Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 271923 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 323 PM EDT Sat May 27 2017 .SYNOPSIS... A weak ridge of high pressure will bring pleasant temperatures and result in mainly dry weather on Sunday, other than perhaps a brief spot shower or two. An approaching low pressure system will bring periods of showers and unseasonably cool temperatures on Memorial Day. Seasonable temperatures will follow for much of next week, with dry weather mixed in at times with scattered showers. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... 320 pm update... Tranquil weather tonight with a weak ridge of high pressure in control. Partly cloudy skies this evening should give way to mostly cloudy skies after midnight. This a result of a cooling boundary layer allowing for more in the way of low clouds to develop. A decent shortwave will also drop down in northwest flow aloft, but with little in the way of low level forcing. Therefore, dry weather will dominate and do not expect anything more than perhaps a brief passing sprinkle or two. We also can not rule out a touch of patchy drizzle toward daybreak if cloud bases can get low enough, but again no real impact. Low temps will mainly be in the upper 40s to the lower 50s. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Sunday... An abundance of clouds is one again expected with model cross sections indicating a fair amount of low level moisture. Nonetheless, do expect to see some peeks of sun at times with temporary upper level ridging building into the region. This should allow for temps to be a bit milder than today. Highs are expected to top out between 70 and 75 in most locations, but weak gradient will once again allow for sea breezes on the immediate coast holding high temps in these locations in the 60s. While the vast majority of Sunday will be dry, enough moisture combined with diurnal heating may result in a few brief spot showers. The best chance for this will be in western and northern MA, but even in these locations the vast majority of the day will be dry. Sunday night... Dry weather should prevail the majority of the night. While models differ on specific timing, an approaching shortwave/warm advection aloft will allow for the potential of showers to increase toward daybreak Monday across the interior. Low temps will once again be mainly in the upper 40s to the lower 50s. && .LONG TERM /MONDAY THROUGH FRIDAY/... Highlights... * Risk of rain returns Sun night into Memorial Day * At or below normal temperatures will occur this upcoming week * Unsettled weather pattern continues with hit or miss showers through the period Pattern Overview... 00z guidance continues to be in agreement for the extended forecast. However there are some difference in timing and strength of each system. Mid to upper level ridge across the region on Sunday will begin to give way approaching trough over the Great Lakes. Potent shortwave rounding the trough will develop a surface low over the Mid-Atlantic on Monday and track near southern New England Monday night/Tuesday. Beyond that, broad upper level trough will take hold over the Great Lakes and Northeast through the remainder of the work week as strong ridge builds over the Rockies. Bermuda high pressure will keep the region in a moist southwest flow aloft resulting in a chance of precip with each passing shortwave. Temperatures... Broad upper level trough over the region will keep any summer-like heat at bay through the period. Monday will be the coolest as low pressure moves through. Otherwise anticipate generally seasonable conditions on Tuesday and Wednesday thanks to southwest flow aloft and thermal ridge. Resulting in high temps in the upper 60s to mid 70s. Mid-level wave and associated front on Thursday drop temps aloft to well below average for late May. This will keep temps to below climo with highs in the upper 60s to low 70s into Friday. There is the potential that next Saturday may trend a bit warmer as upper level trough begins to exit the region. However, the low could linger a bit longer into next weekend. Overnight lows will linger in the 50s through the period. Precipitation... A spot shower and/or drizzle is possible on Sunday night despite upper level ridge aloft. Moist east flow from passing surface high will be trapped under an inversion as noticed in model soundings. The Berks and Worcester Hills have the best shot for precip from upslope flow, this is still a low risk. The first chance for widespread rainfall will come on Memorial Day as low pressure system tracks over the Great Lakes and towards the Northeast. A secondary low looks to develop over the Mid-Atlantic and with an increasing LLJ combined with PWATS near an inch, anticipate the risk for showery weather. Timing can still change, but appears that the later half/evening on Monday may dry out from west to east as bulk of the precip moves in morning into early afternoon. There continues to be a chance for some thunderstorms on Monday as LI are below 0 and TT above 50. Why the risk is more elevated GEFS members are indicating some surface CAPE which could be enough for a few thunderstorms when the bulk of the precip moves through. Beyond Monday, there is a hit or miss chance for showers through much of the period as upper level disturbance rotates through the flow. Certainly not a washout by any means but believe that Tuesday and Wednesday have the better shot for showers with Thursday trending a bit drier thanks to northwest flow aloft. && .AVIATION /19Z SATURDAY 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/... Tonight...Moderate confidence. Mainly VFR conditions into this evening. However, a cooling boundary layer and some trapped low level moisture will likely result in some MVFR conditions developing late with perhaps some localized IFR cigs/vsbys. Overall, areal extent of lower clouds and how quickly they develop are uncertain but do feel there will be some especially toward daybreak. Sunday...Moderate confidence. MVFR to perhaps some localized IFR conditions early should improve to mainly VFR by afternoon, despite a scattered to broken deck of clouds persisting and perhaps a brief spot shower or two. Sunday night...Moderate confidence. Mainly VFR conditions for much of the night. However, some lower conditions may arrive toward daybreak Monday especially across the interior depending on the timing of rain showers. KBOS TAF...Moderate confidence in TAF. E sea breeze should shift to SE by late afternoon/early evening and finally SSW by late evening. SE sea breezes should re-develop by late Sunday morning or early afternoon. Mainly VFR, but may see a period of some lower clouds between 7z and 15z Sunday. KBDL TAF...Moderate confidence in TAF. VFR into this evening, before MVFR to perhaps some IFR conditions developing overnight. Improvement to mainly VFR should occur by late Sun morning/early afternoon. Outlook /Monday through Wednesday/...Moderate confidence. Monday...Deteriorating conditions to MVFR/IFR in showers and possibly a thunderstorm. SE winds less than 20 kts. Tuesday into Wednesday... Lingering IFR/MVFR will improve to VFR for most locations. Areas of MVFR in passing showers are still possible for Tuesday and again Wednesday. Light E wind Tuesday becoming S in the afternoon, then W/SW Wednesday. Speeds less than 15 kts. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday Night/... Tonight and Sunday...High confidence. Weak ridge of high pressure will keep winds/seas below small craft advisory thresholds. Sunday night...Moderate to high confidence. Winds and seas will generally remain below small craft thresholds most of the night. However, approaching low pressure will increase the pressure gradient toward daybreak and enough southeast fetch may develop across our southwest outer-waters for some marginal 5 foot seas near 12z Monday. It is still too early to hoist any marine headlines for a potential late 3rd period event. Outlook /Monday through Wednesday/...Moderate confidence. Winds less than 20 knots and seas less than 5 feet through the period. Showers and isolated tstms possible on Monday. Drying trend into the work week. && .TIDES/COASTAL FLOODING... We opted to issue a coastal flood statement roughly between midnight and 3 am Sunday along the eastern MA coast. Boston has another very high astronomical tide of 12.3 feet just before 130 am Sunday. Storm surge values are running a bit higher than guidance, and may still be close to a one half foot during this coming high tide. We did have a few reports very early this morning along the eastern MA coast, so felt it was worth a statement for some of the most vulnerable shore roads experiencing some very minor flooding near high tide. Overall though impact will be minimal, so just went with the statement. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Frank NEAR TERM...Frank SHORT TERM...Frank LONG TERM...Dunten AVIATION...Frank/Dunten MARINE...Frank/Dunten TIDES/COASTAL FLOODING...Frank

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