Area Forecast Discussion
Issued by NWS Boston, MA

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282 FXUS61 KBOX 291701 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 101 PM EDT SUN MAY 29 2016 .SYNOPSIS... A backdoor cold front will bring much cooler temperatures today along the eastern MA coast, but another hot afternoon is in store farther inland where hit and miss showers and thunderstorms are expected. Mainly dry weather is expected this evening, but bands of torrential rain showers along with isolated thunderstorms are expected very late tonight and Memorial Day. Dry conditions with warm afternoons follow Tuesday into Wednesday. Unsettled weather may return by the end of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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100 pm Update... Low clouds are holding their own across eastern MA but have been eroding on southern and western edge across western and south central MA and northern RI. Expect this to continue through late afternoon while some breaks begin to appear across eastern MA. Temperatures have certainly been a challenge with backdoor front essentially splitting SNE in half: Coolest temps were across NE MA where onshore flow was keeping readings in 50s, while it has soared well into 80s around Hartford. Airmass has begun to destabilize across much of western New England early this afternoon, where ML CAPES were approaching 1000-2000 j/kg near Berkshires. While most of activity has developed under more favorable conditions in upstate NY, we have also begun to see some scattered showers form over Berkshires during past hour. We should see additional scattered showers/storms develop through late afternoon in MA, primarily west of Worcester Hills. Potential for organized severe weather remains low given very marginal 0-6km shear of 20-25kt and meager mid level lapse rates (less than 6C/km). Main hazards are brief downpours and lightning, and perhaps one or two storms that produce 40 mph gusts.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... ***Bands of torrential rain showers with isolated thunderstorms develop very late tonight and continue through Memorial Day*** ***Potential for localized flash flooding*** Tonight and Memorial Day... Convection across the interior will quickly dissipate early this evening with the loss of daytime heating/instability. Otherwise, much of the evening should be dry with perhaps just a spot shower or two. May see some patchy fog develop especially near the south coast. Things then become interesting very late tonight and Memorial Day. Tropical Storm Bonnie off the South Carolina coast will remain well to the south of our region. While Bonnie will not directly impact us, its plume of tropical moisture will get pulled northward out ahead of an approaching cold front. PWATs will approach or even exceed 2 inches, which is near record high levels for this time of year based on historical climatological upper air data. These extremely high PWATs will combine with some elevated instability coupled with a low level jet of 30 to 40 knots. The result will be bands of rain showers with torrential rainfall along with isolated thunderstorms. This is one of those scenarios that has the potential to result in very localized 2+ inch rainfall amounts in less than one hour. This will bring the potential for localized flash flooding, particularly if the heaviest bands move across our more vulnerable urban centers. The problem is that this will come down to a lot of mesoscale processes and its uncertain where the highest risk for this will occur. We actually may see two main areas with the heaviest rainfall. The first may occur with the shortwave that moves across interior southern New England overnight into Monday morning. There is also the potential for a second area across RI/southeastern MA on the nose of the low level jet. Depending on how the timing works out, may see bulk of heavy rain threat shift to the coastal plain by mid to late Monday afternoon. If this occurs there may be a small window for destabilization and a few surface based thunderstorms to move into far western MA early Monday evening. Instability/shear do not look to be enough for severe weather, but low risk for an isolated strong storm. So to sum up, main concern will be bands of torrential rain showers/isolated thunderstorms with a localized flash flood threat, particularly if torrential rain bands setup across our more vulnerable urban centers. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Highlights... * Lingering showers & thunderstorms SE MA & RI Mon Night * Mainly dry with above normal temperatures Tue/Wed * Unsettled weather may return toward next weekend Medium range models are in good agreement on the overall synoptic pattern. There are points of uncertainty, including how Tropical Storm Bonnie and her remnants interact with the pattern at large as well as the usual uncertainties further out in time. A mid-level ridge will move over southern New England Tuesday and then move offshore Wednesday. Mid-level troughing then moves into Quebec towards the end of the work week and starts influencing our weather with several shortwaves working around the base of the trough. This will result in more unsettled weather towards the end of the week. Monday night...Showers and isolated thunderstorms will linger across southeastern Massachusetts and Rhode Island through the evening hours before they diminish or move offshore. Clearing conditions are expected through the remainder of the night. Tuesday and Wednesday...Mid-level ridge moves over southern New England. This will bring dry weather to much of the area. A dry cold front will move through southern New England Tuesday, resulting in a wind shift to the north. This is followed by a backdoor cold front on Wednesday. Temperatures will be above normal through both days. Thursday through Saturday...Mid-level trough moves into Quebec allowing several shortwaves rotating through the base of the trough to move through southern New England. This will result in periods of showers throughout this period. Thus have continued with chance PoPs through this period. Temperatures will be around or just below normal for much of the time. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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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 Night/...Moderate Confidence. Eastern MA and RI through this evening... IFR ceilings along E MA coast will continue to slowly lift and should improve to MVFR for a few hours this afternoon, except around Cape Ann where ceilings probably won`t improve much. VFR conditions elsewhere will persist through late afternoon, but an approaching fog bank from the south will quickly bring IFR and even LIFR to Cape Cod and the Islands toward sunset. Western/Central MA and northern CT through this evening... VFR will give way to scattered showers/storms, especially in western MA near the Berkshires through 23z. Storms may bring IFR visibilities for a brief time and possibly gusts to 35kt. All areas tonight, Monday, and Monday Night... IFR and even LIFR becomes widespread as bands of showers/isolated storms approach from the south. Activity should be more numerous 09z-18z Mon, especially closer to the South Coast, before it begins to push offshore later Mon. It is also possible that a few showers or storms reach western New England from eastern NY late Mon afternoon or evening, but confidence is low. KBOS TAF...Moderate confidence. Should see ceilings lift to MVFR for a few hours before IFR ceilings return around 00z Mon. KBDL TAF...High confidence. Any storms should remain well to the north and west, but an isolated storm is possible through 21z. Outlook /Tuesday through Thursday/... Tuesday and Wednesday...Moderate confidence. VFR. Thursday...Moderate confidence. Mainly VFR conditions expected. Increasing clouds with diminishing conditions through the night, particularly along the south coast.
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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 Monday/...High confidence. Winds and seas should generally remain below small craft advisory thresholds through Monday, but seas may approach 5 feet across our far outer-waters by Monday afternoon. Main concern though for mariners will be for areas of fog, particularly tonight into Monday across our southern waters. In addition, heavy showers and isolated thunderstorms will result in poor visibility. Outlook /Monday Night through Thursday/... Monday night and Tuesday...Moderate confidence. Some uncertainty on wave heights with swell from Tropical Storm Bonnie potentially moving up into the coastal waters. At this point there is potential for 5 foot seas, especially on the outer waters. Southwesterly winds remain below 20 kts, shifting to the north Tuesday night. Visibilities may be limited at times Monday night in both fog and showers and thunderstorms. Wednesday...Moderate confidence. Northeasterly winds and seas will remain below Small Craft Advisory criteria. Thursday...Moderate confidence. Easterly winds and seas increase. Seas may rise above 5 feet, especially on the outer waters. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/RLG NEAR TERM...JWD SHORT TERM...Frank LONG TERM...RLG AVIATION...JWD MARINE...Frank/RLG

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