textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes have been made to the forecast. We continue to monitor the potential for a bit of snow sometime Fri into Fri night...but the main focus continues to be on an arctic outbreak this weekend with dangerously cold wind chills as well as gale to storm force wind gusts/heavy freezing spray over the waters.

KEY MESSAGES

- Tranquil weather into midweek with very cold night/s but many locations reach or break freezing Tue afternoon

- More active Friday into the weekend. Minor accumulating snow from a passing Clipper system Fri/Fri night. Then a period of strong winds and deep Arctic air brings the potential for dangerous wind chills this weekend, with gale-storm force winds and heavy freezing spray over the waters.

DISCUSSION

Key Message 1...Tranquil weather into midweek with very cold night/s but many locations reach or break freezing Tue afternoon

Overall tranquil weather continues into midweek with a ridge of high pressure in control. While there is some shortwave energy around that will bring some mid-level clouds at times...little low level moisture or forcing will be available. Therefore...we maintained a dry forecast. Given the deep snowpack in place...expect to see a large range in low temps from the urban centers to the outlying locations the next two nights. Lows in the outlying areas will be in the single digits with some below zero readings tonight. Meanwhile the urban centers will see low temps in the teens. 925T generally between -6C/-7C on Tue allowing highs to reach between 30 and 35 degrees in many locations.

Key Message 2...More active Friday into the weekend. Minor accumulating snow from a passing Clipper system Fri/Fri night. Then a period of strong winds and deep Arctic air brings the potential for dangerous wind chills this weekend, with gale-storm force winds and heavy freezing spray over the waters.

A benign weather week is followed by more active weather late Friday into the weekend. The first thing of note is an Alberta clipper system that swings through the Northeast late Friday/Friday night. This a quick hitting system with limited moisture and these factors will keep snowfall amounts in check, more likely only adding up to a coating to an inch or so. Best shot of the higher end will be the extreme eastern MA coast where ocean effect snow may linger Saturday. Ensemble guidance only indicates a 10-30% chance of seeing 1".

Immediately behind/accompanying this system will be a blast of truly arctic air, giving us perhaps the coldest wind chill values of the already cold season. As the low deepens over the maritimes the pressure gradient ramps up between it and high pressure over the Great Lakes which will lead to strong winds Saturday into Sunday. Given the anomalous airmass overhead (850mb temps approaching -20C) this could make temperatures in the single digits to negative single digits feel like -10 to -20F across most of SNE Saturday morning (closer to -30F in the Berkshires). This is dangerous cold, but thankfully it should be relatively brief as significant moderation is on the horizon as early as the start of next week. Finally, this combination of wind and cold will once again lead to the risk of heavy freezing spray over the water next weekend.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

18z TAF Update...

High confidence in VFR conditions through Tue night. NW winds become SW by Tue afternoon but speeds will be light...10 knots or less with some locations decoupling during the overnight and early morning hours.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High Confidence in TAF.

Outlook /Wednesday through Saturday/...

Wednesday through Thursday Night: VFR.

Friday: Mainly VFR, with local MVFR possible. Slight chance SN.

Friday Night: Mainly VFR, with local MVFR possible. Windy with local gusts up to 30 kt. Chance SN.

Saturday: VFR. Strong winds with local gusts up to 40 kt. Slight chance SN.

MARINE

Forecaster Confidence Levels...

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

Tonight through Tuesday night...High confidence.

A ridge of high pressure in the vicinity will keep winds gusts below 25 knots through Tue night. Left over swell from yesterday/s ocean storm will continue to subside...but small craft headlines will still be needed into tonight for our waters. No marine headlines will be needed Tue into Tue night.

Outlook /Wednesday through Saturday/...

Wednesday: Winds less than 25 kt.

Wednesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

Thursday through Thursday Night: Winds less than 25 kt. Seas locally approaching 5 ft.

Friday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of snow.

Friday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Chance of snow, chance of freezing spray. Local visibility 1 to 3 nm.

Saturday: gale force winds with gusts up to 45 kt. Rough seas up to 12 ft. Chance of snow, chance of freezing spray.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ231- 232-235-237. Small Craft Advisory until 7 AM EST Tuesday for ANZ250-254>256. Small Craft Advisory until 1 AM EST Tuesday for ANZ251.