textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes have been made to the forecast.

KEY MESSAGES

- A few brief spot showers possible across northern MA into mid- evening. Otherwise...dry and pleasant through Fri night outside of the wildfire smoke this evening. Lows mainly in the 50s to the lower 60s. Highs Fri mainly in the lower to middle 80s.

- Chances for beneficial showers and thunderstorms on the uptake for Saturday PM into the overnight period.

- A cooler start to the work week with unsettled conditions through the middle of next week.

DISCUSSION

KEY MESSAGE 1...A few brief spot showers possible across northern MA into mid-evening. Otherwise...dry and pleasant through Fri night outside of the wildfire smoke this evening. Lows mainly in the 50s to the lower 60s. Highs Fri mainly in the lower to middle 80s.

A cold front will cross the region this evening. However...the lack of low level moisture coupled with the main shortwave forcing passing to our north will keep most of us dry. A few brief spot showers may survive into northern MA and perhaps the remote risk for a rumble of thunder in far northeast MA. Otherwise...generally a dry/very pleasant weather through Friday night. We will have to deal with some more smoke moving into the region through late afternoon...But the worst of it will likely stay to our southwest. And the good news is that it will get shoved into the mid-Atlantic after midnight and will not be an issue for Fri.

High pressure builds across the region on Friday behind tonight/s cold frontal passage. This high pressure system will shift east of us Friday night...But we will maintain dry/pleasant weather. Highs on Friday will mainly be in the lower to middle 80s with plenty of sunshine and comfortable humidity. Lows tonight and Friday night will mainly be in the 50s to the lower 60s with middle 60s in the urban heat island of Boston.

KEY MESSAGE 2...Chances for beneficial showers and thunderstorms on the uptake for Saturday PM into the overnight period.

Chances for showers and thunderstorms begin to increase heading into the weekend as a surface low approaches Saturday, bringing prolonged southwesterly flow and surging PWATs. Latest guidance suite has increased confidence in PWATs over 2.0", with some as high as 3.0", which lends favor to some heavy downpours developing overnight. ECMWF and CMC ensembles indicate a 60-80% chance of at least 0.5" of QPF (mostly across the southern coastal areas and up into central CT and RI), while the GFS ensemble is trending those higher percentiles off our southern shores and further north into northern New England. Southern New England is currently in a Marginal (1/4) risk for flash flooding, but discussion has started with neighboring offices (and will continue with the next forecast cycle) on potentially increasing that risk to a Sight (2/4), particularly across the southern coastal areas of CT and RI given the relatively high consensus in the model guidance that some heavier bands could develop across those areas.

Instability profiles continue to look relatively weak, but CSU Machine Learning probabilities continue to indicate low (5-15%) chances that some storms could turn severe.

KEY MESSAGE 3...A cooler start to the work week with unsettled conditions through the middle of next week.

A cooler airmass moves in Sunday once the cold front pushes offshore, with temperatures making a return to seasonable norms... in the low to mid 80s through at least the middle of next week. A brief spell of drier conditions is possible Monday as high pressure builds somewhere over the Appalachian region. Chances for showers then increase again for the middle of next week as a surface low moves east across Ontario and a trailing cold front sweeps through the mid-Atlantic region into New England.

AVIATION /19Z THURSDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

18z TAF Update...

Tonight through Friday night...High confidence.

VFR through Friday night except for areas of smoke this evening and perhaps a few brief spot showers across northern MA. We will be on the northeast edge of the smoke...so not sure visibility will be reduced that much but may see a period of MVFR vsbys with the greatest risk of reductions southwest of a KBDL to KPVD line. This smoke should be shoved into the mid-Atlantic after midnight into Fri behind this evening/s cold front.

W wind gusts 25+ knots diminish this evening. NW winds 10 knots or less overnight into Friday morning before they shift to the SW by mid-late Friday afternoon. A few hours of sea breeze conditions are also possible Friday afternoon along portions of the immediate coast.

KBOS Terminal...High confidence in TAF. Main risk of MVFR vsbys in smoke will be southwest of the terminal this evening...But can not rule out the low risk for it briefly occurring at KBOS.

KBDL Terminal...High confidence in TAF. We may see some MVFR vsbys flirt with the terminal this evening before pushing southwest.

Outlook /Saturday through Tuesday/...

Saturday: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA, chance TSRA.

Saturday Night: MVFR/IFR conditions possible. Windy with local gusts up to 30 kt. SHRA, slight chance TSRA.

Sunday: VFR. Breezy.

Sunday Night through Monday Night: VFR.

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

MARINE

Forecaster Confidence Levels...

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

Tonight through Friday night...High confidence.

Gusty near shore small craft W wind gusts will diminish this evening and shift to the NW behind the cold front. Otherwise...high pressure builds in from the west behind this evening/s cold front keeping winds/seas below small craft advisory thresholds.

Outlook /Saturday through Tuesday/...

Saturday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Seas locally approaching 5 ft. Chance of rain showers.

Saturday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft. Rain showers, slight chance of thunderstorms.

Sunday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas.

Sunday Night: Winds less than 25 kt. Areas of rough seas.

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

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

Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Chance of rain showers, slight chance of thunderstorms.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Air Quality Alert until midnight EDT tonight for CTZ002>004. MA...Air Quality Alert until midnight EDT tonight for MAZ002>024- 026. RI...Air Quality Alert until midnight EDT tonight for RIZ001>008. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ230>237-250-251-254>256.