Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 300542 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 142 AM EDT SAT JUL 30 2016 .SYNOPSIS...
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A period of drier conditions follows for Saturday with the slight chance of showers over Southwestern New England. A warm front will develop south of New England on Sunday with a few waves of low pressure passing eastward along it from Sunday through early Tuesday. Scattered showers are possible into early Tuesday, especially in western sections. Low pressure will move out to sea Tuesday. High pressure returns with dry and seasonable conditions for the middle and latter portion of next week.
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&& .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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130 AM Update... No significant changes to near term forecast. Patchy fog has developed across portions of the CT River Valley and a few other interior valleys. Areas of fog with visibilities less than 1 mile have persisted along much of the Plymouth County coast and portions of the Cape. Temperatures remain reasonably on target from prior forecast and only very minor adjustments made for the 130 AM update. 10 PM Update... Showers, a few of which were very heavy, had nearly dissipated by 10 PM with what looked to be only sprinkles left over northwest RI. Made just a few adjustments in temperatures and dewpoints to reflect current trends. Main issue during the overnight hours will be forecasting extent of fog areas. Some patchy fog has begun to develop across interior valleys and an area of fog has crept south along the Plymouth County coast with pockets of visibility below 1 mile. 715 PM update... A few heavy showers continued across northern Worcester County and in northern Connecticut as of 715 PM. Another heavy shower was moving south into Middlesex County from the Nashua area. Winds gusted to near 25 mph with one of these showers at Westfield, MA during the past hour. The showers were shallow...below 25 kft...and were not producing lightning. The HRRR shows showers sliding southward through central MA over the next 2 hours before dissipating. Have updated PoPs to reflect this thinking. Otherwise no changes to forecast. Will need to keep a close eye on potential fog development in southeast MA. Previous discussion... Clearing continues across S New England allowing boundary layer destabilization beneath a conditionally unstable environment. Scattered heavy showers developing though low-topped, limited on development with likely warmer and sinking air aloft with slightly rising heights around H5 and in wake of the main mid-level vortex parent with the surface low sweeping out to sea. Slow moving through the rather weak 10 mph mean flow out of the NW, monitoring for possible localized flooding impacts. Development along fine- line convergence boundaries it would seem per observational mesoanalysis. Diurnally driven, should see activity diminish with sunset. Tonight... Clearing out with high pressure and drier air building in. With light winds, a favorable setup for radiational cooling. Noting a somewhat soupy airmass remaining in place with dewpoints hovering around the low to mid 60s, and considering antecedent rains, anticipating fog to develop. Confident within the CT River Valley, E CT, interior Southeast MA of some visibility restrictions. Perhaps some issues along the coasts though may see more clouds than fog with the NE onshore flow turning N through the overnight period.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/... Saturday... High pressure and drier air linger lending to mostly clear conditions and light winds. Likely sea-breezes to develop around mid to late morning. Model forecast indications of showers developing along sea- breezes per a measure of lift of available surface based instability and decent low level moisture availability, that or upstream convection from PA becomes an influence. Precipitable waters forecast up to 2 inches. But considering an unfavorable environment given confluent mid to upper level flow and mid level height rises lending to some measure of sinking air, feel there is a low risk of showery weather and mainly late in the day. Thus leaning with slight chance PoPs mainly for S/W New England encompassing much of the N-half of CT into the Springfield MA metro. Forecast +14-16C H85 temperatures warrant mid to upper 80s for highs. Already temperatures were underdone earlier today after clouds started to break, so am going to up the forecast highs a degree or two warmer nudging the Hartford-metro to near 90. Saturday night... Approaching low to mid level warm frontal boundary parent with the surface low over the S Great Lakes Region. Continued moistening of the low to mid levels per isentropic upslope over-running flow out ahead of the system. Leaning that high pressure and drier air lingers long enough to buffer the onset of wet weather into the E-half of New England much as the 29.09z SREF would suggest. There is as well continued mid to upper level height rises. So will go with chance PoPs for the W, lesser to the E. Overnight lows slightly more mild with anticipated cloud cover and winds at the surface slightly more ashore, though beginning to see surface low pressure take shape S/W of New England towards Sunday morning. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Highlights... * Unsetlled Sunday through early Tuesday with scattered showers, mainly in western sections. * Mainly dry and seasonable weather Tuesday afternoon through Friday, with a warming trend. Overview and model preferences... Models in reasonably good agreement through the period. An upper level trough moves from the eastern Great Lakes Sunday across New England early Tuesday, then out to sea. A ridge of high pressure builds aloft across the northeast states, cresting over the region on Friday. At the surface, a warm front will develop to our south Sunday. Several waves of weak low pressure are forecast to move along the front, but remaining to our south. The low finally consolidates then moves out over Georges Bank by Tuesday. High pressure settles over New England Tuesday afternoon through Friday. A cold front is then poised to move through the area next Saturday. Used a consensus blend of available model and ensemble guidance for this portion of the forecast. Details... Sunday through early Tuesday... Expect waves of low pressure to move slowly along a stalled front just south of New England, keeping low and mid level moisture in place with a light east-southeast flow gradually becoming northeast. On Sunday afternoon and evening, models have been consistently showing instability over the Hudson Valley in southeast NY. With upslope flow, our best chances of showers will be in the higher terrain of western MA and perhaps also in the Worcester hills. The ECMWF is an outlier in showing heavy convection/thunderstorms moving eastward from the Hudson Valley into CT and then into southern RI, as it travels along and just north of the warm front. For now have 50-60 percent probabilities in western MA and northwest Hartford County, with lesser chances as one heads east. Generally the same reasoning continues Sunday night through early Tuesday. During this time, low pressure consolidates and moves out sea, southeast of Cape Cod/Islands. There could be scattered showers at any time, with the best chances in the western hills. But most of the time it will be rain-free. Temperatures will run slightly below seasonal normals with highs Sunday in the 70s and mainly 75-80 Monday. Tuesday afternoon through Friday... A high amplitude 500 mb ridge moves east from the eastern Great Lakes and crests over New England on Friday. By Wednesday, our winds will shift to a southwesterly direction and the gradual warming trend will begin. Maximum temperatures will rise a few degrees each day, reaching the mid and upper 80s Thursday and upper 80s to lower 90s on Friday. No precipitation is forecast, although we cannot rule out an isolated shower or thunderstorm in far northwestern sections late Friday afternoon. A cold front is then expected to move through the area next Saturday with a chance of showers or thunderstorms, but that`s beyond our current forecast period. && .AVIATION /06Z SATURDAY 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 Sunday/... Overnight...Moderate confidence. Areas of MVFR-IFR in fog during the early morning hours, especially across the CT River Valley, as well as interior E CT and SE MA. Pockets of dense fog have developed along the Plymouth County coastline and may spread across the Cape and Islands before sunrise. Saturday...High confidence. SCT-BKN cigs especially towards late in the day. Light winds. Sea-breezes developing along the shores late morning into afternoon. SCT SHRA/TSRA possible across S/W New England late but believe it to be a low risk. Saturday Night...High confidence. BKN-OVC cigs with MVFR-IFR developing along the S-coast of New England towards Sunday morning. Increasing chance of RA from the S/W along with VSBY restrictions. KBOS TAF...High confidence. Conditions remain VFR into this evening. Though watching closely into this evening for TEMPO MVFR with NE onshore winds. Maybe even a SHRA. Believe it to be a low risk. KBDL TAF...High confidence. Low risk +SHRA towards the late afternoon period with TEMPO MVFR-IFR impacts. A moderate risk. Outlook /Sunday Night through Wednesday/... Sunday through early Tuesday...Moderate confidence. Mainly VFR conditions. However, there will be scattered showers at any time. Cannot rule out a heavier shower or thunderstorm, especially in the slopes of the Berkshires and in northern CT on Sunday. Brief MVFR/IFR conditions are possible in the heavier showers. Patchy late night/early morning fog is possible, especially along the south coast, closer to the warm front. IFR conditions are likely in any areas of fog. Tuesday afternoon through Wednesday...High confidence. VFR. Just a few areas of MVFR possible in patchy late night/early morning valley fog and in the usual fog-prone places.
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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 Sunday/...High confidence. 715 pm update... There is the possibility of visibility restrictions with fog during the overnight into early morning hours. Otherwise the majority of the forecast is comprised of winds below 25 knots and seas below 5 feet, with increasing chances of showers mainly Saturday night into Sunday morning. Outlook /Sunday Night through Wednesday/...High confidence. Expect easterly winds (southeast through northeast) and seas below small craft criteria through the period. Seas may build to 4 ft Monday into Tuesday as low pressure passes through the region and out to sea around Georges Bank. Northeast winds may gust up to 20 kt mainly over the eastern outer waters Monday night and Tuesday. Locally reduced visibilities in scattered showers or an isolated thunderstorm through early Tuesday morning. Patchy late night/early morning fog through the period.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Sipprell/GAF NEAR TERM...Sipprell/GAF/Thompson SHORT TERM...Sipprell LONG TERM...GAF AVIATION...Sipprell/GAF/Thompson MARINE...Sipprell/GAF

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