Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 271842 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 242 PM EDT WED JUL 27 2016 .SYNOPSIS... One more day of heat and humidity is in store Thursday before a cold front slowly drops south across the region, possibly bringing scattered showers and thunderstorms. The front is expected to stall near the South Coast Friday. Low pressure will push off the south coast Friday into Friday evening, bringing the chance for showers and thunderstorms. Showers may linger this weekend, with a few thunderstorms possible Sunday. Conditions will improve early next week as high pressure slowly moves in from the northwest. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 240 pm Update...Near and Short Term sections only. Plenty of diurnal cumulus has developed across southern New England, aside from the immediate coast where sea breezes have developed. Temperatures have once again soared into 90s away from coast, making this 7th consecutive day of 90+ heat for many interior locations (including BDL with 94 so far), but even BOS and ORH have come close with a high temp of 87 at both so far. PVD reached 91 before sea breeze developed which is their 3rd day in a row. Clouds will dissipate around sunset with loss of heating. Light S/SW winds prevail tonight with clear skies, which will allow for good radiational cooling in usual inland cool spots (CT Valley and interior E MA). Lows in these areas should drop back into lower 60s while larger urban centers stay around 70. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... SW flow gets underway Thu as high pressure moves offshore and cold front approaches from northern New England. Some of models such as 12z NAM/GFS want to bring showers and storms into southern New England during afternoon and front draws closer. However, it appears most of the instability and better lift stays north of our area, which is where we expect most of activity to be favored. This is in agreement with most ensemble solutions, including high-res NCAR ensemble, which show better chances for storms across VT and NH. It`s certainly possible we see few storms manage their way into western or north central MA late in day, so will keep chance PoPs in these areas. Not looking at severe threat given lack of strong 0-6km shear and weak mid level lapse rates. We are more confident in one more day of heat and humidity as highs reach 90s in many locations (aside from higher terrain and immediate South Coast). Even E MA beaches should reach 90 given SW flow. Dewpoints will be a bit higher than today, getting into upper 60s to near 70, which results in heat index into low to mid 90s. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Highlights... * Temperatures near seasonal levels into early next week, then warming again by Tuesday * Low pressure wave looks to pass near or south of the region Friday and Friday night, which may bring steady rainfall along with scattered thunderstorms * Spotty showers/thunderstorms through the weekend as front lingers * High pressure builds slowly south out of Quebec early next week Overview and model preferences... Medium range models continue to show digging H5 trough across the Great Lakes region while a surface front slowly works S out of northern New England Thu night/Friday. As the H5 flow backs to SW, the front will tend to stall across the region. Looks like best shot for steady rainfall as well as convection during Friday/Friday night. The H5 trough will slowly shift E during this weekend. The cold front will slip S of the region Saturday with mainly dry conditions. However, may see another wave move off the south coast during Sunday with the chance for scattered showers, with some thunderstorms possible near and S of the Mass Pike as well as the E slopes of the Berkshires. Lower confidence with this feature as models showing wide solution spread with this feature. Models also showing the H5 trough flattening out as it shifts E while high amplitude ridge builds toward Hudson Bay. Expect the NW upper flow that develops with this H5 ridge to bring high pressure into the region early next week. Can not rule out isolated diurnal convection during Monday, but should be mainly dry with seasonal temperatures early next week. Details... Thursday night...Will be a muggy and warm night as clouds increase from the NW. Looks like there will be fair chance for sct showers/thunderstorms, mainly after midnight. PWATs increase to 1.6 to 1.8 inches, so might see a few downpours with any convection. Temps will only fall back to the upper 60s to lower 70s, possibly warmer in the urban centers. Friday and Friday night...Model suite remains in pretty good agreement with stalled front across the region. Will see rather potent H5 short wave move along the front. Noting PWATs on order of 1.6 to 1.9 inches, highest along the S coast, with this feature. So, could see some heavy downpours especially in any convection. This signal has been increasing over the last few model runs, so have fair confidence that we may actually see some pretty good rainfall from this system. 00Z QPF suggests 0.5 to 0.8 inches of precip during this timeframe, highest amounts along the S coast. Big question will be whether this will be widespread or spotty, depending upon organization of the short wave as it comes across. Looks like pretty good elevated instability as TQ values up to around 20 during the day Friday into Friday evening. Also noting surface based LIs in the zero to -2 range and K indices in the lower 30s. Most parameters maximize during Friday afternoon/evening then tend to weaken Fri night. As short wave exits after midnight, should see slowly improving conditions across NW Mass. Will also see late night patchy fog with dewpts lingering in the 60s. Highs on Friday will be from 80-85 for most areas, a bit cooler along the coast. Saturday and Sunday...With the departing low, expect mainly dry conditions during Saturday. May see a few showers lingering across the region as a muggy airmass remains in place along with a light N-NE wind. Have kept slight chance of showers going for Saturday. May see another weak short wave move across during Sunday, but low confidence due to wide model solution spread. Have chance POPs going for this feature, mainly for sct showers. However, some instability works in across the E slopes of the Berkshires as well as S of the Mass Pike, so have mentioned possible thunderstorms there mainly from late Sunday morning into the evening. Monday and Tuesday...High pressure builds out of Quebec, with a drier NW flow in place. However, it is still summer so can not rule out a few isolated showers during Monday. Also have a slight chance of showers across the higher inland terrain Tuesday afternoon. Expect highs Monday in the lower-mid 80s, then in the mid-upper 80s on Tuesday. && .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. High confidence through Thu. VFR. Sea breezes decay this evening around sunset with S/SW flow tonight. Local MVFR/IFR in patchy valley fog overnight. Continued S/SW flow Thu. Scattered thunderstorms possible after 18z mainly across western and north central MA. KBOS TAF...High confidence. KBDL TAF...High confidence. Outlook /Thursday Night through Sunday/... Moderate confidence through the period. Thursday night...Mainly VFR. Areas of MVFR-IFR in patchy fog late at night mainly along the south coast. MVFR CIGS/VSBYS possible in any scattered showers/thunderstorms. Friday-Friday night...VFR early Friday, lowering to MVFR throughout the region by afternoon. Areas of IFR conditions possible in showers and scattered thunderstorms Friday afternoon/night. Locally heavy downpours possible. Areas of IFR in patchy fog Friday night. Saturday and Sunday...Mainly VFR, except MVFR CIGS/VSBYS possible in scattered showers. Chance for thunderstorms across E slopes of the Berkshires and S of the Mass Pike Sunday with local MVFR-IFR conditions. Potential for local MVFR-IFR in patchy fog and low CIGS after midnight both nights. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/...High confidence. Winds remain below 25 knots and seas below 5 feet through the period. Sea breezes will diminish around sunset and give way to S/SW flow tonight and Thu. Outlook /Thursday Night through Sunday/... Moderate to High confidence through the period. Thursday night...Winds and seas below small craft criteria. South winds 10 kt or less. Patchy late night/early morning fog with reduced visibilities. Isolated showers/thunderstorms possible. Friday-Friday night...Winds and seas remain below small craft, mainly S-SE winds Fri...becoming N-NE Friday night. May see gusts up to 15 kt Fri night. Reduced visibilities in patchy fog as well as scattered showers and thunderstorms. Best chance for showers from late Friday morning into Friday evening. Saturday and Sunday...Expect N-NE winds around 10 kt with gusts up to 15 kt Saturday morning, then becoming light/variable Saturday afternoon/night. Mainly E-SE winds 10 kt or less Sunday. Seas may build to around 4 ft on the southern outer waters Saturday night. Visibility restrictions in late night/early morning fog each day, and in scattered showers. Isolated-scattered thunderstorms possible Sunday, mainly on the waters south of the RI coast. && .FIRE WEATHER... Dry conditions will persist Thursday, except possibly in western and north central MA where scattered showers/storms may bring localized rainfall Thu afternoon. Minimum RH values of 25 to 35 percent are expected Thursday across much of southern New England, except 40 to 60 percent on the South Coast, Cape Cod, and the Islands. South to southwest winds will stay under 20 mph. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Sipprell/JWD NEAR TERM...JWD SHORT TERM...JWD LONG TERM...Sipprell AVIATION...Sipprell/JWD MARINE...Sipprell/JWD FIRE WEATHER...JWD

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