Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 222019 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 319 PM EST Sat Jan 22 2022 .SYNOPSIS...
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Ocean effect snow showers come to an end over the South Shore this evening but may linger over The Cape this evening and tonight. Increasing clouds Sunday precede a dry frontal passage Sunday night. Cold and dry weather Monday precedes a Clipper system for Monday night into Tuesday night. Light snow possible into early Tuesday, with brief milder than normal temperatures south of the Mass Pike supporting rain to light snow Tuesday night. Arctic cold returns Wednesday and Thursday with very low wind chills possible Wednesday night. Another weather system passes off the coast by Saturday and could affect parts of the region, mostly with snow.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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Tonight Mid-level ridge and surface high pressure builds east of southern New England this evening and tonight. This will bring an end to any remaining ocean effect snow showers along the South Shore as we transition to a prevailing southwesterly flow. May see some ocean effect snow showers linger a bit longer over the outer Cape and Islands as it will take a bit longer for the winds to shift. Even after the transition to southwest winds over The Cape/Islands, there will remain a chance for ocean effect snow showers from the south/southwest over The Cape and Islands. Drier air aloft works its way over the interior tonight which will support clearing skies for most of the evening. Shortly before sunrise we`ll begin to see increasing cloudiness from west to east as a new plume of moisture approaches from the west. Southwesterly flow increases temperatures aloft slightly with 925 hPa temps rising to around -10C. This will support less frigid temperatures Sunday morning ranging from the single digits in northwest MA to the upper teens across southeastern MA. Areas along the immediate coast may hang in the low 20s.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
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Sunday Deep southwest flow allows temperatures in the low-levels to warm to the -5 to -10 C range at 925 hPa. This will support a more mild afternoon by mid-January standards with highs perhaps getting into the mid-upper 30s. Plume of low-level moisture advances eastward ahead of an approaching cold front. This will result in increasing cloudiness throughout the day tomorrow. Generally expecting dry conditions across the region tomorrow, but there is a slight chance for some isolated upslope snow-flurries over the Worcester Hills. Sunday Night We`ll return to a deep northwest flow pattern Sunday night as a dry- cold front pushes through southern New England. Northwest flow over Cape Cod Bay may produce another opportunity for ocean effect snow showers over the outer Cape tomorrow night. Low-level CAA brings temperatures at 925 hPa back down to the -10 to -15C range over southern New England. This will support another frigid morning on Monday with single digit temperatures north and west of I-90 and low-mid teens elsewhere.
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&& .LONG TERM /MONDAY THROUGH SATURDAY/... Big Picture... Broad trough over the Northeast Monday, balanced by a ridge off the Pacific coast. Individual shortwaves move through this pattern through midweek. One shortwave diving down from Western Canada digs over the Eastern USA late week, forming either a south-north flow or a southwest-northeast flow. Temperature fields aloft are forecast below normal Monday, near normal Tuesday, then below normal again Wednesday-Thursday. Strong differences develop late week and weekend, with the GFS and GGEM above normal, and the ECMWF near normal. Mass fields are in agreement through Wednesday, then diverge late week. This along with the temperature field differences suggests moderate-high confidence early week, trending to low confidence by next Saturday. Details... Monday... High pressure along the East Coast will bring subsidence and dry weather. The airmass will be cold, with 925-mb temps minus 8 to minus 12C, supporting surface max temps in the 20s and lower 30s. Monday night-Tuesday... Clipper low pressure approaches through the Great Lakes Monday night and Tuesday, generating weak lift and scattered light snow showers with the best chance along and north of the Mass Pike. Accumulations may reach a coating, but low QPF suggest it won`t be more than that. Min temps will range from the mid teens to mid 20s. Light snow continues Tuesday morning before diminishing in the afternoon. Temps at 925-mb climb from Monday, with a range of zero to minus 5C, supporting 30s and low 40s. Wednesday-Thursday... High pressure builds over the region late Tuesday night and Wednesday. Tight pressure gradient between the departing low and approaching high. This will bring gusty winds Wednesday and Wednesday night with lower wind chills. Subsidence will bring clearing skies. Expect another surge of cold air with max temperatures, as on Monday, in the 20s and low 30s. Similar max temps are expected Thursday. Friday-Saturday... High pressure moves offshore Friday. Clipper low pressure approaches through the Great Lakes. Models then disagree on how the weather evolves. The GFS forms low pressure over the Gulf of Mexico, sweeps it up the east coast before sending it out to sea well south of the 40N/70W benchmark. The GFS brings some precipitation to the Cape and Islands and possibly interior SE Mass but is mostly offshore. The ECMWF takes the clipper low and redevelops it off the Carolinas...then takes it just outside the benchmark. Precip extends a little more deeply into interior Southern New England, but with limited amounts. Given the differences in the various mass fields at the end of the week, and with the respective coverage of precipitation, confidence is low for this system. It is a Day 6-7 system, with potential to affect Srn New England but showing signs of staying offshore. Will show slight chance and low-end chance Pops, highest over the Cape and Islands and lowest west of the CT River. && .AVIATION /20Z SATURDAY THROUGH THURSDAY/... Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 18Z Update: Through 00Z...High Confidence. Any remaining ocean effect snow showers near BOS and north shore should taper off in the next hour or so. OES showers continue over The Cape terminals with MVFR ceilings and periods of IFR visibilities to 2SM. VFR elsewhere. Tonight...High Confidence. VFR with light SW winds. Sunday...High Confidence. VFR with WSW winds of 5-15 knots. KBOS Terminal...High Confidence in TAF. Only issue will be thru 15z, where some marginal MVFR ceilings and perhaps a few light snow showers briefly impact the terminal. KBDL Terminal...High Confidence in TAF. Outlook /Monday through Thursday/... Monday: VFR. Monday Night: Mainly VFR, with local MVFR possible. Slight chance SN. Tuesday: Mainly VFR, with local IFR possible. Chance RA, chance SN. Tuesday Night: MVFR/IFR conditions possible. Windy with local gusts up to 30 kt. Slight chance SN. Wednesday: Mainly VFR, with local IFR possible. Windy with gusts up to 30 kt. Wednesday Night: VFR. Windy with gusts up to 30 kt. Slight chance SN. Thursday: VFR. Windy with local gusts up to 30 kt. && .MARINE...
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Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Tonight Surface high pressure moves offshore this evening bringing mostly calm conditions over the coastal waters. Seas forecast to rise to 4- 6 feet on the outer waters after Midnight, thus have raised SCY for outer waters through Monday morning. Marginal SCY wind gusts possible for the near-shore waters with gusts up to 24 knots. Ocean effect snow-showers possible over the south coastal waters tonight as well. Sunday Winds shift to the west/southwest tomorrow and pick up to 15-20 knots with 20-25 knot wind gusts. 4-6 foot seas over the outer waters. Sunday night Gusty winds from Sunday afternoon diminish to 10 knots Sunday night. Dry cold front moves over the coastal waters resulting in a wind shift to the west/northwest. 4-6 foot seas linger on the outer waters through Monday morning. Outlook /Monday through Thursday/... Monday: Winds less than 25 kt. Seas up to 5 ft. Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of snow. Tuesday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain. Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain, chance of snow. Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Slight chance of snow. Wednesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 9 ft. Freezing spray, slight chance of snow. Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 9 ft.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 5 AM EST Monday for ANZ250-254-255. Small Craft Advisory from 3 AM Sunday to 5 AM EST Monday for ANZ256.
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&& $$ SYNOPSIS...WTB/RM NEAR TERM...RM SHORT TERM...RM LONG TERM...WTB AVIATION...WTB/RM MARINE...WTB/RM

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