Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 080757 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 357 AM EDT Thu Jun 8 2023 .SYNOPSIS...
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Similar conditions expected Thursday, Friday and Saturday, not a washout, but scattered afternoon showers each day, perhaps most numerous Friday. Temperatures will continue to run slightly cooler than normal. There will also be some near ground level smoke at times, as a result of the ongoing Canadian wildfires. A brief pattern change occurs Sunday and possibly lingering into Monday, bringing drier and warmer conditions to the region. Then the next frontal system may bring widespread rain to the region around Tuesday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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330 AM update... * Dry this morning, then scattered afternoon showers Vertically stacked low over Maine early this morning retrogrades westward into NH today. As this mid level circulation moves closer to SNE, the main belt of westerlies and associated short wave energy shifts farther west and south of SNE. Thus, forcing for ascent remains weak today. Also, with highs only 65-70 combined with dew pts only in the upper 40s and lower 50s, this only generates SB Capes on the order of 100-200 j/kg. Hence, not much SB instability to work with, despite cyclonic flow aloft. Cold pool of -20C at 500 mb will provide steep mid level lapse rates, and this should be sufficient for scattered afternoon showers. Low risk of an isolated thunderstorm, but thinking overall activity is isolated to scattered given lack of deep layer shear and SB instability. Otherwise, many hours of dry weather today. Lots of clouds, most abundant away from the south coast. Hence, most sunshine along the south coast this morning, then filling in with diurnal clouds as strong June sunshine combines with -20C at 500 mb. Cold pool aloft cools the column with only +11C at 925 mb, yielding highs only 65- 70 today. Normal high is 72-77. Light WNW winds becoming locally onshore at the coast, yielding cooler high temps for the day.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
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345 AM update... * Showers may become more widespread Friday Tonight... Any diurnal early evening scattered showers diminish with or shortly after sunset. Given cold pool aloft, light winds and decreasing diurnal clouds, another chilly night. Lows 45-50 with low 50s along the coast, including the city of Boston. Normal low, 52-57. Friday... Vertically stacked low remains over northern New England, but some short wave energy dives into the backside of the trough and backs the mid level flow to more SW over New England. This results in more cyclonic flow aloft and greater moisture & instability advection into SNE. PWATs rising to near 1 inch and surface dew pts climb into the 50s. This combined with steep mid level lapse rates will provide sufficient instability for scattered showers and and isolated thunderstorms. Given the increased instability coupled with weak forcing for ascent, showers could be more widespread Friday than Thursday. Cold pool aloft (-21C at 500 mb) limits highs to the mid and upper 60s Friday, perhaps a few 70 deg readings in the CT River Valley. Winds light and variable except locally onshore.
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&& .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
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345 AM update... Highlights * Warmer this weekend with more showers on Saturday and drier weather on Sunday * Unsettled weather returns early next week as a new area of low- pressure moves over The Northeast Saturday The upper low that`s been sitting over The Northeast this week will finally lift out and fill during the first half of this weekend. This will allow warmer air to advect in from the west as a mid-level ridge builds east. Despite the upper-low ejecting away from the region, cold air aloft will continue to support steep lapse rates through the column. Additionally, there will remain sufficient moisture in the column to support more diurnal showers and thunderstorms on Saturday afternoon. With 925 hPa temps warming to 12 to 13 Celsius on Saturday, we`re currently expecting surface temperatures to top out in the low to mid 70s. This combined with steep lapse rates will support modest diurnal instability with CAPE values getting as high 500 J/Kg across southeastern MA and RI. Wind fields are forecast to be very week, thus no organized severe convection is a concern at this point. Nonetheless, a few isolated to scattered thunderstorms capable of producing small hail will be possible on Saturday afternoon. Sunday Sunday looks to be the pick of the weekend as a mid-level ridge building in from the west will result in the lowest precipitation chances we`ve experienced since last week. A drier low-level air mass will support sunshine for most of the day, but we may see increasing cloudiness during the mid to late afternoon hours as a new system approaches from The Great Lakes. 925 hPa temps climbing to 15 Celsius should support highs in the upper 70s to low 80s across southern New England Sunday afternoon. Next Week After a nice taste of summer weather on Sunday we`ll return to another wet/unsettled pattern early next week. Low-level wind fields will turn south ahead of a robust upper-level low that will bring the region its next opportunity for substantial rainfall. Southerly flow will bring increasing moisture and cloud cover on Monday as well as the opportunity for some diurnal showers and thunderstorms. At this point guidance is not insistent on forcing strong enough to support a wash out on Monday, but Tuesday is a different story. As the upper-low advances further east Monday into Tuesday, continued southerly flow is forecast to support PWATs rising to near 1.5 inches across southern New England. As the surface low and associated cold front push through the region during the day Tuesday, southern New England should experience a more widespread rainfall event. Guidance suggests this would be followed up by more rainfall on Wednesday as a secondary area of low-pressure moves over The Northeast. Details are vague at the 7 day time range, but the signal is for a wet/unsettled first half of next week. Despite the wet/unsettled pattern, there is also a strong signal that more seasonable temperatures will prevail next week with daily high/low temps in upper 70s/low 60s respectively.
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&& .AVIATION /08Z THURSDAY THROUGH MONDAY/...
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Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 06z update... Thru 12z...High confidence. Mainly VFR cloud bases and vsbys, however occasional marginal VFR/MVFR in smoke across western MA into CT. Also MVFR in patchy fog across Cape and Islands, especially ACK. Light W/NW winds. Thursday...High confidence. VFR cloud bases with marginal VFR/MVFR in smoke across western MA into CT and RI. Isolated to scattered showers develop this afternoon. Low risk of an isolated -TSRA. Light WNW winds become locally onshore late this morning and afternoon. Thursday Night...Moderate confidence. Early evening scattered showers quickly diminish. VFR conditions trend toward MVFR overnight across eastern MA and RI. Light and variable winds in the evening trend to NNE overnight. Friday... Moderate Confidence. Light NNE winds in the morning become ESE in the afternoon. MVFR conditions across RI and eastern MA trend toward VFR cloud bases in the afternoon. VFR elsewhere. Showers and thunderstorms develop in the afternoon, although areal coverage remains uncertain at this time. KBOS Terminal...High Confidence in TAF. Light predawn west winds become north late this morning, then NE early this afternoon then SE. Mainly dry with VFR conditions, but can`t rule out a shower or two this afternoon. KBDL Terminal...High confidence in TAF. VFR and dry this morning, giving way to scattered afternoon showers. Isolated -TSRA possible. Light WNW winds. Outlook /Friday Night through Monday/... Friday Night: Mainly VFR, with local MVFR possible. Chance SHRA. Saturday: Mainly VFR, with local MVFR possible. Chance SHRA, isolated TSRA. Saturday Night through Sunday: VFR. Sunday Night: VFR. Slight chance SHRA. Monday: VFR. Chance SHRA.
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&& .MARINE...
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Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 345 AM update... Weak low pressure over Maine remains nearly stationary through Friday. Scattered showers and patchy fog will reduce vsby at times. Outlook /Friday Night through Monday/... Friday Night through Saturday: Winds less than 25 kt. Chance of rain showers. Saturday Night through Sunday: Winds less than 25 kt. Sunday Night: Winds less than 25 kt. Slight chance of rain showers. Monday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.
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&& .FIRE WEATHER...
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345 AM update... Latest model simulations have the smoke conditions improving somewhat Thursday, with highest concentrations of smoke along and near the south coast. Nonetheless, Air Quality Alerts remain posted for western MA, and all of CT/RI.
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&& .TIDES/COASTAL FLOODING...
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345 AM update... Astronomical tides remain high (11.1 ft MLLW at Boston and 4 ft MLLW at Nantucket) and combined with residual surge. Based on latest observations, will continue with the Coastal Flood Advisory for Nantucket and a Coastal Flood Statement elsewhere along the eastern MA coastline, where pockets of minor coastal flooding remain possible until about 6 am or 7 am.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...Air Quality Alert until midnight EDT tonight for CTZ002>004. MA...Air Quality Alert until midnight EDT tonight for MAZ002-003- 008>011. Coastal Flood Advisory until 7 AM EDT this morning for MAZ024. RI...Air Quality Alert until midnight EDT tonight for RIZ001>008. MARINE...None. && $$ SYNOPSIS...Nocera/RM NEAR TERM...Nocera SHORT TERM...Nocera LONG TERM...RM AVIATION...Nocera/RM MARINE...Nocera/RM FIRE WEATHER...Nocera TIDES/COASTAL FLOODING...Nocera

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