Marine Weather and Tide Forecast for Chatham, NY

NEAR TERM /UNTIL 6 PM THIS EVENING/
Key Messages:

- Below normal temps and brisk conditions with diminishing lake effect snow showers and flurries west of the Hudson River Valley.

The Lake Effect Snow Warning for northern Herkimer Co. and the Winter Weather Advisory for Hamilton County were canceled.

The mid and upper level trough axis continues to move down stream of the region this morning. The low level flow is veering to the west to northwest with the lake effect tapering to narrow multi-bands of snow showers and flurries. The west/northwest upslope snow showers along the southern Greens and Berkshires should diminish by the late morning. Additional snow accumulations of a coating to an inch. Flat mid and upper level ridging will be building in. The flow will veer further to the northwest with the snow showers/flurries impacting the western Mohawk Valley, Schoharie Valley, northern and eastern Catskills with very light accums into the afternoon.

It will be partly to mostly cloudy across the forecast area with the clouds more dominate over the higher terrain and west of the Capital District. The winds will be brisk from the west to northwest at 10-20 mph with some gusts 25-35 mph due a notable a sfc pressure gradient and deeper mixing. H850 temps are still 1-2 STDEVs below normal and expect highs to run about 5-7 degrees below normal with mainly mid and upper 20s in the valley areas with a few lower 30s in the mid Hudson Valley and teens to lower 20s over the higher terrain.

SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/
Key Messages:

- A warm front and an upper level disturbance brings scattered snow showers with light accumulations Thursday.

- Dry conditions with moderating temps closer to seasonable levels for Friday.

A 1032 hPa sfc anticyclone over WV will attempt to ridge in tonight. Mid and upper level ridging will build in over eastern NY and western New England. The low level flow will back and we could see some scattered snow showers and flurries linger from the Schoharie and western Mohawk Valley northward into the western Adirondacks. The skies will be partly to mostly cloudy with more clearing south of the Capital Region. Any snow accums upstream of Albany will be in the coating to half inch or so range. Lows were accepted close to a MAV/NAM MOS blend with single digits over the southern Dacks, Lake George Region and southern VT, and mainly teens south of these areas.

By Thursday, the mid level ridges axis weakens and moves down stream over eastern NY. A mid and upper level trough approaches from the Great Lake Region. The short-wave and the warm front will increase the isentropic lift by late in the day for some light snow or snow showers/flurries developing west of I-87. The synoptic forcing is weak with limited moisture. The best isentropic lift moves through early Thursday evening. Any snow looks like dustings to a few tenths of an inch from this disturbance. PoPs were kept in the slight chance to low chance range (15-30%). Max temps Thu will be mainly in the 20s with some teens over the Adirondack Park and some 30F readings near KPOU. Lows with the trough passage will predominately be teens with some single digits north and northwest of the Capital District.

Heights increase aloft with ridging building in over NY and New England on Friday. The ridging combined with low-level warm advection will allow temps to moderate closer to seasonal climatological normals for mid-Jan with partly sunny conditions.
Highs will be in the low to mid 30s in the valleys and 20s over the higher terrain with light winds. The next cold front and northern stream wave tracks toward the region Fri night. The ridge moves down stream, as heights begin to fall. Dry conditions persist with mid and high clouds increasing. Lows will be in the upper teens to mid 20s.

LONG TERM /SATURDAY THROUGH TUESDAY/
Key Messages:

- A slow moving cold front Saturday afternoon into early Sunday will usher in a period of rain and higher elevation snow. There is a 40- 60% chance for more than 3 inches of snow in the western and southern Adirondacks with less than 20% in the southern Greens and eastern Catskills.

- Watching for a potential coastal storm Sunday into Monday to graze the Northeast. There is a 20 - 30% chance for more than 2 inches of snow for areas mainly south and east of the Capital District.

- Moderate to high confidence for a period of colder than normal temperatures Monday through Tuesday across the region. Outside of the mid-Hudson Valley, there is greater than 70% chance for daytime temperatures to fall near or below 15 degrees on Tuesday.

Strong southwest flow on Saturday looks to usher in a brief period of seasonably mild temperatures rising in the mid to upper 30s with low 30s in the higher terrain areas with breezy conditions as a cold front slowly approaches from the west. Ahead of this front, a weak southern stream shortwave tracking northeastward looks to provide a period of enhanced warm air/moisture advection and CVA to result in a period of precipitation Saturday afternoon into Saturday evening.
While initial temperatures are mild enough to support mainly rain or rain/snow mix as the p-type, especially in valley areas, once the warm nose exits to our east and we lose daytime, wet-bulbing and diabatic cooling processes can help facilitate a changeover to wet snow, especially in the hill towns and higher terrain. Valley area may struggle and remain a rain/snow mix. However, by the time the column is cold enough to support a changeover, most of the precipitation/moisture looks to escape off shore so overall wet snow accumulations look minor at best. In fact, probabilistic guidance shows just 25% for 2 or more inches of snow in the higher peaks of the eastern Catskills and southern Greens with 40-60% chance for 3 inches or more in the southern Adirondacks. Medium range guidance shows potential for coastal storm to develop but latest trends keep that well off shore.

By Sunday/Monday, a broad parent upper level trough will be slowly rotating south and eastward through Canada. This trough will be responsible for the upcoming cold spell that will likely impact much of the eastern CONUS. Its associated arctic cold front will be slowly progressing eastward on Sunday with another shortwave rotating around the base of this parent trough. As a result, the medium range guidance has been in good agreement suggesting that cyclogenesis occurs offshore as the shortwave interacts with the boundary Sunday into Sunday night. The GEPS and GEFS ensemble still maintain two vastly different clusters regarding the position/overall track of this coastal low. While the GEFS suggest the low remains far enough off shore that its deformation zone grazes only our farthest south/east zones, the GEPS are much farther north/west and allow the deformation zone to impact most areas from the Capital District south and east. Probabilistic guidance also has a large spectrum of solutions with the 10th and 90th percentile for 24 hour snowfall amounts by 7AM Monday ranging from 0 to 5 inches for these areas. Thus, we maintain a large coverage of chance POPs during this period with high end POPs for NW CT and the mid-Hudson Valley. The p-type will likely be all snow given our area would be on the NW side of the coastal low and the incoming arctic boundary.

There is increasing confidence that the Monday through Wednesday period will feature much below normal temperatures with the NAEFS showing the incoming air mass 2 to 3 standard deviations below normal or ranking in the less than 1 percentile of the CFSR climatological analysis. Probabilistic guidance shows 60 - 90% chance for daytime temperatures Monday and Tuesday to fall below 15 degrees for much of eastern NY and western New England with 50 - 80% chance for overnight lows both nights to fall below 5 degrees. Given breezy winds, the "feel-like" temperatures look to fall into the sub-zero range and even sub-teens for the western/southern Adirondacks both nights. Thus, the upcoming cold spell combined with breezy winds may necessitate cold weather advisory. More lake effect snow for the western Adirondacks also looks to develop Monday into Tuesday as strong westerly flow and the cold air mass track over the lakes.

AVIATION /08Z WEDNESDAY THROUGH SUNDAY/
Through 06z/Thu...VFR conditions should prevail at KALB/KGFL/KPOU through the TAF period with mid-level clouds clearing for a period shortly after sunrise before we reach our convective temperature and mid-level clouds return resulting in BKN 3.5 - 5kft ceilings. At KPSF, upslope flow will maintain MVFR ceilings with occasional light snow showers and flurries through sunrise resulting in high end MVFR vsby. While snow showers diminish during the day, MVFR cigs linger through much of the remainder of the TAF period. Additional mid- level clouds overspread the terminals towards the end of the TAF period as upper level ridging builds into the Northeast. Did not include any snow showers at this point as guidance suggest snow showers remain to the west of the terminals.

Westerly sustained winds between 10-15kt with gusts up to 25kt are expected through the TAF period with winds becoming northwesterly by 12 - 15 UTC.

Outlook...

Thursday Night: Low Operational Impact. Slight Chance of SHSN.
Friday: No Operational Impact. NO SIG WX.
Friday Night: No Operational Impact. NO SIG WX.
Saturday: High Operational Impact. Breezy
Likely SHRA
SHSN.
Saturday Night: Moderate Operational Impact
Chance of SHRA
SHSN.
Sunday: Moderate Operational Impact. Chance of SHSN.

ALY WATCHES/WARNINGS/ADVISORIES
CT...None.
NY...None.
MA...None.
VT...None.