Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 291914 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 314 PM EDT FRI JUL 29 2016 .SYNOPSIS...
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* Updates to near and short term forecast portions only... Low pressure will sweep south of New England into the overnight period. A brief period of drier conditions follow for Saturday with the slight chance of showers over Southwestern New England. Another area of low pressure approaches New England towards Sunday, passing south of New England into Monday bringing with it a better chance of showers and thunderstorms. High pressure returns with dry and seasonable conditions for the middle and latter portion of next week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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315 pm update... Heavy rain and embedded thunderstorms push out to sea. You win a few and you lose a lot and in this case as all the ingredients came together along a SW to NE axis offshore of New England. While over- shooting around 5-10 kft agl, Dual-Pol radar estimates have rough storm-total estimates of 2 to 3 inches over the waters S/E of the S-coastline of New England. If only displaced by about 50 to 100 miles N/W over S New England, there would`ve likely been a bigger impact. Live and learn, gaining experience and perspective for the next event. Otherwise, clearing continues across S New England allowing boundary layer destabilization beneath a conditionally unstable environment. Scattered heavy showers developing though low-topped, limited on development with likely warmer and sinking air aloft with slightly rising heights around H5 and in wake of the main mid-level vortex parent with the surface low sweeping out to sea. Slow moving through the rather weak 10 mph mean flow out of the NW, monitoring for possible localized flooding impacts. Development along fine-line convergence boundaries it would seem per observational mesoanalysis. Diurnally driven, should see activity diminish with sunset. Tonight... Clearing out with high pressure and drier air building in. With light winds, a favorable setup for radiational cooling. Noting a somewhat soupy airmass remaining in place with dewpoints hovering around the low to mid 60s, and considering antecedent rains, anticipating fog to develop. Confident within the CT River Valley, E CT, interior Southeast MA of some visibility restrictions. Perhaps some issues along the coasts though may see more clouds than fog with the NE onshore flow turning N through the overnight period.
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&& .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
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Saturday... High pressure and drier air linger lending to mostly clear conditions and light winds. Likely sea-breezes to develop around mid to late morning. Model forecast indications of showers developing along sea- breezes per a measure of lift of available surface based instability and decent low level moisture availability, that or upstream convection from PA becomes an influence. Precipitable waters forecast up to 2 inches. But considering an unfavorable environment given confluent mid to upper level flow and mid level height rises lending to some measure of sinking air, feel there is a low risk of showery weather and mainly late in the day. Thus leaning with slight chance PoPs mainly for S/W New England encompassing much of the N-half of CT into the Springfield MA metro. Forecast +14-16C H85 temperatures warrant mid to upper 80s for highs. Already temperatures were underdone earlier today after clouds started to break, so am going to up the forecast highs a degree or two warmer nudging the Hartford-metro to near 90. Saturday night... Approaching low to mid level warm frontal boundary parent with the surface low over the S Great Lakes Region. Continued moistening of the low to mid levels per isentropic upslope over-running flow out ahead of the system. Leaning that high pressure and drier air lingers long enough to buffer the onset of wet weather into the E-half of New England much as the 29.09z SREF would suggest. There is as well continued mid to upper level height rises. So will go with chance PoPs for the W, lesser to the E. Overnight lows slightly more mild with anticipated cloud cover and winds at the surface slightly more ashore, though beginning to see surface low pressure take shape S/W of New England towards Sunday morning.
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&& .LONG TERM /SUNDAY THROUGH FRIDAY/...
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Highlights... * High pressure and mainly dry conditions Saturday * Showers and a few thunderstorms possible Saturday night - Monday * Drier and seasonable weather Tuesday through Thursday Overview and model preferences... Fast mid and upper level flow across central and southern Canada has left weaker steering currents across the northern tier of the U.S. into early next week. Noting a slow moving H5 short wave out of the Great Lakes which will cause upper level winds to shift to W-SW across New England. Weak surface low will move slowly along a stalled front south of the region, keeping the chance for showers/ thunderstorms. Models and ensembles continue to signal that the short wave will finally move east Monday night into Tuesday, so should see improving conditions as mid level winds shift to NW. Also noting building heights by late next week, so will see temps run near or slightly above seasonal normals. Used a consensus blend of available model and ensemble guidance for this portion of the forecast. Details... Sunday through Monday... With relative weak steering currents between the active northern stream flow across southern and central Canada and the normal summer ridging across the southern tier states, expect low pressure to move slowly along a stalled front south of New England keeping low and mid level moisture in place along with marginal instability during this timeframe. PWATs of 1.8 to 2 inches will also linger mainly near and south of the Mass Pike, which could lead to some locally brief, heavy precip mainly Sunday into Sunday night. With the low passing S of the region, winds will generally be E-SE off the cooler ocean, which tend to stabilize any surface based convection but could see some spotty elevated activity. As the H5 short wave slowly pushes across the region on Monday, any showers should push E. However, some may linger across inland areas mainly during the afternoon, though there is individual model solution spread so not a lot of confidence with this. Expect temps to run close to or slightly below seasonal normals especially on Sunday with the steadiest precip. Tuesday through Thursday... H5 high amplitude ridge moving E across Hudson Bay on Tuesday will help push the trough offshore. This will bring generally dry conditions as NW winds aloft take over, albeit on the light side. Noting the 00Z ECMWF is trying to keep some troughing lingering across interior central and southern New England for Wed-Thu, which could mean some isold diurnal convection. With somewhat higher H5 heights, temps should return to near or slightly above normal levels by late next week.
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&& .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
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Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/...High confidence. 19z update... Rest of Today... Improving W to SE. Light N/NE winds. Lingering MVFR for ACK with -RA/RA but only for a few more hours. SCT +SHRA over N/W interior terminals down through the CT River Valley. TEMPO MVFR-IFR possible. Tonight... All terminals VFR, improving to SKC. Overnight, monitoring for likely MVFR-IFR fog development. Especially focused across the CT River Valley, as well as interior E CT and SE MA. Could bee some issues along the E/SE coast of MA but lesser confidence with respect to the dense fog. Saturday... SCT-BKN cigs especially towards late in the day. Light winds. Sea-breezes developing along the shores late morning into afternoon. SCT SHRA/TSRA possible across S/W New England late but believe it to be a low risk. Saturday Night... BKN-OVC cigs with MVFR-IFR developing along the S-coast of New England towards Sunday morning. Increasing chance of RA from the S/W along with VSBY restrictions. KBOS TAF...High confidence. Conditions remain VFR into this evening. Though watching closely into this evening for TEMPO MVFR with NE onshore winds. Maybe even a SHRA. Believe it to be a low risk. KBDL TAF...High confidence. Low risk +SHRA towards the late afternoon period with TEMPO MVFR-IFR impacts. A moderate risk. Outlook /Sunday through Wednesday/... Sunday through Monday...Moderate confidence. SCT SHRA with a few TSRA the best chance of which will be Sunday into Sunday night. TEMPO MVFR-IFR but likely VFR dominates. Could see some VSBY issues during the overnight into early morning periods with patchy fog. Monday night and Tuesday...High confidence. Mainly VFR. May see brief IFR CIGS/VSBYS in patchy fog after 06Z through 12Z-13Z in the normally prone areas as well as along the coast.
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&& .MARINE...
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Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/...High confidence. 315 pm update... While heavy rain and thunderstorms dissipate over the SE waters into early this evening, and there is the possibility of visibility restrictions with fog during the overnight into early morning hours, the majority of the forecast is comprised of winds below 25 knots and seas below 5 feet, with increasing chances of showers mainly Saturday night into Sunday morning. Outlook /Sunday through Wednesday/...High confidence. Saturday night through Monday...Expect winds and seas below small craft criteria. Seas 4 ft or less. Locally reduced visibilities in scattered showers through the period, with patchy late night/early morning fog. A few thunderstorms possible. Monday night and Tuesday...NE winds gusting up to 20 kt mainly across the eastern outer waters. Seas may brief build up to 5 ft Tuesday.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...None.
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&& $$ SYNOPSIS...Sipprell/EVT NEAR TERM...Sipprell SHORT TERM...Sipprell LONG TERM...EVT AVIATION...Sipprell/EVT MARINE...Sipprell/EVT

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