textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Increasing clouds today with beneficial rainfall moving in tonight and Thursday.

- Unsettled and cooler this weekend into early next week.

DISCUSSION

KEY MESSAGE 1...Increasing clouds today with beneficial rainfall moving in tonight and Thursday.

Should be a mostly dry start to the day outside coastal areas of Massachusetts where drizzle and patchy fog will likely be ongoing. Otherwise, expect a lull in the activity by the late morning and early afternoon. Areas of rain and scattered showers increase in coverage later this afternoon and evening. Initially, there will be two areas of precipitation, showers associated with the inverted trough near the coast, and a more widespread shield of rain associated with incoming low pressure. The bulk of the rain falls overnight into Thursday morning with passage of upper trough from Ohio Valley and secondary surface low that tracks from mid Atlantic to Cape Cod. Still looks like a fairly quick hitting event, with the bulk of the rain wrapping up from west to east through the morning. Any lingering areas of showers and drizzle across the Cape and Islands come to an end around sunset. Could also see a few rumbles of thunder embedded within any heavier elements Thursday morning.

Overall, this will be a quick hitting and weak system with meager dynamics aloft. Rainfall totals should be more beneficial with most areas areas picking 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 2...Unsettled and cooler this weekend into early next week.

Amplified pattern later this week and over the weekend as a building ridge of high pressure over central Canada traps a upper level low 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 /12Z WEDNESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

12z TAF Update:

Today...Moderate confidence (ceilings).

VFR for western/central terminals. IFR for east coast terminals this AM. Ceilings may briefly lift to MVFR or scatter briefly near the coast early afternoon. This is lower confidence, but is more likely to happen at BOS than the Cape/Island terminals if anything. In that scenario, IFR would likely re-develop by mid to late afternoon with a chance of a isolated -SHRA/-DZ. LIFR re-develops for Cape/Island terminals. NE-Easterly winds 8-12 kts. Stronger winds for Cape/Islands this morning with a few gusts to 22 kts.

Tonight...High confidence.

IFR/LIFR conditions develop across the eastern terminals tonight, becoming more widespread as rain overspreads region from west to east after 03Z.

Thursday...High confidence in trends.

Rain continues through early afternoon with improving ceilings late afternoon. Light SE winds become westerly later in afternoon.

KBOS Terminal...Moderate confidence in TAF timing. Very slow improvement to MVFR late in the afternoon. There is the potential for IFR ceilings to persist all day.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday Night through Sunday/...

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

Friday: VFR. Breezy.

Friday Night through Saturday: VFR.

Saturday Night: Mainly VFR, with local MVFR possible.

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.

Pressure gradient between slow-moving low pressure SE of the 40/70 benchmark and high pressure over the Canadian Maritimes keeps E/NE winds in play through the end of the week.

NE winds may approach SCA around Cape Cod with 20kt gusts. Main issue will be the long fetch of NE winds resulting in 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.

Outlook /Thursday Night through Sunday/...

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

Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 AM EDT Friday for ANZ250-254>256.