textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Very comfortable temperatures this weekend with mainly dry conditions. There is a moderate risk for rip currents as well this weekend.

- Rain returns late Sunday into Monday, followed by quieter weather through most of next week.

- Seasonably warm temperatures and moderate humidity return through the middle of next week, followed by increasing shower chances late in the week.

DISCUSSION

KEY MESSAGE 1...Very comfortable temperatures this weekend with mainly dry conditions.

Clear skies and light winds early this morning are supporting effective radiational cooling. Lows fall into the 50s across the cooler outlying locations, while urban centers remain near 60 degrees by sunrise. Given these conditions, areas of valley fog have begun to develop and can be seen on satellite imagery using the Nighttime Microphysics RGB, with fog gradually filling the valleys. Any morning fog will erode with daytime heating and lift by mid- morning.

Quiet weather is the theme for the weekend as high pressure originating from northern Canada settles across the Northeast through the first half of Sunday. However, there remains a very low chance for an isolated shower from mid to late afternoon, mainly across eastern Massachusetts, as a potent mid-level shortwave with an associated cold pool of -18C brushes the eastern fringes of the region. Given PWATs are quite low, between 0.6 and 0.8 inches, and a notably dry airmass remains in place, the threat for a stray shower is very low. Our thinking is that this robust shortwave will result in more cloud cover than anything else across eastern areas.

Temperatures remain seasonable, with highs generally ranging from the upper 70s to lower 80s. Another cool night is expected Saturday night, with clear skies and light winds supporting effective radiational cooling. Lows fall into the lower to middle 50s across the cooler outlying locations, while urban centers remain near 60 degrees.

Despite the pleasant weather, a moderate risk for rip currents is expected today and Sunday. Those heading to the beach should remain aware of local conditions and check with lifeguards or beach staff regarding rip current risks at their specific location.

High pressure begins to shift offshore Sunday as a low pressure system approaches from the Great Lakes. Increasing warm air advection will bring increasing clouds through the afternoon, while temperatures remain seasonable in the upper 70s and lower 80s. Humidity will gradually increase as dew points rise into the lower 60s. Most, if not all, of the daylight hours remain dry, with the next opportunity for rainfall arriving Sunday night into Monday.

KEY MESSAGE 2...Rain returns late Sunday into Monday, followed by quieter weather through most of next week.

Confidence remains high that most, if not all, of the daylight hours Sunday remain dry. Rainfall arrives late Sunday, with the steadiest rain anticipated overnight through early Monday. We are now entering the time range where high-resolution guidance can begin to better resolve this period. While some guidance brings rain into western Massachusetts and western Connecticut as early as late afternoon, prior to sunset, ensemble guidance supports a later arrival, with measurable rainfall generally arriving between 8 PM and midnight.

There is increasing certainty in the overall evolution of this system, with one area of low pressure likely passing across northern New England and a secondary low tracking south of New England across the Mid-Atlantic. This evolution is also supported by the ECMWF EFI and Shift of Tails for QPF, which highlight both of these regions. With southern New England positioned between these two areas, confidence in the highest rainfall totals occurring across the region has diminished, lowering the threat for widespread flash flooding.

However, PWATs increase to between 1.8 and 2.1 inches overnight into Monday, supporting the potential for locally heavier downpours. A Marginal Risk for Excessive Rainfall (level 1 of 4) remains in place for much of New England Sunday night into Monday, primarily due to the potential for localized flash flooding. Ensemble guidance currently supports a general range of 0.25 to 0.50 inches across southern New England, though localized higher amounts are possible, especially beneath heavier downpours.

Given the expected cloud cover and showers, Monday will be cooler, with highs generally ranging from the mid-70s to around 80 degrees. It will also be fairly humid, with dew points remaining elevated and resulting in rather sticky conditions.

KEY MESSAGE 3...Seasonably warm temperatures and moderate humidity return through the middle of next week, followed by increasing shower chances late in the week.

Drier air advects in from the northwest beginning Monday night into Tuesday, leading to another dry stretch Tuesday through Wednesday, and possibly into the first half of Thursday, as surface high pressure builds back into the region. Temperatures remain seasonable, with highs in the lower to middle 80s and tolerable humidity as dew points remain in the lower to middle 60s. Ensemble guidance continues to signal a transition toward more unsettled weather late in the week, with shower chances returning and temperatures potentially trending slightly below normal.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

Today & Tonight...High confidence.

VFR. North to northwest winds 5 to 10 kt, with sea breezes developing near the coast during the daytime hours. Patchy river valley fog may result in IFR visibilities overnight.

Sunday...High confidence.

VFR through much of the day. South to south-southwest winds 10-12 kt. Conditions lower to MVFR late in the afternoon, then IFR Sunday evening as SHRA and embedded TSRA develop.

KBOS Terminal...High confidence.

VFR. Sea breeze developing by 14Z.

KBDL Terminal...High confidence.

Low probability of brief IFR visibilities in valley fog between 09- 12Z.

Outlook /Sunday Night through Wednesday/...

Sunday Night: MVFR/IFR conditions possible. Breezy. SHRA.

Monday: Mainly VFR, with local IFR possible. Breezy. Chance SHRA.

Monday Night through Wednesday: VFR.

MARINE

Forecaster Confidence Levels...

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

Through Sunday...High confidence.

Tranquil boating conditions are expected as high pressure traverses the Northeast through the weekend. Unsettled conditions arrive late Sunday into Monday with the passage of a low pressure system. Winds from the north today become somewhat variable as surface high pressure moves overhead. Nearshore sea breezes develop, with winds generally 10 to 15 kt.

On Sunday, winds shift to the south and increase to less than 20 kt. Sunday night into Monday, seas build to 4-6 ft with wind gusts up to 25 kt. These are marginal conditions for a Small Craft Advisory, but one may need to be considered for Sunday night into Monday.

Outlook /Sunday Night through Wednesday/...

Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Seas locally approaching 5 ft. Chance of rain showers.

Monday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft. Rain showers likely.

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

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

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

Wednesday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

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