Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 201915 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 315 PM EDT FRI MAY 20 2016 .SYNOPSIS...
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High pressure over the northeast USA will bring dry, mild weather through much of Saturday. Coastal low pressure then passes south of New England Saturday night and Sunday. It then stalls in the Gulf Of Maine Sunday, with rain transitioning to showers. The unsettled conditions continue Monday and Tuesday.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Seabreezes diminish this evening. High pressure remains in control, but does shift farther offshore overnight. Increasing high level moisture will bring some clouds into southern New England late. Radiational cooling for at least a part of the night. Dew points of 45 to 50 will allow temps to fall to near that level, with high temperatures in the urban centers.
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&& .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
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Saturday... High pressure moves off to the east, but remains close enough to maintain dry air over New England below 10 thousand feet. Meanwhile moisture increases above 10 thousand feet bringing increasing and thickening sky cover. The big question remains how quickly the lower levels saturate, and if there will be enough lift to produce some light rain during the afternoon. Consensus timing would place the earliest risk along and west of the CT River late morning. The more likely scenario is rainfall holds off until late afternoon, mainly across northern CT and southern RI. This timing will need to be refined over the next day. Saturday night... Low pressure intensifies and passes by southern New England close to the 40N/70W benchmark. 20/12z guidance has the deepest moisture axis and lift right across much of southern New England. Increased PoPs to categorical across northern CT, RI and southeast MA. rain is likely all the way to the MA/VT and MA/NH border.
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&& .LONG TERM /SUNDAY THROUGH THURSDAY/...
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Highlights... * Rain, especially along the S coast into Sun. * Unstable but milder Monday and Tuesday. * Warmer still and drier Wednesday. Overview and Model Preferences...20.00Z model guidance suite still shows reasonably good agreement through the middle of next week in the synoptic-scale, impressive given the highly amplified flow pattern across the CONUS. Building ridge upstream of New England across the plains and Great Lakes, leads to gradual deepening/digging of the trof developing across New England. This feature then cuts off and meanders near to south of the region for much of the late weekend and early half of this coming week. Ensembles show H5 anomalies almost 10dm below normal. The attendant cold pool reaches -20C at it`s coldest, which suggests unstable conditions linger into the early portions of the week until it fills and warms aloft. Since there is good agreement with all of these over-arching issues, a consensus blend will work as a starting point. Only caveat will be the initial coastal low pres developing Sat night into Sun, will lean more on ensembles due to differences in the precip shield spatially. Details... Sun...Low pres will be shifting into the Gulf Of Maine yielding breezy NE flow, clouds and continued low-mid lvl moisture spilling into the region. Therefore...expect a period of gray, cool and damp conditions for much of Sun. This also will limit destabilization in spite of cooling at H5. Latest guidance has shifted the instability trof further W where more sunshine is expected. Will follow this trends given the flow off of the Gulf. Highs mainly in the upper 50s and low 60s. May need some wind headlines /mainly advisories/ for portions of E MA and RI as pres gradient deepens further with the low pres shifting E. Mon and Tue...Cutoff low pres in place will allow several shortwaves to rotate across Srn New England. The most robust looks to occur late Mon night into Tue, so will feature an increase in POPs during this time. Diurnal cloud cover is likely with cold H5 temps in place, and could allow for the development of some T-storms occasionally with the wave passages. Too uncertain for exact timing, but expect on-off showers and potential storms through the period. Temps near to slightly above normal thanks to H85 temps still holding near +8C in spite of the cold temps above. Wed...Brief ridge of high pres regains control before sfc warm front approaches from the W. Will continue with mainly dry conditions and mild temps, as highs shift solidly in the 70s across much of the region. Thu...With the potential for a warm front to shift N of the region, looking at temperatures reaching above normal. However, weak cutoff energy to the E could allow for diurnally driven shra/tstms each day thanks to the warm and somewhat destabilized airmass. No certain solution here, but both ensembles and operational ECMWF and GFS are supporting this broad thinking.
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&& .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
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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 Night/... Tonight...High confidence. VFR in dry weather and light winds. Seabreezes diminish this evening. Saturday...High confidence. VFR conditions through the day, with a light south-southwest wind. Increasing sky cover through the day. There is a low potential for MVFR cigs/vsbys developing in the late afternoon/evening in light rain. Saturday night...Moderate Confidence. Mix of MVFR/IFR likely as rain, fog and low clouds build from south to north over the region. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Sunday into Tuesday/... Sunday...Moderate Confidence. Conditions slowly improve as rain moves offshore. Wind gusts 20-30 kt possible at times Sunday morning. Mix of MVFR/IFR likely, especially east. Mon and Tue...Moderate Confidence. Although VFR is likely to dominate, some periods of MVFR/IFR are possible in shra and fog development especially during the overnight hours.
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&& .MARINE...
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Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Tonight...High confidence. High pressure move farther offshore. Light winds/dry weather and good vsby. Seas remain below 5 feet. Saturday...High Confidence. Low pressure develops along the Mid Atlantic coast. Winds will increase from the south but remain below 25 knots. Low risk for winds to become easterly across the southern outer coastal waters of MA and RI late in the day. Seas will remain below 5 feet. Saturday night...Moderate confidence. Low pressure intensifies as it moves past New England near the 40N/70W benchmark. Winds will become east to northeast across all the waters and increase. Some potential for gale force gusts, especially after midnight Sunday. Outlook /Sunday through Tuesday/... Sunday...Moderate Confidence. Winds will be shifting to the N-NE with time and increasing, especially over the SE waters. Some gusts to gale force possible, but small craft thresholds can be expected. Seas increase to as high as 8-10 ft on the ocean waters. Mon and Tue...HIgh Confidence. Low pres churning in the gulf of maine will keep a swell going for much of Monday even if seas drop below SCA thresholds. Therefore, expect small craft advisories to continue Mon, but possibly drop by Tue as the low pres moves east.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Belk/Doody NEAR TERM...Belk SHORT TERM...Belk LONG TERM...Doody AVIATION...Belk/Doody MARINE...Belk/Doody

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