textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Beautiful and refreshing fall weather continues into Sunday, though clouds increase during the afternoon. Showers arrive late Sunday afternoon/evening and become widespread Sunday night, potentially lingering into the Monday morning commute.

- Sharp temperature drop expected for the start of the week, then a return to dry, fall-like conditions with seasonable temperatures.

DISCUSSION

KEY MESSAGE 1...Beautiful and refreshing fall weather continues into Sunday, though clouds increase during the afternoon. Showers arrive late Sunday afternoon/evening and become widespread Sunday night, potentially lingering into the Monday morning commute.

WOW. B-E-A-U-tiful conditions this afternoon! A true fall airmass has settled over southern New England, and what a notable difference from the lower 80s and dewpoints in the 60s yesterday afternoon. Refreshing! 925mb temperatures have settled around +10C, resulting in highs in the 60s this afternoon along with dewpoints in the 40s. For tonight, high pressure remains in control with mainly clear skies. Winds do not fully decouple, though still expect some radiational cooling with lows dipping well into the 40s. Not out of the question for a few upper 30s across the Berkshires.

High pressure transits northern New England on Sunday, leading to another quiet start to the day. Clouds will thicken from southwest to northeast by early afternoon ahead of a weak surface low developing off the Mid-Atlantic coast. Temperatures aloft are a touch cooler, with 925mb temperatures around +8C. Thus, expect highs a few degrees cooler than this afternoon, generally in the lower 60s, with more clouds than sun during the afternoon. Sunday is not a washout. Based on the 12z suite of CAMs, showers could arrive as early as 3-5 PM, especially across western and southern portions of the region. However, the better chance for more widespread rainfall comes after 7 PM and continues through the overnight into early Monday morning.

Highest confidence in appreciable rainfall is across areas closest to the south coast, Cape Cod and Islands. Heavy rainfall is unlikely, as most convective elements should remain well south of Nantucket overnight Sunday into Monday morning. That being said, cannot rule out embedded thunder with showers south of Nantucket. The HREF does pick up on this potential, though probabilities remain low at less than 20 percent. How much rainfall? Generally a few hundredths to around a tenth of an inch for many, with totals of one to two tenths favored south of Route 44. Amounts could approach a quarter of an inch across Nantucket.

Rain should begin wrapping up during the Monday morning hours, though timing could result in a wet ride to school and work for at least portions of southern New England. Otherwise, no significant wind concerns with this system as easterly winds develop while the weak low passes nearby Sunday night.

KEY MESSAGE 2...Sharp temperature drop expected for the start of the week, then a return to dry, fall-like conditions with seasonable temperatures.

A deep Canadian low to our north tracks eastward heading into the start of next week with strong high pressure tracking just behind it, building in over the start of the week. Associated with this deep low, much cooler air is injected in across New England. 12z guidance continued to flirt with the possibility of bringing the 540dam line closer to southern New England, but at this time, it generally remains across Maine and New Hampshire with the latest run. 925 mb temperatures early Tuesday morning/late Monday night may sink to around 0C, then only climb to around 5C in the afternoon hours Tuesday into Tuesday night. This profile will be more supportive of highs barely making it to 60F and lows dipping into the 30s, especially Tuesday night with this cold air and diminishing winds.

The low continues eastward and the flow aloft then shifts more SW behind it, extending through the lower levels as well. High pressure at the surface exits towards Thursday with another high just behind it building in towards the Great Lakes. With the return of SW flow and drier conditions, more seasonable temperatures take hold for the back half of the week; 925 mb temperatures climb back to around 10C, supporting highs generally in the 60s, approaching 70F towards Thursday and Friday.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

00z TAF Update...

Tonight...High confidence.

VFR. Winds generally E to ENE and diminishing overnight tonight.

Sunday and Sunday Night...High confidence in trends, moderate confidence in timing of showers.

VFR through much of Sunday with increasing mid-level clouds. Ceilings lower to MVFR from SW to NE between 20z-00z. Showers become more widespread Sunday evening and overnight, reducing visibilities to 3-5SM at times. Ceilings lower to MVFR/IFR overnight into early Monday morning.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Monday through Thursday/...

Monday through Tuesday: VFR. Breezy.

Tuesday Night: VFR.

Wednesday: VFR. Breezy.

Wednesday Night through Thursday: VFR.

MARINE

Forecaster Confidence Levels...

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

This Afternoon through Sunday Night...High confidence.

Quiet conditions for the rest of Saturday and the first half of Sunday. High pressure located near the Great Lakes tracks east- northeast across northern New England Sunday as weak low pressure develops near the Mid-Atlantic coast Sunday afternoon, then tracks northeast toward southern New England Sunday night.

Seas are generally 2-4 feet through much of Sunday, though build to 5+ feet across the outer waters Sunday night. East to northeast winds are generally 10-15 knots, with gusts increasing to 20-25 knots Sunday night. There is the potential need for a Small Craft Advisory Sunday night into early Monday morning. As conditions remain marginal, held off on issuance for now, though an advisory will be considered in upcoming forecasts.

Outlook /Monday through Thursday/...

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

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

Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft.

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

Wednesday through Thursday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

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