Area Forecast Discussion
Issued by NWS Boston, MA

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331 FXUS61 KBOX 131125 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 725 AM EDT Sun Jul 13 2025 .SYNOPSIS... Mainly dry with seasonably warm and humid conditions continue Sunday and most of Monday. A frontal system could bring showers and thunderstorms on Monday evening. Increasing heat and humidity around the middle of next week, which then looks to break around Friday as a cold front brings yet another risk for showers and thunderstorms. && .NEAR TERM /THROUGH TONIGHT/... Key Point * Seasonably warm and dry today Very little change in airmass today as high pressure remains offshore over the Gulf of Maine with a mid-level ridge over the region. Low stratus and fog have once again spread across the region as a result of the dewpoints in the 60s and light onshore ESE flow. The fog should burn off between 7am-9am again today, later across the Cape and Islands. After the low clouds and fog burn off and lift, we should see mostly sunny skies once again for the afternoon. High temperatures warm into the low to mid-80s, with dewpoints still in the mid-to-upper 60s. Storm remains well west of the SNE today as the axis of instability moves further NW with the convergence boundary. && .SHORT TERM /MONDAY/... Key Points * Seasonably weather again on Monday * Frontal system may bring heavy rain and localized flash flooding late Monday Tonight: Another rinse and repeat with low stratus and fog forming first along the south coast and gradually lifting north through the night with continued ESE onshore flow. Low temperatures remain bound by the dewpoints again in the mid to upper 60s. Monday: A shortwave trough and weak frontal system exit the Great Lakes and reach SNE late in the day. Before the frontal system gets here, a rather similar day to Sunday with low clouds and fog burning off by mid-morning, giving way to partly to mostly sunny skies and highs in the low to mid-80s. MLCAPE values should climb into the 500-1000 J/kg range across the interior in the afternoon. Shear and mid-level lapse rate are still lacking on Monday despite the weak shortwave moving through. With the frontal system likely arriving in the evening, possibly even after sunset, this should limit the severe wind threat. The primary risk associated with thunderstorms will be heavy rain and localized flash flooding. Weak shear means storms will be slow-moving with little upscale growth. PWATS will increase to around 1.8 inches on Monday, with warm cloud depths reaching as high as 14,000 feet. Don`t think a flood watch will be needed at this time due to uncertainty on the frontal timing and convective placement, but future shifts may consider if confidence begins to increase. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Key Messages: * Very warm to hot during the middle of next week, with elevated heat indices around 95-100F. Heat headlines possible. * Becoming more unsettled late Thursday-Friday with increasing chances for showers/storms, especially Friday with a cold front. Details: Tuesday-Thursday: Tuesday through Friday, a mid-level ridge builds over the regions. Temperatures aloft increase with 850mb temperatures peaking at around 20C in the Weds-Thurs timeframe. A good amount of moisture gets transported over the ridge by Wednesday adding humidity to the mix. Temperatures Tuesday through at least Thursday will range in the upper 80s to mid 90s with the exception of the immediate coast. With the the added element of higher humidity, it will feel more like mid to near 100 Wednesday and Thursday. Overall, there are no major disturbances embedded in the flow during that timeframe which will reduce the threat for widespread showers/thunderstorms. Ensemble members display potential for a few showers. Members are still spread across the board with timing and given the low coverage nature has been difficult to message in the forecast. Until better agreement on timing, no major adjustment have been made to the forecast. There will be a better signal for forcing later Thursday with corresponding increased chances for showers and thunderstorms. Thursday - Friday: A mid-level trough approaches the region, Thursday into Friday. This will shift the pattern to becoming more unsettled with increasing potential precipitation starting later Thursday. Ensemble members are still across the board when it comes the the precipitation chances and the timing leading to lower confidence this far out. A front will eventually push through on Friday with the main trough axis. This should bring the highest chances of seeing precipitation. && .AVIATION /11Z SUNDAY THROUGH THURSDAY/...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 12z Update: Sunday: Moderate confidence. IFR/LIFR Stratus and fog burning off between 13-16z, then VFR conditions for the rest of the day. South winds at 5-10 knots. Sunday Night: High Confidence IFR/LIFR CIGS build north again tonight with continued ESE flow. stratus should have similar timing to last night. Monday: Moderate Confidence VFR after IFR CIGS burn off again. Chance for showers and thunderstorms mainly across the interior KBOS Terminal...Moderate confidence in TAF. IFR CIGS lifting to M/VFR 14-15z similar to the last couple days. VFR this afternoon. IFR stratus likely around the same time tonight KBDL Terminal...High confidence in TAF. IFR CIGS lifting to M/VFR 12-13z similar to the last couple days. VFR this afternoon. Less certain about low status again for tonight. Outlook /Monday Night through Thursday/... Monday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA, slight chance TSRA. Tuesday: VFR. Slight chance SHRA, slight chance TSRA. Tuesday Night: VFR. Wednesday through Wednesday Night: VFR. Slight chance SHRA, slight chance TSRA. Thursday: VFR. Breezy. Chance SHRA, chance TSRA.
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&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today through Monday...High confidence. Weak pressure gradient will keep winds/seas below Small Craft Advisory thresholds through Sunday: seas 2-3 ft with E winds over the southern waters and SE winds over the eastern waters up to 15 kts during the afternoon hours, remaining light in the overnight hours. Main concern for mariners will be areas of fog tonight that may redevelop again tonight. Outlook /Monday Night through Thursday/... Monday Night through Wednesday: Winds less than 25 kt. Wednesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers, slight chance of thunderstorms. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Mensch/KP NEAR TERM...KP SHORT TERM...KP LONG TERM...Mensch AVIATION...McMinn/KP MARINE...KP