Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 271350 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 950 AM 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/... 950 am update... A scattered to mainly broken deck of clouds covered most of the region at mid to late morning. The exception was portions of northeast MA where partly to mostly sunny skies have developed, but clouds will likely fill back in this afternoon. Despite a weak ridge of high pressure overhead, model soundings continue to show an area of trapped low level moisture in the 2 to 5 thousand foot range. So while some peeks of sunshine will occur at times today, expect to see clouds dominate through the afternoon. Generally dry weather is anticipated, although the low risk of a spot sprinkle or two can not be ruled out. High temps are tricky this afternoon because just an hour or two of late May sunshine can result in temps jumping quickly. Overall though given lots of clouds, expect high temps to top out in the 60s to lower 70s. Weak gradient will allow for afternoon sea breezes on the immediate coast with temps in the upper 50s to the lower 60s in those locations. && .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 /14Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday/...Moderate Confidence. 950 am update... Today... SCT-BKN CIGS should persist into the afternoon. MVFR CIGS though should give way to mainly VFR by mid afternoon as boundary layer warms. Sea- breezes developing around 15-16z. Tonight... CIGs becoming BKN-OVC, lowering to IFR, possible LIFR, especially across the interior. Collocated threat of -DZ into the early morning hours which may lead to VSBY restrictions. Light onshore flow out of the S/E. Sunday... BKN-OVC CIGs slowly rising IFR towards MVFR / low-end VFR mix. Continued light onshore S flow. KBOS TAF...MVFR to low-end VFR stratus will be a nuisance a majority of the forecast timeframe. Expect a sea-breeze around 15-16z today with sustained onshore flow up around 10 kts. KBDL TAF...IFR-LIFR mix with -DZ possible overnight towards the early morning hours Sunday. Outlook /Sunday Night 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. Small Craft Advisory for hazardous seas until 11 AM EDT this morning for ANZ235-237. && $$ SYNOPSIS...Dunten/Sipprell NEAR TERM...Frank SHORT TERM...Sipprell LONG TERM...Dunten AVIATION...Frank/Dunten/Sipprell MARINE...Dunten/Sipprell TIDES/COASTAL FLOODING...Sipprell is the U.S. government's official web portal to all federal, state and local government web resources and services.