textproduct: Boston / Norton

WHAT HAS CHANGED

Increase in confidence regarding the overall severe weather risk Friday.

KEY MESSAGES

- Dry weather for much of today before the risk for scattered showers and a few thunderstorms returns tonight into Friday.

- Showers Saturday followed by a warming and drying trend that carries into next week.

DISCUSSION

KEY MESSAGE 1...Dry weather for much of today before the risk for scattered showers and a few thunderstorms returns tonight into Friday.

High pressure continues to dominate for much of the day today, continuing the drier weather we saw yesterday. Highs will reach once more into the 80s and upper 70s.

The pattern changes as we head into tonight and Friday. A warm front associated with a surface low whose center will track through southern Ontario into Quebec will cross over the region. With it, a line of showers with some embedded thunder will be likely, progressing over the region from west to east. With regards to thunder and the risk for severe storms, that risk is quite low due to the lack of instability present overnight as indicated by the latest CAMs. Some embedded rumbles of thunder over western MA aren't out of the question, though. The main concern for any storms turning severe is towards Friday afternoon/evening.

As the warm front moves through, winds shift more southerly and dewpoints climb into the mid to upper 60s. Compared to Thursday, it may feel slightly more humid as a result. Previous model runs have not been in much agreement regarding the development of instability over the region, though they have been supportive of good jet dynamics with >40 kt of effective bulk shear. However, with the latest runs, more of a consensus has been reached with increased instability in the afternoon. A number of CAMs are favoring around 1000 J/kg of MUCAPE with areas of 1500 J/kg of MUCAPE in western MA and CT. MLCAPE values in these models are not far behind them, and effective bulk shear ranges between 40-50 kt. All of this combined with the forcing that will come with the aforementioned low's cold front could aid in the development of isolated to scattered severe storms. It is worth noting that southern New England is also under a Marginal (1/5) risk for severe weather Friday. Continue to check back for updates regarding this risk.

KEY MESSAGE 2...Showers Saturday followed by a warming and drying trend that carries into next week.

Another wave of low pressure is expected to track to our south Saturday. Some showers associated with this wave are more likely to scrape along the south coast into the Cape and Islands, but they are not expected to be very significant at this time. Aside from these showers, dry weather is expected to return heading into the start of next week as high pressure associated with an amplified upper level ridge moves into southern New England. A warming trend also kicks off for the start of the work week, continuing into midweek. However, details on just how warm it may get are still uncertain at this time. The outlook for hazardous temperatures next week keep the elevated risks to our SW, but we will see how this evolves as we get closer in time.

AVIATION /07Z THURSDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

06Z TAF Update...

Through this afternoon...High confidence.

VFR with southwesterly winds 10 kts, or less. There is a potential for a localized sea breeze to develop across portions of the immediate coast this afternoon.

Tonight...Moderate confidence.

Chances for showers and thunderstorms after 00z tonight increase from W to E. The greatest risk for isolated thunderstorms remains in western MA between 06z-12z. Included a PROB30 for BDL to account for this risk. VFR ceilings steadily drop to MVFR and even IFR heading into Friday morning. Fog along the south coast and into SE MA is also likely overnight.

Friday...Moderate confidence.

Showers expected in the morning hours, then the risk for isolated thunderstorms picks back up in the afternoon. However, coverage of possible storms for the afternoon period is still uncertain. Generally lower-end VFR through much of the day expected with areas of MVFR not out of the question.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Friday Night through Monday/...

Friday Night: VFR. Slight chance SHRA.

Saturday: VFR. Chance SHRA.

Saturday Night through Monday: VFR.

MARINE

Forecaster Confidence Levels...

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

Through Friday...High confidence.

Expect winds to remain generally light through this afternoon, before becoming a little breezy (gusts possible up to 20 kt) Friday afternoon. SSW winds also shift more S-ly tonight into Friday. Seas should remain 2 to 4 ft. Showers and thunderstorms may start to impact the waters Thursday night into Friday.

Outlook /Friday Night through Monday/...

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

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

Sunday through Monday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

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