textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Breezy through sundown, then mostly clear and dry with decreasing winds tonight through Saturday.

- The next quick moving round of rain comes Sunday afternoon and evening, continuing overnight and exiting Monday morning.

- Quick round of rain around mid week, then dry weather returns by Thursday.

DISCUSSION

KEY MESSAGE 1...Breezy through sundown, then mostly clear and dry with decreasing winds tonight through Saturday.

It's been a partly sunny day but also quite breezy with a mixing depth to 800 mb, supporting westerly wind gusts in the 25 to as much as 35 mph this afternoon. Expect those conditions to continue through sundown, bringing a decrease in gust speeds as the mixed layer decreases. The main issue for tonight is if winds can slacken enough to support patchy frost. A sprawling area of high pressure centered over western NY/PA is forecast to move eastward overnight tonight but not really crest over Southern New England until Saturday morning. Efficient radiational cooling is expected tonight; there may be just enough of wind (around 5 mph) to keep frost from developing or in isolated coverage, and for those reasons haven't issued frost headlines for those non-Northwest MA zones where the growing season continues. If you do have crops or plants, it may not be a bad idea to consider taking protective actions to prevent frost damage, but I think the coverage ends up being too isolated. Lows forecast in the mid/upper 30s in the coolest outlying areas similar to surface dewpoints, and into the low to mid 40s for the urban areas and coastlines. A chilly start to Saturday but high pressure becomes established across Southern New England. Much of the day features full or mostly- full sunshine and light northwest winds, but a canopy of high-level clouds/cirrus will be streaming in from the south and southwest. Seasonable highs in the mid 60s under full sun. High pressure then retreats eastward by Saturday night, supporting lows in the upper 30s to the mid/upper 40s.

KEY MESSAGE 2...The next quick moving round of rain comes Sunday afternoon and evening, continuing overnight and exiting Monday morning.

The latest guidance suite continued to exhibit large uncertain with the timing of rainfall ending Monday morning. The deterministic GFS was on the more progressive side, with many of the international models more closely aligned with a slower timing and closer track to southern New England. However, there is agreement on the overall trend of drier conditions developing through the day. It is the timing that will need to be refined with later forecasts. For now, held on to a chance of showers towards the Cape and islands for a time Monday morning.

The timing will also impact rainfall totals. At present, expecting this will be a modest rainfall, with rainfall amounts generally between one half to one inch. A slower timing, should it occur, opens the door for rainfall up to 1.50", mainly towards the Cape and islands.

A brief dry period is anticipated for Monday afternoon and most of Monday night.

KEY MESSAGE 3...Quick round of rain around mid week, then dry weather returns by Thursday.

Our region should then get clipped by a pair of low pressures, each taking a different track. The first should pass by to our north later Monday night into Tuesday. Its cold front likely does not clear the coastal waters until late Tuesday night. This will be a period of more showery precipitation.

Another dry period is expected Wednesday though most of Thursday night, with high pressure moving across northern New England.

The forecast for next Friday is uncertain. A low pressure near James Bay could swing its associated fronts across our region Friday into Friday Night. Have a mention in the forecast for more showers some time Friday. However, this timing could be delayed with later forecasts.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

18z TAF Update:

Through 00z Saturday: High confidence.

VFR. Westerly wind gusts 25-30 kt continue through sundown (22-23z).

Tonight through Saturday Night: High confidence.

VFR. NW winds around 5-10 kt, becoming light N to NE by late- afternoon, then turning easterly Saturday night into overnight Sunday.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Saturday Night through Wednesday/...

Sunday: VFR. Chance RA.

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

Columbus Day: Mainly VFR, with local IFR possible. Breezy.

Monday Night: VFR.

Tuesday through Tuesday Night: VFR. Breezy. Chance SHRA.

Wednesday: VFR. Breezy. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Through Saturday Night: High confidence.

SCAs remain in effect until 7 PM this evening to allow westerly gusts 25-30 kt to subside. Thereafter, gradually easing NW winds around 15-20 kt early tonight continue to decrease to around 10-15 kt by Saturday. Light northeasterly winds late Saturday into Saturday night. Seas 3 ft or less all waters.

Outlook /Saturday Night through Wednesday/...

Sunday: Winds less than 25 kt. Chance of rain.

Sunday Night: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Local rough seas. Rain, slight chance of thunderstorms.

Columbus Day: Winds less than 25 kt. Rough seas up to 9 ft. Chance of rain.

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

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

Tuesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Rain showers likely, slight chance of thunderstorms.

Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 7 PM EDT this evening for ANZ230>237-250-251-254>256.