Area Forecast Discussion

620 FXUS61 KBOX 300442 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1242 AM EDT Wed Apr 30 2025 .SYNOPSIS... A cold front crosses the region tonight...but nothing more than brief scattered showers are possible across parts of interior southern New England as the activity rapidly weakens as it moves east. Dry weather with pleasant temperatures is on tap for Wednesday and Thursday with fire weather concerns. Next chance for showers arrives early Friday with a few rounds of showers possible Friday and another round of rain for Saturday. Temperatures trend slightly above normal. Cold front moves in late Saturday bringing cooler temperatures for Sunday. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... Key Messages... * Decaying showers approach NW zones overnight * Breezy conditions continue overnight with frontal passage Details... A cold front will move through the region overnight into early Wednesday morning. Robust LLJ of 40-50+ knots will likely continue to bring periods of gusty winds, especially this evening. Southwest wind gusts should stay between 25 and 35 mph with perhaps a few brief gusts near 40 mph. Convection ahead of the cold front will quickly weaken as it approaches our CWA with the loss of daytime instability. Still, a shower, or downpour will be possible, mainly across northern and western Massachusetts. Most guidance has trended in line with this thinking, including even the HRRR, which has trended drier. Otherwise, it will be warmer than last night, with lows falling into the 50s for most locations. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/... Key Messages... * Cold front passage brings a drier airmass Wednesday * Another breezy and mild day with some fire weather concerns Details... Wednesday... A very pleasant post-frontal airmass will be ushered into the region on Wed. Plenty of sunshine and a bit of a northwest breeze especially during the first part of the day. While we will see cool advection working in aloft...the mild start coupled with the strong late April sun angle will result in highs mainly in the middle 60s to the lower 70s with the coolest of those readings mainly in the high terrain. Could see some fire weather concerns as much drier air aloft mixes to the surface. The NAM and GFS have -35C dewpoints near 800 mb, and so RH values will likely fall to between 15 and 25 percent for the CWA. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Key Messages: * Dry weather for Thurs...then turns unsettled by late week into at least the weekend. * Possible showers/thundershowers Thurs night/Fri, with perhaps another round of showers and embedded thunderstorms (a couple strong?) Fri aftn. * Another round of rainy conditions Sat. * Large uncertainty in pattern for early next week...including either dry weather and mild temps under high pressure, or cloudy/cooler and unsettled with periods of rain as low pressure lingers offshore. Details: Wednesday Night and Thursday: High pressure builds in for Wed night into Thurs, offering mostly clear skies and dry weather. Cooler Wed night with lows in the upper 30s to mid 40s under good radiational cooling, but temps then warm back up into the 60s to lower 70s with sunny skies for Thurs. Thursday Night and Friday: This period begins a rather unsettled stretch that lingers into the weekend, as a longwave trough over the central Plains sends a couple spokes of vort energy NE into New England. The first of these comes in Thurs night into Fri night, associated with a sub-1000 mb sfc low that treks through the St. Lawrence Valley. Warm front brings increased cloud cover and an initial period of showers moving in from SW to NE from eastern NY/parts of NJ. There is a modest burst of elevated instability associated with this activity and there could be some rumbles of thunder, with this shower/isolated t-storm activity during the 2nd half of the overnight into early Fri AM. Another round of showers and scattered t-storms could move in during the 2nd half of Fri or into early Fri night. Midlevel flow increases to produce effective shear magnitudes around 45-50 kt with MUCAPE values around 1000-1500 J/kg per GFS solutions; so it`s possible a couple storms could approach strong levels, especially if we can muster any surface heating. The extent of post-warm frontal cloudiness is the larger question not just on the t-storm potential, but also with respect to temps. NBM high temps well into the 70s to low 80s, perhaps a consequence of bias correction, could be too warm if we stay locked in with cloud cover. Rather large spread in temperature guidance suggests a lower-confidence high temp forecast. We may briefly dry out early Fri night, but the system`s frontal boundary stays nearby or washes out, setting the stage for the next round of showers/t-storms for Sat. Saturday: Second wave of sfc low pressure comes in on Sat along the stalled frontal boundary. There are some timing differences in the guidance as far as when the next round of rain comes in, but offered increasing PoPs into the Likely range for early Sat aftn into early Sat night before gradually tapering off toward early Sunday morning. Again pretty substantial difference in temperature guidance for Sat but offered highs in the mid 60s to low 70s. If rain is delayed, then temps could be quite a bit warmer. Sunday into Early Next Week: Weather pattern Sunday into early next week becomes lower-confidence with pretty large differences in mass-field depictions. The GFS offers drier weather with ridging and milder temperatures. However the international guidance (ECMWF/GEM) offer up a rather dreary, unsettled weather pattern as an upper low closes off near or offshore of Southern New England, with clouds, onshore flow and periods of rain showers. Very messy, changeable pattern and stuck with NBM until there`s better agreement. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 06z TAF update... VFR. Gusty SW winds continue, especially across the Cape/Islands. Tonight...High Confidence. SW wind gusts of 20 to 30 knots with a few gusts near 35 knots possible towards the Cape. LLWS will also develop across much of SE Massachusetts and are included in many of the TAFS. Wednesday...High Confidence. VFR. NW wind gusts of 20 to 25 knots with the strongest of the winds through mid-afternoon. KBOS TAF...High Confidence in TAF. KBDL TAF...High Confidence in TAF. Outlook /Thursday Night through Sunday/... Wednesday Night through Thursday: VFR. Thursday Night: Mainly VFR, with local MVFR possible. Chance SHRA, isolated TSRA. Friday: Mainly VFR, with local IFR possible. Breezy. Chance SHRA, isolated TSRA. Friday Night: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA, slight chance TSRA. Saturday: Mainly MVFR, with local IFR possible. Breezy. SHRA likely, slight chance TSRA. Saturday Night: Mainly VFR, with local MVFR possible. SHRA likely, slight chance TSRA. Sunday: Chance SHRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today and tonight...High Confidence. High pressure moves off the mid-Atlantic coast as a cold front approaches from the northwest later today and tonight. The result will be a modest LLJ allowing for SW wind gusts of 25 to 35 knots to develop this afternoon and persist into tonight. We went with strong small craft advisories for most waters...but did go with Gale Warnings for Buzzards Bay/MVY sound and Cape Cod Bay where where excellent mixing nearshore should allow for 35 knot wind gusts at times. Seas will become quite choppy this afternoon and continue into tonight. Wednesday...High Confidence. Winds shift to the NW by daybreak Wed behind the cold front. We may have some marginal morning small craft northwest wind gusts near shore across eastern MA. While these winds should diminish some during the afternoon...lingering swell will result in the need for continuation of small craft advisories for seas across our southern waters. Outlook /Thursday Night through Sunday/... Wednesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Thursday: Winds less than 25 kt. Thursday Night: Winds less than 25 kt. Chance of rain showers. Friday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers. Friday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers, slight chance of thunderstorms. Saturday: Winds less than 25 kt. Local rough seas. Chance of rain showers, slight chance of thunderstorms. Saturday Night: Winds less than 25 kt. Local rough seas. Chance of rain showers, isolated thunderstorms. Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. && .FIRE WEATHER... After collaboration with our surrounding WFO/s and Fire Weather Partners...an SPS remains in effect today for the potential of elevated Fire Spread. This is for the combination of minimum afternoon relative humidity values dropping to between 25 and 35 percent with SW wind gusts on the order of 25 to 35 mph later today. As for Wednesday...winds will not be quite as strong but some NW 25+ mph wind gusts will be possible especially during the first part of the day. Minimum relative humidity values will be lower on the order of 15 to 30 percent with drier NW flow behind the cold front. We will be reaching out to the Fire Weather partners for the potential of additional statements. && .TIDES/COASTAL FLOODING... Despite very quiet weather, very high astronomical tides will result in the potential for splashover or very minor coastal flooding again during the early Wednesday morning high tide along parts of the eastern MA coast. The MLLW Astro tide at BOS is 12.0 feet shortly before 130 AM Wed morning. We may need another Coastal Flood Statement for some minor splashover, but really not looking at any real impacts especially given the time of occurrence. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until noon EDT today for ANZ230-232-235- 237-251. Gale Warning until 2 AM EDT early this morning for ANZ231-233- 234. Small Craft Advisory until 8 AM EDT this morning for ANZ236- 250. Small Craft Advisory until 10 PM EDT this evening for ANZ254>256. && $$ SYNOPSIS...Belk/Loconto/FT NEAR TERM...Belk/FT SHORT TERM...Belk/FT LONG TERM...Loconto/McMinn AVIATION...Loconto/McMinn MARINE...Belk/KJC/Loconto/FT FIRE WEATHER...Belk/Loconto/FT TIDES/COASTAL FLOODING...Belk/Frank/FT NWS BOX Office Area Forecast Discussion