


Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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-- Discussion containing changed information from previous version are highlighted. --927 FXUS61 KBOX 162002 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 402 PM EDT Wed Jul 16 2025 .SYNOPSIS...-- Changed Discussion --Increasing cloudiness tonight with risk for showers during the pre-dawn hours. A cold front will bring showers and thunderstorms tomorrow, with some becoming strong in interior Southern New England. Relief from the heat then arrives late this week and into the weekend. Other than a risk for showers and storms late Saturday or early Sunday, drier and more seasonable weather otherwise prevails for early next week.-- End Changed Discussion --&& .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...-- Changed Discussion --350 PM Update: Key Messages: * Dry weather thru the predawn hours, though fog and low clouds return from the southern waters early tonight. * Showers with embedded rumbles of thunder possible early Thurs AM, but severe or hazardous weather is not anticipated. Details: Although a couple of buildups in the heat and humidity of the day were briefly able to overcome background subsidence from ridging aloft and pop a couple short-lived showers, these have fizzled quickly and in turn has led to a largely dry day. Stratus which has retreated to the southern waters and the Islands is expected to return back northward tonight once the sun goes down. This has been the case the last few nights. However ridging aloft will weaken and shift eastward early in the overnight, with modest 500 mb height falls associated with a lead shortwave disturbance aloft over Lake Erie/southern Ontario vicinity. Current satellite and composite radar mosaic shows scattered to numerous storms across western NY into western PA and eastern OH. While the vast majority of the overnight ends up being dry, models indicate some of this activity working its way ENE into Southern New England during the pre dawn to mid-morning Thursday period. Did increase PoPs to Chance levels during the early morning hours; there is some elevated instability around to support some potential for rumbles of thunder. The bigger issue is that models are still pretty much mixed in terms of outcomes regarding coverage, including the "7-10 Split" idea mentioned by the previous forecaster where activity passes to our north and also into the southern waters. Later shift(s) will need to refine this once it becomes more clear, but other than passing downpours, we`re not likely to see hazarous weather from any of this activity. Very muggy and warm night with lows in the mid 70s, close to dewpoint temps.-- End Changed Discussion --&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...-- Changed Discussion --350 PM Update: Key Messages: * Heat Advisory still in effect for Thurs for elevated heat indices, although areas in eastern MA and RI will be slow to shake free of cloud cover. * Possible severe thunderstorms late in the day (soonest after 4 PM, more likely 6-10 PM) in interior Southern New England, but the coverage could be more limited. Details: Overcast conditions are likely to begin the day, along with some areas of showers, perhaps accompanied by rumbles of thunder. Shower activity should be pulling eastward and offshore of Southern New England by around noontime. This occurs as a seasonably strong, 992 to 1000 mb low pressure treks through the St. Lawrence River Valley. After early-day showers come to an end, it leaves Southern New England in a narrow warm sector during the early to midafternoon, with uncertainties on the extent to which we can turn mostly clear or at least partly cloudy. Current thinking is that the area from western and central MA into CT stands the best chance at trending mostly clear to partly cloudy. The coverage of cloudiness during the afternoon will greatly influence both the heat and humidity forecast for Thursday but also on the potency of potential strong thunderstorms tomorrow afternoon to early evening. We opted to leave the Heat Advisory as is with no changes to its status for Thursday. If cloud cover is slow to dissipate, that could really cut into how warm we get tomorrow and could reduce heat indices substantially, though even in cloud cover it will still be quite humid. This looks to be the case for eastern MA and into portions of RI, where stronger heating will at best be delayed until late in the day. A better chance at warming temperatures into the lower 90s is more likely in the interior, and with that will be a large degree of surface based instability to values around 2500-3000 J/kg of CAPE from the Berkshires/Litchfield Hills east to central MA and northeast CT. Wind fields in the lowest 3-km or so of atmosphere are fairly strong with some curvature too, although the strongest deeper-layer shear lies to our north and west. Latest guidance indicates a pre-frontal trough developing somewhere either into the Champlain/Hudson Valley or the MA/NY/CT border area, with scattered t-storms developing along it later in the day. We think the timing of widely scattered thunderstorms looks to be later in the day, probably not sooner than 4 PM but more likely after 6 PM into the Berkshires, then moving eastward into western MA/CT and perhaps into central MA closer to 8-10 PM. It is possible but unlikely that storms could make it further east from there. If storms can develop into western and central MA and CT, they could pose both gusty to damaging straight line winds, but also a smaller risk for a tornado or two given the curving hodographs with 0-1 km shear magnitudes as high as 25 kt. We also included mention of gusty winds and heavy rain enhanced wording in the forecast for the western roughly half of Southern New England. A cold front moves in later Thursday evening and overnight, which as it passes will act to bring an end to the spell of heat and humidity. PWATs actually tumble below 1 inch by daybreak, with NW winds 10-15 mph and gusts 20-25 mph.-- End Changed Discussion --&& .LONG TERM /FRIDAY THROUGH WEDNESDAY/...-- Changed Discussion --Key Messages: * Relief from the heat and tropical humidity arrives Fri. * Showers and possible thunderstorms late Sat and into Sun. * Trending more seasonable by early next week. It now appears that a cold front will finally cross southern New England some time Friday morning. This will finally break the heat and tropical humidity across our region. In addition, there is very little chance of rainfall as well. These conditions are expected to persist through most of Saturday as well. A warm front late Saturday into Sunday should feature our next chance for some showers and thunderstorms. This will be accompanied by a spike in humidity closer to feeling tropical again, but its brief. High pressure over eastern Canada brings a return to more average conditions for late July early next week. Not seeing much risk for rainfall, at least until the middle of next week.-- End Changed Discussion --&& .AVIATION /20Z WEDNESDAY THROUGH MONDAY/...-- Changed Discussion --Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 18z TAF Update: Through 00z Thursday: High confidence. VFR, with IFR-LIFR stratus adjacent to the New England south- coastal waters. A pop-up SHRA possible but largely dry weather prevails. S to SW winds around 10 kt, although with SE seabreezes flipping to SW by 20-21z. Tonight: High confidence in TAF/trends but moderate on both the timing and on SHRA coverage. Mainly VFR, although should see IFR-LIFR stratus and fog returning northward to areas near/south of I-95 and in the CT Valley between 00-08z. Risk for warm frontal SHRA/rogue TS between 08z to 13-15z Thu, but uncertainty on how widespread the shower threat may be. PROB30s included in TAFs given this uncertainty but may need to opt for TEMPOs or include as prevailing FM groups in later issuances. S winds 5-10 kt. Thursday: Moderate confidence. Warm frontal SHRA/possible TS moving eastward and offshore thru 15z Thu. Sub-VFR cloudiness likely to continue until then as well, and we should then see conditions improving to at least SCT-BKN VFR ceilings. Risk for TSRA / possible +TSRA for western New England TAFs (ORH, BAF, BDL) after 20z, but for now will message with PROB30s give uncertainties on coverage. TSRA risk further east is less likely, if any develop at all. S/SW winds around 10-12 kt with gusts to 20 kt. Thursday Night: High confidence. Cold front moves through the TAFs; any TSRA should weaken to showers after 02z, with conditions becoming all VFR at all airports. Winds become W/NW around 10-15 kt with low 20s-kt gusts post-frontal. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Friday through Monday/... Friday through Saturday: VFR. Saturday Night: VFR. Chance SHRA, slight chance TSRA. Sunday: Mainly VFR, with local IFR possible. Breezy. Chance SHRA, chance TSRA. Sunday Night: VFR. Chance SHRA. Monday:-- End Changed Discussion --&& .MARINE...-- Changed Discussion --Forecaster Confidence Levels... Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. High confidence through end of the week. Winds and seas are expected to remain below SCA levels through Thursday with south winds around 10-15 kt. Main concern through Thurs is areas of fog during nighttime and morning hours, in addition to scattered showers and thunderstorms late tonight into Thu morning and possibly again Thu night. A cold front arrives on Friday, which could bring conditions to near SCA levels as NW winds increase to around 20-25 kt and seas nearing 5 ft. Outlook /Friday through Monday/... Friday: Winds less than 25 kt. Areas of seas approaching 5 ft. Friday Night through Saturday: Winds less than 25 kt. Saturday Night: Winds less than 25 kt. Chance of rain showers. Sunday: Winds less than 25 kt. Chance of rain showers, slight chance of thunderstorms. Sunday Night: Winds less than 25 kt. Chance of rain showers. Monday: Winds less than 25 kt.-- End Changed Discussion --&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...Heat Advisory until 7 PM EDT Thursday for CTZ002>004. MA...Heat Advisory until 7 PM EDT Thursday for MAZ003>007-010>021- 026. Air Quality Alert until 11 PM EDT this evening for MAZ008>011. RI...Heat Advisory until 7 PM EDT Thursday for RIZ001>007. MARINE...None. && $$ SYNOPSIS...Belk/Loconto NEAR TERM...Loconto SHORT TERM...Loconto LONG TERM...Belk AVIATION...Belk/Loconto MARINE...Belk/Loconto