Area Forecast Discussion
Issued by NWS Boston, MA

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450 FXUS61 KBOX 262314 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 714 PM EDT TUE JUL 26 2016 .SYNOPSIS... High pressure will bring dry but continued hot conditions through Thursday. A cold front will drop southward across southern New England late Thursday and stall near the south coast Friday. Low pressure will move from the Mid-Atlantic northeastward toward southeast MA by Fri night, then exiting the coast Saturday. This has the potential to bring some rain to much of the area. A few showers are possible over the weekend. Then dry high pressure builds over the northeast states early next week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... 715 PM update.. Daytime cloudiness is dissipating. Forecast is right on track. Just a minor tweak or two to current temps/dewpoints, otherwise no changes. Previous discussion... High pressure builds into New England resulting in diminishing winds out of the W/NW becoming light as conditions remain mostly clear. Considering the overall dry soils across the region and observed dewpoints during max-heating of the day falling into and around the mid-50s, leaning lowest forecast guidance for overnight lows with the expectation of radiational cooling. Looking at lows around the upper-50s to low-60s, warmer along the coast and within urban centers. Would not be surprised to hear a few isolated locations falling into the mid-50s for lows by Wednesday morning. A low risk of patchy fog, mainly in sheltered low lying locations with bodies of water (i.e., CT River Valley). && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... Wednesday... High pressure remains in control. With a H85 airmass aloft around +16-18C and abundant sunshine, in addition to dry-air subsidence, expect temperatures to warm easily back into the 90s. With light and variable winds, expect sea-breezes to develop along the shores around late morning into midday. Likely mix-down of drier air, another day of 50 degree dewpoints and the absence of muggy air. Wednesday Night... Continued high pressure, light winds, mostly clear conditions. Expect another opportunity of radiational cooling to push temperatures lower overnight. Leaning once again with lowest guidance advertising upper-50s to low-60s. Focus on dewpoints during max-heating of the day which will indicate the depth at which temperatures can drop. Perhaps a fly in the ointment is some mid-level clouds drifting into W New England late which could put a lid on radiational cooling. Winds perhaps begin to turn S towards morning resulting in rising dewpoints. This in addition to some patchy fog issues but thinking a low risk. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Highlights... * Will a storm system come close enough to give substantial rain to parts of the area Friday and Friday night? Overview and model preferences... At upper levels, zonal flow Thursday becomes west-southwest as a Great Lakes short-wave trough approaches and then crosses the area Friday night and early Saturday. Another short-wave trough over the Great Lakes Saturday exits New England late Sunday and Monday. Drier and increasingly warm upper northwest flow then develops over New England early next week as a strong high pressure ridge develops over the Midwest. At the surface, a weak frontal boundary will move southward into southern New England late Thursday into Friday and stall along the south coast. 12Z models are in much better agreement that a low pressure storm system will develop in the Ohio Valley...move to the Mid-Atlantic, then head northeast toward our area. GFS is now the farthest south solution. GEFS low track is farther north, though, closer to the GGEM, ECMWF, and NAM. While it is way too early to gets hopes up about substantial rain, this is our best chance in a while. Good model agreement on high pressure building in from the north by Monday and Tuesday of next week. Details... Thursday...Main weather word will be HOT. With nearly full sunshine in the morning and all models showing 925 mb temperatures of +26-27C, expect highs getting up to the mid and perhaps upper 90s away from the south coast. Am expecting mixing to reduce surface dewpoints to the upper 50s to mid 60s in the afternoon, which will mean that Heat Index values will be close to the ambient temperatures and may be just shy of Heat Advisory criteria. A weak cool front will sag southward during the afternoon and there could be a wind shift to the north as far south as the Route 2 corridor by evening. However, 700-500 mb lapse rates of less than 5C/km and warm temps. at 500 mb will reduce precipitation chances. However, have 20-30 percent chance of a thunderstorm in northwest and north central MA in the late afternoon. Expect highs in the lower-mid 90s away from the coast, warmest across the CT valley, ranging to the upper 70s-mid 80s near the coast possibly touching 90 in Boston and on the north shore. Thursday night...Increasingly muggy. Can`t rule out a chance of a shower or isolated thunderstorm. Lows in the upper 60s to near 70. Friday and Friday night... All models are coming into more agreement...giving us more confidence...that a low pressure storm system will move from the Mid-Atlantic northeastward toward southeastern MA. All models give some rain to our region. Some are much more prolific than others. Of course, we are in a drought and even missed out on yesterday`s convection, so it will be important to see consecutive model runs over the next couple of days. For this model cycle, the NAM has an intense low moving into SE MA Friday. afternoon and evening, with heavy rains in parts of RI and SE MA. The ECMWF is very similar with track and heavy rains even a little farther north, but not until Friday night. The GGEM is also on board with a low, albeit weaker, passing southeast of Nantucket with light amounts. The GFS is farthest south, with just a few hundredths of rain. However, the GEFS ensembles are farther north than the operational GFS, more in line with the other models. That said, have forecast cloudy skies with showers and isolated thunderstorms likely...both Friday and Friday night, except high chance PoPs in northwesternmost areas. Highs only in the lower to mid 80s. Saturday and Sunday... Low pressure departs the coast Saturday morning. A weak pressure pattern exists, with some lingering moisture around. So, basic summer weather with partly cloudy skies, highs in the 80s, and a low chance of a scattered mainly afternoon and evening shower or thunderstorm. Monday and Tuesday...Expecting high pressure to build over northern New England, providing increasing sunshine. Just a slight chance of a shower in northwest areas Monday and dry on Tuesday. Highs Monday 80 to 85 with mid and upper 80s possible on Tuesday. && .AVIATION /23Z 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/...High confidence. Tonight... VFR. Very low risk of MVFR-IFR cigs/vsbys with fog towards Wednesday morning, mainly focused in the CT River Valley. Sea-breeze washes out. Winds becoming light and variable. Wednesday... VFR. VRB wind becoming onshore along the coastline towards late morning. If any fog during the morning period, it will quickly burn off. Wednesday night... VFR. VRB winds becoming S but remaining light towards morning. Low risk of MVFR-IFR patchy fog developing, mainly focused again in the CT River Valley and possibly along the S-coast of RI and MA. KBOS TAF...W/NW winds diminishing as a sea-breeze washes out off- shore. With VRB winds more likely Wednesday, expect a sea-breeze to develop close to mid-morning (15z) with potential gusts up to 15 kts out of the E into midday and afternoon. KBDL TAF...W/NW winds diminishing. VRB into Wednesday. VFR and SKC. Outlook /Thursday through Sunday/... Thursday...High confidence. VFR except MVFR cigs/vsby possible in widely scattered showers and thunderstorms mainly in northwest and north central MA. Thursday night...Moderate confidence. VFR except areas of IFR in patchy fog late at night especially south coast. Also, MVFR possible in any scattered showers/thunderstorms. Friday into early Saturday morning...Moderate confidence.. VFR early Friday lowering to MVFR throughout the region by afternoon. IFR possible in showers and thunderstorms. Locally heavy downpours possible. Areas of fog. Rest of Saturday and Sunday...Moderate Confidence. Mainly VFR, except MVFR CIGS/VSBYS possible in scattered showers and thunderstorms. Potential for local MVFR-IFR in patchy fog and low CIGS Sat night. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday Night/...High confidence. W/NW winds diminishing overnight. High pressure settling over the waters which will make for good boating weather. Sea-breezes developing along the shores around mid- morning Wednesday, so watch out for some gusts out of the S/E around 15 kts. Low risk for patchy fog along the S-coast of RI and MA towards Thursday morning. Outlook /Thursday through Sunday/...Moderate to High confidence. Thursday and Thursday night...Winds and seas below small craft criteria. Patchy late night/early morning fog with reduced visibilities. Isolated showers/thunderstorms possible Thursday night. Friday-early Saturday...Southeast winds become northeast. Speeds generally 10-20 kt, depending on strength of possible low pressure approaching from the mid-Atlantic. Swells will build to 4 to 5 ft on the southern outer waters by Friday night into early Saturday. Patchy fog. Reduced visibilities in showers and thunderstorms. Rest of Saturday and Sunday...Seas subsiding with northeast winds becoming southeast...generally 10-15 kt or less. && .FIRE WEATHER... Drier conditions are expected to persist through Thursday across S New England as much of the region is in drought with significant year-to-date rainfall deficits. An elevated fire weather potential is forecast as minimum relative humidity values range from 30 to 40 percent. While overall winds are anticipated light and variable, sea-breezes are expected to develop around mid-morning into midday behind which S/E wind gusts up around 15 mph are possible. Some moderation in relative humidity is expected with marine-layer air coming ashore. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Sipprell/Field NEAR TERM...Sipprell/Field SHORT TERM...Sipprell LONG TERM...Field AVIATION...Sipprell/Field MARINE...Sipprell/Field FIRE WEATHER...Sipprell

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