textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes. Minor snow accumulations still expected Tuesday generally on the order of 1 to 3 inches. Increasing confidence on colder temperatures for Friday into the weekend but low confidence on precipitation forecast.

KEY MESSAGES

- Diminishing wind with below normal temps today.

- Minor snow accumulations of 1-3" likely Tue into Tue night.

- A few lingering snow showers possible near the coast Wednesday. Otherwise, dry and chilly Wednesday into Christmas Day. Seasonable high temps mainly in the 30s to lower 40s.

- Low confidence forecast Friday into next weekend with the potential for shallow cold air along with snow/ice and/or rain at times.

DISCUSSION

KEY MESSAGE 1...Diminishing wind with below normal temps today.

Mid level trough moves east of New Eng this morning with subsidence and rather dry airmass providing dry weather and abundant sunshine. Breezy conditions into the morning but as high pres moves to the mid Atlc coast weakening gradient will allow winds to diminish. Cold airmass in place as 925 mb temps bottom out around -10 to -12C this morning. These temps moderate some today but highs will be mainly upper 20s to lower 30s.

KEY MESSAGE 2...Minor snow accumulations of 1-3" likely Tue into Tue night

We have higher confidence on timing of snowfall for Tue with snow overspreading SNE from W to E during the morning but likely not reaching portions of eastern and NE MA until closer to midday. Snow or a mix will likely continue into the evening, especially across the east and may linger overnight with minor additional accums. The recent trend of colder thermal profiles has held firm as most of the column above 925/950mb expected to remain below 0C suggesting a mostly snow event, but there will be some surface and boundary layer issues closer to the south coast. This is where snow may mix with rain during the afternoon, especially south of PVD-TAN-PYM with potentially a change to all rain along immediate south coast and Cape Cod. The islands will probably be mostly rain for this event. This is not expected to be a significant QPF event with total QPF around 0.15" to 0.3". We have modest isentropic lift but omega in the DGZ is not particularly strong so expecting mostly light snowfall rates. Overall, we expect total accums through Tue night of 1-3 inches north and west of I-95 with an inch or less south of PVD- TAN-PYM. Surface temps are expected to rise slightly above freezing in the lower elevations during the afternoon, even in the interior which may limit accums somewhat on paved surfaces given light snowfall rates.

KEY MESSAGE 3...A few lingering snow showers possible near the coast Wednesday. Otherwise, dry with seasonable high temperatures mainly in the 30s to lower 40s Wednesday into Christmas Day.

Mostly dry weather expected for Wednesday into Christmas Day, except a low pressure system lingering offshore could help some light snow showers to linger over the far eastern coast, Cape, and Islands.

Seasonably temperatures in the 30s to the lower 40s expected for both Wednesday and Thursday. As a high pressure system begins to move over the Great Lakes, the pressure gradient will start to compact over New England and result in gusty northwest winds on Wednesday. This high builds further east by Thursday, leading to calmer winds along with slightly milder temperatures.

KEY MESSAGE 4...Low confidence forecast heading into the weekend with shallow cold air along with the potential for a snow/ice/rain mix.

We've seen a slight uptick in consensus across the latest deterministic, ensemble, and AI guidance that a boundary separating a very cold airmass to our north and unseasonably mild temperatures to our southeast will set up somewhere south of southern New England... allowing cold air to sink down from Canada. Thus, felt appropriate to maintain a colder solution with temperatures. However, model guidance continues to vary wildly regarding the timing and placement of any precipitation heading into the weekend. P-type will depend upon depth and amount of cold air that ends up pushing into southern New England, and given the high amount of uncertainty, the potential for a snow/ice/rain mix remains for Friday into Saturday.

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 changes.

Today through Tuesday...High Confidence.

VFR through tonight. Cigs and vsbys lowering to MVFR-IFR during Tue as snow overspreads the region from W to E. Snow may mix with rain along and south of PVD-TAN-PYM. NW and gusty winds this morning then gradually diminishing throughout the rest of the day. Light winds tonight becoming SE-SW Tue.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday Night through Friday/...

Tuesday Night: MVFR/IFR conditions possible. Breezy. Chance SN.

Wednesday: VFR. Windy with local gusts up to 30 kt.

Wednesday Night: VFR.

Christmas Day: VFR. Breezy.

Thursday Night: VFR. Slight chance SN.

Friday: MVFR/IFR conditions possible. Breezy. RA likely, chance SN.

MARINE

Forecaster Confidence Levels...

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

Gale warnings were converted to SCAs as winds have dropped below gale force. Expect 25-30 kt gusts through much of the morning then winds will drop off fairly quickly this afternoon with gusts below 20 kt by evening. W winds 10-20 kt tonight becoming S-SW Tue. Rough seas will begin to subside this afternoon and fall below 5 ft over outer waters tonight. Rain or mixed rain/snow develops Tue with lowering vsbys.

Outlook /Tuesday Night through Friday/...

Tuesday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Chance of rain. Local visibility 1 to 3 nm.

Wednesday: Strong winds with gusts up to 35 kt. Areas of rough seas. Chance of rain.

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

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

Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain.

Friday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Rain likely.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 1 PM EST this afternoon for ANZ230>235-237-251. Small Craft Advisory until 11 AM EST this morning for ANZ236. Small Craft Advisory until 7 PM EST this evening for ANZ250- 256. Small Craft Advisory until 1 AM EST Tuesday for ANZ254-255.