Marine Weather and Tide Forecast for Penn Yan, NY

NEAR TERM /THROUGH SUNDAY/
915 AM Update...

Light snow has been more widespread than previously forecast for this morning. There is an upstream jet streak and shortwave that is pushing into the Great Lakes and will be spreading into our region later this afternoon. At the surface/low levels there is warm air advection and weak isentropic lift. Expecting snow to become more widespread later today, but uncertain how far south into our CWA we will see snowfall. Best chance for accumulating snow will be from the Southern Tier on northward into Central NY with the best lift/forcing likely setting up north of the NYS Thruway Corridor. For now, increased PoPs across most of NY and spread some slight chance to low chance PoPs further south into NE PA. Accumulations across most of the area will be less than an inch, but north of the NYS Thruway, 2 to 6 inches will be possible as this system pushes through tonight. This snow will be additional from the lake effect snow that is ongoing across much of Oneida County this morning.

650 AM Update:

Some minor adjustments to PoPs and temperatures in the near term, otherwise, the forecast remains on track.

455 AM Update:

Lake effect snow off of Lake Ontario will continue this morning and into the early afternoon before the band of snow lifts to the north between 18-20Z, although the break from the snow will be brief. This band of snow is expected to remain mostly concentrated over Northern Oneida County but it will drift at times through the early afternoon. Aside from a few flurries across the Southern Tier, conditions are expected to be dry across the rest of the area into the early afternoon. Highs today range from the upper 20s to the mid 30s.

By about 20Z or so, a more widespread snow is expected to develop, mainly west of I-81 at first, but as a warm front that extends over the northern Great Lakes and into north-central NY lifts northward, this warm advection snow will spread to the north and east over much of the area by this evening. Light to moderate snow continues overnight as the surface low associated with the front moves east across southern Ontario. Temperatures will start to rise late tonight and that can allow for some rain to possibly mix in around the Syracuse Metro before daybreak as temperatures reach the mid 30s. A mix of rain and snow showers will taper off Sunday morning as the surface low progresses into southern Quebec. While 850mb temperatures won't be nearly as cold in the wake of the low (generally -3 to -4C), with a west- northwest flow developing off the lakes, additional lake enhanced rain and snow showers are possible through the afternoon north of the Southern Tier. Highs Sunday range from the mid 30s to the low 40s with the Wyoming Valley reaching the mid 40s in the afternoon.

With there being little time in between the end of the lake effect snow and then the more widespread synoptic snowfall, the current Winter Storm Warning over Northern Oneida County and Winter Weather Advisory for Southern Oneida County has been extended through 10 AM Sunday morning. Additional snowfall accumulations from this morning through Sunday morning of 6 to 12 inches are expected over Northern Oneida County, while an additional 3-7 inches of snow is expected for Southern Oneida County. A general 1 to 3 inches of accumulation is expected from late this afternoon through early Sunday across the rest of CNY, with a coating to an inch stretching from the western Finger Lakes south and east in NE PA.

SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/
430 AM Update

Starting off rather quiet Sunday night with mainly dry weather and even some partial clearing over NE PA and the Twin Tiers possible.
South-southeast surface winds gradually increase between 5 to 12 mph overnight out ahead of the next, fast moving storm system. At this time, it looks to stay dry through sunrise Monday morning, as overnight lows dip down in the mid-20s to lower 30s.

On Monday morning, a fast moving frontal system will quickly spread steady precipitation over the forecast area from SW to NE. For most areas this will be in the form of a cold rain, as temperatures aloft are above freezing; around +4C at 850mb. A few pockets of subfreezing air may linger at the surface, in elevated, protected valleys and over the higher terrain. This may lead to a brief period of freezing rain in these isolated pockets. Uncertainty remains in how long the subfreezing temperatures may linger, and thus probabilities for freezing rain remain on the low side. Did make a brief mention of this potential in the HWO...but again it is looking isolated. It looks to be about 8 hour period of steady, moderate rain/precipitation with this system, with rain totals between a 1/4 and 1/2 inch expected.

Mainly cloudy skies and a few on and off rain showers linger Monday night, through Tuesday as our area will be under the influence of a mild, moist southwesterly flow. Overnight lows stay above freezing Monday night for most locations; in the mid to upper 30s. Tuesday will be one of the mildest days this week, with highs in the mid-40s to lower 50s in the forecast.

A period of steady rain develops and moves over the area from the south/southwest Tuesday night. This is due to a deep, high amplitude trough swinging into the Mississippi/Tennessee Valley creating cyclogenesis over the Mid-Atlantic. Deep moisture surges northward into our area as a 150kt jet at 300mb develops over the Appalachians. With the deep southerly flow in place, overnight lows are once again generally in the 30s, which will likely keep precipitation type mainly all rain overnight. This will bring another 1/3 to 1/2 inches of rain to the area just Tuesday night.

LONG TERM /WEDNESDAY THROUGH FRIDAY/
450 AM Update

The main story in the long term will be a low pressure system and strong cold front that is progged to impact the area Wednesday into Wednesday night. This low will be supported by a full latitude trough extending south to the Gulf of Mexico. A power 175 kt jet a 300mb will be over the region Wednesday afternoon, with good upper level diffluence and strong mid level vertical motions (omega) in the 850-300mb layer over Central NY and NE PA. This will likely support a slow moving, south to north oriented band of precipitation over the region through the day on Wednesday. There will be wave(s)
of low pressure that develop along the strong cold front, along the East Coast...and these low may enhance the precipitation, and halt the eastward progression. There remains uncertainty in the exact timing of the cold front, and polar air filtering in from the NW.
For now kept the official forecast very close to the ensemble (NBM)
for temperatures and PoPs this period. This allows temperatures to initially surge up into the 40s for much of the area, and even low 50s for the Wyoming Valley, and Delaware river valley along the NJ border in NE PA.

Eventually, colder air moves in by Wednesday afternoon or evening, changing any lingering rain over to snow or snow showers as temperatures aloft fall to -12C overnight at 850mb.
This will initiate a lake effect snow response off of Erie and Ontario...but it is too early to pin down details such as wind direction or inland extend. Turning much colder with lows 15-25F Wednesday night.

Thursday features more lake effect snow showers and below average temperatures. Thursday night will be very cold with lows in the upper single digits to teens expected...with again some lake effect snow showers possible. Friday and Friday night are generally quiet and cold with slightly below average temperatures continuing. There looks to be a slight warming trend by next Saturday as the southerly flow increases for our area once again.

AVIATION /17Z SATURDAY THROUGH WEDNESDAY/

More widespread snow will be pushing into the region late this afternoon and tonight. This will lead to mainly MVFR restrictions for the CNY terminals with periods of IFR or worse visby restrictions possible as well. Confidence is highest at SYR and RME for potential IFR conditions with lower confidence at ELM, ITH and BGM.

As the warm front with this system lifts north, low level winds will increase just above the surface. Low level vertical profiles show some borderline wind shear at most terminals, Sunday morning, but for now, have added LLWS to only Central NY terminals and exclude BGM and AVP, but it may be added with later forecast or amendments as confidence increases.

Outlook...

Sunday...Mainly VFR. Some restrictions may linger at KSYR and KRME as rain/snow showers depart the area.

Monday through Wednesday...Periods of rain and mixed rain/snow likely.
Restrictions possible.

BGM WATCHES/WARNINGS/ADVISORIES
PA...None.
NY...Winter Storm Warning until 10 AM EST Sunday for NYZ009.
Winter Weather Advisory until 10 AM EST Sunday for NYZ037.