Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 261910 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 310 PM EDT TUE JUL 26 2016 .SYNOPSIS... * Updates to near- and short-term forecast portions only, including aviation, marine, and fire weather. High pressure will bring dry but continued hot conditions through Thursday. A cold front will drag S towards New England into Friday as an area of low pressure emerges from the Mid-Atlantic. A cooler and wetter pattern is possible through the weekend. && .NEAR TERM /THROUGH 6 AM WEDNESDAY/... 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 THROUGH 6 AM THURSDAY/... 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... * Cold front approaches the region during Thursday * Showers and isolated thunderstorms remain possible Friday into the weekend Overview and model preferences... 00Z model suite remains in pretty good agreement through Thursday, then continue to show wide model spread from Thursday night onward. This appears to be dependent upon development of short waves in the nearly zonal H5 flow across the northeast, which will start to back to SW as broad mid level troughing develops across the Great Lakes into the weekend. The big differences come into play as models handling the slow movement of the front out of northern New England differently, along with any low pressure waves that move along it. One thing that is in somewhat good agreement is that the front should push into the region around Friday, then will stall in the W-SW mid level flow through most if not all weekend. Used a blend of available guidance through Thursday, then went with mainly ensemble approach beyond that. Details... Thursday...Models begin their solution variance during this timeframe, but in fair agreement. Will see another hot and humid day, especially along the south coast. Timing of slow moving front remains in question, but does appear scattered showers/isold thunderstorms may push into N central and W Mass into N central CT during the afternoon/evening hours ahead of the front. Have carried low chance POPs there, with isold showers possible further S and E. Kept isold convection going, can not rule out entirely with marginal instability in place. Decent H85-H5 lapse rates of 6-6.5C/km, with best shot during max heating of the day. 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 and Friday...Model solutions continue to widen during this timeframe with the movement, or lack thereof, of the front out of S VT/NH. Also questions on development of low pressure along this front, with the GFS being most robust. Have kept chance POPs going, as models do generally bring in scattered showers, and kept isold thunder as well. With more clouds around, will see high temps on Friday 5-10 degrees cooler than Thursday, mainly in the 80s. Saturday and Sunday...High uncertainty remains during this portion of the forecast, with a continued low confidence forecast. Both the ECMWF and Canadian GGEM models move low pressure off the mid Atlantic coast during Saturday, with precip working into the region, while the GFS remains the outlier. More questions on timing of short wave in the H5 flow on Sunday, so kept low chance POPs going there as well. Monday...Low confidence continues. Do have low chance POPs going inland into the afternoon, then have trended drier. Expect temperatures to run close to seasonal normals. && .AVIATION /19Z 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. Rest of Today... VFR. W/NW winds with gusts 15-20 knots. Sea-breeze hanging along the immediate E shore of Essex and Plymouth County MA. Tonight... VFR. Low risk of MVFR-IFR cigs/vsbys with fog towards Wednesday morning, mainly focused in the CT River Valley. Sea-breeze washes out. VRB winds developing. 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 through Saturday...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 each 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/...High confidence. Wednesday-Thursday...Winds and seas below small craft criteria. Patchy late night/early morning fog with reduced visibilities. Isolated showers/thunderstorms possible late Thursday/Thursday night. Friday-Saturday...Winds shift to S-SE but remain below small craft levels. Swells will build to around 5 ft on the southern outer waters Friday night into Saturday, then should subside. Patchy fog and scattered showers/thunderstorms will reduce visibilities. && .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...EVT/Sipprell NEAR TERM...Sipprell SHORT TERM...Sipprell LONG TERM...EVT AVIATION...Sipprell/EVT MARINE...Sipprell/EVT FIRE WEATHER...WFO BOX Staff

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