textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Coastal low clouds move inland tonight.

- Beneficial rainfall Wednesday night into Thursday.

- Cooler pattern prevails Friday through weekend but mostly dry.

DISCUSSION

KEY MESSAGE 1...Coastal low clouds move inland tonight.

High pressure will remain in control through Wednesday with ridging aloft and dry weather expected. However, an inverted trough from low pressure that is well offshore was producing some low clouds that can be seen on satellite south and east of Cape Cod. These low clouds were being held offshore by daytime heating but will eventually expand inland tonight as boundary layer cools, most likely across much of eastern MA and RI, perhaps as far west as Worcester per model cross sections. Moist E/NE flow will also produce areas of fog, and perhaps some spotty drizzle, mainly near Cape Cod and the Islands.

KEY MESSAGE 2...Beneficial rainfall Wednesday night into Thursday.

We may see some showers sneak into eastern MA Wednesday evening associated with inverted trough, otherwise showers will become more widespread Wednesday night into Thursday with passage of upper trough from Ohio Valley and secondary surface low that tracks from mid Atlantic to Cape Cod. Timing has sped up a bit and now it looks like most of the rain will come to an end early Thursday afternoon as dry slot comes through quickly.

Speed of system, combined with modest dynamics and moisture, will limit rainfall totals from being excessive, but most areas should still pick up 0.25 to 1.00" of much needed rainfall, perhaps a little more in northern MA.

Astro tides are fairly low so coastal flooding is not much of a concern along E MA coast. Persistent onshore flow may bring a surge of up to 1 foot later in week, but by then winds turn offshore as surface low lifts farther to the north.

KEY MESSAGE 3...Cooler pattern prevails Friday through weekend but mostly dry.

Blocky pattern takes hold later this week and over weekend as upper low takes up residence over southern Ontario. Southern New England should be far enough removed from coldest air aloft to keep us mostly dry, especially given W/NW flow, but pattern certainly favors diurnal clouds and perhaps a few afternoon sprinkles Friday, Saturday, and Sunday.

It does look like upper low may lift farther north early next week, allowing for more of a zonal flow across northern tier of states which would lead to drier and milder weather Monday and Tuesday. However, models are notorious for breaking down these blocky patterns too quickly, such that it may take a little longer to see improving conditions. For now, forecast reflects model blend to iron out the uncertainty.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

00z TAF Update:

Only minor adjustments this cycle, primarily slowing the inland progression of marine stratus by ~2 hours. Overall trend remains unchanged.

IFR ceilings develop quickly after sunset along the coast, then expands inland to roughly KORH between 04z-06z. VFR conditions persist father west. Patchy -DZ/BR expected across Cape Cod and the Islands.

On Wednesday, slow improvement at best. Ceilings may briefly lift to MVFR near the coast late morning to early afternoon, but IFR likely redevelops by mid to late afternoon with a chance of -SHRA/-DZ. VFR continues across the western terminals.

By Wednesday night, MVFR/IFR conditions become more widespread as showers overspread the region, continuing into Thursday.

KBOS Terminal...Moderate confidence in TAF. Improvement to MVFR Thu may be optimistic, IFR ceilings could persist all day.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday through Sunday/...

Thursday: MVFR/IFR conditions possible. Breezy. Chance SHRA.

Thursday Night: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHRA.

Friday: VFR. Breezy.

Friday Night through Saturday Night: VFR.

Sunday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

High confidence through the end of the week.

Persistent E/NE winds continue as high pressure remains over the Maritimes and low pressure meanders well offshore SE of 40/70 benchmark for next few days.

NE winds may approach SCA around Cape Cod with 20kt gusts but main issue will be rough seas of 5 to 8 feet on outer waters through Thu where SCA remains posted. May have to extend it into Rhode Island and Block Island Sounds should confidence increase in later forecasts.

Otherwise, areas of fog and drizzle should develop tonight, especially on south coastal waters, with little improvement Wed. Showers expected Wed night and Thu as low pressure tracks from the mid Atlantic to Cape Cod and Gulf of Maine.

Outlook /Thursday through Sunday/...

Thursday: Winds less than 25 kt. Rough seas up to 10 ft. Rain showers.

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

Friday through Friday Night: Winds less than 25 kt. Seas up to 5 ft.

Saturday through Saturday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 6 PM EDT Thursday for ANZ250- 254>256.