textproduct: Boston / Norton

WHAT HAS CHANGED

The heaviest rainfall has come to an end, with remaining showers tapering off from west to east through early this evening. Additional significant rainfall is not expected, though localized nuisance flooding may linger given the 2 to 4 inches of rain that fell across portions of Rhode Island and southeast Massachusetts today. Lastly, Small Craft Advisories issued for most waters starting Monday afternoon through Monday night for gusty winds.

KEY MESSAGES

- Heaviest rainfall ending, drier overnight, though low clouds and areas of fog are possible. A stray early morning shower remains possible too.

- Dry and fall-like Monday into Tuesday, with a chilly start Tuesday morning.

- High pressure in control next week brings generally quiet weather. Brief bout of summer warmth and humidity expected Wed- Fri.

DISCUSSION

KEY MESSAGE 1...Heaviest rainfall ending, drier overnight, though low clouds and areas of fog are possible. A stray early morning shower remains possible too.

The back edge of the heaviest rain is now working from west to east across southern New England, with clouds thinning across eastern New York and approaching western Massachusetts. Rainfall totals have been impressive today, with many areas seeing 2 to 4 inches, mainly across Rhode Island and southeast Massachusetts. The Flash Flood Watch remains in effect through 6 PM. While the heaviest rain is over, light to moderate showers linger and could still lead to nuisance flooding. Expect these showers to continue for the next couple of hours before wrapping up between 4 PM and 6 PM, though a few may linger an additional hour or so across the outer Cape.

Drier conditions arrive overnight, though low clouds and areas of fog may persist into early Monday morning. A final push of showers is possible toward daybreak, though guidance has generally shown this activity weakening as it approaches southern New England, leaving just a spotty shower or two, mainly in the 4 AM to 8 AM time frame. It is worth mentioning that some of the high-resolution guidance indicates a bit of a resurgence in shower activity as it approaches the coast, possibly picking up on some instability near the shore. Nevertheless, this would not lead to impactful weather and would be nothing like what we saw today.

KEY MESSAGE 2...Dry and fall-like Monday into Tuesday, with a chilly start Tuesday morning.

Surface high pressure around 1020-1025 mb builds in from the Great Lakes region on Monday, settles overhead Monday night, and remains with us through Tuesday as a 1030 mb surface high. Little weather to talk about during this time frame. While there is lingering moisture early Monday morning, with some areas of fog, a much drier airmass arrives by noon as PWATs fall below half an inch.

CAA during the day allows for a period of breezy northwest winds. Forecast soundings through BUFKIT show a well-mixed boundary layer upwards of 850 mb, which should allow most of the wind aloft to mix to the surface. Winds aloft are 25 to 30 kt, resulting in surface wind gusts of roughly 20 to 30 mph from the north-northwest. Highs Monday afternoon are largely in the lower to middle 70s.

With high pressure overhead Monday night, winds decouple, allowing for effective radiational cooling. Have opt'd to do a model blend to show the coldest of the guidance. This would mean many of us wake up Tuesday morning in the 40s; however, would not be shocked if towns in far northwestern Franklin County dip to 38 to 40 degrees. That being said, urban centers remain in the upper 40s to lower 50s. Boston may retain enough heat due to the urban heat island effect to maintain lows in the middle 50s. Lastly, there could be areas of ground fog due to the abundant recent rainfall.

Heading into Tuesday, a crisp and dry day with dew points in the 50s, with some upper 40s possible in northern Massachusetts. Meanwhile, 925 mb temperatures settle around +9C to +12C, which would suggest high temperatures in the middle 60s to lower 70s. High pressure slowly drifts east during the day, with winds shifting to a north-northeasterly direction.

KEY MESSAGE 3...High pressure in control next week brings generally quiet weather. Brief bout of summer warmth and humidity expected Wed- Fri.

High pressure firmly in control by Tuesday will bring much drier weather with it. Under dry NW flow dewpoints will be very comfortable to start the week, in the 40s. This will be a comfortable taste of Fall Tuesday when combined with high temperatures in the upper 60s (coasts) to low 70s (inland). As the high shifts over the Atlantic Wednesday flow turns southerly bringing the return of more summer- like temperatures and dewpoints in the upper 70s and mid 60s respectively. Still some uncertainty with regard to the forecast for late week and next weekend. Zonal mid level flow continues with potential for a low to cross somewhere in the vicinity of southern New England; whether that stays to our north or goes overhead is uncertain, but generally looking at a better shot of unsettled weather late Thursday onward.

AVIATION /00Z MONDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

00z TAF Update: Widespread rain ending from west to east this afternoon.

Through 00z...Moderate confidence in trends and timing.

While much of the night will be dry, a decaying line of showers pushes through southern New England from 06z-10z. Ceilings are generally LIFR to IFR, with some improvement overnight to high- end IFR, if not MVFR. A drier airmass arrives predawn, which will erode cloud cover and allow conditions to trend VFR between 10- 14z Monday.

Monday and Monday Night...High confidence.

VFR. NW to NNW winds 8 to 12 kt with gusts 20 to 25 kt. Winds ease overnight, becoming light and variable under clear skies. Isolated areas of ground fog are possible due to abundant recent rainfall.

Tuesday...High confidence.

VFR. Light N to NNE winds, becoming E/SE by the end of the day.

KBOS Terminal...Moderate confidence in TAF.

KBDL Terminal...Moderate confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday: VFR. Breezy.

Tuesday Night through Wednesday Night: VFR.

Thursday: Mainly VFR, with local MVFR possible. Slight chance SHRA.

Thursday Night: Mainly VFR, with local MVFR possible. Chance SHRA.

Friday: VFR.

MARINE

Forecaster Confidence Levels...

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

Through Tuesday...High confidence.

Surface low pressure moves northeast from the southern coastal waters Sunday afternoon, crossing into the Gulf of Maine overnight before reaching Nova Scotia Monday morning. Meanwhile, high pressure builds in from the Great Lakes region on Monday, resulting in a tightening pressure gradient and gusty northerly winds Monday afternoon through the overnight hours. There may be a brief period of gusts around 25 kt, thus a marginal Small Craft Advisory has been issued. Seas during this time are 2 to 3 ft across the nearshore waters and 3 to 4 ft across the outer waters. However, the outermost portions of the forecast zones may approach 5 ft.

Outlook /Tuesday through Friday/...

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

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

Thursday: Winds less than 25 kt.

Thursday Night: Winds less than 25 kt. Chance of rain showers.

Friday: Winds less than 25 kt. Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 11 AM Monday to 2 AM EDT Tuesday for ANZ231>235-237-250-254>256.