textproduct: Boston / Norton

WHAT HAS CHANGED

Snowfall amounts increased slightly for late Tuesday into Tuesday night, mainly across northern and northeast MA.

KEY MESSAGES

- Moderating temps today but another cold night tonight with less wind.

- A quick moving clipper system will bring a period of accumulating snow late Tue into Tue night.

- Drier for the second half of the week following Tuesday's clipper system. More seasonable temperatures make a return.

DISCUSSION

Key Message 1...Moderating temps today but another cold night tonight with less wind.

Rising heights today and ridging aloft moves east from the Gt Lakes. After a very cold start to the morning, this will allow temps to recover into the upper 20s with mostly sunny skies. Mixed boundary layer is shallow but enough wind in the low levels to support gusts to 25 mph at times. Winds should decouple tonight but there will be some increase in mid-high clouds which may limit radiational cooling somewhat. Expect lows in the single numbers and teens.

Key message 2...A quick moving clipper system will bring a period of accumulating snow late Tue into Tue night.

Fairly potent northern stream shortwave moves into New Eng Tue night as the parent surface low passes to the north. A modest LLJ ahead of the trough will advect higher PWATs over 0.5" into SNE. Forcing for ascent ahead of the warm front will be enhanced at the nose of the LLJ to bring a period of snow late Tue into the first half of Tue night. The snow growth region dries out pretty quickly after midnight which should bring and end to the snow. The column is plenty cold enough for snow for much of the event, but low level warming may introduce a mix or change to rain along the immediate south coast and Cape/Islands before the precip ends. This does not appear to be a significant QPF event but will have to watch for secondary low development further south Tue night. Consensus of the guidance favors development mostly east of New Eng which would favor areas to the north for the heavier QPF and snowfall. Inverted trough expected to develop but convergence is favored across Maine at this time. Preliminary snowfall forecast is 1-3 inches with the highest amounts favored across northern and NE MA where locally up to 4 inches is possible. Amounts may be limited to less than an inch along the immediate south coast.

Key Message 3...Drier for the second half of the week following Tuesday's clipper system. More seasonable temperatures make a return.

As the clipper system continues east Wednesday, some snow showers may linger in the afternoon and evening hours towards eastern MA. These could last longer for the outer Cape, but exact details are still unknown this far out. NW flow returns as a secondary low that develops offshore circulates and shifts off to the northeast before winds weaken more heading into Friday. Behind this whole clipper system, high pressure starts to build back in over the region for the second half of the week and drier conditions prevail. With the arctic airmass overhead gone, a more climatologically normal airmass for this time of year settles in with 925 mb temperatures back to around -10C to -5C. Highs make it back to the mid to upper 30s over southern New England from Wednesday onward, though nighttime lows will still fall into the teens and low 20s, with some spots in the interior in the single digits. Though, notably, wind chills will not be as brutally cold.

AVIATION /12Z MONDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

12z TAF Update...No major changes.

VFR through much of Tue, but some MVFR possible by late in the day across portions of northern and NE MA as light snow develops. NW gusts to 20-25 kt today diminishing and becoming light N-NW tonight.

Outlook /Tuesday Night through Friday/...

Tuesday Night: Mainly VFR, with local IFR possible. Chance SN.

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

Wednesday Night: VFR. Slight chance SN.

Thursday: VFR. Breezy.

Thursday Night through Friday: VFR.

MARINE

Forecaster Confidence Levels...

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

Marginal SCA gusts today 20-25 kt diminishing tonight, then becoming SW around 10 kt Tue. Seas subsiding through tonight and dropping below SCA on the outer waters Tue. Freezing spray gradually diminishing through today.

Outlook /Tuesday Night through Friday/...

Tuesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain, chance of snow. Local visibility 1 nm or less.

Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of snow.

Wednesday Night: Winds less than 25 kt. Local rough seas. Slight chance of snow.

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

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

Friday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Cold Weather Advisory until 10 AM EST this morning for CTZ002>004. MA...Cold Weather Advisory until 10 AM EST this morning for MAZ002>004-008>012-026. RI...None. MARINE...Small Craft Advisory until 5 PM EST this afternoon for ANZ230. Small Craft Advisory until 7 PM EST this evening for ANZ231- 232-251. Freezing Spray Advisory until 1 PM EST this afternoon for ANZ231>237-250-251-254>256. Small Craft Advisory until 7 AM EST Tuesday for ANZ250-254>256.