Area Forecast Discussion
Issued by NWS Boston, MA

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769 FXUS61 KBOX 200202 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1002 PM EDT TUE JUL 19 2016 .SYNOPSIS... High pressure in control will bring dry and warm afternoons through Thursday with comfortable humidity. The heat and humidity will return Friday along with the risk for scattered showers and thunderstorms during the afternoon and evening. Hot weather is expected to continue this weekend and an approaching cold front may bring us another round of scattered showers and thunderstorms sometime next Monday and/or Tuesday. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... 10pm update... Last of the diurnal CU continues to dissipate across the region. Plenty of room for cooling thanks to dwpts still in the upper 40s and low 50s. Adjusted mins down a bit with this update, otherwise the forecast remains on track. Previous discussion... Cool and comfortable conditions forecast overnight which have not been observed in the last week given the hot and humid conditions. Lows down into the low to mid 50s for most locations, warmer in the urban centers while cooler N/W with the likelihood for lows into the upper 40s. Dewpoints a few degrees lower will make for considerably pleasant and dry conditions overnight. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... Wednesday... Roughly 1024 hPa high pressure building into the region in wake of the mid-level trough pushing E and ridging building in from the W. Light winds overall with accompanying H85 airmass aloft around +10C. Warming up to around the low-80s and with the weak wind field expect sea-breezes to develop along the coast roughly around late morning. Comfortable and dry conditions, mostly clear conditions. Wednesday night... Quiet and pleasant weather. Light winds continuing from the S/SW under mostly clear conditions, another opportunity for radiational cooling and followed with MOS guidance closely. Comfortable conditions continue. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Highlights.. * Very warm/dry Thursday with comfortable humidity * Heat/humidity returns Fri with afternoon/eve severe wx potential * Hot weather this weekend with highs mainly in the 90s * Another round of sct showers/thunderstorms poss next Mon and/or Tue Details... Thursday... High pressure will be moving off the coast, but still provide us with a partly to mostly sunny day. Afternoon highs should reach into the upper 80s to near 90 away from the marine influence of the south coast/Cape and Islands. Dewpoints will be in the 50s, so humidity levels will be in check and tolerable for July standards. Thursday night... Low level moisture will begin to increase Thu night ahead of an approaching shortwave/cold front, but expect dry conditions to continue. Low temps will only drop into the 60s to around 70 in response to increasing low level moisture. Patchy fog may develop late in the typically prone locations. Friday... Main concern is the potential for scattered severe thunderstorms across southern New England, sometime Friday afternoon and/or evening. While much of the day will be dry, it will become hot and humid. High temps should recover into the upper 80s to lower 90s with dewpoints well into the 60s. West to northwest flow aloft will allow a remnant EML to work into our region. Just how steep the mid level lapse rates get still needs to be determined, but the potential is there for them to rise to between 6.5 to 7C/KM. At the same time, shortwave energy will be dropping down from the northwest as low level moisture returns. SPCSREF indicating fairly high probs for MLcapes greater than 1000 J/kg and 0 to 6 km shear greater than 30 knots later Friday into Friday evening. So with all that said, there is definitely the potential for scattered severe thunderstorms during the afternoon and/or evening, but this is far from set in stone. Severe weather often comes down to very subtle mesoscale details, which are hard enough to detect in the near term let alone 3 days in the future. Timing/location of the shortwave, area of best forcing, amount of instability still need to be determined. A remnant EML and west northwest flow aloft can result in high end severe weather in the northeast, but that comes down to timing. For example, if the shortwave arrives too early or late we can be spared much in the way of severe weather. Nonetheless, this certainly has potential and will need to be watched closely. Saturday and Sunday... Overall, this weekend looks hot as GFS ensembles show 925mb temperature anomalies 2+ standard deviations above normal. This should allow high temps mainly in the 90s away from the immediate coast and any risk for seas breezes. The majority of the weekend looks dry right now, but that can sometimes change quickly this time of year with west to northwest flow aloft. Monday and Tuesday... Very warm to hot temperatures likely continue with increasing humidity ahead of an approaching cold front. Depending on how far south the cold front make it and timing, there will be the risk for a round or two of scattered showers/thunderstorms Mon and/or Tue but a washout is not expected. && .AVIATION /02Z WEDNESDAY 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 into Wednesday... VFR. Variable winds becoming S/SW. Wednesday Night... VFR. SW winds with potential gusts up to 20 kts for the S/SE coast terminals. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Thursday through Sunday/... Thursday...High confidence in VFR. Friday...Moderate to high confidence. Mainly VFR but scattered showers/thunderstorms may result in brief lower CIGS/VSBYS Friday afternoon and evening. Southwest wind gusts of 25 to 30 knots develop Friday afternoon along and southeast of a Boston to Providence line. Saturday and Sunday...Moderate to high confidence in mainly 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 Night/...Moderate confidence. Mainly quiet boating weather through Wednesday Night thanks to high pressure building across the region from the W. NW winds veering out of the S/SW with time. Sea-breezes anticipated along the near-shore. Outlook /Thursday through Sunday/... Thursday...High confidence. Winds/seas mainly below sca thresholds most of the day. However, near shore southwest wind gusts of 20 to 25 knots and choppy seas are expected to develop along the south coast during the afternoon. Friday...Moderate to high confidence. Increasing southwest low level jet expected ahead of a cold front. This should allow southwest wind gusts of 25 to 30 knots to develop Friday afternoon. Long southwest fetch will allow seas to build to between 4 and 7 feet, with the highest of those seas across our souther most waters. Saturday and Sunday...Moderate to high confidence. Left over swell will likely require the need for small craft headlines across our southern waters into the first part of Saturday. Otherwise, relatively weak pressure gradient should keep winds and seas below small craft advisory thresholds. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/Sipprell NEAR TERM...Doody/Sipprell SHORT TERM...Sipprell LONG TERM...Frank AVIATION...Frank/Sipprell MARINE...Frank/Sipprell

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