textproduct: Boston / Norton

WHAT HAS CHANGED

Minor downward adjustments to snow accumulation expectations, otherwise no significant changes. Winter Weather, Wind, Coastal Flooding, Marine (Gale/Storm/Freezing Spray) and Cold Weather headlines remain valid. Snow may end up more showery than steady today, with manageable snow rates.

KEY MESSAGES

- Frigid temperatures and low wind chills in northern Connecticut and western Massachusetts this morning. While still breezy today, full sun and dry weather are expected for interior Southern New England.

- A coastal storm passing offshore of southern New England brings minor accumulating snow, strong winds, hazardous marine conditions (strong winds, high waves and freezing spray) to eastern and southeast New England today into tonight.

- Minor coastal flooding (1 to 2 ft inundation) with beach erosion along the eastern MA coast, with pockets of moderate coastal flooding for Nantucket. Due to cold roads and cold temperatures, storm surge could freeze and lead to prolonged impacts and delaying drainage.

- Largely dry workweek with less-below-normal temperatures. A fast-moving Clipper low pressure brings potential for minor- accumulating snow Fri night into Sat, but following it is a likely shot of well below normal temperatures and gusty northwest winds late next weekend.

DISCUSSION

Key Message 1...Frigid temperatures and low wind chills in northern Connecticut and western Massachusetts this morning. While still breezy today, full sun and dry weather are expected for interior Southern New England.

Cold Weather Advisory issued yesterday for interior portions of Southern New England still is valid into this morning. Modest low level warm advection and increased northerly winds have led to air temps in the single digits, but producing wind chills ranging from the -5 to -10F range. Might be a couple more hours as winds pick up for wind chills to dip below -10F across a larger portion of the Cold Weather Advisory area. Still pretty breezy as we move into the morning hours, but temperatures should rebound here into the lower to mid 20s moving through the day.

Key Message 2...A coastal storm passing offshore of southern New England brings minor accumulating snow, strong winds, hazardous marine conditions (strong winds, high waves and freezing spray) to eastern and southeast New England today into tonight.

A rapidly-organizing low pressure area south of the NC Outer Banks will continue to move NE and pass offshore of Southern New England, making its closest (though still distant) pass to our area later this afternoon and early tonight. 00z suite of forecast guidance reflects this offshore trend well.

Situation Overview in Southern New England (as of early this morning): Cloud cover was on the increase from south to north, but the lowest cloud bases have been in an enhanced NE flow offshore associated with ocean enhanced low clouds/stratus across much of eastern RI and eastern MA. Spotty bands of ocean effect snow showers are being sensed by KBOX Doppler radar and in area METARs at sites such as Boston Logan, Marshfield, Plymouth and Provincetown, although visbys have been no worse than 8 miles. NE winds have started to pick up along the immediate coastline with gusts in the 25-30 mph range.

Status of Storm-Related Headlines: For what is turning out to be a fringe pass, certainly no shortage of headlines between marine, coastal flooding, freezing spray, wind and winter weather. We opted to not make changes to those headlines with the overnight package. However, the Winter Weather Advisory is the one that's admittedly becoming more difficult to justify, both due to expected modest snow accumulation rates and lower totals. As ocean effect snows are really just beginning, we opted to keep it going and then re-assess if the ocean effect snows are leading to worsening conditions; an early cancellation to that headline is possible pending those trends.

Snow: Models have continued to decrease the amount of liquid- equivalent precipitation across southeast New England; even the moister ECMWF has backed off considerably. We ended up making only very slight downward adjustments to the snow accumulations for now, which are in the 1 to 3 inch range, with Nantucket having the best shot at seeing accumulations up to 4 inches. It now appears that snows will end up being more intermittent and showery due to the ocean enhancement versus persistent, and the best chance at steadier light snow is mainly for Nantucket and the elbow of Cape Cod. It might be a small thing, but we ended up messaging in the weather grids as snow showers vs steady snow since that probably better describes the nature/persistence of the snow. No significant change to snow growth expectations (poor), leading to more modest/manageable snow rates and visbilities on the higher side. Periods of snow showers will continue to increase this morning into the afternoon across South Shore, Cape Cod and the Islands, then tapering off from NW to SE by late this afternoon and early tonight across the Cape and Islands.

Winds: NE winds have started to increase, but should really begin to ramp up across Cape Cod and the Islands (and the adjacent waters) through the morning, peaking around the afternoon to early evening as the core of a 950 mb jetstreak of 50 kts moves overhead. Over land, NE to N wind gusts of around 45-50 mph are expected across Cape Cod and the Islands, highest gusts over Nantucket. Sporadic wind-related impacts could be possible, with downed branches and possible power outages. The strong winds will also contribute to blowing/drifting snow off the standing areas of snow. Winds then turn around to NW tonight with gusts decreasing to around 25-30 mph by midnight.

Key Message 3: Minor coastal flooding (1 to 2 ft inundation) with beach erosion along the eastern MA coast, with pockets of moderate coastal flooding for Nantucket. Due to cold roads and cold temperatures, storm surge could freeze and lead to prolonged impacts and delaying drainage.

There have been no significant changes regarding expectations for coastal flooding after reviewing latest tide/surge forecasts; Coastal Flood Advisories remain valid for the eastern coast of MA as well as Cape Cod and Martha's Vineyard, with Coastal Flood Warnings for Nantucket. The coastal flood and beach erosion (waves around 20 ft) threat is expected to exist across three high tide cycle periods: around late this morning, tonight, and Monday morning. The rapid deepening rate of the surface cyclone down to sub-970 mb levels can itself cause elevated water levels (approx 1 ft of water rise per 30 mb decrease is a rough rule- of- thumb, due to less pressure/mass over the water). We still expect a 1.5 to 2.5 ft storm surge, with the highest surge near Nantucket where northerly winds will be the strongest. It still looks like this surge peaks around Sunday afternoon to early evening, when most tidal locations are in or slightly after low tide. Due the recent stretch of frigid temperatures and cold pavement, storm surge could freeze on shoreline roads and become slippery, while also leading to delayed water evacuation/drainage.

Key Message 4: Largely dry workweek with less-below-normal temperatures. A fast-moving Clipper low pressure brings potential for minor- accumulating snow Fri night into Sat, but following it is a likely shot of well below normal temperatures and gusty northwest winds late next weekend.

Dry northwest flow is maintained through much of the upcoming workweek, with the 500 mb pattern across CONUS being governed by a stubborn Rex block over the West Coast. Temperatures through late week modify to something closer to less-below-normal (relative to where we've been much of the week). Highs most days in the upper 20s to around freezing, though briefly dipping to around the upper 20s around midweek with a modest shot of colder air.

A mid-level shortwave disturbance rounding the top of the West Coast ridge around Thu/early Fri helps energize a Clipper system moving through the Northeast Fri night into Sat. Accumulating snow is possible with the passage of this Clipper; being 6 days away plenty of time to evaluate this, but the progressive nature of the system probably caps how much falls. Perhaps the bigger story though is what lies behind the system: a period of strong NW winds with a shot of Arctic air (850 mb temps -18 to -21C, more typical of the type of cold we've had the last couple days) during the latter part of next weekend. Potential exists for additional cold and freezing spray headlines over the water for this, but there is time to evaluate this also.

AVIATION /08Z SUNDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

06z TAF Update:

Today: Moderate Confidence

VFR west of I-95, MVFR east of I-95 from PVD to BOS. Light snow will stay mainly confined to the Cape and Islands today between 12-00z. Still a chance most snow stays offshore with only off and on ocean effect snow showers. Low chance for IFR CIGS today if heavier bands of snow pivot onshore. Increasing NW winds today, gusting 20-25 knots across for interior terminals, 25-30 knots for coastal terminals, and 35-45 knots for the Cape and Island terminals.

Sunday Night: 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.

KBOS Terminal...Moderate Confidence in TAF.

VFR turning MVFR this morning. Confidence remains low on if BOS will get any ocean effect snow. Current thinking is that if there is any snow, it will be very light and unmeasurable, hence continuing to include the prob 30 for light snow showers this morning. CIGS become VFR 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 through Thursday/...

Monday: VFR. Breezy.

Monday Night through Thursday: VFR.

MARINE

Forecaster Confidence Levels...

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

* DANGEROUS MARINE CONDITIONS EXPECTED TODAY

A potent low pressure system will bring gale to storm force winds today and dangerous waves. Winds begin to increase this morning from the north gusting 30-40 knots in the near shore waters and 40-50 knots in the offshore waters including the ACK sound. Seas today quickly increase to 8-12 feet in the southern waters, and 12-15 feet in the eastern waters. On top of the dangerous winds and waves, freezing spray will also be a concern as cold air from over land gets advected out over the waters.

Winds begin to diminish tonight and into Monday down to 15-20 knots from the west. Seas will lag behind the winds, still in the 5-10 foot range through Monday and dropping below 5 feet Tuesday morning.

Outlook /Monday through Thursday/...

Monday: Winds less than 25 kt. Rough seas up to 15 ft. Freezing spray.

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

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

Tuesday Night through Wednesday Night: Winds less than 25 kt.

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

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- 003-008>011. Coastal Flood Advisory from 8 AM this morning to 2 PM EST Monday for MAZ007-015-016-019-022-023. Winter Weather Advisory until 4 AM EST Monday for MAZ019- 022>024. Wind Advisory until 11 PM EST this evening for MAZ022>024. Coastal Flood Warning from 8 AM this morning to 2 PM EST Monday for MAZ024. RI...None. MARINE...Gale Warning from 7 AM this morning to 1 AM EST Monday for ANZ230. Gale Warning until 4 AM EST Monday for ANZ231. Freezing Spray Advisory from 10 PM this evening to 10 AM EST Monday for ANZ231-232-255. Storm Warning from 7 AM this morning to 1 AM EST Monday for ANZ232. Freezing Spray Advisory until 10 AM EST Monday for ANZ233-234. Gale Warning until 1 AM EST Monday for ANZ233-234. Freezing Spray Advisory until 7 AM EST Monday for ANZ235-237. Gale Warning until 1 AM EST Monday for ANZ235-237-256. Freezing Spray Advisory until 1 PM EST this afternoon for ANZ236-256. Gale Warning until 11 PM EST this evening for ANZ236. Gale Warning from 7 AM this morning to 4 AM EST Monday for ANZ250. Freezing Spray Advisory until 1 PM EST this afternoon for ANZ251. Gale Warning until 4 AM EST Monday for ANZ251. Storm Warning from 7 AM this morning to 4 AM EST Monday for ANZ254-255.