673 FXUS61 KBOX 100034 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 734 PM EST Sat Mar 9 2024 .SYNOPSIS... Widespread rain tonight, heavy at times with renewed minor river/stream flooding possible, along with street/highway flooding. Minor tidal flooding likely Sunday morning into early afternoon along both MA and RI coastlines. Drying on Sunday, with gusty winds but mild. Dry weather continues into early next week, but blustery and colder, then milder by mid week. Unsettled weather is possible late next week and/or weekend. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... 730 PM update: Previous forecast remains on track, thus no major changes with this update. Winds slowly increasing, now up to 29 kt at KBID. Leading edge of low level jet and PWAT plume arrive into western CT/MA around 03z, then eastward across the region overnight before departing eastern MA/Cape Cod around 12z Sunday. Thus, strongest winds and heaviest rain roughly 1 AM to 6 AM from west to east overnight. Any wet snow mix will be brief later this evening and confined to the high terrain of the Berks and Worcester Hills. Little if any impact with temps above freezing. Previous discussion. The real trouble with this system comes overnight as low pressure links up with mid level trough pivoting into the region from the Great Lakes, which will allow for substantial deepening of the low after midnight tonight. As a result, will see more widespread moderate rain to fall between 00-12Z tonight. This system is quite progressive, with rain/snow exiting the region by 12Z Sunday morning; a notable shift in the 00Z hi-res guidance compared to yesterday's 12Z runs. PWATs climb to near 1" overnight which should be able to tap into some LLJ forcing, ringing out between 1 and 1.5" of rain across the area; isolate pockets of 2" of rain are possible. Given Flood Warnings remain in place for many rivers from our last system, decided to forgo a Flood Watch, as the main flood threat associated with this rainmaker is continued river flooding. Outside of the highest peaks of the Berkshires, precip should begin as all rain, but will transition to snow above 800ft as temperatures cool overnight. Guidance remains split on the high elevation accumulation potential, with the NAM highlighting a possibility of more than 6"of snow!, but given warm and wet antecedent conditions, relied on positive snow depth change amounts to derive our forecast of pockets of 2-4" of snow in western Franklin and Hampshire counties. Its certainly not out of the question that portions of Franklin county exceed winter weather advisory snowfall, but confidence was too low to issue the product with hopes that the afternoon shift will have more consensus between models. LLJ, briefly mentioned above, appears quite impressive as low deepens overnight, with 925mb winds forecast between 70-85kt; the NAM is far and away the strongest guidance, and may potentially be picking up on some convective feedback. Nonetheless, winds will be quite strong off the deck, but a deep inversion combined with southeast flow, traditionally very bad for mixing out an inversion, should keep the worst of the winds off the surface. Given the strength of the jet, even 50% of gusts mixing to the surface will easily approach wind advisory criteria across the Cape and Islands. Thus, a Wind Advisory has been hoisted for Nantucket and Cape Cod overnight tonight. The advisory may be expanded to Martha's Vineyard and perhaps eastern Essex County in future updates depending on how guidance trends over the next 12 hours. Given the faster anticipated departure of this system compared to 12 hours ago, coastal flooding appears to be significantly less of a threat as the worst of the winds/LLJ will be northeast of our area by the morning high tide. Enough clarity was gained overnight to convert the Coastal Flood Watch to an Advisory for the eastern MA coast. However, the forecast shifted quite considerably for the south coast and RI, such that what looked to be solid moderate coastal flooding may now amount to less than minor coastal flooding. Given the wild swing in guidance in just 12 hours, elected to keep the watch in place for the next shift to take one last look. More details in the Coastal Flooding section of this AFD. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... Precip comes to an end by 12Z Sunday as rain/snow lifts north into NH and VT. Drier air begins to advect into SNE as winds shift to the W/NW. Anticipating it will be blustery on Sunday as 25-30kt winds mix to the surface behind departing low pressure. 500mb low settling in the base of the trough will keep mid level RH values between 60 and 75%, which will battle PWATs falling to near 0.25" by late Sunday afternoon. Anticipating this will lead to a mix of sun and clouds late day, with the chance of some rain and snow showers across the high terrain where what little moisture there is can tap into the upsloping winds to ring out a little QPF. Despite lingering scattered clouds, it should be a seasonably mild day across SNE, with highs warming into the upper 40s to mid 50s outside the high terrain. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... 335 PM update... Key Points... * Dry much of next week, then possibly unsettled Fri/Sat * Blustery & chilly Mon, moderating Tue then a warming trend with highs in the 50s and 60s beginning Wednesday and into Saturday Sunday night and Monday... Northern stream short wave and associated strong CAA overspread the region, with 850 mb temps lowering to about -8C this period. This will yield a winter chill with lows Sun night 25-30, but gusty west winds 15-25, up to 40 mph at times will yield WCI in the teens and 20s. Cold air aloft combined with downslope winds Mon will only support highs of 40-45, upper 30s high terrain. Monday could be very windy as maritime cyclone deepens to a sub 980 mb low. This combined with CAA and strong March sun promoting a deep mixed layer, possibly yielding gusts up to 50 mph! Wind headlines may be needed. Also, these strong winds and cold airmass will yield WCI in the 20s and 30s. Other than a brief rain/snow shower from lake effect moisture and upslope flow across the high terrain inland, dry weather will be featured, along with SCT-BKN diurnal SCU. Tuesday thru Saturday... Closed maritime low slowly exits into the NW Atlantic, thus not as windy or cold Tue. Then more of a Pacific regime airmass overspreads SNE mid week, with temps warming into the 50s and 60s Wed/Thu/Fri and possibly into Sat. Dry weather appears likely Wed and Thu, then possibly becoming unsettled Friday/Saturday. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 00z update...high confidence on trends, slightly lower on exact timing details. No major changes to the 00z TAFs. Strongest surface winds, LLWS and heaviest rain roughly 05z to 11z west to east tonight/early Sunday morning. Earlier discussion below. ------------------------------------------------------------------- Rest of Today...High Confidence MVFR with dry conditions this afternoon. Light rain should hold off until this evening. Winds pick up this afternoon with southerly gusts up to 20 knots. Tonight...Moderate Confidence IFR with localized LIFR. Light rain starts this evening between 22-02z in the west and 00z-04z in the east. Rain becomes moderate to heavy around and after midnight. Winds will continue to pick up esspically near coastal zones where 35-45 knots are possible. Otherwise gusts of 25-35 knots will be widespread tonight. Wind direction turns ESE tonight. Wind shear will also be a concern tonight with a 50-60 knot winds above 2kft. Tomorrow...Moderate Confidence Rain should come to an end from west to east tomorrow between 09z-12z. As rain comes to an end, wind and wind shear will decrease, along with ceilings improving rapidly from IFR/LIFR to MVFR/VFR. completely VFR by tomorrow afternoon. KBOS TAF...Moderate Confidence. MVFR this afternoon will give away to IFR this evening as light to moderate rain works in. Winds turn ESE tonight with gusts of 35-40knots. Winds above 2k ft will be at 60 knots. Rain ends early tomorrow morning between 10z and 12z with rapid improvement's to MVFR/VFR thereafter. KBDL TAF...High confidence. MVFR this afternoon. IFR with light to moderate rain and gusty ESE winds. Rain ends around 09z with IFR improving MVFR/VFR. Outlook /Sunday Night through Thursday/... Sunday Night: VFR. Strong winds with local gusts up to 40 kt. Monday: Mainly VFR, with local MVFR possible. Strong winds with gusts up to 45 kt. Monday Night: VFR. Strong winds with gusts up to 50 kt. Tuesday: VFR. Strong winds with local gusts up to 40 kt. Tuesday Night: VFR. Breezy. Wednesday through Thursday: VFR. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 330 PM update... * SE Gales tonight/early Sun, then west gales likely Sun night into Monday Tonight... Strengthening low pressure takes an inside track along the coast then into SNE, with SE gales overspreading the waters. Heavy rain at times and fog will yield poor vsby. Strongest winds roughly 1 AM to 7 AM west to east. Sunday... WSW winds 15-25 kt, drier with vsbys improving in the morning with the wind shift from SE to SW. Although, rough seas continue with leftover SE swells combining with WSW wind waves. Sunday night... West winds trending to WNW and increasing to near gale force by Monday morning. Dry weather and good vsby. Outlook /Sunday Night through Thursday/... Monday: Strong winds with gusts up to 40 kt. Rough seas up to 11 ft. Monday Night: gale force winds with gusts up to 40 kt. Rough seas up to 11 ft. Tuesday: Low risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Tuesday Night: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Areas of seas approaching 5 ft. Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Wednesday Night through Thursday: Winds less than 25 kt. && .TIDES/COASTAL FLOODING... 335 PM update... * The entire coastline of MA & RI is now covered by a Coastal Flood Advisory for the Sunday morning and early afternoon high tide. Given the strongest winds, peak storm surge and max pressure falls will not coincide with high tide Sunday morning/early afternoon, moderate coastal flooding is not expected. Therefore, a coastal flood advisory has been issued for the entire MA/RI coastline, to message the expectation of minor coastal flooding. As for coastal erosion, not expecting significant erosion given the reasons listed above along with large wave development not expected due to the short duration of strong winds and the storm only impacting one tide cycle. Storm surge values of 1.5 to 2.5 ft are expected. Given high astronomical tides, this will be sufficient to produce widespread minor inundation and erosion along the entire MA/RI coastline. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Flood Watch through Sunday morning for CTZ002>004. MA...Flood Watch through Sunday morning for MAZ002>021-026. Wind Advisory from midnight tonight to 10 AM EST Sunday for MAZ006-007-014>024. Coastal Flood Advisory from 9 AM to 4 PM EST Sunday for MAZ007- 015-016-019. Coastal Flood Advisory from 6 AM to 2 PM EST Sunday for MAZ020>024. RI...Flood Watch through Sunday morning for RIZ001>004-006-007. Wind Advisory from midnight tonight to 10 AM EST Sunday for RIZ002>004-006>008. Coastal Flood Advisory from 6 AM to 2 PM EST Sunday for RIZ002- 004>008. MARINE...Gale Warning from 4 AM to 9 AM EST Sunday for ANZ230-236. Gale Warning until 11 AM EST Sunday for ANZ231-232-250-254-255. Gale Warning until 8 AM EST Sunday for ANZ233>235-237-256. Gale Warning from midnight tonight to 11 AM EST Sunday for ANZ251. && $$ SYNOPSIS...Nocera/KS NEAR TERM...Nocera/KP SHORT TERM...KP LONG TERM...Nocera AVIATION...Nocera/KP MARINE...Nocera TIDES/COASTAL FLOODING...Nocera