textproduct: Boston / Norton

WHAT HAS CHANGED

The risk for snow showers or squalls late afternoon and early evening has ended. The threat for an impactful coastal storm late in the week has diminished.

KEY MESSAGES

- Overall quiet weather through Tue, then the chance of rain or snow showers Tue night

- Unsettled mid to late week with periodic chances for showers

DISCUSSION

KEY MESSAGE 1...Overall quiet weather through Tue, then the chance of rain or snow showers Tue night

A couple fast moving northern stream shortwaves will be moving through New Eng through Tue night One shortwave moves through late tonight and early Tue. Moisture is limited and forcing for ascent is weak so only expecting an increase in cloud cover later tonight, mainly across northern MA. This shortwave will be followed by brief shortwave ridging on Tue which will bring sunshine and milder temps as a SW flow develops. 925 mb temps increase to 0 to +2C which supports highs Tue reaching into the mid 40s. A second stronger shortwave approaching from the Gt Lakes will bring increasing high clouds during the afternoon, then this shortwave lifts NE into northern New Eng and SE Canada Tue night. Moisture ahead of the shortwave is a bit more plentiful as PWATs increase to over 0.50" Tue night which may lead to some rain or elevation snow showers developing as a mid level front moves through. Guidance is indicating a band of showers accompanying the mid level front and deep moisture plume. But little to no impact expected with localized snow accum less than inch confined to the northern Berkshires. SW flow ahead of the shortwave will result in a milder night Tue night with lows in the low-mid 30s.

KEY MESSAGE 2...Unsettled mid to late week with periodic chances for showers.

Ensemble guidance continues to have good agreement in the overall synoptic pattern through the later part of this week. A deep trough moving into the Great Lakes by midweek progresses east into the northeast US and exiting heading into the weekend. Some smaller shortwaves may also move along this deepening trough's flow and impact southern New England, leading to the chance for some light snow/rain showers for Wednesday evening into Thursday morning. Ensemble mean QPF values remain light for this time period. Global guidance generally agrees on less QPF across SE MA and RI up into NE MA (especially in the ensembles), but the latest NAM disagrees, indicating higher amounts across those areas. This spread lines up with the uncertainty that remains regarding track for these shortwaves.

We are monitoring the chance for a coastal storm towards the end of the week. The latest trends are pointing towards the low passing to the north of southern New England, which would mean that more significant impacts would all shift to northern New England. Ensemble probabilities for an inch or more of total snowfall (using a 10:1 ratio) through Friday evening remain below 10-20 percent, and are closer to 0 percent for 24 hour snowfall across much of the region. The only exception is the Berkshires where ensembles have around 50 to 60 percent probabilities for +1" of snow over 24 hours (ending midnight Friday). Much can still change this far out from the event, and the system could still shift towards a more favorable track for more significant impacts for southern New England depending on how the mid level trough evolves. But the latest guidance backing off from this system is worth noting, especially with agreement across different model suites.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

00z TAF Update:

Through Tuesday...High confidence.

W wind diminishing and becoming SW around 10 kt through the overnight. SW winds continuing into Tue then becoming more southerly in the afternoon.

Tuesday night...Moderate confidence.

Mainly VFR, but brief MVFR possible as a few rain showers and elevation snow showers move through. Chance for low level wind shear especially at eastern terminals.

KBOS Terminal... High confidence.

KBDL Terminal... High confidence.

Outlook /Wednesday through Saturday/...

Wednesday: Mainly VFR, with local MVFR possible. Breezy. Slight chance RA.

Wednesday Night: Mainly VFR, with areas MVFR possible. Chance RA.

Thursday: Mainly VFR, with local MVFR possible. Breezy. Chance RA, chance SN.

Thursday Night: VFR. Breezy. Chance SN.

Friday: VFR. Breezy. Slight chance SN.

Friday Night: VFR. Breezy.

Saturday: VFR. Slight chance RA, slight chance SN.

MARINE

Forecaster Confidence Levels...

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

Through Tuesday night... High confidence.

Gusty W winds will continue into tonight, especially over southern waters where 25 kt gusts likely. SCAs extended into tonight. Winds diminish late tonight through Tue while shifting to SW, then increase again Tue night as a low level jet moves through. Another period of 25-30 kt gusts expected.

Outlook /Wednesday through Saturday/...

Wednesday: Winds less than 25 kt. Local rough seas.

Wednesday Night through Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain.

Thursday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Chance of rain, chance of snow, chance of freezing spray.

Friday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft. Chance of freezing spray, slight chance of snow.

Friday Night: Winds less than 25 kt. Rough seas up to 10 ft.

Saturday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ231- 251. Small Craft Advisory until 1 AM EST Tuesday for ANZ232>234. Small Craft Advisory until 4 AM EST Tuesday for ANZ235-237-250. Small Craft Advisory until 7 AM EST Tuesday for ANZ254. Small Craft Advisory until 1 PM EST Tuesday for ANZ255-256.