textproduct: Boston / Norton

WHAT HAS CHANGED

Introduced a slight chance of showers/t-storms this afternoon though most will stay dry.

KEY MESSAGES

- Mostly dry Saturday with a mix of clouds and sun, but there remains a chance for some widely scattered showers or t-storms.

- A cold front brings the return of heavy rain and gusty winds Sunday night and Monday, perhaps lingering into Tuesday.

- Periodic rain chances will be with us for much of next week.

DISCUSSION

KEY MESSAGE 1...Mostly dry Saturday with a mix of clouds and sun, but there remains a chance for some widely scattered showers or t- storms.

A warmer airmass remains overhead thanks to brief mid level ridging. This will continue to deliver highs in the mid to upper 80s Saturday and Sunday. The ridge axis crosses SNE this morning then begins to break down slowly over the next 24-36 hours. For this reason, despite the surface high pressure nearby, introduced a slight chance of rain showers or a thunderstorm this afternoon, mainly over the interior. That being said, the forecast for a mostly dry day persists, with just some widely scattered showers or thunderstorms given a few 1000 J/kg of CAPE. Any convection that does fire up has the potential to induce a quick downpour given PWATs still over 1". For most locations we'll see a mix of sun and diurnal low level clouds. High clouds will be thickening and lowering through the day ahead of the approaching system.

KEY MESSAGE 2...A cold front brings the return of heavy rain and gusty winds Sunday night and Monday, perhaps lingering into Tuesday.

The mid level ridge continues to break down on Sunday as an anomolous mid-level low digs into the Ohio Valley inducing a deepening surface low which itself very slowly tracks northeast. This wave moves into New England by Monday, accompanied by and preceded by an anomalous subtropical moisture plume with PWATS over 2" (2+SD above normal). Isentropically forced rain arrives by late Sunday evening (west) or Sunday night (east) as warm advection takes hold. The heaviest rainfall rates likely occur on Monday as the cold front advances at the surface. This, combined with forcing for ascent from a 35-45kt LLJ and placement under the RRQ of a 120kt 300mb jet will lead to moderate to heavy rainfall across SNE. Still too soon to say where the heaviest amounts will be or how much, but ensemble guidance is not excited about potential for 2+ inches through Tuesday morning despite some deterministic guidance suggesting it. This will come into focus as we get into range of more high resolution guidance. The previously mentioned LLJ will bring gusty winds on Monday, especially over the Cape/islands and over the waters.

KEY MESSAGE 3...Periodic rain chances will be with us for much of next week.

Low confidence forecast when it comes to how much, if any, of a break we see in wet weather between the exiting shortwave Monday night/early Tuesday and the next. That being said, no sprawling or persistent high pressure ridge is in the cards so periodic rain chances likely persist.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

06Z TAF Update:

Through 12Z: High confidence overall, low on fog coverage.

VFR at most terminals, but patchy fog will increase in coverage before dissipating by 13z. Best chance at BDL, BED and ORH. SW winds around 5 kt, becoming light/calm overnight.

Saturday: High confidence.

VFR. SW winds around 5-10 kt, with seabreezes developing at BOS around 14-15z. Low chance of a shower or thunderstorm 17z-00z. Low clouds/fog dissipated by 13Z.

Saturday night:High confidence.

VFR to start. MVFR cigs move in after 06z, mainly SFZ-GHG south.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Sunday through Wednesday/...

Sunday: VFR. Breezy.

Sunday Night: Mainly VFR, with local IFR possible. Chance SHRA.

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

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

Tuesday through Wednesday: VFR. Chance SHRA, slight chance TSRA.

MARINE

Forecaster Confidence Levels...

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

Winds and seas below small craft advisory levels through Sunday. Light SW tonight then pick up to around 10-15 kt this afternoon and to 15-20 kt tonight. Seas 3 ft or less through tonight, then increase to 3-4 ft.

Outlook /Sunday through Wednesday/...

Sunday: Winds less than 25 kt.

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

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

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

Tuesday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers, slight chance of thunderstorms.

Tuesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, slight chance of thunderstorms.

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

BOX WATCHES/WARNINGS/ADVISORIES

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