Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 292033 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 333 PM EST Sun Jan 29 2023 .SYNOPSIS...
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Low pressure passes to our north tonight, bringing enhanced cloud cover and continued mild nighttime lows tonight. A spot shower or two are possible mainly in eastern and southeast New England. Another weak frontal system moves across later on Monday, with arrival of more seasonable air Monday night. Quiet with near seasonable temps for the middle portion of the work week as a few precipitation makers are suppressed to our south. Brutally cold airmass arrives for a 24 hour period late Friday into Saturday with the potential to drop temperatures below zero; chance for some ocean effect snow showers across the Cape Saturday as well. Temperatures rebound quickly for the second half of the weekend.
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&& .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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315 PM Update: Mild Sunday afternoon across Southern New England, with current temps in the mid 40s to mid 50s. However mostly cloudy skies (of largely mid-level cloud cover) along with modest south breezes also are in place, associated wth a broad warm sector associated with a weak sfc wave low pressure near Toronto ON. Regional radar mosaic shows some echoes being returned but dry air below cloud base is keeping these rain showers from reaching the ground. For tonight, the weak surface wave low pressure area moves NE along the St. Lawrence River Valley in adjacent far northern NY/VT and into adjacent northern NH/ME. Its surface cool front/trough to traverse across Southern New England early tonight, reaching the offshore waters during the overnight. Model soundings show dry air between 900-800 mb not fully saturating up enough to allow for steady rain to develop; if anything were to reach the ground it would amount to sprinkles with dry pavement/sidewalks. While there is a fairly good 925 mb SW jet of 35-40 kt across eastern and southeast MA, with shallow mixing progged, gusts across Cape Ann and SE MA/Cape Cod and the Islands probably won`t get any higher than 30 mph and 20-25 mph gusts should be more common. While the weak cold front will shift winds to the west with lowered speeds late, it won`t be enough to allow for the leading edge of more colder air across the Gt Lakes to advect NW. In fact should again be a fairly mild night. Other than across the Berkshires where lows in the upper 20s to near freezing should be common, elsewhere lows should be in the mid 30s to low 40s as cloud cover and neutral thermal advection takes place.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
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315 PM Update: Monday is close to a facsimile of Sunday, with another sheared-out vort 500 mb vort max and weak surface low to move across SNE. Similar to Sunday as well, the front looks to again suffer from a poorly-saturated column but may be a little more in support of light rain showers (amounting to no more than a couple hundreths, again roads/sidewalks mostly dry vs wet). Light west winds to become south in the pre-frontal environment. Increasing clouds, and highs may be a touch cooler than today but generally in the 40s, perhaps a spot 50F for eastern CT, RI and SE MA. Front clears off the coast early on Monday night; winds to shift to the NW and increase to around 15-20 mph. Despite still a fair amount of post-frontal cloud cover, sharp if shallow cold advection takes place with 925 mb temps fall from 0 to +3C by early Monday evening to -1 to -8C by Tuesday early morning. Some decrease in clouds toward morning but all in all a mostly cloudy evening with lows in the upper teens to mid 20s across NW MA, upper 20s to around 30 for Hartford to Worcester metros NE to the North Shore, and around freezing to mid 30s eastern/southeast MA and RI.
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&& .LONG TERM /TUESDAY THROUGH SUNDAY/...
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Highlights * Generally quiet and seasonably mid week * High confidence in a short lived cold snap late Friday and early Saturday that will bring sub-zero temperatures to portions of our region * Temperatures rebound for the second half of the weekend Tuesday through Thursday... Given we are in the midst of the most climatologically active period of the year for winter weather, between now and mid February, the long term is looking eerily quiet in terms of appreciable snowfall. Temperatures return to climatological means for the better part of the work week given a generally zonal mid level flow pattern. Guidance continues to suppress a weak precipitation maker to our south late Tuesday through Wednesday as a broad area of high pressure parks itself between the Ohio River Valley and New England. At best, expecting the impact from this system to be restricted to some light rain or snow showers along the south coast on Wednesday, with little to no appreciable precipitation. A second low tracking across the mid-Atlantic Thursday also appears to be shunted to our south. Friday and Saturday... The most interesting part of the long term period comes late Friday through Saturday morning as a very quick blast of arctic air makes its way into New England. With a strong 1050mb high across northern NY and southern Quebec, there is growing confidence in a significant cold airmass with 850 mb temperatures dropping between -30 and - 40C, and yes you read that right, BELOW zero. In addition tthe raw GFS and ECMWF coming into agreement about these bone chilling temperatures, ensembles show high probabilities, between 60-70% chance, of surface temperature dropping to 30 degrees below normal. For this time of year, an anomaly of -30F drops overnight lows below zero, and daytime highs in the upper single digits. Went with the NBM during the period, but if current trends in the GFS and ECMWF verify, there will be significant wiggle room in the lower bound of temperatures; the 12Z ECMWF currently diagnoses a low of -12F in Boston Saturday morning. Fortunately, this blast of cold air will be quick hitting, with the brunt of the impact expected between about 00Z-18Z Saturday before much warmer temperatures advect into our region. For reference,it is possibly that temps could rival those that occurred Valentine`s Weekend of 2016. Cold temperatures will be amplified by gusty NW winds driven by strong CAA, dropping apparent temperatures to -20 to 30F overnight Friday into early Saturday. While we do not currently have a wind chill watch in place, it is very likely that one will be hoisted in the coming days given growing confidence in this high impact cold event. As an early notice, southern New Englanders should consider taking action to prepare for this shot of cold air, including making contingency plans for any livestock or animals that reside outside. While cold air is generally associated with clear conditions, there is a shot for some ocean effect snow across the outer Cape Saturday, likely driven by boundary layer delta temperatures approaching 30C. The chance for these snow showers will be dependent on the position of the high and the direction of the surface flow, but if NE flow sets up across our waters, Cape Cod could see light accumulations of fluffy snow. Freezing spray is also likely to be an issue across the waters as subfreezing temperatures and winds gusting 30-35kt will produce hazardous conditions for mariners. Sunday... Temperatures rebound quickly for the second half of the weekend as 850mb temperatures rebound to -3 to -8C by Sunday evening. After a chilly start to Sunday, temps may rebound as much as 20-30F across portions of eastern MA.
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&& .AVIATION /20Z SUNDAY THROUGH FRIDAY/...
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Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 18z TAF Update: Rest of the Afternoon (thru 00z Mon): High confidence. Mainly VFR ceilings thru the day; however lower-VFR/MVFR ceilings possible late-day in NW MA and the terrain but away from TAF sites. Still generally dry weather but an outside shot at unrestricted -SHRA around ~20-00z especially east of ORH; runways dry. S winds become SW around 10-13 kt this afternoon. Occasional low-20s kt range for gusts across Cape and Islands. Tonight: High confidence. VFR ceilings, with lower-prob MVFR ceilings across northwest MA. Mainly dry but a spot light shower possible thru 03z SE MA/Cape Cod. SW winds around 10-13 kt (occasional 20 kt gusts Cape Cod and Islands airports), veering to west after 05z and diminish to 5-10 kt. Monday: High confidence. Mainly VFR, lowest ceilings around 035-040 west of ORH. Spotty light rain after 20z but runways dry. W winds 4-8 kt, becoming S late- day. Monday Night: High confidence. OVC lower VFR ceilings with MVFR ceilings for the south coast, cape and islands. SW winds become WNW and increase to 10-15 kt, with gusts around 20-25 kt. KBOS Terminal...High confidence in TAF. Occasional 20 kt gusts from the S but thinking more sustained winds. Outside shot at a sprinkle, runways dry. KBDL Terminal...High confidence in TAF. Outlook /Tuesday through Friday/... Tuesday: VFR. Breezy. Tuesday Night: VFR. Slight chance SN. Wednesday through Wednesday Night: VFR. Thursday through Thursday Night: VFR. Breezy. Friday: VFR. Windy with gusts up to 35 kt.
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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. Small craft advisories remain in effect for the outer waters, though for borderline SW gusts around 25 kt and seas in the 3-5 ft range. Rest of Today: High confidence. SW gusts around 15 to 25 kt, strongest offshore. Seas 3-5 ft. Good visibility. Tonight and Monday: High confidence. SW gusts around 15-25 kt become W and ease to 15 kt tonight. Winds become S around 10 kt Monday. Seas decrease to 2 to 4 ft tonight and remain at that range through Monday afternoon. Monday Night: Moderate to high confidence. SW winds shift to NW and increase to around 20 kt. Chance that gusts may reach into the SCA range for a brief period late- overnight. Seas build to 3 to 5 ft. Outlook /Tuesday through Friday/... Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Tuesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of snow. Local visibility 1 nm or less. Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Wednesday Night: Winds less than 25 kt. Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Thursday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft. Friday: Low risk for gale force winds with gusts up to 40 kt. Areas of rough seas. Chance of freezing spray.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 5 AM EST Monday for ANZ250. Small Craft Advisory until 7 AM EST Monday for ANZ254>256. && $$ SYNOPSIS...Loconto/KS NEAR TERM...Loconto SHORT TERM...Loconto LONG TERM...KS AVIATION...Loconto/KS MARINE...Loconto/KS

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