Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 260736 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 336 AM EDT SUN JUN 26 2016 .SYNOPSIS...
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High pressure ridge extending across the Northeast U.S. into the Gulf of Maine will slowly shift to the south of our region, with very warm and dry conditions through Monday. An approaching cold front brings showers and possibly some thunder Tuesday and Wednesday. High pressure then brings dry seasonable weather for the late week. Another cold front may bring more showers sometime Saturday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1045 PM Update... Other than a few wispy cirrus clouds and some mid layer patchy clouds, skies were mainly clear across the region at 02Z. Wide range of temperatures noted, down to the lower-mid 50s across the Cape and Islands ranging to around 70 in the lower CT valley. Mainly calm winds with high pres overhead, but noting some light S winds across W MA and N Central CT. Noting the ridge axis running across E and central Mass into RI and Long Island, which should slowly shift S overnight. With diminishing winds overnight, expect patchy fog to redevelop in some of the normally susceptible inland locations after 05Z- 06Z, though dewpts running a bit lower than last night across interior E Mass /on the order of the mid-upper 40s/. Will need to see temps start to drop off mainly after midnight to get the fog to develop. Remainder of the forecast in good shape. Have updated to bring conditions current. Previous discussion... Anticipating a good setup for radiational cooling. Areas with sandy soils likely to cool quickest, namely Marthas Vineyard which is notorious for doing so. Closely looking at the dewpoints during max heating of the day, ranging in the upper 40s to low 50s. Identifiers as cross-over thresholds for the development of fog. The lower the overnight temperature below the cross-over, the greater likelihood of fog, although it has been reasonably dry as of late. Continued patchy thinking mainly late towards daybreak. Lows in the upper 40s to low 50s, warmer in urban centers. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... Sunday... As the ridge begins to push S of the region, light winds will become more S-SE across the region. Mostly sunny and very warm humidities still on the comfortable side. 925 mb temperatures will be 2 or 3 degrees warmer than today, which means that high temperatures could approach 90 degrees in the Connecticut River valley, with mid and upper 80s across the rest of interior southern New England. Onshore sea breezes will once again keep coastal areas cooler...in the mid and upper 70s. Sunday night... Clear skies initially. With continued southerly flow, dewpoints will slowly rise to the upper 50s along the south coast. The NAM 1000 mb Relative Humidity forecast shows a distinct area of marine-layer stratus invading the coast and then moving across southeast MA, RI, and perhaps northeast CT toward Monday morning. While the NAM may be overdoing this, have forecast partly to mostly cloudy skies in that area with patchy fog after midnight. Lows mainly 55-60. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
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Big Picture... Longwave scale continues to show a ridge-west/trough-east pattern over North America. One shortwave rippling through the northern flow moves from the Great Lakes into New England midweek and then off through the Maritimes by Thursday. A second shortwave moves down from Northern Canada midweek and moves into New England during next weekend. Each shortwave will be driving a cold front through our area, one midweek and the second next weekend. The models continue to handle the midweek system differently. The GFS continues to be the fast outlier of the group while the ECMWF focusses on Wednesday. As noted yesterday the northern stream shortwave digs over the Great Lakes Monday night and turns the upper flow more SW-NE and parallel to the surface cold front. With more push along the front rather than across it we would expect the slowing shown by the ECMWF et al rather than the GFS solution. Details... Monday night through Wednesday... As noted above, the upper flow over the Northeast USA turns SW-NE as the first upper shortwave approaches. This supports a slower approach of pcpn. We will continue with slight chance and low-end chance pops in Western/Central MA and Northern CT but with a feeling that most action will focus north and west of our area. Cold front slowly moves east across Central and Eastern NY on Tuesday. Jet dynamics and stability support most convection in that area, perhaps eventually bleeding over into Southern New England. Best chance for this would be in Western MA and adjacent CT. Low level flow does bring in increasing dew points with values climbing into the low to mid 60s. Cold front crosses Southern New England late Tuesday night and Wednesday. This should provide an additional chance of showers/thunder until fropa. Thursday through Saturday... High pressure builds over New England for Thursday and Friday. This should be a dry period with temps aloft in the mid teens C, supporting surface max temps in the 80s. Second northern stream shortwave approaches on Saturday and brings potential for showers and possible thunder, although timing of a day seven feature carries low confidence.
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&& .AVIATION /08Z SUNDAY THROUGH THURSDAY/...
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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 Monday/... 03Z update...No changes to previous forecast. Overnight and Sunday...High Confidence. VFR. Low risk for patchy MVFR conditions in fog late after midnight tonight in normally prone locations. Sunday night...Moderate Confidence. VFR north of the MA Pike and much of northern CT. VFR initially over RI and southeast MA. Then potential for IFR ceilings and patchy IFR fog overspreading that region and possibly northeast CT toward daybreak Monday. KBOS TAF...High confidence. VFR. Light winds tonight. Winds shift back to E-SE around 10 kt by midday Sunday, then light southerly Sunday night. Some potential for a thin layer of IFR ceilings toward daybreak Monday, especially south of KBOS. KBDL TAF...High confidence. VFR. Very low chance for MVFR-IFR conditions in patchy fog 07Z-11Z tonight and again Sunday night. Outlook /Monday night through Thursday/... Monday night through Wednesday... Moderate confidence. Mostly VFR. Areas of IFR/LIFR in late night/early morning fog. Also brief MVFR cigs/vsbys in scattered showers/thunderstorms, mainly Tuesday and Wednesday. South to southwest surface winds will turn West to northwest behind the front on Wednesday. Thursday...Moderate confidence. VFR.
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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. Short Term /through Monday/...High confidence. 11 PM update...No changes to the previous forecast. Winds and seas below small craft criteria through Sunday night as high pressure ridge moves slowly southward across the waters. Outlook /Monday night through Thursday/... Moderate confidence. Monday night through Wednesday... Seas of 5 feet may linger east of Cape Ann Monday night, driven by southerly winds gusting near 20 knots. The Small Craft Advisory for Seas may need to be extended much of the night. South winds Tuesday will continue to gust near 20 knots. A cold front moves across the waters Wednesday, which will turn winds out of the west and northwest during the afternoon/evening. Scattered showers and thunderstorms may bring brief poor vsbys Tuesday and Wednesday. Also potential for low vsbys in fog, especially Tuesday and Wednesday early mornings. Thursday... Winds and seas remain below small craft thresholds. Expect dry weather.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas from 1 PM to 6 PM EDT Monday for ANZ250.
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&& $$ SYNOPSIS...WTB/GAF NEAR TERM...EVT SHORT TERM...GAF LONG TERM...WTB AVIATION...WTB/EVT MARINE...WTB/EVT

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