Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 271742 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 142 PM EDT Sat May 27 2017 .SYNOPSIS... Weak high pressure building across the region pushing E round which onshore flow will usher slightly cooler air and an abundance of clouds along with the possibility of drizzle. Into next week, low pressure in the Great Lakes generates a coastal low late Monday that passes off Nantucket on Tuesday. This will bring wet weather on Memorial Day. Daytime clouds and scattered showers will pop up each day Tuesday through Friday keeping seasonable temperatures. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 140 pm update... Partly sunny skies at mid afternoon with temps well up into the 60s in most locations, except upper 50s to the lower 60s on the immediate coast as a result of sea breezes. Overall, highs will top out well into the 60s to the lower 70s in most locales by late afternoon. However, sea breezes will hold temps in the upper 50s and lower 60s along the immediate coast. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... Tonight... Turning cloudy with the possibility of drizzle. With high pressure shifting E, will see return S onshore flow. This beneath a building mid to upper level ridge, moisture pools beneath the dry inversion. A weak upslope component, at minimum would expect marine stratus to expand, but also given a sweeping weak mid-level trough and impulse energy, can not rule out the possibility of drizzle. All aside, it would appear to be a cool and damp night. Lows around the upper 40s. Sunday... So then the question becomes as to whether overnight marine stratus lifts and/or breaks up or rather holds out and remains low across the region. Subsequent temperature implications. The mid to upper level ridge in place as high pressure remains offshore. The onshore flow continues beneath the dry inversion. Clouds and cool conditions not out of the question, but the magnitude even WRF-model solutions can`t agree upon. A consensus blend given the uncertainty yields broken to overcast cloud decks that lift through the day. Would see temperatures warm to seasonable levels, upper 60s to low 70s, the coolest of conditions along the shores in the low to mid 60s. && .LONG TERM /SUNDAY NIGHT 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 /18Z 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/... This afternoon...High confidence. Mainly VFR conditions dominate under a scattered deck of mid level cloudiness. 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, it is uncertain in areal extent of lower clouds and how quickly they develop 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/...High confidence. Beneath high pressure, winds will remain light while mainly onshore southerly throughout the forecast period. Seas subsiding, good boating weather though cool given expected broken to overcast marine stratus at times, along with the threat of drizzle overnight into the early morning hours Sunday. Outlook /Sunday Night 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... Though astronomical tides will be high for another night in a row, winds as well as swell and wave action will be light. Given such conditions, do not expect there to be much in the way of impacts along the coast in regards to vulnerable shoreline roads becoming inundated. Thus no coastal flood statement issued with this forecast package. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas until 2 PM EDT this afternoon for ANZ254>256. && $$ SYNOPSIS...Dunten/Sipprell NEAR TERM...Frank SHORT TERM...Sipprell LONG TERM...Dunten AVIATION...Frank/Dunten MARINE...Dunten/Sipprell TIDES/COASTAL FLOODING...Sipprell

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