textproduct: Boston / Norton

WHAT HAS CHANGED

Small Craft Advisory remains in effect for the southern waters through at least tomorrow morning.

KEY MESSAGES

- Scattered showers tapering off tonight. Mainly dry conditions Wednesday with scattered showers and storms arriving overnight into Thursday.

- Still unsettled Thursday with showers and thunderstorms, with a low chance that some storms could become strong.

- Mix of clouds and sun with diurnally driven spot showers Friday into the early part of Labor Day Weekend, but drier weather most of the time. Dry and seasonable Sunday and on the Monday holiday, with onshore breezes.

DISCUSSION

KEY MESSAGE 1...Scattered showers tapering off tonight. Mainly dry conditions Wednesday with scattered showers and storms arriving overnight into Thursday.

Expect scattered showers for the remainder of the afternoon, decreasing in coverage this evening as higher pressure builds in from the west. Can't rule out a few isolated showers overnight, otherwise most locations remain dry.

High pressure remains in place Wednesday supporting mainly dry conditions with temperatures in the upper 60s and low 70s. A surface low pressure system tracks across Canada bringing a series of fronts across the region later Wednesday through Thursday. A warm front pushes into southern New England Wednesday night accompanied by advection of a plume of above normal moisture. Precipitable water values rise to 1-1.8" overnight. Lift provided by the jet positioned to the west and warm front will support the return of showers and perhaps some embedded storms. There is uncertainty regarding the finer details such as timing and thunderstorm probabilities due to spread across model guidance. Showers/storms more likely arrive in west and central portions of southern New England 11 PM to 2 AM arriving in the I-95 corridor 09-12Z. There are indications of marginal elevated instability that accompanies the plume of richer moisture. This may support a few embedded thunderstorms. This has been reflected across the simulated reflectivity in the high-res guidance, some more aggressive than others. This has led to lower confidence on how widespread embedded storms/heavy downpours will be. Steering flow appears strong enough to support quicker storm motion which would limit the risk for flash flooding. If there are embedded storms and downpours, can't rule out the potential for poor drainage/urban flooding in the more vulnerable spots.

KEY MESSAGE 2...Still unsettled Thursday with showers and thunderstorms, with a low chance that some storms could become strong.

Carrying over from Wednesday night is a continued risk for showers and thunderstorms into Thursday, as a stronger shortwave impulse moves through. The main question mark is on if storms could become strong in this timeframe. Although the airmass is plenty humid and mid and upper level wind fields are seasonably strong, considerable cloud cover could temper how much destabilization occurs. GFS- based CAPE profiles show about 800-1600 J/kg of most-unstable CAPE with moist-adiabatic mid-level lapse rates also tempering instability. It's still debatable if storms could become strong but the chances seem low with more tempered instability favored. Still, Thursday looks to be a washout with good chances for rains during the daytime hours, with more substantial clearing taking place Thursday evening.

KEY MESSAGE 3...Mix of clouds and sun with diurnally driven spot showers Friday into the early part of Labor Day Weekend, but drier weather most of the time. Dry and seasonable Sunday and on the Monday holiday, with onshore breezes.

Still under cyclonic flow aloft for Friday into the early part of Labor Day Weekend. This will keep weather pattern somewhat unsettled with a mix of clouds and sun. Spot showers are possible Friday and Saturday afternoon but drier weather prevails most of the time. much of the time. Broad high pressure then works in from the north Sunday into Labor Day, leading to onshore breezes, but with partly sunny skies and dry conditions.

AVIATION /20Z TUESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

18z TAF Update...

Through 00Z...Moderate confidence in trends, lower confidence in timing.

Mixture of IFR and MVFR ceilings with periodic showers and isolated TSRA. East-southeast winds of 10-15 kt are expected at coastal terminals and 6-10 kt for interior terminals.

Tonight...Moderate confidence.

MVFR ceilings generally prevail along and east of I-95, while areas farther inland remain IFR to LIFR. Localized fog possible. Onshore easterly winds and chances for SHRA ending after 06z.

Wednesday...High confidence.

VFR after 15z, however, mid-level clouds remain throughout the day. Easterly to east-southeasterly wind prevail.

Wednesday Night...High confidence in trends, moderate confidence in timing.

Showers returning overnight with embedded thunder, ceilings lowering to IFR/LIFR. Southeast winds.

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

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

Outlook /Wednesday Night through Sunday/...

Thursday: Mainly VFR, with local IFR possible. Breezy. SHRA likely, chance TSRA.

Thursday Night: VFR. Chance SHRA.

Friday through Friday Night: VFR.

Saturday: VFR. Breezy. Slight chance SHRA.

Saturday Night through Sunday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

Through Wednesday Night...High confidence.

Scattered showers across the water this afternoon and evening, a few showers moderate at times. Low chance for an embedded thunderstorm. Easterly flow less than 25 kts across the eastern waters. There is potential for a period of SCA gusts (~25 kts) this evening and overnight for the southern waters tonight with seas 3-5 ft. A SCA is in effect for the southern waters through Wednesday morning. It is possible this may need to be extended if 5 ft seas linger across southern outer waters off Block Island Wednesday.

Outlook /Wednesday Night through Sunday/...

Thursday: Winds less than 25 kt. Seas locally approaching 5 ft. Rain showers likely, slight chance of thunderstorms.

Thursday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers, slight chance of thunderstorms.

Friday: Winds less than 25 kt.

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

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

Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas.

Sunday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 AM EDT Wednesday for ANZ235-237- 255-256.