textproduct: Burlington

WHAT HAS CHANGED

As of 415 AM EST Thursday...Increased wind gusts today as model soundings indicate deep mixed layers and steep lapse rates that have the potential to bring us wind gusts 30-40 knots or higher. Also adjusted temperatures Friday night slightly with the latest MOS guidance, we still anticipate lows exclusively below zero F and wind chills -20 to -40 F Friday night-Saturday morning.

KEY MESSAGES

As of 213 AM EST Thursday...

1. Rounds of lake effect snow and scattered snow squalls are expected today and tomorrow. Gusty winds, heavy snowfall, and rapid snow accumulation will make for hazardous travel, including for the Thursday evening and Friday morning commutes. A Winter Weather Advisory is in effect for southeastern st. Lawrence County today into tomorrow.

2. Dangerously cold conditions are increasingly likely late this week, with wind chills of -20F to -40F possible. An Extreme Cold Watch is in effect for Friday night and Saturday morning.

3. Widespread Snow Increasing Likely Sunday Night into Monday.

DISCUSSION

As of 213 AM EST Thursday...

.KEY MESSAGE 1: Rounds of lake effect snow and scattered snow squalls are expected today and tomorrow. Gusty winds, heavy snowfall, and rapid snow accumulation will make for hazardous travel, including for the Thursday evening and Friday morning commutes. A Winter Weather Advisory is in effect for southeastern st. Lawrence County today into tomorrow.

Low pressure currently located just north and east of Lake Superior early this morning will move northeastward throughout the day today, dragging a warm front and then a cold front through northern New York and Vermont in quick succession. We anticipate scattered snow showers, particularly along a lake effect band off Lake Ontario, to occur today into tomorrow. Models continue to indicate steep low level lapse rates as cold air flows into the region aloft, likely resulting in efficient atmospheric mixing throughout the day today. 850mb level jet continues to look strong around 45-55 knots that could mix down to the surface, and surface-based CAPE values run around 50-100 J/kg throughout the afternoon. Snowfall rates could exceed 1 in/hr briefly with these squalls, reducing visibility to 1/2 mile or less. This will be especially true downwind of Lake Ontario which will help to enhance moisture and instability in a lake effect band that will produce on and off heavy snow in southeastern St. Lawrence County.

Gusty winds of 30 to 40 mph will blow around falling snow as well as any freshly fallen snow and make travel hazardous. Anyone traveling today or tomorrow, including during the evening and tomorrow morning commutes, should be prepared for highly variable road conditions, with sharply reduced visibility, gusty winds, and snow-covered roads with little warning in squalls. Flash freeze, however, is not anticipated with these snow squalls. Areas in southeastern St. Lawrence County will see the most in terms of overall accumulations with 3 to 7 inches as snow is expected to continue on and off overnight tonight, and higher accumulations are possible around Star Lake to Horseshoe Lake. Elsewhere, snow accumulations will be only a dusting to a couple inches through tomorrow.

.KEY MESSAGE 2:Dangerously cold conditions are increasingly likely late this week, with wind chills of -20F to -40F possible. An Extreme Cold Watch is in effect for Friday night and Saturday morning.

An arctic cold front is expected to cross the region on Friday, ushering us into cold air advection with northwesterly winds gusting as high as 20-40 knots both Friday into Friday evening. We anticipate 925mb level temperatures crashing into the -25 to -31 C range Friday night, resulting in temperatures at the surface falling into the 0 to -20 F range by early Saturday morning and wind chills as low as 15 to 35 degrees below zero. Coldest conditions are expected across the Adirondacks and at highest elevations of the Greens. Although some of our area may not reach Extreme Cold Warning criteria (-30F), it will be dangerously cold for anyone who might be outdoors Friday evening through Saturday morning. If you are unable to avoid being outside, make sure to wear plenty of warm clothing, including hats and mittens or gloves. And don't forget about your pets; bring them inside if able. If not, make sure they have adequate shelter from the cold.

While Saturday night will also be very cold with lows in the 0 to negative 20 range as well, we are lacking the wind component for similar brutal wind chills as high pressure moves overhead. A powerful nor'easter will develop on Sunday and track up the eastern seaboard, potentially sending some overshooting clouds to cover the forecast area Saturday night, which may also limit how cold we get with regular lows. Additional cold weather headlines might be needed, but confidence remains low.

KEY MESSAGE 3: Widespread Snow Increasingly Likely Sunday Night into Monday.

A deepening coastal low will track through the Mid-Atlantic Sunday into Sunday night and then somewhat up the East Coast into Monday. Our weekend cold maker 1040mb high looks to keep the low from truly riding up the coastline, but the precipitation shield with this particular system is uncharacteristically wide, extending several hundred miles to the north into New England. Recent trends have continued to suggest a stronger system with several northward jogs pushing more widespread snowfall into much of the region. The most likely solution is that the heaviest snow stays to our south, however, near or at advisory level snowfall amounts appear likely. NBM probabilities have increased northward with probabilities of 4 inches of snow up to at least 50% for the entire region, and up to 70-80% for the southern regions of the area. Furthermore, probabilities for 8 inches or greater have come up 10-20% to a range of 30-50% along the central and southern spine of the Greens, southern Vermont, and around the High Peaks of the Adirondacks. While it will be difficult initially to see any snowfall with a dominating dry 1040mb high preceding the system, a stronger low solution will help to erode that air mass faster with recent trends. One additional note is that ensembles have slowed the system with an arrival later into Sunday night with snow showers lingering perhaps into midday Monday across central and southern Vermont. Areas in New York, especially the northern St. Lawrence Valley will see snow taper off the quickest, and hence will likely see the least snow from this system. All said, an impactful more typical winter system from what we have seen this season is looking increasingly likely to start next week. Current 48 hour NBM snowfall thresholds using 15- 20:1 snow ratios are as follows:

Southern Areas: 2" 70-90% 6" 50-70% 12" 20-30%

Northern Areas: 2" 55-75% 6" 30-50% 12" 10-20%

AVIATION /07Z THURSDAY THROUGH MONDAY/

Through 06Z Friday...Light to moderate snow in association with a passing weak cold front is shifting east through the region with visibilities at times as low as 1SM, primarily at SLK. Radar shows a line of light to moderate snow showers passing through the Adirondacks with some steadier lighter snow showers across Vermont at RUT/EFK/MPV. This line of snow showers will shift east through about 12-13Z with reductions in flight categories to MVFR and perhaps brief IFR mainly due to vsbys drops to MVFR/IFR. Ceilings will generally stay prevailing above 3000ft agl, however, under any bands of snow showers cigs may briefly reduce to 2000-3000 ft agl. Beyond 12Z, the line of moderate snow showers will shift east of most terminals with lingering snow showers from a developing lake effect snow band, impacting SLK/PBG/EFK, and perhaps BTV at times. There is still uncertainty how where the band exactly sets up. Aside from the snow forecast, south/southwest winds will remain gusty through the TAF period with a persistent 40-45 kt jet. Surface gusts will generally be in the 20-30kt range. LLWS will weaken by 12Z as the peak of the jet shifts east by daybreak. Winds across the region will shift from south this morning to southwest by the afternoon and prevail southwest to west through the remainder of the TAF period.

Outlook...

Friday: VFR. Chance SHSN. Friday Night: VFR. Slight chance SHSN. Saturday: VFR. NO SIG WX. Saturday Night: VFR. NO SIG WX. Sunday: VFR. Chance SN. Sunday Night: Mainly VFR, with areas MVFR possible. Chance SN. Monday: MVFR. Chance SN.

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 Watch from Friday evening through Saturday afternoon for VTZ001>011-016>021. NY...Extreme Cold Watch from Friday evening through Saturday afternoon for NYZ026>031-034-035-087. Winter Weather Advisory from 10 AM this morning to 7 PM EST Friday for NYZ029.