textproduct: Boston / Norton

WHAT HAS CHANGED

Winter Weather Advisory has been canceled for Nantucket. We replaced the Coastal Flood Warning for Nantucket with an Advisory as the next two high tide cycles will result in pockets of just minor coastal flooding and splashover.

KEY MESSAGES

- 130PM Storm Update: Winter Weather Advisory for Nantucket has been canceled while the High Wind Warning continues through this evening.

- Minor coastal flooding/splashover along the eastern MA coast during the overnight and midday high tide cycles Monday. Sub- freezing temperatures and very cold road surfaces may allow some of the storm surge to freeze, prolonging impacts and delaying drainage after high tides.

- Mostly dry weather and not as cold into the middle of next week, turning colder and more active late next week/early weekend.

DISCUSSION

Key Message 1...130PM Storm Update: Winter Weather Advisory for Nantucket has been canceled while the High Wind Warning continues through this evening.

As the winds become primarily out of the northwest this afternoon, ocean enhanced snow gets pushed further down the South Shore and onto the Cape and begins to lighten up. A northeasterly streamer offshore is slowly making its way onto Nantucket, with the potential to drop another coating to 1", possibly up to 2" in spots. Given the relatively low accumulations expected this afternoon, elected to drop the Winter Weather Advisory.

The High Wind Warning remains in effect through 7PM for Nantucket, with recent observations at ACK reporting 47-50 knots. Model soundings indicate relatively good mixing through the evening, possibly up to 900 mb, bringing high winds 45-50 knots down to the surface. Winds slowly begin to die down tonight as the coastal storm moves further east.

Key Message 2...Minor coastal flooding/splashover along the eastern MA coast during the overnight and midday high tide cycles Monday. Sub-freezing temperatures and very cold road surfaces may allow some of the storm surge to freeze, prolonging impacts and delaying drainage after high tides.

We received several reports of coastal flooding with today/s high tide cycle. We have two more high tide cycles of concern...the first a few hours on either side of midnight and the second will be a few hours on either side of noon Monday. The first astro high tide overnight is over a foot lower than today/s. So despite seas being more built up offshore...just expecting splashover and very minor coastal flooding on the typically vulnerable roads /not as impactful as what we saw today/. Therefore...we opted to go with just a coastal flood advisory for the entire eastern MA coast including Nantucket. Now the Monday midday astro high tide is similar to the one we had today...but our winds will be lighter and more offshore coupled with lower seas as well. This tide will probably have more minor coastal flooding/splashover than our overnight high tide...but below the impacts of today/s so we are just running with a coastal flood advisory. Beach erosion will be a concern given the impact on multiple high tide cycles.

Lastly...because of the very cold temperatures some of the storm surge may freeze. This may not only delay drainage after the high tides...but also result in those typically vulnerable roads becoming icy and needing treatment.

Key Message 3...Mostly dry weather and not as cold into the middle of next week, turning colder and more active late next week/early weekend.

Dry NW flow continues most of this week with a moderating airmass (925 mb temps up to near -5C) which allows for a dry and "warmer" week. When we say warmer, we're talking high temperatures in the upper 20s and low 30s each day. The next truly arctic blast comes with a strong cold front around Saturday which will bring 925 mb temps from near -8C on Friday to closer to -20C Saturday. This arctic front will usher in a harshly cold and windy airmass behind it with potential for more extreme cold and freezing spray headlines being needed. Precipitation-wise, a weak, moisture starved disturbance moves through the mid level flow which could produce some flurries Tuesday night into Wednesday but the next shot for a few inches of snow comes with a clipper system late week into the weekend that accompanies the front. This is a quick hitter and doesn't look to drop more than a few inches of snow as it passes by. Ensemble guidance shows a 10-30% chance of seeing at least an inch.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

18z TAF Update:

This afternoon: Moderate Confidence

VFR outside of southeastern MA terminals. NW winds gusting 20-25 knots across for interior terminals, 25-30 knots for coastal terminals, and 35-45 knots for the Cape and Island terminals.

Tonight: Moderate Confidence

Remaining MVFR CIGS become VFR by midnight. Snow should come to an end by 00z for the Cape and Islands with lingering gusty winds up to 30 knots. Inland terminals will see gusty winds end between 22-00z as the boundary layer decouples, however, this will create LLWS as winds aloft remains around 35-40 knots.

Monday: High Confidence

VFR with decreasing NW winds from 20 knots to under 10 knots.

Monday night: High Confidence.

VFR. Light winds becoming calm at some terminals.

KBOS Terminal...Moderate Confidence in TAF.

MVFR with intermittent VFR-visby ocean effect flurries/SHSN thru 15z. CIGS become VFR late this afternoon with gusty winds up to 30 knots.

KBDL Terminal...High Confidence in TAF.

VFR. Increasing northerly winds today, becoming gusty sunday afternoon up to 25 knots. Surface winds diminish after sunset Sunday, leading to LLWS concerns with winds aloft still around 35-40 knots.

Outlook /Monday Night through Friday/...

Tuesday through Thursday Night: VFR.

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

MARINE

Forecaster Confidence Levels...

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

* DANGEROUS MARINE CONDITIONS EXPECTED TO CONTINUE INTO THIS EVENING

Gale to storm force winds dangerous waves continue into this evening. Winds 40-50 knots continue through this evening, eventually diminishing to 15-20 knots overnight and into Monday morning. Seas this evening remain 8-12 feet in the outer southern waters, and 12- 15 feet in the eastern waters, but 3-5 feet in Buzzards Bay and Vineyard and Block Island Sounds. Seas will lag behind the winds, still in the 5-10 foot range through Monday and dropping below 5 feet Tuesday morning.

On top of the dangerous winds and waves, freezing spray will continue be a concern as cold air from over land gets advected out over the waters.

Outlook /Monday Night through Friday/...

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

Tuesday Night through Thursday: Winds less than 25 kt.

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

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...Coastal Flood Advisory until 2 PM EST Monday for MAZ007-015- 016-019-022>024. Wind Advisory until 7 PM EST this evening for MAZ022-023. High Wind Warning until 7 PM EST this evening for MAZ024. RI...None. MARINE...Gale Warning until 1 AM EST Monday for ANZ230-233>235-237-256. Gale Warning until 4 AM EST Monday for ANZ231-250-251. Freezing Spray Advisory from 10 PM this evening to 10 AM EST Monday for ANZ231-232-251-255. Storm Warning until 1 AM EST Monday for ANZ232. Freezing Spray Advisory until 10 AM EST Monday for ANZ233-234- 236. Freezing Spray Advisory until 7 AM EST Monday for ANZ235-237. Gale Warning until 11 PM EST this evening for ANZ236. Storm Warning until 4 AM EST Monday for ANZ254-255.