textproduct: Boston / Norton

WHAT HAS CHANGED

General forecast trends remain unchanged from the previous update.

KEY MESSAGES

- Some showers possible later this afternoon. Return of onshore flow and cooler temperatures.

- Strong cold front brings a round of widespread showers late Saturday night into Sunday, leaves colder temperatures and drier conditions in its wake.

- Mainly dry and unseasonably cool Mon-Tue, then moderating temperatures toward midweek. Next chance of showers will be Tue night into early Wed.

DISCUSSION

KEY MESSAGE 1...Some showers possible later this afternoon. Return of onshore flow and cooler temperatures.

Cooler day ahead over the interior compared to yesterday as the low associated with the backdoor cold front begins to shift offshore today. With it sitting offshore, onshore flow kicks back up and cloud cover becomes persistent across southern New England. 925 mb temperatures also fall slightly from just over 20C in some spots to closer to 10C across the region as the ridge breaks down and the shortwave that provided some showers earlier this morning pushes through the region. Highs today will mostly be in the 60s and 70s across the region, with the warmest temperatures in the mid 70s possible in the CT Valley and the coolest temperatures remaining closer to the eastern coastline. Some isolated showers are possible later in the afternoon with a low chance (20%) for some embedded thunder over parts of the interior where some surface-based CAPE 500- 1000 J/kg may be present. The slightly cooler conditions continue into tonight with 925 mb and 850 mb temperatures falling below 10C and flow remaining N and NE. Lows tonight should be more widespread 40s-50s.

KEY MESSAGE 2...Strong cold front brings a round of widespread showers late Saturday night into Sunday, leaves colder temperatures and drier conditions in its wake.

The low lingers offshore Saturday while surface ridging takes hold in the wake of today's shortwave. With that, onshore flow continues and drier weather prevails. Highs Saturday should be more seasonable, only climbing into the 50s and 60s.

Our attention then turns to an incoming strong cold front during the latter half of the weekend that will likely bring a round of more showers. This front is part of a potent upper level trough that will be shifting east from the Great Lakes this weekend. Ahead of this front and trough, PWAT values climb to around 1.25" Sunday morning after dropping mostly below an inch during the day Saturday. As this front pushes through, the forcing from it interacting with this increased moisture will lead to widespread showers for Sunday. Some guidance is hinting at some MUCAPE around 500 J/kg during the day that could be a factor in some embedded thunderstorms with these showers. Colder and drier air is left in this frontal passage's wake, reinforced by breezy W to NW winds starting Sunday afternoon. Showers may end with a mix of some snow in the higher elevations of the Berkshires Sunday evening as this colder air takes hold, but any accumulations are not expected at this time. Lows Sunday night may dip into the upper 20s in the highest elevations with the rest of the region falling into the 30s.

KEY MESSAGE 3...Mainly dry and unseasonably cool Mon-Tue, then moderating temperatures toward midweek. Next chance of showers will be Tue night into early Wed.

The upper level trough settles overhead Monday, and with that, temperatures aloft drop to unseasonable values. 925 mb temperatures fall below 0C and may even dip to -5C by Monday morning; 850 mb temperatures may approach -10C as well. Breezy W to NW winds continue as we sit in a CAA pattern, and highs may not climb out of the upper 40s and low 50s Monday afternoon. These winds will start to diminish as high pressure approaches from the west, and lows Monday night may fall into the 20s for much of southern New England. This high pressure should keep the region dry for the start of the week before it exits heading into Wednesday. Some showers are a possibility once again Tuesday night into Wednesday morning, particularly in northern MA as another shortwave passes to the north, but dry weather is expected to dominate the pattern for much of next week.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

12z TAF update:

Today: Moderate confidence.

Quick round of shower this morning moving offshore 12-13z. MVFR-IFR along the immediate coast, otherwise conditions lowering to MVFR elsewhere and eventually to IFR eastern MA and RI during the afternoon. Secondary round of scattered showers and a few t-storms developing later today. Exact spatial extent still a bit uncertain. North to northeast winds 5-10 kt.

Tonight through Saturday...Moderate confidence.

Any lingering showers should dry up heading into tonight. Light N to NE winds continue, then increase to around 10 kt during the day Saturday. Periods of IFR/MVFR possible, especially heading into Sat.

KBOS Terminal...Moderate confidence in TAF. Showers move offshore by 13z. CIGS drop to MVFR/IFR later this morning and likely persists through much of today. Scattered showers and possibly a t-storm developing around midday and into the afternoon.

KBDL Terminal...High confidence in TAF.

Outlook /Saturday Night through Tuesday/...

Saturday Night: MVFR/IFR conditions possible. Slight chance SHRA.

Sunday: Mainly VFR, with local IFR possible. Breezy. SHRA.

Sunday Night: VFR. Breezy. Slight chance SHRA.

Monday: VFR. Breezy.

Monday Night through Tuesday: VFR.

MARINE

Forecaster Confidence Levels...

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

High confidence through the weekend.

Seas 2-4 ft and winds less than 25 kts. Localized 5 ft seas possible in the southern waters today; not expected to be persistent enough for Small Craft Advisories. SW winds shift to NE later today. Passage of stronger cold front Sun should bring SCA conditions to at least outer waters Sun into Mon. Wind gusts may locally approach 25 kt late Sunday in the outer waters.

Outlook /Saturday Night through Tuesday/...

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

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

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

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

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

Tuesday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...None.