textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Scattered showers possible tonight and dry during the day Monday, though cooler with few clouds following a backdoor cold front.

- Unsettled Monday night through Thursday, with several opportunites for showers and thunderstorms. Timing which days may have better storm chances is still low-confidence.

- 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 possible tonight and dry during the day Monday, though cooler with few clouds following a backdoor cold front.

Cloud cover continues to build in today as high pressure continues to push eastward and eventually offshore. Weak low pressure tracks near the region tonight as well, increasing chances for some scattered showers towards CT, RI, SE MA, Cape Cod, and the Islands. Not anticipating any washouts with any that move through tonight, and these should clear the region heading into Monday morning. Lows tonight will generally fall into the upper 50s and low to mid 60s.

A backdoor cold front is expected to make its way across southern New England late tonight into tomorrow morning, clearing skies and ushering in drier air. Winds aloft shift more N then NE after midnight, reaching the surface after daybreak. This onshore flow will also aid in keeping eastern parts of the region slightly cooler; highs closest to the coast will generally be in the low 70s. Still, much of the region can expect a less humid day with highs in the upper 70s. Heading into Monday evening/night, high pressure shifts full offshore, which will introduce the start of a more unsettled pattern.KEY MESSAGE 2...Backdoor cold front Monday brings onshore flow, decreased cloud cover and lower temperatures.

KEY MESSAGE 2...Unsettled Monday night through Thursday, with several opportunites for showers and thunderstorms. Timing which days may have better storm chances is still low-confidence.

We still look to enter into a cloudy and unsettled weather pattern, as a stalled frontal boundary in the vicinity of Southern New England or just to our southwest focuses several opportunites for showers and storms Monday night through Thursday. The wavy frontal boundary separates hot, humid and conditionally unstable air to our southwest, with more seasonable and less humid air over northern/eastern New England, with strong NW flow aloft. It likely won't be raining the whole period of time, but in a pattern governed by convection and hard-to-time shortwaves in the NW flow aloft, timing which period(s) and the location of showers and storms is still subject to change and is low-confidence, with poor run-to-run consistency across the model suite.

Right now the two periods that appear to have the best chance of showers and storms looks to be Monday night and into the first part of Tuesday, and again later Wednesday afternoon into part of Thursday. Tried to introduce higher PoPs (high Chance to Likely) for these days, but a general slight chance to chance governs the Monday night thru Thursday period. It looks like the potential for storms to become strong to severe looks limited, but a slightly better chance exists later Wednesday into Thursday as a stronger, more- coherent shortwave aloft allows for at least some of the more unstable warm sector to work its way in. Temperatures were kept in the 70s to low 80s Tue thru Thurs, with rather mild lows in the mid 60s (climo low temperature values are in the upper 50s/around 60). 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.

Stalled frontal boundary finally moves offshore Thursday, although cyclonic flow aloft will keep our weather pattern somewhat unsettled with a mix of clouds and sun. Spot showers are possble Friday and Saturday afternoon but should be drier much of the time. Broad high pressure then works in from the north Sunday into Labor Day, leading to an onshore flow but with sunny and dry conditions.

AVIATION /19Z SUNDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

Rest of Today...High confidence.

VFR. SW winds continue today with occasional gusts to around 20 kt, which should diminish heading into the evening hours.

Tonight...Moderate confidence.

VFR, though showers are possible across CT/RI/SE MA and into the Cape and Islands. Periods of MVFR visibilities in any SHRA that develop are possible, though confidence in timing and location is low at this time. Winds shift more NW heading into Monday morning, though remain light.

Monday...High confidence.

VFR. Light N to NE winds.

Monday Night...Moderate confidence.

MVFR with pockets of IFR possible further in the interior. Rain chances increase from W to E after 00z Tuesday. Some embedded thunder possible as well.

KBOS Terminal...High confidence.

KBDL Terminal...High confidence.

Outlook /Tuesday through Friday/...

Tuesday: MVFR/IFR conditions possible. SHRA likely, slight chance TSRA.

Tuesday Night: Mainly VFR, with local IFR possible. SHRA likely, slight chance TSRA.

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

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

Thursday: Mainly VFR, with local MVFR possible. Chance SHRA, slight chance TSRA.

Thursday Night: Mainly VFR, with local MVFR possible. Chance SHRA.

Friday: VFR. 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.

Through Monday Night...High confidence.

SW winds continue over the waters as high pressure continues shifting offshore. Brief Small Craft Advisory-level gusts are expected over the nearshore waters of the Cape and Islands through midnight tonight at the latest. Showers and some embedded thunder with them are possible tonight, particularly towards the southern waters.

A backdoor front moves over the waters from N to S late tonight into Monday morning, shifting winds more NE initially, then more S heading into the evening hours. Light S winds over the waters Monday night, along with more chances for showers and thunderstorms.

Outlook /Tuesday through Friday/...

Tuesday: Winds less than 25 kt. Chance of rain showers, isolated thunderstorms.

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

Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers, isolated thunderstorms.

Wednesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, slight chance of thunderstorms.

Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers.

Thursday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers.

Friday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until midnight EDT tonight for ANZ231>234.