Marine Weather and Tide Forecast for Shelburne, VT

KEY MESSAGES
As of 205 AM EST Friday...

1. Localized hazardous travel is expected today due to a combination of scattered snow showers, snow squalls, and a lake effect snow band. Sharply reduced visibility due to both falling and blowing snow, and a rapid accumulation of snow will make for slippery and hazardous travel, including today's morning and evening commutes.

2. Dangerously cold conditions are expected tonight and tomorrow, with wind chills of -20F to -40F likely. Risk of hypothermia and frostbite is unusually high due to the extreme nature of the cold, especially for vulnerable populations and anyone venturing outdoors without proper cold weather gear.

3. A Winter Storm Watch has been posted for the entire region for the potential of 7 inches or more of snow late Sunday through Monday.

DISCUSSION
As of 205 AM EST Friday...

.KEY MESSAGE 1: A narrow lake effect band is visible on radar imagery to the northeast of Lake Ontario as gusty west winds continue early this morning. This band will shift northwards, crossing through southern St Lawrence County again today.
Additional snowfall accumulations between 2 and 4 inches are expected with a storm total of 3 to 9 inches in southern St Lawrence County, with the highest totals along and south of Route 3. Hence the Winter Weather Advisory remains in effect until 7 pm today.

Another round of snow squalls is looking likely today as a secondary, arctic front currently located near Barrie and Algonquin Park, Ontario, moves through the forecast area from northwest to southeast. With better frontal forcing today than yesterday, the squalls should be less scattered, forming a few broken lines through the afternoon and evening. As winds turn more northwesterly behind this frontal boundary, we'll see lake effect come to an end sometime this afternoon or evening.

Either from today's squalls or the lake effect band, heavy snowfall rates and gusty winds (gusts as high as 20 to 40 mph possible) will make for localized treacherous travel due to visibility reduced to below 1/2 mile and rapid snow accumulations resulting in slippery roads. Anyone driving today needs to remain alert and be prepared for highly variable driving conditions. You may want to consider postponing travel until after the squalls/lake effect have ended.

.KEY MESSAGE 2: An arctic frontal boundary will cross our region throughout the day today, followed by a much colder air mass with 925mb temperatures falling into the -25 to -31 C range, resulting in surface temperatures as low as 5 to 25 degrees F below zero by early Saturday morning. Winds will be breeziest during the early portion of the night with northwesterly gusts 20 to 40 mph decreasing to 15 to 30 mph early Saturday morning as the atmosphere remains mixed. With temperatures and winds combined, we expect wind chills to be at least 20 to 40 degrees below zero, likely lower on summits. The most extreme conditions will therefore be in the Adirondacks and Northeast Kingdom. We are urging people to stay indoors if possible, especially vulnerable populations like the elderly and children. If you must be outdoors, please make sure to wear plenty of warm gear, including gloves or mittens and a hat. Any exposed skin will be susceptible to frostbite in just a few minutes. And don't forget about your pets; bring them inside if at all possible.

Though tonight looks like the worst of the cold, on Saturday we'll remain under the very cold air mass, and temperatures likely won't rise above -5 to 10 F the entire day. 1041mb high pressure will shift over northern New York throughout the day, but the atmosphere at the surface looks to remain mixed, allowing for a few west to northwest breezes throughout the day, enough to keep wind chills -5 to -20 F or lower. Though our Extreme Cold Warning ends Saturday afternoon, cold conditions will continue beyond this time frame, just at a lesser degree. A Cold Weather Advisory may be needed into Saturday night, especially for portions of the Adirondacks and Northeast Kingdom. One limiting factor to this potential will be increasing clouds ahead of a storm system that looks on track to impact to our region early next week. More on that in Key Message 3.

KEY MESSAGE 3: The potential for a widespread moderate to heavy snowfall continues to increase across the area late Sunday through Monday. On a broad scale, large scale troughing across the northern Plains will dig in across the Great Lakes and Ohio Valley Sunday, amplifying a southern stream of energy racing across the southeast CONUS. This amplification of the southern stream of energy will draw a deepening surface coastal low along the East Coast with coupled parent mid/upper low over the eastern Great Lakes drawing in deeper moisture into all of New England. Questions still remain on how much of this deep moisture reaches New England and how far north due to the presence of a retreating strong and dry 1040mb high situated over northwestern Maine. Recent trends have suggested that this high will be north of the International Border allowing additional moisture to advect into northern New England eroding the dry air mass faster than across previous model runs. With that in mind, there is still a wide array of snowfall amounts across the various models.

Strong 850-700mb frontogenesis along the northern periphery of the southern stream of energy and subsequent coastal low will strengthen with strong convergence and mid level troughing across New York. Strong lift coupled with a deep DGZ to 10-15kft (progged on the GFS model soundings) from the surface indicates prolonged periods of heavy snowfall. It is noted that the DGZ from prior runs is not as deep, however, as hi res data increases with closeness to the event, the NAM still is suggesting a potential up to 20,000ft DGZ. Thermal profiles well below freezing with ample deep layer moisture depict the potential for large snow aggregates with big time fluff factors across the region. Snow ratios between 20 to 25:1 are increasingly likely. There is now increased confidence in widespread advisory level snowfall (4" or more), with further confidence in most areas seeing the potential for at least 7" or more. NBMv5 progs a minimum of 50% across the entire region for at least 8" of snow. It is also worth noting that even the 10th percentile of snowfall amounts on the NBM is already 7".
Furthermore, probabilities of 12" or more across Rutland and Windsor Counties are up to nearly 75%. Mesoscale banding within the precipitation shield, and more mesoscale features will become apparent in the coming days which will help refine snow totals. As the system begins to depart midday Monday, lingering troughing extending eastward from deformation associated with the parent low to the west could keep snowfall across the higher terrain and eastern Vermont into parts of Monday evening and early Tuesday. Eventually moisture decreases Tuesday and snow showers taper off.

Temperatures will remain well below normal for this system which could make shoveling hazardous. Overnight lows on Sunday will be in the single digits, with highs Monday and Tuesday in the upper single digits to mid teens.



AVIATION /07Z FRIDAY THROUGH TUESDAY/
Through 06Z Saturday...VFR conditions are expected to continue for most sites through at least the next 6-12 hours. Main impacts this morning will be a shifting lake effect band from Lake Ontario which could lead to periodic visibility and cig reductions to prevailing MVFR with occasional brief IFR, mainly at SLK. Snow showers from this band should largely remain south of BTV and north of RUT, but subtle waffling of this band to BTV, and perhaps downwind to EFK this morning cannot be ruled out. After daybreak, an arctic cold front will sweep across the area with the potential for snow squalls. The best timing for these squalls will be between 18Z and 22Z for most sites. Brief reductions to MVFR cigs and IFR visibilities will be the main impacts. Winds will remain on the breezy to gusty side increasing to 20 to 30 knots by this afternoon through tonight.
Winds will shift from the southwest this morning to the west- northwest as the arctic front passes through each terminal, becoming prevailing west-northwest by this evening.

Outlook...

Saturday: VFR. NO SIG WX.
Saturday Night: VFR. NO SIG WX.
Sunday: VFR. Chance SN.
Sunday Night: Mainly VFR, with areas MVFR and IFR possible.
Definite SN.
Monday: Mainly MVFR and IFR, with local VFR possible. Likely SN.
Monday Night: MVFR/IFR conditions possible. Chance SN.
Tuesday: Mainly MVFR, with local IFR possible. NO SIG WX.

CLIMATE
Record low maximum temperatures are possible on Saturday; below are the current records:

KBTV (Burlington area): -4 in 1907 KPBG (Plattsburgh area): 0 in 1976 KSLK (Saranac Lake area): -10 in 1936 KMSS (Massena): -5 in 2004 KMPV (Montpelier): 0 in 2004 SJBV1 (St. Johnsbury): -3 in 1907

EQUIPMENT
NOAA Weather Radio station WXM-44, transmitting from Mt.
Ascutney, Vermont, on frequency 162.475 MHz is non-operational at this time. NWS technicians have diagnosed the problem, but repairs will likely not be able to occur for quite some time due to circumstances beyond our control. Therefore, the time of return to service is currently unknown. The following NOAA Weather Radio transmitters may be able to provide service during this outage: WWG 50 from Burke Mtn, VT at 162.425 MHz and WNG 546 from Hanover, NH at 162.525 MHz.

The Colchester Reef meteorological station is out of service.
This site is not serviced by the NWS and there isn't an estimated return to service at present. Use extra caution when navigating the broad waters of Lake Champlain. Please contact us if you observe winds significantly deviating from the recreational forecast.

BTV WATCHES/WARNINGS/ADVISORIES
VT...Extreme Cold Warning from 7 PM this evening to 1 PM EST Saturday for VTZ001>011-016>021.
Winter Storm Watch from Sunday afternoon through late Monday night for VTZ001>011-016>021.
NY...Extreme Cold Warning from 7 PM this evening to 1 PM EST Saturday for NYZ026>031-034-035-087.
Winter Storm Watch from Sunday afternoon through late Monday night for NYZ026>031-034-035-087.
Winter Weather Advisory until 7 PM EST this evening for NYZ029.