textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Scattered thunderstorms, some of which could be severe late today. 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 temperatures, dependent on the location of this front.

DISCUSSION

KEY MESSAGE 1...Scattered thunderstorms, some of which could be severe late today. A few hit-and-miss thunderstorms possible again Friday afternoon.

Still looking at a decent setup for a few strong to severe storms across southern New England today. Modest most unstable CAPE values projected between 1,000-1,500 J/kg combined with 0-1 km storm relative helicity of 50-100 m2/s2 support this idea. The primary limitation today will be the timing of it all. In other words, can the peak helicity and instability arrive in southern New England around the same time. Still thinking the greatest threat from thunderstorms remains mainly to our west, and perhaps as far east as the CT River valley. It appears that the peak helicity should arrive after instability starts to wane with sunset. This situation bears monitoring, albeit a level 1 of 5 threat. Mostly concerned about damaging straight-line winds and perhaps some hail. The potential helicity does not completely rule out the risk for a tornado either.

There is also a level 1 of 4 risk for localized flash flooding, again mainly west of the CT River.

A cold front should finally reach southern New England late tonight into Friday morning. Until this front completely moves offshore some time Friday night, still looking at a risk for showers and possible thunderstorms. Given the much different time of day, not expecting severe weather for Friday.

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

High pressure builds into our region for this weekend. The result will be mainly dry and seasonable weather with comfortable humidity.

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 temperatures, dependent on the location of this front.

Still a highly uncertain forecast for early next week. The key synoptic feature will be the location of a backdoor cold front. A slower timing of this front would lead to higher temperatures across eastern MA Monday. This front still appears to be stuck somewhere across eastern MA Tuesday into Wednesday, which should direct a low pressure moving southeast from Canada right across our region. While not raining this entire time, a prolonged period where showers and thunderstorms are possible is expected from Monday into Wednesday.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

Today and Tonight...High confidence in TAF trends. Low confidence in areal coverage and eastward extent of scattered showers and isolated t-storms.

High confidence in mainly VFR conditions into early evening, outside of any scattered showers/isolated t-storms that develop. MVFR to localized IFR conditions will gradually overspread portions of the region from south to north later tonight as more humid air arrives from over the colder ocean.

As for the scattered showers/isolated thunderstorm risk, still 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.

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 today into tonight.

Friday...Moderate confidence.

Another risk for showers and a few thunderstorms until a cold front finally moves east of our region. MVFR with areas of IFR to start, improving to VFR toward mid morning. MVFR possible in afternoon showers and t-storms.

Outlook /Friday Night through Monday/...

Friday Night through Saturday Night: VFR.

Sunday: VFR. Breezy.

Sunday Night through Monday: VFR. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Through Friday...High confidence.

Winds become more S to SW late tonight, then increase late this morning into this evening. Shower and thunderstorm chances increase tonight, mainly around the Cape and islands after midnight. Another round for afternoon showers and thunderstorms possible nearshore Friday.

Outlook /Friday Night through Monday/...

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

BOX WATCHES/WARNINGS/ADVISORIES

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