuesday morning, which could bring the water level to over 6 feet in Nantucket Harbor and to 13.5 feet in Boston, although wave impacts along the coastline would result in greater impacts (likely Moderate) as well as coastal erosion. Keep in mind large pressure falls would also add to the water level. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Today...Moderate confidence. CIGS gradually improve to MVFR/VFR late morning to early afternoon. Snow showers may linger into the afternoon esspically across western MA/CT, with light accumulations expected Tonight and Sunday...Moderate confidence. Mainly MVFR, with brief improvement to VFR this evening into Sunday morning. KBOS Terminal...Moderate confidence in TAF. KBDL Terminal...Moderate confidence in TAF. Outlook /Sunday Night through Wednesday/... Sunday Night: Mainly IFR, with local MVFR possible. Strong winds with gusts up to 50 kt. Chance SN. Monday: Mainly IFR, with areas MVFR possible. Strong winds with gusts up to 55 kt. SN. Monday Night: Mainly VFR, with local MVFR possible. Strong winds with gusts up to 50 kt. Chance SN. Tuesday through Tuesday Night: VFR. Breezy. Wednesday: Mainly VFR, with local IFR possible. Chance SN. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. High confidence. Rough seas will linger awhile longer offshore, then the developing coastal low as outlined above is expected to bring dangerous marine conditions later Sunday night and into Monday night. Outlook /Sunday Night through Wednesday/... Sunday Night: gale force winds with gusts up to 45 kt. Rough seas up to 17 ft. Snow, rain. Areas of visibility 1 nm or less. Monday: Moderate risk for storm force winds with gusts up to 55 kt. Rough seas up to 24 ft. Snow, rain. Visibility 1 nm or less. Monday Night: Low risk for storm force winds with gusts up to 55 kt. Rough seas up to 24 ft. Chance of snow. Local visibility 1 nm or less. Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 13 ft. Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain, slight chance of snow. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Winter Storm Watch from late tonight through Tuesday morning for CTZ002>004. MA...Winter Storm Watch from late tonight through Sunday morning for MAZ002>016-026. Winter Storm Watch from Sunday afternoon through Tuesday morning for MAZ002>024-026. Coastal Flood Watch from late Sunday night through Tuesday morning for MAZ007-015-016-019-022>024. RI...Winter Storm Watch from Sunday afternoon through Tuesday morning for RIZ001>008. MARINE...Gale Watch from late Sunday night through Monday evening for ANZ230. Storm Watch from Monday morning through Monday evening for ANZ231. Storm Watch from late Sunday night through Monday evening for ANZ232>234. Storm Watch from late Sunday night through Monday afternoon for ANZ235-237. Storm Watch from Monday morning through Monday afternoon for ANZ236. Storm Watch from Monday morning through Monday evening for ANZ250-251. Storm Watch from late Sunday night through Monday evening for ANZ254>256. && $$