textproduct: Boston / Norton

WHAT HAS CHANGED

Snowfall amounts were increased slightly for late Monday into Monday night. Confidence has increased in light icing across the interior Tuesday night.

KEY MESSAGES

- Clearing and cold tonight

- Light snow accumulations, a coating to 2 inches, expected Mon afternoon into Monday night

- Chances increasing for mixed precipitation event Tuesday night into Wednesday.

- A brief period of dry weather on Thursday followed by another round of unsettled weather into the weekend.

DISCUSSION

KEY MESSAGE 1...Clearing and cold tonight

Rising heights tonight as mid level trough continues to move east and high pres will be building in from the west. NW winds may become briefly gusty this evening then diminishing overnight as gradient slackens with approach of high pres. With clearing skies expect good radiational cooling overnight as winds become light. Lows should drop into the single numbers interior MA, with teens elsewhere.

KEY MESSAGE 2...Light snow accumulations Mon afternoon into Mon night

A modest mid level shortwave will be quickly moving into the region Mon afternoon and evening. Ahead of the shortwave a warm front will approach from the SW with modest overrunning developing. Synoptic scale forcing is not overly impressive but the column does saturate through the snow growth region and low levels are quite cold which will help to enhance isentropic lift. This should result in a period of widespread light snow, starting 1-3 pm in the west and 3-6 pm in eastern New Eng. Temps will be in the 20s when snow begins so it will stick immediately which will have some impact to the evening commute, especially in the west where the snow begins earlier. But snowfall rates will be more than manageable at 0.5 inch or less per hour.

It's a fairly quick moving system so snow should be tapering off before midnight as drier moves in. The snow growth region dries out quickly which could lead to snow ending as a period of freezing drizzle. QPF amounts are light, generally under 0.2", and expected SLR will be 12-15:1. Probably not much more than that as snow growth omega is not that strong. Looking at accums of 1-2 inches for much of the region, except a coating to an inch closer to the south coast. Ptype all snow, but may mix with or change to rain on the Islands Mon evening as BL warms with light S flow.

KEY MESSAGE 3...Chances increasing for mixed precipitation event Tuesday night into Wednesday.

A good portion of Tuesday looks to remain dry once the snow showers move out in the early to mid-morning. However, another short wave and low pressure system look to move into southern New England by Tuesday night, bringing chances for a mixed precip event. Excluding the NAM, the rest of the models are indicating a warm nose of air with 850mb temperatures ranging +2C to +5C. Guidance is beginning to hone in on the higher terrain areas of the Berkshires and Worcester Hills having a higher likelihood of surface temperatures remaining at or below freezing, leading to higher chances of seeing freezing rain. Starting to see the latest round of guidance creep up in the ice accumulation, bringing consensus to above 0.01" but below 0.1" in the higher elevations. Soundings continue to favor this period of freezing rain before switching to all rain as surface temperatures increase heading into the mid-morning hours on Wednesday.

KEY MESSAGE 4...A brief period of dry weather on Thursday followed by another round of unsettled weather into the weekend.

The Tuesday/Wednesday system should make its exit by Wednesday night, and a mid-level ridge with a surface high moves in to bring a period of dry weather on Thursday. Unfortunately, not expecting the dryness to last as another system is projected to push into southern New England at some point on Friday. Temperatures Friday and Saturday remain above freezing, with ensemble guidance indicating surface high temperatures 10-15F above normal, leading to precip remaining solely as rain. Given this is still quite a while out, uncertainty regarding timing, placement, and precip totals remains high.

AVIATION /00Z MONDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

00z TAF update...

No major changes. Trends remain on track.

Tonight...High confidence.

VFR-MVFR cigs trending all VFR tonight as cloud cover decreases. NW wind 5-15 kt becoming light toward 12z, except towards the Cape and Islands where winds may continue longer and occasionally gust to 20 kt.

Monday...High confidence.

VFR to start, then lowering to MVFR after 19z across central/W MA and CT as light snow overspreads the region. Snow may reach eastern MA/RI after 21z.

Monday night...Moderate confidence.

MVFR with areas of IFR in snow in the evening. Minor accums possible. Snow ending around midnight.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday: Mainly VFR, with local IFR possible. Slight chance RA, slight chance FZRA.

Tuesday Night: MVFR/IFR conditions possible. RA likely, FZRA likely.

Wednesday: Mainly VFR, with local IFR possible. Chance RA.

Wednesday Night through Thursday: VFR.

Thursday Night: VFR. Slight chance RA.

Friday: Mainly VFR, with local MVFR possible. Breezy. Chance RA.

MARINE

Forecaster Confidence Levels...

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

Through Monday night...High Confidence.

A period of NW gusts to 25 kt should develop this evening, especially over the eastern waters. SCA was issued for eastern MA waters and outer southern waters. Winds diminish late tonight through Tue while shifting to SW late Tue and Tue night. Lowering vsbys late Mon into Mon night in snow, changing to rain over southern waters.

Outlook /Tuesday through Friday/...

Tuesday: Winds less than 25 kt. Slight chance of rain, slight chance of freezing rain.

Tuesday Night: Winds less than 25 kt. Chance of rain.

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

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

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

Friday: Winds less than 25 kt. Chance of rain.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 5 AM EST Monday for ANZ231-232-251- 255-256. Small Craft Advisory until 5 AM EST Monday for ANZ250-254.