


Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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142 FXUS61 KBOX 182346 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 746 PM EDT Fri Jul 18 2025 .SYNOPSIS... Dry and pleasant weather with comfortable humidity levels continues tonight into Saturday. Another cold front may bring scattered showers and a few thunderstorms to the region toward daybreak Sunday with perhaps another round sometime late Sunday into Sunday evening. Much less humid along with cooler than normal temperatures and dry weather for early next week. Warming trend then begins around the middle of next week, with heat and humidity returning for Thursday and Friday. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... Key Messages... * Mostly clear & cool tonight with lows mainly in the 50s Details... A ridge of high pressure builds over the region tonight. This will allow for mainly clear skies...light/calm winds and a good night of radiational cooling given the dry airmass in place for July standards. Low temps will bottom out mainly in the 50s with perhaps even some upper 40s in the normally coolest outlying locations of western MA. Meanwhile...the Urban Heat Islands of Boston/Providence only bottom out in the lower to middle 60s. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Key Messages... * Mostly Sunny Sat...Highs mainly in the middle to upper 80s * Milder Sat night with lows in the upper 60s to the lower 70s along with scattered showers & a few t-storms possible after midnight Details... Saturday... High pressure slides east of the region on Sat. This will allow a warmer airmass to begin to overspread the region...but with comfortable humidity levels. High temps should reach mainly in the middle to upper 80s with a few spots in the lower CT River Valley perhaps flirting with 90. It will be a few degrees cooler along portions of the immediate eastern MA coast with sea breezes. Saturday night... Dry weather should prevail Sat evening...but clouds will be on the increase ahead of an approaching shortwave and associated mid-level warm front. There is a pretty good elevated instability burst ahead of this warm front as Showalter indices quickly drop from over 10 to below zero overnight. Therefore...expect scattered showers and a few thunderstorms to be possible after midnight and especially toward daybreak Sunday. There also might be pockets of heavy rainfall as Pwats climb into the 1.50 to 2 inches. Low temps will be much milder than tonight...only bottoming out in the upper 60s to the lower 70s. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Key Messages: * Showers/embedded storms early-day Sunday, possibly a second round of storms later in the day. * Drie, cooler than normal and low humidity levels for Mon and Tue. * Warming trend mid to late next week, with heat and humidity Thu/Fri. Daily chances for showers/storms Thu and Fri. Sunday looks more active, with early-day showers and embedded thunderstorms carrying over from the Saturday-overnight period. Then a slowly-sagging cold front will be moving southward during the afternoon to early evening hours, in association with a seasonably- strong upper level trough. That could lead to a risk for scattered stronger storms, although with a couple of potential limiting factors: (1) weak mid-level lapse rates, (2) best deep layer shear of 35-40 kt for more persistent storms lies behind the cold front and (3) the extent to which we can clear out from early-day shower and embedded storm activity. Currently view the severe weather risk as on the lower side but it isn`t zero. Given the very humid, higher PWAT airmass and that the surface front is nearly or becomes nearly parallel to the 500 mb heights, it could favor slow- moving heavy rainers, but it is conditional on thunderstorms developing. Clearing then takes place from north to south late Sun aftn to early evening, and with it will come a substantial change in airmass as we open the workweek. Mon and Tues then trend dry as a strong 1020+ mb high pressure area extends ridging through Southern New England. The bigger story for this period is cooler temperatures and substantially lower humidity levels. 850 mb temps could slip below 10C, and it may feel closer to conditions more typical of early to mid September than late July with highs in the 70s to low 80s and dewpoints in the low 50s. Temps to run some 5-10 degrees cooler than late-July normals. Not exactly summerlike but still overall ideal for outdoor activities. High pressure then moves offshore for mid to late in the workweek, which will allow for warming temps and rising humidity levels back to summerlike levels. This is especially the case as we move into Thu/Fri with moderately high probs of highs reaching 90 or above. While generally dry on Wed, the risk for showers and thunderstorms will also increase into Thu and Fri; but in a quasi-zonal flow pattern, the coverage and strength of this activity will hinge on the strength of upstream trough energy, which varies fairly substantially across the ensemble systems. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 00z TAF Update: Tonight: High confidence. VFR. Seabreezes along the eastern coast of MA turn offshore/light SW by 01z; winds remainder of the evening and overnight are light out of the NW. Saturday...High confidence. VFR. SSW winds around 10 knots except for localized sea breezes developing along portions of the immediate coast. Saturday night...Moderate confidence. VFR during the evening...but some MVFR cigs may develop across parts of the region after midnight. In addition...the risk for scattered showers and a few t-storms will increase after midnight and especially by daybreak. SSW winds 5-10 knots. KBOS terminal...High confidence in TAF. KBDL terminal...High confidence in TAF. Outlook /Sunday through Wednesday/... Sunday: Mainly VFR, with areas MVFR possible. Breezy. Chance SHRA, chance TSRA. Sunday Night: VFR. Chance SHRA. Monday through Tuesday Night: VFR. Wednesday: Breezy. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Tonight through Saturday night...High confidence. High pressure moves off the waters tonight and then pushes east of the waters Sat as a warm front approaches by Sat night. Winds will be light tonight into Sat morning...with sustained speeds generally under 15 knots. S winds may gust to 20+ knots and perhaps briefly up to 25 knots Sat night across our northern outer-waters. Later shifts may need to consider a marginal small craft advisory for the northern outer-waters...but other than that not expecting any marine headlines over this time period. Outlook /Sunday through Wednesday/... Sunday: Winds less than 25 kt. Chance of rain showers, chance of thunderstorms. Sunday Night: Winds less than 25 kt. Slight chance of rain showers, slight chance of thunderstorms. Monday through Wednesday: Winds less than 25 kt. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/Loconto NEAR TERM...Frank SHORT TERM...Frank LONG TERM...Loconto AVIATION...Frank/Loconto MARINE...Frank/Loconto