textproduct: Boston / Norton

WHAT HAS CHANGED

No significant forecast changes.

KEY MESSAGES

- Scattered showers and isolated thunderstorms return Sunday afternoon into early evening, focused mainly across eastern New England. Cooler and drier conditions arrive Sunday night. - Dry with seasonable temperatures Monday. - Summerlike heat and humidity returns next week, no notable storms, though a front may bring a period of showers and thunderstorms mid to late week.

DISCUSSION

KEY MESSAGE 1...Scattered showers and isolated thunderstorms return Sunday afternoon into early evening, focused mainly across eastern New England. Cooler and drier conditions arrive Sunday night.

Subsidence behind the departing front allows for mainly clear skies this morning, though this will be short-lived as a mid-level trough and accompanying shortwave push south out of northern New England this afternoon. While forcing aloft appears favorable, surface-based instability remains limited, generally less than 500 J/kg. Continued thinking supports mainly showery activity this afternoon rather than a widespread washout. That said, some showers may be capable of producing locally heavy downpours given PWAT values around 1.5 inches. While severe storms are not anticipated, thunder remains possible and, due to colder temperatures aloft, small hail cannot be ruled out. Although a few showers will be possible across the entire region, areal coverage should be greatest across central and eastern MA as well as RI, where instability appears slightly more favorable. Cooler air arrives more gradually, which may allow highs to still reach the upper 70s to lower 80s before northeast flow develops later in the evening. Otherwise, drier and much cooler air works into the region overnight. Lows by daybreak Monday will fall into the middle to upper 40s across outlying locations and the lower to middle 50s in the urban centers.

KEY MESSAGE 2...Dry with seasonable temperatures Monday.

Sundays mid-level trough exits east of New England by early Monday morning as an amplified ridge shifts toward the eastern third of the CONUS. The trough eventually evolves into a cutoff mid-level low over the Canadian Maritimes, helping to slow the eastward progression of the ridge and supporting another stretch of summerlike temperatures across southern New England. Monday will likely be the coolest day of next week due to north-northeast flow aloft draining a cooler airmass southward into the region. Forecast soundings Monday afternoon depict a well-mixed atmosphere with the boundary layer extending to around 850 mb and temperatures at that level ranging from +7C to +10C. Naturally, the farther east, the cooler temperatures will be, with Cape Cod, the Islands, Boston, and the eastern coastal plain largely remaining in the 70s, while the Connecticut River Valley reaches the lower 80s.

KEY MESSAGE 3...Summerlike heat and humidity returns next week, no notable storms, though a front may bring a period of showers and thunderstorms mid to late week.

Through much of next week, an anomalous ridge extending north toward Hudson Bay in Canada favors mainly dry and increasingly hot conditions. 850 mb temperatures rise to around +15C Tuesday, then increase to around +18C Wednesday through Friday. This should support highs in the middle 80s to near 90 Tuesday, followed by upper 80s to lower 90s through much of the remainder of the week. The first half of next week should feature relatively comfortable dewpoints in the 50s. However, by late week, dewpoints rise into the 60s, leading to a more humid airmass. While outside the forecast period, there is a signal for heat to continue into next weekend, reflected in CPC outlooks depicting a Slight Risk (20 to 40 percent probability) for extreme heat across portions of the Northeast. There is still time to assess this signal in forthcoming guidance, though heat headlines may eventually be needed for portions of the period. In terms of precipitation, there does not appear to be anything appreciable on the horizon through much of next week. However, a frontal passage later in the week may bring a period of showers and thunderstorms as heat and humidity continue to build.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

12Z TAF Update:

Today...Moderate confidence in the areal extent of shower activity and period of MVFR.

VFR. Showers develop after 16Z across northeastern MA, expanding across eastern MA and RI after 18Z through the early evening hours. While the risk remains low, a few embedded thunderstorms are possible as well. Breezy WSW/W winds gusting to 20 to 25 kt today shifting WNW this afternoon. Winds shift more NW with the arrival of showers.

Tonight...High confidence.

Ceilings may briefly lower to MVFR as shower activity comes to an end, though conditions should return to VFR by 03Z at BOS and by 08Z at FMH/HYA/ACK. Showers end across eastern MA and RI between 03-05Z. Winds shift more N behind exited showers. Winds shift more NNE for BOS and Cape/Island terminals with a period of gusts around 20 kts. Winds/gusts decrease after 03Z.

Monday...High confidence.

VFR. NE winds around 10 to 15 kt.

KBOS Terminal...High confidence in trends, moderate confidence in timing.

A few showers or a weak thunderstorm are possible Sunday between 18Z and 00Z, with showers ending between 00-02Z.

KBDL Terminal...High confidence.

Outlook /Monday Night through Thursday/...

Monday Night: VFR.

Tuesday: VFR. Breezy.

Tuesday Night: VFR.

Wednesday: VFR. Breezy. Slight chance SHRA.

Wednesday Night: Mainly VFR, with local IFR possible. Breezy. Chance SHRA, slight chance TSRA.

Thursday: VFR. Breezy. Slight chance SHRA, slight chance TSRA.

MARINE

Forecaster Confidence Levels...

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

Today through Monday...High confidence.

Marginal 5 ft seas will continue across portions of the southern waters into Sunday, while the remainder of the waters remain below Small Craft Advisory criteria. However, a surge of northerly Small Craft Advisory-level wind gusts is expected Sunday night behind the departing cold front, especially across the eastern waters, which may briefly increase seas as well.

Additional Small Craft headlines may eventually be needed once current advisories expire. Seas gradually subside and NE winds fall below advisory criteria Monday.

Outlook /Monday Night through Thursday/...

Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft.

Tuesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft.

Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers, slight chance of thunderstorms.

Thursday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers, slight chance of thunderstorms.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 AM EDT Monday for ANZ254>256.