textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Scattered thunderstorms, some of which could be severe late Thursday, with a few hit and miss thunderstorms possible again Friday afternoon.

- Mainly dry and seasonable weather follows for this weekend with comfortable humidity.

- A period or two of unsettled weather may return early next week with a backdoor cold front in the vicinity of southern New England. Large spread/high uncertainty on temps dependent on backdoor cold front/s location.

DISCUSSION

KEY MESSAGE 1...Scattered thunderstorms, some of which could be severe late Thursday, with a few hit and miss thunderstorms possible again Friday afternoon.

A decent set-up for some strong to severe storms on Thursday, albeit better to our west where the better forcing is more likely to overlap the favorable dynamics. Even so, especially for western MA/CT, particularly along and west of the Connecticut river valley, some severe storms are certainly possible in the Thursday afternoon to midnight time frame. This comes courtesy of a marginally deep upper trough that becomes slightly negatively tilted as it digs into the northeast. The trough axis remains west of SNE on Thursday into Friday placing us beneath moist SW flow advecting in PWATS of 1.5-2" and dewpoints in the upper 60s. This moist flow in the warm sector will lead to potential for localized downpours some of which, could cause localized flooding. There is a marginal risk (level 1 of 4) for flash flooding in western/central MA and CT. This is in addition to the marginal severe risk (level 1 of 5) thanks to the 1000-2000 J/kg CAPE and 0-6km bulk shear. As previously mentioned, the slower frontal passage means the better forcing will be to our west, so the best chance of damaging storms is west of the CT river valley. The greatest threat is from straight line winds and hail, but 0-1km SRH values 150-200m2s2 mean a tornado can't be ruled out. By Friday the front moves through and some scattered afternoon thunderstorms are possible before a much drier airmass drops in.

KEY MESSAGE 2...Mainly dry and seasonable weather follows for this weekend with comfortable humidity.

High pressure builds in behind the departing shortwave/cold front for this weekend. The result will be mainly dry and seasonable weather Sat into Sun with comfortable humidity. High temps will mainly be in the upper 70s and 80s with lows in the 50s to the lower 60s.

KEY MESSAGE 3...A period or two of unsettled weather may return early next week with a backdoor cold front in the vicinity of southern New England. Large spread/high uncertainty on temps dependent on backdoor cold front/s location.

Quite a tricky forecast for the first half of next week with a backdoor cold front in the vicinity. If we end up on the northern side of the front...it will be cool with highs in the upper 60s and 70s. If we end up south of the backdoor cold front...highs may reach 85-90+. Given the uncertainty we blended the guidance. Current thinking is we may be on the warmer side Mon and then cooler Tue. It does seem a decent shot the backdoor cold front temporarily drops south into at least part of our region on Tue. But again...high uncertainty on temperatures in the Mon through Wed time frame.

There also will be the risk for some showers at times in the Mon through Wed time frame. While we are not expecting a complete washout...thinking a round or two scattered showers and perhaps a few thunderstorms is reasonable. Timing though remains quite uncertain at this point.

AVIATION /00Z THURSDAY THROUGH MONDAY/

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 outside some very localized brief patchy ground fog possible late tonight in the typically most prone locations.

Thursday and Thursday night...High confidence in TAF but low confidence in areal coverage and eastward extent on the potential of scattered showers and isolated t-storms.

High confidence in mainly VFR conditions into early Thursday evening outside any scattered showers/isolated t-storms that develop. MVFR to localized IFR conditions will gradually overspread portions of the region from west to east later Thu night.

As for the scattered showers/isolated thunderstorm risk...uncertain on how far east activity advances into our region. The main risk will be in the 20z to 03z time frame generally across interior MA/CT with the greatest risk west of the CT River Valley. Eastward extent of convective potential remains highly uncertain.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF. We will need to watch for a few thunderstorms in the vicinity of the terminal later Thu into Thu night.

Outlook /Friday through Monday/...

Friday: VFR. Chance SHRA, slight chance TSRA.

Friday Night: VFR. Breezy.

Saturday through Saturday Night: VFR.

Sunday: VFR. Breezy.

Sunday Night: VFR. Slight chance SHRA.

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

MARINE

Forecaster Confidence Levels...

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

Through Thursday night...High confidence.

Fairly quiet boating conditions with high pressure over the waters. Light NW to W winds to start with local seabreezes towards the coast late this morning and afternoon. Winds become more S to SW tonight, the increase Thursday. By Thursday evening, rain and thunderstorm chances increase from east to west through midnight.

Outlook /Thursday Night through Monday/...

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

Friday Night through Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft.

Saturday Night through Sunday: Winds less than 25 kt.

Sunday Night: Winds less than 25 kt. Slight chance of rain showers, slight chance of thunderstorms.

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

BOX WATCHES/WARNINGS/ADVISORIES

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