563 FXUS61 KBOX 180614 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 214 AM EDT Wed Jun 18 2025 .SYNOPSIS... Mostly cloudy through Wednesday as a couple of weak disturbances bring a threat for hit-or-miss showers, although with several hours of dry weather in between. Hot and humid weather for Thursday with heat indices 95 to near 100, with a risk for strong to severe thunderstorms Thursday afternoon as a cold front moves through. Drier and seasonably warm Friday and Saturday. A multi-day stretch of significant heat is possible starting early next week. && .NEAR TERM /THROUGH TODAY/... Key Messages: * Near to slightly above normal temperatures. * Hit-or-miss showers for most tonight into mid morning Wednesday, with a greater risk across the western half of southern New England. The main feature of our weather tonight into Wednesday will be the approach of a warm front from the southwest. Until this front actually moves through, a high pressure over the North Atlantic will be the main forcing. Lots of clouds with relatively chilly conditions into this evening. A mid level shortwave passing overhead will trigger some light drizzle or light rain showers into this evening. The greater risk for showers will be with the warm front itself. That front should move of to our north later Wednesday morning. Not expecting much in terms of accumulation, with most locations at one tenth inch or less, where it rains at all. Once we get into the warm sector, looking at temperatures starting to rise to near to above normal levels. Thinking by that point that most areas will be dry heading into Wednesday night. There is still a low risk for an afternoon or evening shower or thunderstorm just due to the increased heat and humidity. These should dissipate after sunset Wednesday. && .SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/... Key Messages: * Potentially dangerous heat Thursday afternoon with areas across southern New England experiencing "feels like" temperature between the upper 90s into the lower 100s. * A cold front brings scattered severe thunderstorms to interior Massachusetts and Connecticut. There is uncertainty on just how far east this threat will extend. A true taste of summer is on tap for Thursday with temperatures and humidity on the rise. Plus, a cold front brings potential for severe thunderstorms across the western-half of southern New England during the afternoon and evening hours. Let`s breakdown these hazards. As advertised, Thursday is peak of the heat and humidity (at least for this week) and could be dangerous for sensitive groups. Forecast 850mb temperatures are +19C to +21C. Will be able to tap into those temperatures with a well-mixed boundary layer, resulting afternoon temperatures from the lower to middle 90s across interior southern New England. It is a touch cooler at the south coast where southwest flow coming off the relatively cooler ocean water, likely highs are in the 80s. Additionally, it will be humid, dewpoints in the lower 70s is "air you can wear", apparent temperature range from mid-90s through the lower 100s. It`s not out of the question a Heat Advisory may become needed for parts of southern New England, as there are several hours during the afternoon with apparent temperatures greater than 100F, which meets the criteria for a single day Heat Advisory. NWS heat risk shows most of the region with a moderate risk and major risk for City of Boston and the metro west. Those sensitive groups or those working outdoors need to practice appropriate heat-related precautions. Lastly, there is little relief overnight as many locations fall into the middle 60s. Urban areas hold the heat with lows in the upper 60s to perhaps 70F. The next hazard is the severe threat Thursday afternoon through the evening hours, roughly 2pm to 10pm timeframe, with an approaching cold front. There is uncertainty on just how far east this threat will extend. However, there is certainly enough energy to get storms going, CAPE values range between 2,000 and 3,000 J/kg depending on which guidance source. There are favorable mid-level lapse rates of ~7C/km (which continues past sunset timeframe, this could lead to storms surviving all the way to the coast), deep-layer shear of 35+ knots, and helicity of 100 to 200 units. High-res guidance, NAM3KM and RRFS, illustrate a few discreet cells developing and then a discontinued line of storms. Primary concerns are stright-line damaging wind and large hail, a secondary and lower risk would be a brief tornado and localized flash flooding. Most of southern New England is highlighted in a "marginal risk" (level 1 out of 5), but far western Massachusetts and northwest Connecticut is under a "slight risk" (level 2 out of 5). Those with outdoor plans Thursday afternoon and evening should remain weather aware and prepare to seek shelter indoors in the event of a thunderstorm. && .LONG TERM /FRIDAY THROUGH TUESDAY/... Key Messages: * Cooler Friday and Saturday with temperatures around-slightly above normal. * Mainly dry Friday. Potentially unsettled Saturday with low chances for a few showers or storms. * Signal for well above normal temperatures next week, potentially impactful given higher humidity levels. Friday-Weekend: Weak mid level troughing persists over the region Friday and much of Saturday. Pattern is otherwise quiet with no shortwaves and limited moisture which will support mainly dry conditions. Cooler post- frontal airmass expected with 850mb temperatures 5-8 degrees cooler than Thursday. This will yield highs around normal to just above normal in the upper 70s to mid 80s Friday/Saturday. By Saturday afternoon, a weak piece of shortwave energy moves through the flow combined with the arrival of anomalous moisture. Models show marginal instability around as well. Models show a weak signal for precipitation with differences with respect to coverage and timing. This keeps chances on the lower side until there is more agreement among model/ensemble guidance on if it will stay drier or wetter. Can`t rule out a few storms given the marginal instability if it does lean more active Saturday. Sunday through Early Next Week: Ensemble guidance shows good agreement that an anomalously strong upper level ridge shifts into the northeast by early next week. Unsurprisingly, this is coupled with a signal for 850mb temperatures a couple standard deviations above normal. NAEFS, ECMWF EFI also displays a strong signal for well above normal heat. Ensemble guidance also shows a stream of above normal moisture transporting into the region over the top of the upper ridge. This will help bring in higher moisture air which mean higher humidity. This will provide an additional factor on top of the heat that will increase the risk for heat impacts. Rising heat and humidity begin Sunday extending through at least early next week. NWS Heat Risk, displays this potential clearly with values increasing into the Moderate Category Sunday and into the High Category Monday for most places except the south shore and Cape/Islands.This is still further out, so stay tuned as confidence increases in this signal. At this point, awareness/preparedness are beneficial given the potential for impactful heat/humidity next week. Find/have a location that provides cooling/AC and plan more strenuous activities outside of the hotter parts of the day. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 06Z TAF Update: Through 12z Wed: High confidence overall, though lower on visbys. At least IFR conditions have set in across the airports mainly from stratus but with areas of fog as well. IFR to LIFR conditions continue and probably lower further through 12z. Better chance at steadier -SHRA after 09z at BAF and BDL, which gradually pivots ENE. SE to S winds around 5 kt. Today: Moderate confidence. IFR-LIFR from overnight should linger into the morning along with shower chances, but slow improvement toward MVFR-IFR levels expected for the afternoon but is more likely after 16z. Exact timing of this slight improvement is still uncertain. Although most areas trend generally dry after 15z, rain showers again return mainly HFD/BDL to PVD and the Cape airports after 22z, perhaps with a rumble or two of thunder. S/SW winds 5-10 kt. Tonight: Moderate confidence. MVFR to IFR early with periods of south-coastal -SHRA/psbl TS, with showers pulling away after 03-05z. Categories deteriorate to IFR-LIFR again as stratus/fog returns from south to north. Light SW winds. Thursday: Moderate confidence. Early IFR-LIFR fog/stratus should disperse by mid morning to period of VFR, but the exact timing still isn`t clear. VFR with hazy conditions from very humid air then gives way to a round of SCT strong to severe T-storms; wouldn`t rule out a rogue t-storm by 18z, but anticipate a line of strong to severe t-storms after 20z for BAF- BDL- ORH and could make it into the BOS- BED- PVD corridor 22-00z. Frequent lightning, strong to locally damaging gusts and IFR-LIFR visby in rain are the main risks from storms. SW winds increase to 10-15 kt. KBOS Terminal...Moderate confidence in TAF. KBDL Terminal...Moderate confidence in TAF. Outlook /Friday through Sunday/... Saturday: VFR. Breezy. Saturday Night: VFR. Breezy. Slight chance SHRA, slight chance TSRA. Sunday: Breezy. Sunday Night: Monday: Breezy. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Relatively light winds and seas through Wednesday night. Periods of showers possible through Wed, but risk for thunderstorms is low. Areas of fog with visibility less than 1 mile possible tonight and Wed night. Outlook /Friday through Sunday/... Saturday through Sunday: Winds less than 25 kt. Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Monday: Winds less than 25 kt. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Loconto NEAR TERM...Loconto SHORT TERM...Loconto LONG TERM...Loconto AVIATION...Loconto MARINE...Loconto