Marine Weather and Tide Forecast for Old Greenwich, CT

KEY MESSAGES
1) A major winter storm will impact the region early Sunday through at least early Monday. A widespread 9 to 15 inches of snowfall and significant travel disruptions expected.

2) Arctic air will remain over the region through next week. Cold Weather Advisories could eventually be needed.

3) Minor coastal impacts likely around the times of high tide Sunday night/early Mon AM.

DISCUSSION

KEY MESSAGE 1

A major winter storm will impact the region Sunday into at least early Monday. A Winter Storm Warning remains in effect for the entire area.

Arctic air has settled over the area courtesy of a sprawling 1042 mb high pressure shifting into the Northeast tonight as a winter storm materializes over the southeastern states.

Low pressure will develop over the south and be forced to track around the deep cold air damming signature east of the Appalachians tonight, with secondary low development taking place along the Mid Atlantic coast on Sunday. This low will then deepen as it tracks towards the Long Island coast late Sunday into Sunday night before shifting offshore on Monday.

Snow will quickly develop from south to north across the area Sunday morning as the region lies underneath an intense polar jet streak lifting into southeast Canada. The snow will fall into arctic air with surface temperatures only in the low to mid teens. This is a bit unusual for the area as most snow events over the Tri-State occur with temperatures in the 20s or low 30s. The snow will quickly accumulate as the intensity picks up through the morning. Mid level thermal forcing will increase over the area, especially heading into the afternoon. The 850-700 mb frontogenesis is impressive and the overall deep layer of vertical velocities over the area strongly support heavy snow over the region in the afternoon. Only a slight increase in temperatures is expected in the afternoon, except the southern half of the area where temperatures rise into the mid 20s.

As the warming in the mid levels continues, the chance for a mix with sleet near the coast increase sometime in the afternoon. Latest model trends this morning have a stronger warm layer with the coastal low development being a bit closer to the coast. This may allow for the mix of sleet to be a bit earlier than previously expected, beginning first as mainly snow mixed with sleet as early as 1-3 PM but becoming more of a primary period of sleet thereafter along the coast into Sunday evening. It needs to be emphasized that the overall impacts will not change and significant snow will occur before any wintry mix. There is a possibility the heavy snowfall rates will be able to hold back the warm nose just enough or create an isothermal layer on the 0C isotherm to prolong heavy snow for even just an hour two. Given the expected heavy snowfall rates of 1- 2" per hour (or possibly higher), even just an hour or two of mainly snow rather than sleet can result in a 2-5" difference in snow accumulation prior to the transition to sleet. Additionally, a few lightning strikes cannot be ruled out in the heaviest bands with the impressive dynamics aloft and deep moisture being lifted over the low level arctic air.

The strong mid level frontogenesis lifts northeast between 00-06z Monday and this should serve to gradually reduce precip rates. There may also be drying aloft, which will start to reduce snowfall rates where it remains all snow. The southern half of the area should see a wintry mix of sleet, potentially mixed with snow if the warm nose is not as deep. There is also a chance for some light freezing rain, mainly for Long Island and the NYC metro as the drying aloft occurs, cutting off snow growth along with the thinning of the depth of the low level cold air. This may also be dependent on how close the low pressure ends up to Long Island. The consensus of the modeling keeps the low just south and east of Long Island, but if it were to end up closer to the shore, some parts of eastern Long Island could briefly rise above freezing with light plain rain briefly possible.

The system starts pulling away from the area late Sunday night into Monday morning. Some bands of light snow may return as the trailing upper trough approaches and the thermal profiles become colder heading into Monday. Probabilities for precip decrease significantly Monday afternoon and there is potential anything that falls may just be flurries.

Overall, snowfall totals were adjusted slightly downward, mainly for the coast with increasing potential for sleet and an earlier timing of the mixing cutting down a bit on total accumulations. Long Island, the NYC Metro, and NE NJ are expected to see 8-12" total, but this may be in the form of 6-9" of snow and 1-2" of sleet. For more inland areas, total accumulations of 12-15" are expected consisting of primarily snow with less than an inch of sleet.

As noted above, snowfall rates of 1-2 inches per hour are expected in the afternoon and early evening. Winds will pick up in the afternoon and evening, especially near the coast and could create near white-out conditions/near blizzard conditions with winds gusting 30 to 40 mph at times, especially for coastal Long Island and coastal Connecticut. A mix or change to sleet will reduce this potential as visibilities would not be as low.


KEY MESSAGE 2

Another shot of arctic air will follow the winter storm after Monday with lows well into the single digits Monday night and highs on Tuesday again struggling to rise above 20 degrees. Only some slight moderation is currently expected Wednesday through the end of the week with highs in the upper teens to mid 20s. Lows will continue to be in the single digits to around 10 degrees. There is potential for multiple nights/early mornings with wind chills ranging from around 0 to around -10 Monday night through Friday night. Additional cold weather advisories may eventually be needed.


KEY MESSAGE 3

As coastal low pressure passes nearby Sunday Night into Monday, ENE to NE winds should be sufficient to elevate water levels enough to just above the minor coastal flood benchmarks during times of high tide late Sunday night into early Monday morning across the south shore of Nassau County, eastern bays of LI (particularly N/NE facing shores), and along western Long Island sound.

3 to 5 ft breaking wave actions along N/NE facing coasts along W LI Sound and Gardiner's Bay will locally exacerbate shoreline erosion and flooding.

A Coastal Flood Statement has been issued for these areas.

Minor beach flooding issues anticipated along the oceanfront from 4- 6ft breaking waves with an east to west sweep. Low probability of dune erosion.

AVIATION /18Z SATURDAY THROUGH THURSDAY/
High pressure will build from the W through this evening, then retreat NE late tonight into Sunday morning. Low pressure approaching from the SW will then impact the area very late tonight into Sunday morning.

NNW flow with some gusts to 20 kt still possible this afternoon, then winds diminish to under 10 kt tonight and veer more northerly tonight and NE very late tonight into Sunday. Snow should arrive at more of the terminals either very late tonight or around daybreak, but should take until around 14Z to arrive at KGON. Exact timing of onset uncertain so have handled via TEMPO, but once snow begins cond should quickly become IFR. LIFR in moderate to heavy snow expected at the NYC metros north/west after 13Z, then later in the morning at the CT and Long Island terminals. NE winds should increase to 10- 15G20kt at the coastal terminals as snow increases in intensity.

Snow accumulation by 18Z Sunday: 5 inches at the NYC metros, 4 inches at KSWF/KHPN/KISP, 3 inches at KBDR, and 1-2 inches at KGON.

...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...

No unscheduled AMD expected.

OUTLOOK FOR 18Z SUNDAY THROUGH WEDNESDAY
Sunday afternoon and night: LIFR in heavy snow should transition to IFR in moderate sleet by late afternoon or early evening at most terminals, especially along the coast, then to light freezing rain after midnight at the NYC metros and KISP.

NE winds increase to 15-20G25-30kt toward evening at the coastal terminals as well, then back more northerly and diminish after midnight.

Total snow/sleet accumulation: Up to 10 inches at the NYC metros and KISP, 11-12 inches at KHPN/KBDR/KGON, and 15 inches at KSWF. Except at KSWF where precip should remain all snow, 1-2 inches of this could be from sleet.

Monday: Light snow likely in the morning, tapering off from W to E through the day. MVFR or lower cond still possible. N-NW winds 15- 20G25kt.

Tuesday and Wednesday: VFR. W winds 10-15G20kt.

Thursday: VFR. NW winds 10-15G20kt.

Detailed information, including hourly TAF wind component forecasts, can be found at: https:/ www.weather.gov/zny/n90

MARINE
A brief lull in SCA conditions expected late this afternoon into tonight. Winds will increase on the waters later Sunday into Sunday night. Have upgraded to gale warnings for the ocean, Great South Bay and Eastern Long Island Sound. A gale watch remains in effect on all the remaining waters Sunday afternoon through Sunday night. SCA conditions are then likely Monday into Tuesday, with potential of gales on the ocean Monday night.

SCA conditions are then likely Monday into Tuesday, with potential of gales on the ocean Monday night into Tuesday. Sub-advisory conditions otherwise for Wednesday through most of Thursday.

CLIMATE
Record Low Maximum Temperatures:

January 24: KEWR: 15/1936 KBDR: 20/2014 KNYC: 6/1882 KLGA: 18/1987 KJFK: 19/1987 KISP: 19/2014

OKX WATCHES/WARNINGS/ADVISORIES
CT...Winter Storm Warning from 3 AM Sunday to 6 PM EST Monday for CTZ005>012.
NY...Winter Storm Warning from 3 AM Sunday to 6 PM EST Monday for NYZ067>075-078>081-176>179.
NJ...Winter Storm Warning from 3 AM Sunday to 6 PM EST Monday for NJZ002-004-006-103>108.
MARINE...Gale Watch from Sunday afternoon through late Sunday night for ANZ331-335-338-340.
Gale Warning from 1 PM Sunday to 1 AM EST Monday for ANZ332- 345-350-353-355.