textproduct: Boston / Norton

WHAT HAS CHANGED

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

KEY MESSAGES

- Another cold night tonight, but with less wind.

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

- Upcoming period of dry, sunny days with seasonable temperatures.

DISCUSSION

Key Message 1...Another cold night tonight, but with less wind.

Ridge of high pressure advecting west to east across New England tonight. This will support mainly clear conditions and diminishing winds, combined with a deep snowpack. This will result in lows in the single digits regionwide. The exception will be along the immediate coast, Cape and islands, along with the urban areas where mins will settle in the teens. Not as cold as previous nights, nonetheless, colder than normal. Also, not as much of a wind chill factor given the light winds. Minimum temps were derived from the NBM and MOS datasets. We didn't want to follow the coldest guidance, as some mid level cloudiness from time to time overnight by preclude the coldest temp from verifying. Nevertheless, a chilly/colder than normal night.

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 northern New England Tue night...as the parent surface low passes to the north. First band of warm advection light snow/flurries will overspread the area 4PM-7PM west to east. Little if any accumulation will occur with this first round. The steadier/accumulating snowfall will occur roughly between 7 PM and midnight. This will be more dynamical driven and will be accompanied by a 2-4 hour window of moderate snow, supported by 10-15 ubar/s of lift in the DGZ. This strong forcing for ascent induces a weak secondary low that tries to develop along the boundary over or near SE MA.

Snow may end as period of rain along the south coast, in response to modest low level WAA. Elsewhere, snow may end as a brief period of freezing drizzle, as the DGZ dries out after midnight. Given all the parameters above, expecting a coating up to 2 inches of snowfall across CT/RI and southeast MA, possible followed by a trace of ice before ending. For northern MA, 1-3" is likely with localized amounts of 4+ in northeast MA, followed by a trace of ice before ending. If 00z guidance trends stronger/more qpf, the evening/night shift may issue winter weather headlines. Stay tuned.

Key Message 3...Upcoming period of dry, sunny days with seasonable temperatures.

Expecting a few days of dry weather after the clipper system moves through Tuesday night/Wednesday morning. Winds return to predominately northwesterly Wednesday, then high pressure begins to build in over the Midwest/Mid-Atlantic regions Thursday. Once the arctic airmass finally gets pushed offshore, we'll see a return to more seasonable temperatures. High temperatures 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. Thankfully though, wind chills will not be as low as we have seen over the last few weeks.

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...

This evening and overnight...High confidence.

VFR. Breezy winds diminish by 03Z. Otherwise NW winds 5-10 kts. Mid-level cloud decks in central and western southern New England overnight.

Tuesday...High confidence. Moderate on timing of -SN and drop to MVFR.

VFR and dry to start. VFR cloud bases as light snow/flurries move in during the afternoon from west to east (19-20Z arrival in western MA and 23-00Z arrival at BOS). Ceilings should drop to MVFR around or little after 00Z for ORH, BED, BOS. Light NW winds in the morning trend toward the SW after 15Z.

Tuesday night...Moderate confidence.

IFR/LIFR in snow, moderate at times possible across northern MA, including KBOS. 1-3" snow accums likely, isolated 4+ northeast MA. Steadiest snow roughly 00z-05z. Snow may end as rain along the south coast, possibly ending as a period period of -fzdz elsewhere. Low prob of LLWS 00z Wed - 06z Wed.

KBOS Terminal...Moderate Confidence. -SN arrives more likely between 23-00Z. Confidence is moderate on how quickly VFR ceilings drop to MVFR with the onset of -SN, but should drop by 01Z. There is potential for a period of moderate snow Tuesday night between 02-06Z. This would bring briefly lower visibilities (1/2 to 1SM) and IFR/near-LIFR ceilings. Snow moves out by 10Z.

Outlook /Wednesday through Saturday/...

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

Wednesday Night: VFR. Breezy. Slight chance SN.

Thursday: VFR. Breezy.

Thursday Night through Saturday: VFR.

MARINE

Forecaster Confidence Levels...

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

This evening...high confidence.

Gusty WNW winds up to 25 kt diminish with sunset, along with freezing spray ending.

Tuesday...high confidence.

Light west wind in the morning, becoming SW in the afternoon, 10-15 kt. Light snow/flurries may briefly limit vsby late.

Tuesday night...moderate confidence.

SSW winds 10-15 kt Tue evening, becoming west after midnight. Snow may lower vsby to 1 mile or less across the northern MA waters, 1-3 miles elsewhere, possibly ending as rain southern waters.

Outlook /Wednesday through Saturday/...

Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain, slight chance of snow.

Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Slight chance of snow.

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

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

Friday Night through Saturday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ231- 232-251. Small Craft Advisory until 7 AM EST Tuesday for ANZ250-254>256.