Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 241105 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 705 AM EDT Fri Mar 24 2017 .SYNOPSIS... High pressure along the eastern seaboard will move offshore later today, resulting in warmer and gusty weather today. A cold front will push south across the region Saturday. This stalled front will move northward on Sunday, resulting in a battle of airmasses. This could bring a period of wintry precip Saturday night, and again Sunday night. Heavy precipitation is possible Monday as low pressure system moves over southern New England. Another shot of precip is possible late Tuesday from passing cold front. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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7 AM Update... Overall trend in the forecast remains on track. surface temperatures have remain steady overnight as precipitation begins to move into upstate NY. Precipitation is struggling eroding the low and mid level dry air per model soundings. this has slowed the timing down by a few hours. Then a battle of what the surface temps will be when precip moves into the area. 2m temps are indicating temps will be warm enough for just rain thanks to southerly winds ahead of the system. However, there is a shot that the profile could moisten up just enough for a few flakes to develop out ahead of the system. Still do not anticipate much of a hazard issue. SPS will continue. Previous Discussion... Today`s forecast will critically hinge on timing, and strength of precipitation. Very dry air remains in place near the ground. This dry air will delay the onset of precipitation until after sunrise. Given the late March sun, and an strengthening southwest wind, expecting a transition to all rain across southern New England by afternoon. Until that time, wetbulb cooling and temperatures starting out in the teens and 20s will mean a window where some snow is possible. The harder this snow falls, the greater the wetbulb cooling, and the longer it will persist. Not expecting much snow accumulation, with the greatest amounts towards northwest MA. Once the transition begins, cannot rule out a period of sleet or freezing rain. Low confidence on the timing for this, so no Winter Weather Advisory at this time. High pressure moving offshore will shift the flow enough where a strong southwest low level jet develops towards southeast MA and the coastal waters. The core of this jet is approaching 50 kt later this afternoon. Have some concerns for stronger gusts reaching the ground, but not a lot of confidence in sufficiently deep mixing to maximize momentum transfer. Will hold off on Wind Advisories for the Cape and islands.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Tonight... Clouds and a southwest flow of milder air will keep temperatures from falling too much, and most of that should be this evening. Still thinking temperatures may even rise a little overnight. With a front just to our north, maintained a chance of rain across northern MA, but low values for pops. Saturday... This front slowly moves south across our region. Near normal temperatures expected, so any precipitation should be rain. Not expecting a washout. The greatest risk for these showers will be toward the western half of southern New England. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Highlights... * A period of wintry precip is possible Saturday night and again Sunday night * Unsettled weather pattern will continue into Wednesday * Improving conditions during the later half of next week Pattern Overview... 00z models and ensembles are in agreement with the general synoptic pattern for the extended. Still some timing and thermal issues but overall confidence is improving. Active pattern for the region with split flow aloft and several shortwaves ejecting in from the Pacific. First wave is a 500mb closed low over the Midwest on Sunday. This low deamplifies into an open wave as it approaches the Northeast Monday. Due to the confluent flow aloft, high pressure persists over northern New England keeping surface temperatures cool, resulting in mixed precip at times for the weekend into early next week. Heavier precip possible on Monday as first open wave moves overhead. A second wave will follow a similar path from the Plains towards the Northeast before meshing or partially interacting with the northern jet stream on Tuesday. This will result in another system for New England Tues/Wed with high pressure to follow. Details... Saturday night into Sunday...Moderate confidence. Confluent flow aloft with surface cold front south of southern New England. Cold air drainage from the high pressure over northern New England will drop surface temps below freezing. This is shown in surface winds which are due north. Mid-level ridging will keep a warm layer around 850 mb which would aid in the potential for mixed p-type. Biggest question is if there is enough low level lift and/or overrunning for precipitation to develop overnight. The higher theta- e values are well south of the Pike and moreso near the south coast, which would limit the mixed precip type as surface temps should remain above freezing that far south. Still a lot of uncertainty with this time, but believe that with the flow aloft, there appears to be enough low level moisture for some spotty precip. If this occurs than a winter weather advisory may be needed for the freezing rain potential. For Sunday, cold front will stall near the Mid-Atlantic as high pressure moves southeast into the Gulf of Maine. Guidance indicates that low levels will dry out Sunday morning keeping the first half of the day dry. However, with mid-level ridge axis overhead will see and increase in moisture thanks to southwesterly flow aloft. At the surface easterly flow will begin to dominate increasing the low levels throughout the day. This could result in low clouds and drizzle. Surface temps will warm above freezing thanks to mid-level ridge, but some areas may struggle as cold air may be slow to dislodge/cold air damming. Still a lot of uncertainty with this time frame. Sunday night into Monday...Moderate confidence. Stalled front south of the region looks to return back north as a warm front late Sunday into Monday, as surface low pressure moves into the Great Lakes. Although warmer air aloft should move easily back into the region, the low-level cold air may be a little tougher to dislodge this time due to the nearby surface high pressure. Believe this is the timeframe where we will see the heaviest precip due to passage of the open wave and development of a secondary low over the region. Still some uncertainty with the thermal profiles but cross-sections, soundings and even CIPS analogs show this timeframe has the potential for icing especially north of the Pike. Still some uncertainty with this timeframe as a difference of a degree or two in the thermal profiles will change the p-type. Will continue the mentioning of snow, sleet, ice and/or rain. Winter weather advisories may be needed. Monday night into Wednesday...Moderate confidence. Weak ridging aloft as surface low moves offshore. Any lingering showers will come to an end. 850 mb temps will continue to warm overnight which will help keep surface temps above freezing. Second wave will move into the region late Tuesday into Wednesday. this wave will drag a cold front across the region bringing a periods of rain. Temperatures will remain seasonable for both days. Thursday into Friday...Moderate confidence. Cold front will be offshore as upper level trough begins to take hold over the Northeast. Appears to be the potential for another arctic front with high pressure to follow. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday/...Moderate confidence. Today and Tonight... Mainly VFR with scattered MVFR in heavier showers. The greatest risk for MVFR conditions will be north of the Mass Pike, and especially across the higher terrain. Any frozen precipitation should change to rain during late morning/early afternoon. Southwest winds will gust 25-30 knots during the day, highest along the coast and higher terrain. Winds diminish later tonight. Saturday...Periods of light rain with areas of MVFR cigs and local MVFR-IFR vsbys. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Saturday Night through Tuesday/... Saturday night...High confidence. Northerly winds with spotty precip overnight. Terminals north of the Mass Pike have the best chance for wintry precip. Sunday into Monday...Moderate confidence. Showery weather to start with possible MVFR to IFR cigs. Precip chances increase into Monday which could result in mixed precip for terminals north of the Mass Pike. Tuesday...Moderate confidence. Dry to start with showers in the afternoon from passing cold front. Cigs may start out as VFR lowering to MVFR.
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&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday/... Today...Moderate confidence. High pressure moves well offshore, bringing southwest winds to the waters. Potential for wind gusts 25-35 knots. This will build seas with 5 foot heights on many of the waters by this afternoon. Patchy light rain may bring brief visibility restrictions. Gale Warnings for the eastern outer coastal waters, where confidence is highest for a period of 35-40 kt gusts. Potential for similar gusts across the other coastal waters near the Cape and islands, just not enough confidence there will be a long enough duration to warrant a Gale Warning. Will continue the Small Craft Advisories across the remaining southern New England coastal waters. Tonight...High confidence. Southwest winds diminish overnight, and become west toward morning. Rough seas linger across the outer coastal waters, and ocean-exposed south coastal sounds. Small Craft Advisories will lower on Boston Harbor and Narragansett Bay, but linger on the remaining waters. Saturday...High confidence. West winds becoming north to northwest as a cold front pushes slowly south across the waters. This front is not expected to push south of the waters until late afternoon. Outlook /Saturday Night through Tuesday/... Sunday...Moderate confidence. Cold front will be south of the waters as surface high pressure moves northeast of the region. Conditions should remain below SCA but if the front gets closer than seas and winds may be a bit stronger. Monday...Moderate confidence. Approaching upper level system and passing warm front will increase precip as well as wind and seas of the waters. SCA may be needed. Tuesday...Moderate confidence. Cold front will pass over the waters increasing them to above 5 feet. SCA may be needed. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 10 AM this morning to 6 AM EDT Saturday for ANZ232>235-237. Small Craft Advisory from noon today to 8 PM EDT this evening for ANZ230. Gale Warning from 4 PM this afternoon to 9 PM EDT this evening for ANZ231. Small Craft Advisory from 10 AM this morning to 10 PM EDT this evening for ANZ236. Gale Warning from 1 PM this afternoon to midnight EDT tonight for ANZ250-254. Small Craft Advisory from 10 AM this morning to 3 AM EDT Saturday for ANZ251. Small Craft Advisory from 10 AM this morning to 6 PM EDT Saturday for ANZ255-256. && $$ SYNOPSIS...Belk/Dunten NEAR TERM...Belk/Dunten SHORT TERM...Belk LONG TERM...Dunten AVIATION...Belk/Dunten MARINE...Belk/Dunten

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