Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 260314 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1114 PM EDT SAT JUN 25 2016 .SYNOPSIS... 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 cool front brings showers and possibly some thunder beginning Monday night and continuing through Thursday. High pressure then brings dry seasonable weather for the end of next week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... 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 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... 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 THROUGH SATURDAY/... */ HIGHLIGHTS... - Increasing chances of wet weather from N/W beginning Monday Night - Potential offshore low for late Wednesday into Thursday - Keeping it dry and near-seasonable for Friday into the Weekend */ DISCUSSION... While the Pacific North American pattern shifts positive into July per ridging over the W CONUS with troughing over the Great Lakes region into the NE CONUS, New England seemingly resides on the E periphery of the trough. Subsequently and as been the trend of late, continued maintenance of the Atlantic ridge with sub-tropical flow along the N periphery of which yields a squeeze play of subsidence mainly SW to NE across the Gulf of Maine into SE New England up against synoptic disturbances approaching from the N and W. The overall dry pattern looks to continue with many locations recording rainfall deficits on the order of around 3 to 6 inches since the beginning of the year. Considering the forecast for the next week, this trend looks to continue for SE portions of New England. A non- GFS consensus is preferred with heavier weighting towards ensemble probabilistics and means. From Monday through Wednesday, will see an increasing influx of moisture throughout the atmospheric profile per S flow and as surface dewpoints rise into the 60s. Potentially some issues with marine stratus and fog early on over S/SE New England. Precipitable waters increasing on up around 1.5 inches ahead of low to mid level synoptics beneath broad diffluence aloft out of the N/W invoking a favorable environment of forcing and lift along a slow moving cool front. Can not rule out some pre-frontal boundaries out ahead. Overall the expectation is that with each day PoPs will increase out of the N/W as the more favorable environment approaches throughout which the atmospheric profile becomes more conditionally unstable. With high pressure ridge across the region, will continue to be dry and comfortable as dewpts fall back to the upper 40s to mid 50s. Light/variable winds in place, dropping off to calm across some inland areas. With continued good radiational cooling, will see temps fall back to the upper 40s to around 50 in the normally prone areas of interior E Mass to the lower Cape and the Vineyard, ranging to the mid 50s to around 60 in the urban centers. Once again, may see a few hours of patchy low clouds and fog around or after 06Z in the typically prone locations.y unstable. Difficult to nail down cloud cover and potential diurnal forcing possibly yielding surface based instability, but aside, looking at the broader view of ingredients gives weight and confidence towards PoP trends which again are to gradually increase out of the N and W with time. Monday should be dry, but overnight into Tuesday any activity expected over Upstate NY into PA should drift E with the mean wind before dissipating in prevailing high pressure and drier air S/E. This environment slowly shifts E yielding the best chances for wet weather over a majority of the forecast area Tuesday night into Wednesday. Again, preference to the slower solutions up against a retrograding H5 low offshore. GFS seems just a tad too fast. From Wednesday on into Thursday, will have to watch how efficiently and effectively mid-level synoptics round the broad troughing pattern invoke surface cyclogenesis and low pressure along the long- standing stalled sub-tropical front over the SE CONUS and off the Mid-Atlantic. How the surface low evolves, how far N its pulled by lower heights to the N, whether it can brush New England and bring forth more rain or rather if it stays offshore and we stay dry. EC ensemble exhibits a trend but is widely spread on low location, so a low confidence forecast. Some cooler air behind the system coupled with forcing per additional mid-level energy, could see some activity spark across the interior with diurnal heating of available moisture providing the lift through the atmosphere. For Friday on into the weekend will keep it dry. Continued troughing aloft but will keep it absent of forcing for the time being. Hold temperatures near seasonable with the expectation of both heat and humidity building over the timeframe. && .AVIATION /03Z SUNDAY THROUGH THURSDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday Night/... 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 through Thursday/... Monday through Wednesday...Moderate confidence. S winds. Potential for gusts up to 20 kts at times. IFR-LIFR stratus possible, mainly thinking S/SE of the CT-MA border, including southeast MA. Increasing chances of RA out of the N/W beginning Monday night. Highest likelihood Tuesday into Wednesday. TEMPO MVFR possible, at least low-end VFR. Can not rule out the potential risk of TSRA. Thursday...Low confidence. Offshore low possible. RA impacts with the potential TSRA risk continuing with additional weather possibility across interior New England. Winds backing out of the N/W. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday Night/...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 through Thursday/... Monday through Wednesday...Moderate confidence. S winds with the potential for gusts up to 20 kts at times. Could see some visibility restrictions with low clouds and fog. Otherwise prevalent S flow likely to generate swell and seas above 5 feet towards the later half of the period. Rain chances increase towards this timeframe, though it is possible aside from aforementioned soupy weather, conditions could remain relatively dry. Thursday...Low confidence. Offshore low possible. How close it will brush New England remains uncertain though it does appear forecast trends do not have it sticking around for long. Would expect wet weather and perhaps some enhancement in wind and wave conditions for a brief period out on the waters. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Sipprell/GAF NEAR TERM...Sipprell/EVT SHORT TERM...GAF LONG TERM...Sipprell AVIATION...Sipprell/EVT MARINE...Sipprell/EVT

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