Area Forecast Discussion
Issued by NWS Boston, MA

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692 FXUS61 KBOX 220746 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 346 AM EDT Thu Jun 22 2017 .SYNOPSIS... High pressure in control today. Warm and humid air follows for the remainder of the week into the weekend along with the threat of heavy rain associated with the remnants of Cindy. The cold front will stall across New England Saturday before moving offshore Saturday night. Seasonably warm and less humid conditions Sunday will be followed by cooler and somewhat unsettled weather for early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Cool and comfortable. Surface high pressure pushing S/E, winds veer S with the possibility of sea-breezes along the E-coast. Seasonable with highs around the upper 70s to low 80s given mixing up around H85 where temperatures range around +12C. The deep mixing allows for surface dewpoints to drop around the low to mid 50s, some places in the upper 40s. Few to scattered low clouds prior to increasing high clouds towards evening as sub-tropical air begins to ascend across the region. Expect 60 degree surface dewpoints slip back N towards sunset. && .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/... Tonight... Remaining mild, becoming humid, as the chance of showers increase. Continued ascent of sub-tropical moisture across the region with accompanying elevated instability and higher K-indices, though stronger low-level convergence and deep layer forcing is tied more closely with the deep layer trough digging S out of Canada into the Great Lakes Region. Subsequently, despite lift and column saturation, the better chances of wet-weather are more likely N/W. Expecting scattered light outcomes with the possible risk of thunder. Continued S flow, surface dewpoints continue to rise closing in on 70. Across the cooler ocean waters, more than likely low clouds if not fog and visibility issues for SE New England. Lows in the mid to upper 60s. Friday... Warm, muggy day with the chance of showers and thunderstorms. Sub- tropical air continuing to surge from the SW pushing precipitable waters above 2 inches as remnants of Cindy are stretched N. This ahead of cyclonic flow tightening as mid-level energy continues to push into the Great Lakes Region. Falling heights along with low- level convergent forcing pushing into S New England, presents a favorable environment in which partial clearing is expected, more over the interior NE CONUS, for shower and thunderstorm development. Low clouds along with visibility issues associated with fog / mist are expected to sock in SE New England beneath the remnants of a dry conveyor belt that had wrapped into Cindy. Lapse rates conditionally unstable, more moist adiabatic contributing to thin-tall CAPE in an environment of weak shear. Given the sub-tropical airmass in a broad region of low-level convergent forcing and destabilizing boundary layer, expecting mainly heavy rainers. Freezing levels up around 15 kft with precipitable waters in excess of 2 inches, efficient warm- rain processes forecast with collision / coalescence. So with any thunder will go with a mention of heavy rain. Higher chance PoPs away from the S/E as highs warm well into the 80s. Wherever the boundary layer mixes out it`ll likely be breezy from the SW with gusts up to 25 mph. Friday night... Wet, muggy, mild. An anomalous setup attributable to the remnants of Cindy. Roughly a +4-5 standard deviation (SD) of H85 moisture flux and +3 SD of precipitable waters which exceed record highs recorded at Chatham MA which average around 2 inches but are forecast around 2.25 inches. Will need to closely monitor any focusing mechanisms which can put the squeeze on the atmosphere and possibly yield a predecessor rainfall event. Noting increasing low-level winds per tightening pressure gradient ahead of mid-level troughing across the Great Lakes, convergently focused in and around the S-shoreline of S New England ahead of a sweeping cool front. Tightening baroclinic zone. Indications of height falls within the mid-levels associated with weak troughing signatures contributing to the convergence of sub-tropical air. This as earlier daytime convection will likely shift S/E ahead of said cool front. This in combination with tropical energy and some diffluent motions aloft, can`t rule out a potential predecessor rainfall event. Difficult to nail down at this time as to exactly where but feel there is a risk to S New England around the Saturday AM timeframe. Looking at chance to likely PoPs for possible widespread rain with embedded heavier showers and thunderstorms. Heavy rain threat per efficient warm-rain processes still exists and will continue to mention. Again, focus of heavy rain remains uncertain with respect to potential flooding threats. Surface dewpoints well into the 70s, a muggy and humid airmass for certain, off the cooler ocean waters especially to the S/E, likely dealing with foggy conditions overnight into the morning hours. Could see visibility down to a quarter mile or less at times. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Highlights... * Sct showers and isold t-storms Sat, mainly south of the Pike * Seasonably warm and less humid Sunday * Cooler with showers possible at times early next week Overview... Longwave trof over the Gt Lakes will be the main feature in the extended period. Polar jet will be in the vicinity of New Eng with a series of weak shortwaves moving through the flow as the trof gradually moves into New Eng early next week. This will bring a somewhat unsettled pattern into the middle of next week with cooler temps trending near or below normal. Details... Saturday... Cold front expected to stall across SNE with tropical PWAT plume exceeding 2" and high theta-e air remaining across southern half of the region. Shortwave assocd with the remnants of Cindy tracks near or south of New Eng and will likely bring a period of showers and isold t-storms with brief downpours, especially south of the Pike. A few showers may even extend into northern MA in the morning but trend should be for improving conditions here in the afternoon with developing sunshine. Temps are tricky south of the Pike where clouds and showers may hold temps down. We undercut guidance here with highs mostly in the 70s to near 80 but low to mid 80s NE MA. Remaining rather humid south of the Pike with dewpoints well into the 60s to near 70, but expect dewpoints dropping into the 50s across northern and western MA in the afternoon. Drier air will eventually make its way to the coast Sat night with clearing skies. Sunday... The column is considerably drier Sunday so expect sunshine mixing with diurnal clouds. Mainly dry conditions but mid level shortwave tracking to the north and west may bring a brief showers to NW MA. Seasonable temps in the upper 70s and lower 80s with low humidity as dewpoints will be in the 50s. Monday into Wednesday... Gt Lakes trof will gradually move east into New Eng as a series of shortwaves move through with mid level temps cooling through the period. 500 mb temps -16 to -20C. This will result in an unsettled pattern with showers or even an isold t-storm possible at times, but low confidence on timing. Temps trending cooler to near or a bit below seasonable normals. && .AVIATION /07Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday Night/... Today... VFR. Light winds gradually veering S. Sea-breezes possible along the E-coast. FEW-SCT CIGs around 6 kft. Increasing high clouds from the W towards sunset. Tonight... CIGs becoming SCT to BKN lowering towards 4-6 kft with SHRA moving in, the better chance of which will be across N/W CT and MA with a low risk TSRA. Increasing S winds with the threat of MVFR VSBYs along the S coast. Friday... SCT to BKN low-end VFR CIGs, more OVC across SE New England, as S/SW winds increasing 10 to 15 kts sustained with gusts up to 25 kts. Increasing areal coverage of SHRA/TSRA with embedded threats of +RA. TEMPO MVFR/IFR VSBYs with any RA/+RA while likely MVFR/IFR VSBYs will plague the S-coast towards evening. Friday night... BKN to OVC MVFR/IFR CIGs with areas of IFR/LIFR FG towards SE New England terminals. SHRA/TSRA continue with embedded threats of +RA. There is also the low risk of LLWS impacts across the Cape and Islands. KBOS Terminal...Sea-breeze possible Thursday. VFR for the entire TAF period. Increasing CIGs during the evening hours, lowering into Friday morning. KBDL Terminal...High confidence. VFR throughout. Outlook /Saturday through Monday/... Saturday...Moderate confidence. MVFR and localized IFR in sct showers and isold t-storms, especially south of the Pike with improving conditions, mainly VFR north of the Pike. Sunday...High confidence. Mainly VFR. Monday...High confidence. Mainly VFR cigs with a few showers possible in the interior. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday Night/... High pressure today. Light winds veering though the day becoming S overnight, increasing into Friday with sustained winds 10 to 15 kts and gusts up to 25 kts. This will push seas 5 to 6 feet and require SMALL CRAFT ADVISORIES. With a cold front sweeping down from the N as the remnants of TS Cindy advect N from the S, will likely see the return of mist / fog conditions resulting in low visibility down to a quarter mile or less at times. Outlook /Friday through Monday/... Saturday...Moderate confidence. Some gusty W/SW winds early Sat, possibly near SCA thresholds should diminish in the afternoon. Seas up to 5-6 ft over the south coastal waters. Sunday and Monday...High confidence. Winds should generally remain below small craft advisory thresholds through the period. Lingering 5 ft seas over the south coastal waters will subside Sun night. && .TIDES/COASTAL FLOODING... Astronomical tides are rather high this weekend during the night time cycles. Boston has a 12.4 ft high tide around midnight Sat night and 12.2 ft just after midnight Sun night. Fortunately, offshore winds are forecast with minimal or no surge so do not anticipate any issues. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 8 PM Friday to 8 AM EDT Saturday for ANZ232>235-237. Small Craft Advisory from 2 PM Friday to 8 AM EDT Saturday for ANZ250-254>256. && $$ SYNOPSIS...KJC/Sipprell NEAR TERM...Sipprell SHORT TERM...Sipprell LONG TERM...KJC/Sipprell AVIATION...KJC/Sipprell MARINE...KJC/Sipprell TIDES/COASTAL FLOODING...KJC is the U.S. government's official web portal to all federal, state and local government web resources and services.