textproduct: Boston / Norton

WHAT HAS CHANGED

Tweaked timing of Small Craft Advisories for all waters today. This included adding one for Narraganset Bay.

KEY MESSAGES

- Cooler with westerly breezes this weekend. Risk of scattered afternoon showers and possible thunderstorms through sundown each day. However, the risk for severe weather is very low.

- Periods of heavy rain possible Monday into early Tuesday. Drier air with seasonable temperatures expected midweek.

DISCUSSION

KEY MESSAGE 1...Cooler with westerly breezes this weekend. Risk of scattered afternoon showers and possible thunderstorms through sundown each day. However, the risk for severe weather is very low.

Cyclonic mid-level flow governs our weather across southern New England this weekend. In that broader cyclonic flow aloft, a series of mid level shortwaves will pass by at times. While not particularly strong, these shortwaves are expected to be potent enough to result in scattered diurnal showers each afternoon. Not everyone will see these showers, with the greatest focus across northern and eastern MA. There will be plenty of dry hours for most locations this weekend.

Most unstable CAPE values are projected between 500-750 J/kg today,and between 750-1,000 J/kg Sunday. These values suggest a few thunderstorms are possible, but with not as much effective bulk shear, severe weather is not likely.

Gusty west winds expected to continue through today with peak gust speeds up to 40 MPH. All thing considered, not much different from yesterday. Winds subside with sunset, and should not be as gusty Sunday.

KEY MESSAGE 2...Periods of heavy rain possible Monday into early Tuesday. Drier air with seasonable temperatures expected midweek.

Latest guidance suite has narrowed some of the differences between them. Have increased confidence in rainfall developing Monday, falling most of Monday night, then drying out Tuesday. This could be a substantial rainfall, with the probability of 1 inch or more of storm total rainfall between 70-80 percent across southern New England. Even the probability for 2+ inches of rainfall were about 20-40 percent, greatest across western MA and CT.

Behind this system, high pressure and northwest flow will bring rapidly drying conditions during the day Tuesday. Temperatures are then expected to be pleasant midweek with seasonable highs in the upper 70s to lower 80s. Only isolated rain chances expected for Thursday as a low pressure approaches from the west. A greater risk for showers is anticipated Friday.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

Today: High confidence.

VFR. Some risk for diurnal SHRA with brief MVFR-VFR visibilities after 17Z, mainly from PSF-CEF-TAN-FMH north and east through sundown and indicated with PROB30s. Confidence is highest for these showers for the easternmost terminals with lower confidence across the western terminals. Not impossible for a few TSRA also. WNW winds again gusting 25-28 kt by mid-morning, then easing towards sundown.

Tonight: High confidence.

VFR, any showers diminish post-sundown. WNW winds decrease to 5-10 kt.

Sunday...High confidence.

VFR. Relatively light west winds could lead to afternoon seabreezes. Another risk for afternoon showers and TSRA.

KBOS Terminal...High confidence in shower activity and moderate confidence in the exact timing. Westerly gusts 25-30 kt continue through sundown. KBDL Terminal...High confidence in TAF. Some diurnal showers are possible, but there is lower confidence on how far west they may reach. So, excluded these showers from the TAF.

Outlook /Sunday Night through Wednesday/...

Sunday Night: VFR.

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

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

Tuesday: VFR. Breezy. Slight chance SHRA.

Tuesday Night through Wednesday: VFR.

MARINE

Forecaster Confidence Levels...

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

Small Craft Advisories remain in effect for MA and RI coastal waters today. Could see a few gale force gusts as well, but not thinking it will be prevalent enough to warrant an upgrade to Gale Warnings. Risk for scattered showers and isolated thunderstorms this afternoon, and again Sunday afternoon. Any showers and thunderstorms should diminish after sunset.

Winds and seas should trend below SCA criteria Slate this afternoon into this evening.

Outlook /Sunday Night through Wednesday/...

Sunday Night: Winds less than 25 kt.

Monday: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Chance of rain showers.

Monday Night: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Areas of rough seas. Rain showers, chance of thunderstorms.

Tuesday: Winds less than 25 kt. Areas of rough seas. Chance of rain showers, slight chance of thunderstorms.

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

Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 7 PM EDT this evening for ANZ230- 232>235-237. Small Craft Advisory until 4 PM EDT this afternoon for ANZ231- 250-251. Small Craft Advisory until 4 PM EDT this afternoon for ANZ236. Small Craft Advisory until 1 AM EDT Sunday for ANZ254-256. Small Craft Advisory until 4 AM EDT Sunday for ANZ255.