Area Forecast Discussion

208 FXUS61 KBOX 040418 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1118 PM EST Tue Mar 3 2026 .WHAT HAS CHANGED... No significant changes regarding the wintry mix today into tonight, but temperatures Wednesday lowered slightly to account for lingering morning fog. Growing confidence on a rain- to- wintry mix transition Thursday night and Friday, possibly warranting winter weather headlines. Significant warmup this weekend into early next week, which could causes rises on smaller creeks and larger rivers as snow pack melts. && .KEY MESSAGES... - Mixed precipitation ongoing now through tonight. Snow accumulations between a coating and 2" with ice accretion up to 0.10". Localized higher amounts to 0.25" possible in the higher elevations. - Areas of black ice possible early Wednesday morning, but otherwise drier and milder for the rest of the day. Temperatures may be slow to rise due to lingering fog. - Wavy frontal boundary brings initial plain rain Thurs, but a transition to a wintry mix of freezing rain/sleet for areas north of the Mass Pike Thurs night into early Fri. Winter Weather Advisories could be needed. Expect a chilly, raw Friday after precip ends, with overcast and highs in the mid 30s. - Pattern change toward milder temperatures remains in the cards for the weekend. Snowmelt could cause within-bank rises on streams, creeks and larger rivers. && .DISCUSSION... KEY MESSAGE 1...Mixed precipitation ongoing now through tonight. Snow accumulations between a coating and 2" with ice accretion up to 0.10". Localized higher amounts to 0.2" possible in the higher elevations. Mixed wintry precipitation (mostly snow at this time) is moving across southern New England from SW to NE as this is written, with predominantly rain being reported along the immediate south coast. Not much has changed with regards to expectations with this system; snow accumulations are still expected to be highest north of I-90, reaching up to 2". Most everywhere else can expect around a coating to an inch of snow before the switch over to sleet and freezing rain. Precipitation should switch over to mostly rain in the next few hours, between 5 pm and 8 pm, as midlevel warm air moves in. Surface temperatures northwest of I-95 will remain at or below freezing through tonight, which will increase the risk for freezing rain during the transition from snow. Ice accretion will likely be highest in the higher elevations of the Berkshires and Worcester Hills, ranging between 0.1" to even 0.2" in some spots. Untreated surfaces will likely turn icy tonight. Rain and drizzle will continue through tonight, ending around daybreak tomorrow as the shortwave continues eastward. Lows tonight will mostly sit at or below freezing for most, with areas near the immediate coastlines more marginally above freezing. KEY MESSAGE 2...Areas of black ice possible early Wednesday morning, but otherwise drier and milder for the rest of the day. Temperatures may be slow to rise due to lingering fog. Lingering low level moisture, light winds, and continued marginal temperatures will increase the risk for some areas of fog and black ice for early Wednesday morning. Lower temperatures in the interior could lend to some freezing fog in this environment, too. Depending on how long any fog sticks around, high temperatures tomorrow will also be a bit cooler than previously thought, especially in the CT Valley where fog has the highest chance of lingering until around noon given the weak winds. Local sea breezes along the immediate coasts would also keep temperatures lower there, aside from any lingering fog. Lowered daytime highs to account for this risk using CONSRaw and CONSShort guidance. Highs are still generally in the upper 40s and do reach 50F in some spots across the interior, with mid to low 40s along the immediate coasts. Outside of any areas that see lingering fog, the subsidence following today`s/tonight`s shortwave will allow for significant sunshine and much drier, milder conditions. The midlevels dry out considerably, and weak high pressure builds in over the region for Wednesday. 850 mb temperatures increase to around 0C-4C and 925 mb temperatures increase to around 5C-7C Wednesday afternoon. This calmer period will not last long though, as the next chance for more unsettled weather will arrive Thursday with another passing shortwave disturbance. KEY MESSAGE 3...Wavy frontal boundary brings initial plain rain Thurs, but a transition to a wintry mix of freezing rain/sleet for areas north of the Mass Pike Thurs night into early Fri. Winter Weather Advisories could be needed. Expect a chilly, raw Friday after precip ends, with overcast and highs in the mid 30s. The next system in the parade of shortwave disturbances in WSWly flow aloft begins to affect Southern New England Thurs and lasts into the first part of Fri. This shortwave trough is now over the Colorado Rockies as of Tue late-morning, and is expected to drag an elongated, west-to-east frontal boundary northward to some extent in that Thurs to Fri timeframe. It now appears there are two main periods of precipitation. One comes in Thurs late-AM to early-PM with initial warm-advective burst, although will be falling as plain rain and QPF amts with this Thurs event look light. The somewhat bigger concern from a messaging standpoint however comes in during the Thurs early evening hours into early on Fri, as a more coherent wave of low pressure treks along the wavy frontal zone, while at the same time, shallow colder air entrenched over NH/ME surges southward in a cold-air-damming configuration. This allows for a transition from initial steady light rain Thurs evening to a wintry mix of sleet and freezing rain with the better potential for accreting icing around the higher terrain of the Berkshires, northern hills of Worcester County and in the Merrimack and MA portion of the CT Valleys. Although less impactful, it`s notable that the surge of shallow cold air is robust enough such that even plain rain in locations south and east of the Mass Pike could be mixed with sleet during the overnight to early Fri AM hours, given 950-925 mb temps drop to -2C as far south as southern CT. There are some forecast challenges and uncertainties which still need to be addressed, which include how far north will the warm front make it on Thurs/Thurs early evening (which affects how soon will any wintry precip begin to develop), and also the extent of QPF as model soundings start to dry out the layer above 850 mb. Current thinking is winter weather advisories could be needed for areas north of the Mass Pike; note that the anticipated precip-type-transition going from rain to wintry mix is an especially bad one from a road pre- treatment standpoint, as those pre-treatments would be washed away by the initial period of plain rain. Given active weather/current winter weather headlines ongoing, will refrain from hoisting those with this shift but those could be forthcoming in the coming forecast updates insofar as model guidance continues to agree on that scenario. As precip ends Fri mid morning to noon from west to east, Fri overall looks to be a chilly and raw day; temperatures very likely going nowhere given both the stubborn overcast but also the shallow CAD/cold advection profile surges southward into the Lower Hudson Valley through the day on NE winds. Have made substantial edits to NBM temps as its usual diurnal curve is simply not appropriate for this non-diurnal temperature setup, and instead blended in a fair amount of NAM-based temps for Fri. This supports highs only in the mid 30s to maybe near 40 along the south coast of RI/MA. KEY MESSAGE 4...Pattern change toward milder temperatures remains in the cards for the weekend. Snowmelt could cause within-bank rises on streams, creeks and larger rivers. Although Fri looks chilly and raw, a significant pattern change takes place for the weekend as anomalously strong SWly flow aloft advects in well above normal 850 mb temperatures Sat/Sun. These values could be as high as the mid-teens Celsius! These would be some 15 degrees Celsius warmer than climatological 850 mb temps for early March. While still warm, expectations should be tempered to an extent as both ECMWF/GFS show quite a bit of RH/cloud cover around and it`s not likely we`ll fully mix to that depth. Still, highs some 10-15 degrees above normal should materialize for Sat/Sun with highs in the 50s to even some spot 60s. Rising dewpoints into the mid 40s/around 50 will also eat away at the standing snow depth, too. There is a frontal system which looks to move in around Saturday night into Sunday, bringing light rains. Some rises on rivers could be anticipated during the weekend to early next week based on NAEFS MMEFS forecasts, mainly for the western watersheds. && .AVIATION /04Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 06z TAF Update... Today...Moderate confidence. Lingering areas of rain and freezing rain come to an end in most locations toward daybreak. Otherwise...IFR-LIFR conditions in areas of low clouds and fog linger into early this morning. While we do eventually expect improvement to VFR conditions...timing is uncertain and given weak boundary layer winds this could be a slow process especially in low-lying locations such as the CT River Valley. Most locations should be VFR by afternoon except perhaps parts of the lower CT River Valley. Winds becoming light WSW...but we may see some localized sea breezes along portions of the immediate coast this afternoon. Tonight...Moderate confidence. VFR conditions in the evening...but areas of low clouds and fog may develop late resulting in MVFR-IFR conditions with even localized LIFR cigs/vsbys. While low clouds and fog patches are possible anywhere late tonight...guidance seems to be indicating greatest risk for it being most widespread across CT/RI and southeast MA. Light/calm winds. Thursday...Moderate confidence. The initial morning low clouds/fog patches may briefly burn off. However...widespread MVFR to localized IFR conditions to overspread the region from southwest to northeast along with a shield of rain that may be mixed with sleet especially north of the MA turnpike. Light NE winds. KBOS Terminal...Moderate confidence in TAF. The main uncertainty is how long it takes the low clouds and fog to burn off this morning. The gradient may be weak enough for localized sea breezes to develop for several hours this afternoon. KBDL Terminal...Moderate confidence in TAF. The main uncertainty is how long it takes the low clouds and fog to burn off this morning. Low risk this may even take until sometime this afternoon. Outlook /Thursday Night through Sunday/... Thursday Night: Mainly IFR, with areas MVFR possible. Breezy. RA, PL, chance FZRA. Friday: MVFR/IFR conditions possible. Breezy. RA likely, chance FZRA. Friday Night: Mainly VFR, with areas IFR possible. Slight chance RA, slight chance FZRA. Saturday: Mainly VFR, with local IFR possible. Breezy. Slight chance RA. Saturday Night: Mainly VFR, with local IFR possible. Breezy. Chance RA. Sunday: VFR. Slight chance RA. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through Wednesday Night...High confidence. High pressure continues to move east of the waters today. This will result in long S-SW fetch and build seas into the 3 to 6 foot range late tonight into Wed across our southern waters. Small craft advisories remain in effect for our southern outer waters as a result. Seas start to diminish Wednesday night as Tuesday`s disturbance shifts further away from our waters and weak high pressure over southern New England during the day Wednesday shifts over the waters Wednesday night. S to SW winds become light to calm, particularly over the southern waters. Outlook /Thursday Night through Sunday/... Thursday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain. Local visibility 1 nm or less. Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Rain likely. Friday: Winds less than 25 kt. Areas of rough seas. Rain likely. Friday Night through Saturday: Winds less than 25 kt. Areas of rough seas. Slight chance of rain. Saturday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Chance of rain. Sunday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Winter Weather Advisory until 7 AM EST Wednesday for CTZ002>004. MA...Winter Weather Advisory until 7 AM EST Wednesday for MAZ002>012-014-026. RI...Winter Weather Advisory until 7 AM EST Wednesday for RIZ001. MARINE...Small Craft Advisory until 10 PM EST Wednesday for ANZ254>256. && $$ DISCUSSION...Loconto/Hrencecin AVIATION...Frank MARINE...Loconto/Hrencecin NWS BOX Office Area Forecast Discussion