textproduct: Burlington

WHAT HAS CHANGED

As of 128 AM EST Friday... The Extreme Cold Watch has been upgraded to an Extreme Cold Warning for the St Lawrence Valley and northern Adirondacks. Areas from the Champlain Valley eastward have been upgraded to a Cold Weather Advisory.

KEY MESSAGES

As of 128 AM EST Friday...

1. Snow showers tonight into Saturday afternoon will create hazardous travel conditions. The snow may be briefly moderate to heavy at times, with a general 1 to 3 inches of accumulation expected, with locally higher amounts possible.

2. Dangerously cold wind chills of 20 to 40 below expected over the weekend.

3. Moderating temperatures and chances of snow showers for the rest of the week.

DISCUSSION

As of 128 AM EST Friday...

KEY MESSAGE 1: High pressure will keep the weather tranquil much of the day today, with just increasing mid/high clouds. Given the bitter cold this morning (current temperatures are in the single digits above and below zero) and light winds, daylight may well reveal that Lake Champlain has completely frozen over. This would be the first complete freezing of Lake Champlain since March 8, 2019.

With that aside, the main focus for tonight and Saturday will be widespread snow associated with an arctic cold front. This feature and its parent clipper low will sweep out of Canada and across our region from northwest to southeast tonight and Saturday, with spreading a swath of snow across the area. The frontal boundary will be quite sharp with strong frontogenesis and frontal convergence. At the same time, the overnight/early morning timing of the frontal passage and the lack of significant areas of open water on the Great Lakes will limit instability and available moisture. Hence while true snow squalls aren't anticipated, snow could be briefly moderate to heavy at times, especially along the front. Latest HREF guidance indicates snowfall rates could approach 0.5 in/hr, with the greatest risk of higher snowfall rates generally 9 pm Friday to 9 am Saturday. The snow will be light and fluffy with snow ratios of 18- 20:1 or better. Flow will turn to the west/northwest behind the front and strong cold air advection will allow gusty winds to develop Saturday and Saturday night (see Key Message 2 on additional information regarding cold and winds), so would anticipate areas of blowing snow, especially in open/exposed locations. All this points toward hazardous travel, with roads becoming snow covered and visibility likely reduced to 1/2 mile or less at times, even once the snow ends. Snow will gradually taper to an end during the day Saturday with much drier air spreading in behind the cold front, but the favored upslope areas of the northern Adirondacks/Greens will likely see snow showers continue well into the afternoon. Overall anticipate a widespread 1-3 inches of snowfall, with 2-4+ inches in the higher terrain and/or western slopes where the snow will linger longest.

KEY MESSAGE 2: Temperatures will plummet late tonight into Saturday as as the aforementioned arctic cold front sweeps across the North Country and Vermont. Overall expectations/forecast hasn't changed with this package. The cold air arrives in northern NY late this evening into the overnight, dropping temperatures from the mid teens around midnight to near/below zero by daybreak. Areas from the Champlain Valley eastward will squeak out early daytime highs in the teens Saturday morning before the cold air arrives; anticipate temperatures to of -10F to 0F areawide by sunset. Brisk northwest winds of 10 to 15 mph with gusts of 20 to 30 mph will combine with the cold ambient temperatures to produce wind chills 15 to 25 below zero during the daylight hours Saturday. Winds will be slow to abate overnight Saturday night; while overnight lows will generally be 10 to 20 below zero, wind chills of -20 to -40F below are expected. High pressure will nose into the region Sunday, allowing winds to gradually subside. While it will still be very cold (highs will only be in the single digits), wind chills will improve through the afternoon. At this time, the coldest conditions will be across northern NY, particularly in the Adirondacks and northern St Lawrence Valley, where wind chills of -30 to -40F are expected. With little change in the overall forecast, had enough confidence in these bitterly cold wind chills to upgrade the Extreme Cold Watch to an Extreme Cold Warning. Further east, across the Champlain Valley and northern/central VT, wind chills are not expected to be quite as extreme. This too hasn't changed overly much. Isolated pockets of colder conditions are possible, but confidence in areal and/or temporal coverage of wind chills exceeding -30F (Warning criteria) remains low. However, -20F to -30F is pretty much a certain thing, so the Watch was upgraded to a Cold Weather Advisory for these areas. If the Champlain Valley/VT start to trend colder, additional upgrades to Extreme Cold Warnings may be needed. However, don't focus on Advisory vs Warning overly much; it's going to be dangerously cold, regardless. Anyone with outdoor plans should consider altering and/or delaying outdoor activities this weekend. If you must be outdoors, please make sure to dress for very cold conditions.

High pressure briefly builds overhead late Sunday into Sunday night, before moving east on Monday. As such winds will slacken, but giving way to better radiational cooling conditions. There are some indications that there could be lingering cloud cover over the higher terrain Sunday night/Monday morning which would limit cooling potential. Still, overnight lows are expected to be 5 to 15 below zero areawide, and can't rule out some locations approaching -20F. Additional cold headlines may be needed.

KEY MESSAGE 3: Closed low in the Maritimes will shift east Tue- Wed allowing another shortwave and surface reflection to move across Wed with some scattered snow showers. This shortwave will likely continue to strengthen somewhere across New England/eastern Quebec to continue cyclonic flow and chance of snow showers through Thursday night - Friday, mainly in the northern, higher terrain.

Airmass modification during the week with temperatures approaching seasonable normals by the end of the work week.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Through 12Z Saturday...VFR conditons expected through 21z across the entire area with clouds increasing and lowering throughout the period.

Light snow moves into northern NY sites just prior to 00z Sat and across VT between 00-03z Sat. MVFR-IFR conditons with snow...worsening conditons with time with gradual improvement to MVFR-VFR likely after 12z Sat.

Winds will primarily be less than 10 knots across the entire CWA through 06z Sat then arctic front moves through northern NY between 06-12z and VT 11-18z. As the front moves through winds will become NW 10-16kts with g25kts.

Outlook...

Saturday: Mainly MVFR, with local VFR possible. Chance SN. Saturday Night: VFR. NO SIG WX. Sunday: VFR. NO SIG WX. Sunday Night: VFR. NO SIG WX. Monday: VFR. NO SIG WX. Monday Night: VFR. NO SIG WX. Tuesday: VFR. NO SIG WX.

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. Please contact us if you observe winds significantly deviating from the recreational forecast.

BTV WATCHES/WARNINGS/ADVISORIES

VT...Cold Weather Advisory from 6 PM Saturday to 1 PM EST Sunday for VTZ001>011-016>021. NY...Extreme Cold Warning from 7 AM Saturday to 1 PM EST Sunday for NYZ026-027-029>031-034-087. Cold Weather Advisory from 6 PM Saturday to 1 PM EST Sunday for NYZ028-035.