AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 712 PM EST Wed Dec 17 2025 .WHAT HAS CHANGED... Wind Advisories added for southern New England, except for the Cape and Islands where a High Wind Watch remains. This will be in effect early Friday morning through early Saturday morning. && .KEY MESSAGES... - Dry weather with mild temperatures Thursday. - Widespread rain with strong to possibly damaging winds late Thursday night into Friday. - The risk for minor coastal flooding for south-facing shore during Friday morning high tide has diminished. - System moves through late Saturday into Sunday bringing light rain Saturday and gusty winds for Sunday. && .DISCUSSION... KEY MESSAGE 1...Dry and milder Thursday. Expect to see winds drop off overnight tonight into Thursday morning, with even warmer temperatures in the mid 40s to low 50s. KEY MESSAGE 2...Locally heavy rainfall and strong to possibly damaging winds. A deep trough moves across the northeast late Thursday and Friday. Ahead of this trough a strong LLJ, several standard deviations above normal in magnitude develops. This will help transport above normal moisture into the region (200-300% of normal). PWATS have also been flagged by NAEFS as considerably above normal values. This will support not only rain, but a period of heavy rainfall. In terms of timing of the rain, showers are possible Thursday night, becoming more steady into early Friday morning. Strong convergence and marginal instability later Friday morning into early afternoon will bring the additional forcing to bring a period of moderate to heavy rain with perhaps an isolated rumble of thunder. This system should be quick moving which will limit the potential for this being an excessive rainfall event. Ensemble guidance shows values 0.50-1.00" for rain totals with indications of locally higher amounts. This is consistent with the potential for a few weak thunderstorms and the upper percentiles of ensemble guidance. Localized spots may receive 1-2 inches in the more persistent downpours. Given the morning timeframe, this means it may impact the morning commute on Friday. Minor urban and poor drainage street flooding is possible, but given the quick progression of the rain, no major flooding impacts are expected. As the cold front pushes through in the afternoon, there will be strong drying behind it which will taper off the rain other than some scattered showers in the afternoon/evening as the trough approaches. Any showers over the high terrain will become more favored as light snow showers or flurries in the early evening. Regarding the wind potential...a 70-80 kt LLJ develops across southeast southern New England Friday morning with the strongest core of the winds shifting over the Cape and Islands toward the afternoon. The challenge (as it usually is with southerly LLJ events) is how much wind will mix down to the surface. Model soundings display an inversion in the thermal profiles across southern New England Friday morning with a stronger inversion present over the Cape/Islands. What this means is that we will need additional warming to efficiently mix down the stronger winds aloft. Model guidance indicates continued warm air advection Friday morning with subtle differences in how warm it ends up getting. We will likely need temperatures around 57-59F for the deeper mixing. Now that we are getting in high-resolution guidance, it is appearing to be close with temperatures warming into the mid-50s with some solutions showing temperatures approaching 60 as the LLJ shifts across. Using more conservative approach, given the uncertainty of deeper mixing, 50-60 percent yields gusts 40-55 mph with the strongest gusts SE MA, most consistently for the Cape/Islands late AM to mid-afternoon. If temperatures end up warmer, gusts 60+ are possible. Ensemble guidance continues to highlight moderate probabilities for 50 kts or greater for SE MA as well as portions of the south coast. Pressure falls and even the marginal convection may also be features that can contribute to bringing down stronger gusts. With reasonable justification for the potential of high winds, the Cape/Islands remain in a High Wind Watch. As confidence in the thermal profiles increases this will be converted to either a Warning or Advisory. Wind Advisories have been added for the rest of southern New England. Another round of strong winds are possible Friday night into early Saturday. Strong cold advection behind a cold front and 40-50 kt westerly LLJ will promote a period of strong west winds. Ensembles show high probabilities for gusts 40 mph or greater for the higher terrain of the interior and Cape/Islands. Model soundings show potential for gusts 45-55 mph. With the additional downslope enhancement off the slopes of the Berkshires, can`t rule out a gust or two to 60 mph Friday night. Advisories extend through Saturday morning to cover this period, but it is possible that the more consistent advisory (45 mph+) level gusts stay confined to the higher terrain and Cape/Islands rather than all of southern New England. KEY MESSAGE 3...Diminishing risk for minor coastal flooding Latest guidance continues to suggest the timing of the low level jet and highest surge will occur a few hours after high tide Fri morning which would likely preclude minor coastal flood impacts along the south coast. The greatest risk would be for Narragansett Bay and Buzzards Bay, but it would take a storm surge of 2.5 to 3 ft during high tide to produce minor flooding. Latest guidance from the Stevens Institute indicated a 2-2.5 ft surge for Providence but occurring after high tide. The 95th percentile which represents a 5 percent exceedance probability has Providence slightly exceeding the 7 ft flood stage but this is a very low probability at this time. It would take more favorable timing of the strongest winds at high tide and a worst case wind forecast to realize this potential, which would yield just minor flooding impacts along Narragansett and Buzzards Bay. KEY MESSAGE 4...System moves through late Saturday into Sunday bringing light rain and gusty winds. A mid-level shortwave trough moves through late Saturday into Sunday. Moisture will be fairly marginal which will limit precipitation to scattered light showers. A SW 40-60 kt LLJ nudges northward Sunday night bringing at gusts 30-40 mph to at least the coastal waters. This will be followed by a front which will favor efficient mixing from the higher winds aloft while in the CAA regime on Sunday. Still further out, but gusts 30-40 mph are possible in the afternoon. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 00Z TAF Update: High confidence. Tonight and Tomorrow ...High Confidence VFR. W this evening become light overnight, then shift southerly around 10 kt Thu afternoon. Tomorrow Night...High Confidence in trends MVFR/IFR ceilings overspread the region from west to east tomorrow night with RA. Winds increase out of the south with sustained speeds of 15 to 20 knots and gusts approaching 25 to 35 knots by Friday morning. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Friday Night through Monday/... Friday: Mainly MVFR, with local IFR possible. Strong winds with gusts up to 45 kt. RA. Friday Night: VFR. Strong winds with gusts up to 45 kt. Saturday: VFR. Windy with local gusts up to 30 kt. Saturday Night through Sunday: VFR. Windy with local gusts up to 30 kt. Slight chance RA. Sunday Night: VFR. Windy with local gusts up to 30 kt. Monday: Breezy. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through Thursday...High confidence. Winds decrease and seas subside briefly during the day Thursday. Winds increase late Thursday night into Friday morning with Gale force winds likely by 12Z Friday continuing through Saturday morning. Seas increase to 6-10 ft Friday over the outer waters with 10-12 ft possible for the southern outer waters late AM to early afternoon Friday. Outlook /Friday Night through Monday/... Friday: gale force winds with gusts up to 45 kt. Rough seas up to 16 ft. Rain. Friday Night: gale force winds with areas of gusts up to 45 kt. Rough seas up to 16 ft. Slight chance of rain. Saturday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 11 ft. Saturday Night: Low risk for gale force winds with gusts up to 35 kt. Seas up to 5 ft. Sunday: Strong winds with gusts up to 35 kt. Areas of rough seas. Slight chance of rain. Sunday Night: Strong winds with gusts up to 40 kt. Seas up to 5 ft. Monday: Strong winds with gusts up to 35 kt. Areas of rough seas. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Wind Advisory from 4 AM Friday to 1 AM EST Saturday for CTZ002>004. MA...Wind Advisory from 4 AM Friday to 1 AM EST Saturday for MAZ002>021-026. High Wind Watch from Friday morning through Friday afternoon for MAZ022>024. RI...Wind Advisory from 4 AM Friday to 1 AM EST Saturday for RIZ001>008. MARINE...Gale Warning until 7 PM EST this evening for ANZ230>237-251. Gale Watch from Friday morning through Saturday morning for ANZ230. Gale Watch from late Thursday night through Saturday morning for ANZ231>234-251. Gale Watch from late Thursday night through Saturday morning for ANZ235-237. Gale Watch from late Thursday night through late Friday night for ANZ236. Gale Warning until 1 AM EST Thursday for ANZ250-254>256. Gale Watch from late Thursday night through Saturday morning for ANZ250-254>256. && $$