349 FXUS61 KBOX 220533 AFDBOXArea Forecast Discussion National Weather Service Boston/Norton MA 133 AM EDT Mon Sep 22 2025
.SYNOPSIS... Dry weather continues until the chance for some unsettled weather returns late Tuesday into Wednesday. Temperatures should also average about normal this week, with the exception of above normal temperatures Tuesday. Potential for a more widespread rainfall event Thursday and Friday.
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.NEAR TERM /UNTIL 6 AM THIS MORNING/... Key Messages:
* Not quite as cool tonight but still expect a lot of 40s with the coolest outlying locations bottoming out near 40
* Patchy fog likely late in the typically low-lying locations
Core of a nearby high pressure shifts more towards the Maritimes tonight. Still expecting rather good radiational conditions, despite some higher clouds at times. Low temps mainly in the 40s with some of the normally coolest outlying locations bottoming out near 40. Favored the lowest temperature guidance. We did include some patchy fog in the typical low-lying prone locations after midnight given dewpoints several degrees milder than last tonight.
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.SHORT TERM /6 AM THIS MORNING THROUGH 6 AM TUESDAY/... Key Messages:
* Warming trend kicks off tomorrow
With the high pressure still over the North Atlantic, expecting a general light south flow to develop across our region. Except near the immediate east coast, where the more typical southeast sea breeze direction should prevail from late morning into the afternoon.
Expecting a warming trend tomorrow with continued dry weather.
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.LONG TERM /TUESDAY THROUGH SUNDAY/... Key Messages:
* Warm and humid conditions peak on Tuesday
* Chance for showers and a few thunderstorms Tuesday into Wednesday
* Unsettled weather continues for the rest of the week with a chance for showers each day
Southwesterly return flow advects in higher moisture and warmer temperatures Tuesday. Still thinking the the warmest temperatures will be found the Connecticut and Merrimack River Valleys where highs may rise as high as the lower to perhaps middle 80s. Deterministic guidance is in agreement showing 925 mb temperatures over the region around 20C. Dew points increase into the 60s after a dry weekend, and ensemble mean PWAT values range between 1.5-1.7" for the afternoon. An approaching front arrives Tuesday afternoon and evening providing ample forcing for scattered to widespread showers and thunderstorms. Guidance still shows MLCAPE values around 500 J/kg along with somewhat favorable shear profiles. As such, there could be a low chance for a severe storm or two across the far northwestern interior. Guidance has increasingly hinted at developing a weak wave of low pressure along and just behind the front. This wave could help increase and extend the coverage of light to moderate rainfall Tuesday night into Wednesday especially across the Cape and Islands.
Brief upper level ridging Wednesday afternoon won`t make much of an impact near the surface as stiff onshore flow likely continues the chance for low clouds and an isolated shower or two.Temperatures will be much cooler on Wednesday, only rising into the lower to mid 60s for much of the region. Attention turns to a longwave trough as it digs deeper into the central and midwest CONUS. A warm front extending from surface low pressure over the Great Lakes approaches the area Thurs. Guidance has become more bullish on periods of showers and perhaps steady rainfall associated with this feature Thursday. Kept chance POPs through Friday as the front will be slow to move. Some models such as the ECMWF show the region coming into the warm sector by Friday with dew points potentially rising into the 60s. Such unstable air with a boundary nearby could bring another risk for convection Friday and perhaps into the weekend.
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.AVIATION /06Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels...
Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.
Through Tonight...High Confidence.
VFR outside of some late night/early morning fog patches in the typical low-lying locations. Light/calm winds early this morning become light S winds today with sea breezes on the immediate coast. Light SW winds expected tonight with MVFR/IFR cigs possible by early Tuesday morning.
Tuesday...Moderate Confidence in categories.
MVFR with pockets of IFR possible throughout the day. Ceilings may end up more borderline VFR/MVFR as the day goes on and chances for TSRA/SHRA increase in the evening. SW winds to 10 kts across the region with locally higher winds over the Cape and Islands. Gusts there to 20 kts possible.
KBOS Terminal...High confidence in TAF.
KBDL Terminal...High confidence in TAF.
Outlook /Tuesday through Friday/...
Tuesday Night: Mainly VFR, with local MVFR possible. Chance SHRA, slight chance TSRA.
Wednesday: Mainly VFR, with local IFR possible. Chance SHRA.
Wednesday Night: Mainly VFR, with local MVFR possible. Chance SHRA.
Thursday: VFR. Chance SHRA.
Thursday Night: Mainly VFR, with local MVFR possible. Chance SHRA.
Friday: VFR. Chance SHRA.
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.MARINE... Forecaster Confidence Levels...
Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent.
Through Monday Night...High Confidence.
High pressure south of the Maritimes leads to relatively light winds and seas across the waters. Good visibility.
Outlook /Tuesday through Friday/...
Tuesday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers.
Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers, slight chance of thunderstorms.
Wednesday through Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers.
Thursday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.
Friday: Winds less than 25 kt. Chance of rain showers.
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.BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None.
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SYNOPSIS...Belk/FT NEAR TERM...Belk/Frank SHORT TERM...Belk LONG TERM...FT AVIATION...Belk/Frank/Hrencecin/FT MARINE...Belk/FT
NWS BOX Office Area Forecast Discussion