textproduct: Boston / Norton

WHAT HAS CHANGED

Small Craft Advisories have been issued for Monday night through Tuesday. Higher chances for Rips Currents Monday and Tuesday, but forecast conditions will need to be monitored.

KEY MESSAGES

- Seasonable temperatures and pleasant weather linger through the weekend.

- Rain chances return late Sunday into Monday, followed by quieter weather through late-week. Unsettled weather returns late-week.

DISCUSSION

KEY MESSAGE 1...Seasonable temperatures and pleasant weather linger through the weekend.

Fair weather cumulus today provides some pockets of shade today as temperatures peak in the upper 70s to low 80s, seasonable for late summer in southern New England. Seabreezes will keep the coastline slightly cooler before kicking out around sunset. There remains a low chance for isolated showers, mainly across eastern and southeastern MA, late this afternoon as a shortwave moves through the region. If any showers do form, they are likely to be brief with light rain as opposed to heavier downpours.

Much like last night, skies will clear and winds will calm, allowing for good radiational cooling and chances for valley fog to develop. Temperatures tonight likely bottom out in the low to mid 50s, near 60 for urban areas.

KEY MESSAGE 2...Rain chances return late Sunday into Monday, followed by quieter weather through late-week. Unsettled weather returns late-week.

A mid-level shortwave trough moves through the flow late Sunday into Monday with a surface low developing and tracking offshore. This will support our next shot at rainfall. Most of Sunday is likely to stay dry with most model guidance showing arrival of showers Sunday night-early Monday AM. Batches of rain continue through the day Monday. There is still uncertainty in the details of this system, mainly with respect to the development/track of a surface low pressure tracking near southern New England and how it interacts with the low pressure tracking across New England. This will lead to lower confidence in expected rain amounts with this system. A stronger, closer positioned surface low to southern New England would provide more forcing for more moderate to heavy rainfall. With PWATs 1.5-1.8" and marginal instability, embedded showers/storms with heavier rain rates are supported, especially where there will be that additional forcing with the surface low. In terms of flash flooding potential, mid-level winds will be strong enough to keep any heavier showers or storms moving reducing widespread flash flood threat. At this point, given the potential for some heavier showers, can't rule out isolated instances of flash flood impacts in poor drainage/urban areas. This will become more clear as we get a better idea on the finer details of the system. The WPC ERO as a Marginal Risk (Level 1 of 4) which aligns well with the potential for localized heavier downpours. For total amounts, ensemble guidance shows a range of 0.25" to 0.60" across southern New England though locally heavier amounts possible, especially beneath any downpours. Ensemble probabilities for greater than 1.0" are lower (< 30%), but do show the lower end potential for higher amounts if the surface low were to track closer to the south coast of southern New England.

A cold front moves through the region by Tuesday with a drier airmass advecting into southern New England behind it. Conditions remain generally dry Tuesday and Wednesday with zonal flow aloft. Temperatures will likely be in seasonable ranges in the upper 70s to low 80s. Ensemble guidance signals at transition to a more unsettled weather pattern Wednesday night into late-week with chances for rain returning to the forecast.

AVIATION /19Z SATURDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

18z TAF Update...

Today...High confidence.

VFR. NW winds 5 to 10 kt. Sea breeze kicks out around sunset.

Tonight...High confidence.

VFR outside some touch of very localized ground fog possible near daybreak in typically most prone low-lying locations. Calm- light NW winds.

Sunday...High confidence.

VFR. S-SW winds 7-12 kt...except for a period of localized sea breezes on the very immediate eastern MA coast.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Monday through Thursday/...

Monday: MVFR/IFR conditions possible. Breezy. SHRA likely, slight chance TSRA.

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

Tuesday through Wednesday: VFR.

Wednesday Night: VFR. Chance SHRA, slight chance TSRA.

Thursday: VFR. Chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Through Sunday Night...High confidence.

High pressure dominates through the weekend before a low pressure system pushes through Sunday night into Monday. Generally light north winds today turn southerly Sunday and become breezy 15 to 20 kts Sunday night. Relatively calm seas through the weekend under the high pressure, but will begin to build to 5-8 ft by early Monday morning as the low approaches. Small Craft Advisories have been issued for Monday night through Tuesday.

Chances for rip currents increase Monday for south facing beaches and Tuesday for eastern facing beaches as rougher seas and long-period swells settle in with the passage of the low.

Outlook /Monday through Thursday/...

Monday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Rain showers likely, slight chance of thunderstorms.

Monday Night: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers.

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

Tuesday Night through Wednesday: Winds less than 25 kt.

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

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 8 AM to 11 PM EDT Monday for ANZ231- 232-250-251-254. Small Craft Advisory from 2 AM Monday to 2 AM EDT Tuesday for ANZ233>235-237-255-256.