textproduct: Boston / Norton

WHAT HAS CHANGED

Overall, little change to the forecast, with increasing confidence that most of Sunday remains dry before rain chances increase Sunday night into Monday.

KEY MESSAGES

- Seasonable, less humid, and mainly dry conditions today, though an isolated afternoon shower or thunderstorm is possible.

- Dry, seasonable, and comfortable weather continues through the weekend.

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

DISCUSSION

KEY MESSAGE 1...Seasonable, less humid, and mainly dry conditions today, though an isolated afternoon shower or thunderstorm is possible.

Overall, not much has changed with today's forecast. If kicking off the weekend early this Friday, pleasant weather is expected in the wake of yesterday's cold front. Mainly sunny skies and a well-mixed boundary layer will allow temperatures to climb into the lower to middle 80s, with periodic breezy northwest winds. A sea breeze may develop along Boston's South Shore. Drier air continues to advect into southern New England, with humidity lowering through the day. A surface trough dropping south from northern New England this afternoon may provide enough convergence for an isolated shower or thunderstorm, though coverage is expected to remain very limited. Any shower or storm that develops should move through quickly and remain non-severe.

Despite the pleasant weather, a moderate risk for rip currents is expected today and Saturday. 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.

Clear skies and light winds tonight will support effective radiational cooling. Lows fall into the 50s across the cooler outlying locations, while urban centers remain near 60 degrees.

KEY MESSAGE 2...Dry, seasonable, and comfortable weather continues through the weekend.

Quiet weather is expected this weekend as high pressure originating from northern Canada settles across the Northeast through the first half of Sunday. PWATs lower to between 0.5 and 0.7 inches, resulting in a notably dry airmass with little humidity. 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.

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. Humidity will gradually increase as dew points rise into the lower 60s.

KEY MESSAGE 3...Rain chances return late Sunday into Monday, followed by quieter weather through most of next week.

The next opportunity for rainfall arrives during the second half of Sunday, with the steadiest rain expected Sunday night into early Monday. There is growing confidence that most, if not all, of the daylight hours Sunday remain dry. Ensemble guidance generally keeps the probability of measurable rainfall below 50 percent until around 00-06Z Monday, supporting a later onset to the rainfall.

There remains uncertainty regarding rainfall amounts, however, as the best forcing is associated with the surface low and differences in its track make it difficult to determine where the greatest rainfall will occur. Ensemble guidance continues to depict differing solutions, with some members keeping the primary low farther north while others track it closer to or across southern New England. Regardless of the eventual track, rainfall appears increasingly likely Sunday night, though uncertainty remains regarding how much rain will fall.

Global guidance is in agreement that PWATs may exceed 2 inches, supporting the potential for locally heavy rainfall. The ECMWF EFI and Shift of Tails for QPF also highlight a signal across northern New England, while a Marginal Risk (level 1 of 4) for excessive rainfall remains in place for all of New England, with the exception of northern Maine. Ensemble guidance continues to show considerable spread in potential rainfall totals, with the ECMWF ensemble being the more robust solution and the GFS and CMC ensembles generally depicting lower totals.

The system appears progressive, with a cold front clearing east of New England by Monday afternoon or evening. Drier air then advects in from the northwest, leading to another dry stretch Tuesday through Wednesday, and possibly into 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 60s. Unsettled conditions may return late 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...High confidence.

VFR outside the risk for widely scattered showers and perhaps even an isolated t-storm or two after 20z/21z until about 01z/02z or so. NW winds generally 6-12 knots but winds shift to the S-SW near the south coast by mid to late afternoon.

Tonight...High confidence.

VFR outside of any widely scattered showers/isolated t-storm risk that will dissipate by mid evening. Low risk for brief fog patches toward daybreak in low-lying locations...but if that would be extremely localized and short-lived.

Saturday...High confidence.

VFR. NW winds 6-12 knots outside sea breezes that will develop along portions of coast by afternoon.

KBOS Terminal...High confidence in TAF. Main risk for a few brief showers in the vicinity of the terminal will be after 21z/22z until about 02z. Low risk for a rumble of thunder too. Odds favor sea breeze remains offshore this afternoon...but we do expect one to develop on Sat.

KBDL Terminal...High confidence in TAF.

Outlook /Saturday Night through Tuesday/...

Saturday Night: VFR.

Sunday: VFR. Breezy.

Sunday Night: MVFR/IFR conditions possible. Breezy. SHRA, slight chance TSRA.

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

Monday Night through Tuesday: VFR.

MARINE

Forecaster Confidence Levels...

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

Through Saturday...High confidence.

Tranquil boating conditions are expected as high pressure settles in from the north and remains in place through most of the weekend. Most, if not all, of this period will remain dry, with only a low probability of a spot shower this afternoon. Northwest winds early this morning become southwesterly this afternoon, with wind speeds generally less than 12 kt and seas between 2 and 3 ft. On Saturday, wind direction becomes more variable as surface high pressure builds overhead. Nearshore sea breezes may develop, with winds generally 10 to 15 kt.

Outlook /Saturday Night through Tuesday/...

Saturday Night through Sunday: Winds less than 25 kt.

Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Chance of rain showers.

Monday: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Areas of rough seas. Rain showers likely, slight chance of thunderstorms.

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

Tuesday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

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