Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 231801 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 201 PM EDT Tue May 23 2017 .SYNOPSIS... Drying trend develops today with sunshine and seasonable temperatures. Another wave of low pressure tracks south of New England brining a period of rain to the south coast late tonight into Wed morning followed by another dry and seasonable afternoon Wed. A more potent area of low pressure impacts the region Thu and Fri with widespread showers and cooler temperatures. Dry weather and seasonable temperatures return for the holiday weekend as weak high pressure builds into the area. However the weather pattern remains progressive with the next round of wet weather possible Sunday night into Monday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 2 PM Update... Continued periods of filtered sunshine thru some mainly mid and high deck clouds this afternoon. Anticipating highs mainly in the 70s, except cooler along the shoreline where sea breeze development is occurring. Early morning discussion follows... ================================================================== Today... Weak surface low will be well offshore this morning with mid-level frontal system still stalled over southern New England. Weak mid and low level riding will develop over the area today. This will help break up cloud cover resulting in diurnal heating. Temperatures will warm into the 70s with cooler conditions along the coastline. Dry weather will prevail for most of the day with high level clouds passing through by the late afternoon hours, ahead of the next weather system. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Tonight... Digging shortwave across the Midwest will push a weak disturbance over the Mid-Atlantic. A coastal low will develop in response and move into southern New England along a stalled front tonight. Overall models have come into above average agreement with the evolution of the trough and closed low as it progresses east. The 00z NAM is a bit of an outlier compared to the remainder of the guidance. Therefore trended closer to the RGEM, EC and GFS. As this system moves into the region, showers will overspread across southern RI and SE MA. Right now it appears that the highest QPF over the Cape and Islands. Model guidance may be a bit underdone on the QPF amounts as guidance indicated that the low will close at 700mb resulting in a good Fgen area northwest of the low. This may spread precip farther north and thus have adjusted pops to indicate the potential trend. Wednesday... Showers will come to an end by the morning hours on Wednesday as the system continues to move eastward. Northeast winds will gust during the morning hours across the Cape and Islands due to tight pressure gradient from building high pressure and passing coastal low. Gusts will be near 15 to 25 MPH. Upper and mid level ridge will build into the area during the day resulting in a drying trend. Overall, a great day as temperatures will warm into the mid to upper 70s as skies clear out. Cooler along the eastern coastline as sea breezes may develop. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Highlights... * Widespread Rain Thu and Fri with locally heavy downpours possible * Mainly Dry Sat and Sun then risk of more showers Sun ngt/Mon * Cool Thu and Fri but more seasonable Sat and Sun Details... Thursday...closed low over the OH valley yields deep moist southerly flow into New England with mid level warm front ovespreading the region during the afternoon. This is accompanied by fairly robust mid level jet (50 kts) for late May coupled with PWATs of up to +2 SD from climo. Thus some heavier downpours possible. Could be some embedded thunder as well as nose of mid level dry slot approaches and steepens mid level lapse rates. Modest easterly low level jet up to 40 kt will provide some windswept rain as well. This onshore flow combined with precip and SSTs in the low to mid 50s will hold temps down. Friday...vertically/occluded low over the region with surface low likely tracking along or just off the south coast. This will result in scattered showers especially during the morning hours. Could be some locally heavy downpours given strengthening mid level low. This track will also keep warm sector offshore and another day of cool temps. Although some temp recover to near 70 across CT as conditions improve from southwest to northeast. Holiday Weekend...Closed low moves into the maritimes with rising heights and associated subsidence overspreading the area Saturday, providing a real nice day with highs in the 70s. Most of the guidance keeps dry weather here thru Sun except the GFS which appears on the fast side of the envelope. By Sun ngt and Mon next northern stream trough and associated moisture will overspread our area, thus increasing the chance of showers. Temps seasonable Sat and Sun, likely a bit cooler Mon given cloud cover. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday Night/... 18Z update... This afternoon...High confidence. Mainly VFR across the region. Lower clouds w/IFR cigs may linger just E of outer Cape Cod (just offshore) this afternoon. Sea breezes anticipated along coastlines. Tonight...Moderate confidence. Mainly VFR with MVFR/IFR across the south coast, Cape and Islands in low clouds and fog, as well as passing showers from coastal low later tonight. Also areas of fog south coastal MA/Cape/Islands. Gusty NE winds to near 20 kts possible near daybreak. Chance for showers mainly Cape/Islands later tonight. Wednesday...High confidence. Improving trend to VFR, with the exception of Cape/Islands, where IFR/vsbys cigs may linger thru Wed am, and IFR cigs may last into the afternoon. East wind persists. Passing showers Wed am, mainly across Cape/Islands. Wed night...Across interior southern New England, VFR likely and dry. Along east coastal and south coastal MA including Cape/Islands, IFR possible in low clouds and fog. Light NE/E wind persists thru the night. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Thursday through Saturday/...moderate to high forecast confidence. Thursday and Friday...widespread showers in IFR/MVFR. Saturday...drying trend along with VFR conditions. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/...High confidence. Weak high pressure will build across the waters this afternoon. Another coastal low will develop across the Mid-Atlantic and move over the waters tonight. Visibilities could drop in heavy rainfall. Improving conditions by Wednesday as high pressure builds in the area. Despite the active weather, seas will remain below 4 feet and gusty northeast winds Wednesday morning will remain around 20-25 kts. SCA may be needed, but confidence is low. Outlook /Wednesday Night through Saturday/... Thursday...ENE winds 20-30 kt with strongest winds late in the day and evening with low risk of low end gales. Vsby poor in rain and fog. Friday...winds light and variable in the morning as high pres crest over the area. Vsby poor in showers and fog but improving as the day progresses as winds become more northwest. && .TIDES/COASTAL FLOODING... High astronomical tides will occur over several tide cycles along eastern Massachusetts coast from Thursday into Memorial Day, with tides around 12 feet in Boston and 4 feet on Nantucket. At the very least, minor nuisance flooding will occur in the most vulnerable locations such as Morrissey Blvd in Boston. Any surge on top of these tides would lead to more widespread, but minor, coastal flooding, including on Nantucket. Right now, this looks to be a possibility Thursday into Friday due to expected onshore winds. Model surge guidance (ESTOFS) shows a potential 0.6 ft surge, which would give a storm tide near 13 feet Thursday night in Boston and just under 5 ft on Nantucket. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Nocera/Dunten NEAR TERM...Nocera/Dunten/NMB SHORT TERM...Dunten LONG TERM...Nocera AVIATION...Nocera/Dunten/NMB MARINE...Nocera/Dunten/NMB TIDES/COASTAL FLOODING...Staff is the U.S. government's official web portal to all federal, state and local government web resources and services.