textproduct: Burlington

WHAT HAS CHANGED

As of 203 PM EST Wednesday...

Shower chances have increased with isolated to scattered terrain driven snow showers expected through late Thursday morning. Accumulations will generally be less than 1 inch. Timing continues to slide later for the frontal passage of a strong Arctic Front over this weekend.

KEY MESSAGES

As of 203 PM EST Wednesday...

1. Light terrain snow showers through early Thursday then a strong cold front brings snow showers and cold temperatures late Friday and Friday night. Driving conditions could sharply deteriorate with a quick 1 to 3 inches accumulating with potential for periods of poor visibility as well.

2. Dangerous cold with wind chills of 20 to 30 below zero remain likely over the weekend. Lowest values now look mainly in the later Saturday through Sunday morning timeframe.

3. No significant impacts currently expected for early next week. Temperatures will gradually moderate trend Monday through Wednesday with low, but increasing chances for snow.

DISCUSSION

As of 203 PM EST Wednesday...

KEY MESSAGE 1: Northwest flow is resulting in some orographic snow showers mainly across the northern Greens this afternoon. Coverage of showers likely expand early Thursday morning as a passing trough increases forcing in northwestern Vermont, northwestern slopes of the Adirondacks and especially across the northern Greens. Totals will be minimal, but up to an inch of accumulation will be possible. High pressure builds in Thursday with a good set up for radiational cooling Thursday night. The NEK of Vermont will likely be the location that radiates out the most with low temperatures around 10 degrees below zero.

Friday will be a reload day with winds shifting out of the south supporting highs in the mid 20s, upper 20s if skies can clear. A strong Arctic front will approach late Friday moving through the region overnight. Widespread snow/snow showers are anticipated, but will largely be out of phase with strongest winds as thermal packing will be tightest behind the front. The threat of overnight snow squalls is lower than preceding forecast pointed towards, but cannot rule out some early Saturday squall-like showers in portions of northern New York as surface winds turn northwesterly and increase in excess of 20mph with gusts to 30 mph. These winds will push apparent temperatures towards the dangerous threshold around -20F for the Saint Lawrence Valley. Snowfall totals will not be completely trivial, mainly expected to range 1 to 3 inches through early Saturday, which could create slick driving conditions with periods of poor visibility.

KEY MESSAGE 2: Model agreement is becoming a little better with regards to the well-anticipated Arctic blast. The trend towards a later arrival of Arctic air during the day on Saturday and slightly less intense/extreme cold is becoming more consistent. As such, we have held off on any Extreme Cold Watches at this time. That being said, the air still is on track to become dangerously cold as the day progresses Saturday, with strong cold air advection from west to east. This pattern with a sharp frontal inversion should result in gusty northwesterly winds, and some of the deterministic guidance supports boosting winds and wind gusts a bit from the National Blend of Models with frequent gusts Saturday of 25-30 MPH widespread. High temperatures will be rather misleading relative to hourly temperatures, especially in the valleys and in Vermont; early high temperatures in the teens will fall into the single digits and potentially below zero during the day. This is consistent with forecast soundings showing 925 millibar temperatures dropping steadily while the inversion height gradually lowers towards that level.

The coldest conditions are on track for Saturday night into Sunday morning. Low temperatures will be dependent somewhat on winds diminishing overnight, and note both Saturday night and Sunday night these temperatures are challenging with large spread in model guidance. The deep snowpack combined with additional fresh snow expected Friday night into Saturday will support high reflectance/ideal radiational cooling conditions where skies become clear and winds light. Therefore potential for very low minimums in the -20 to -30 range without wind will exist in sheltered valleys Saturday night. As a result, the greatest risk of wind chills below - 20 continues to be Saturday night through Sunday morning, with probabilities largely in the 50-80% range. The air mass does look to moderate Sunday night enough that the risk of dangerous cold is more marginal, with probabilities of temperatures below -20 mainly in the 10-20% range in north central/northeastern Vermont and the Adirondack region.

KEY MESSAGE 3: The longer range forecast appears more uncertain than normal, especially with regards to precipitation. There is good consensus that temperatures will tick upward day to day, with lower elevations flirting with above freezing temperatures on Wednesday in a warmer scenario. While high temperature spread is not particularly large, precipitation is all over the place. Most model guidance is dry. However, there is some uncertainty in development/track of any waves along a quasi-stationary boundary to our south and west. The frontal zone, if it stays too far to the south as the consensus shows at this time, will prevent us from having any significant precipitation. At this time, accumulating snow is unlikely areawide Monday and Tuesday, but moves into the chance category Tuesday night into Wednesday, when probabilities of 12 hour precipitation of at least 0.1" increases into the 5-10% range.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Through 18Z Thursday...A mix of MVFR and VFR conditions are expected for much of the period with light winds. Currently behind a weak boundary there is somewhat stronger winds, mainly northwesterly in Vermont and southwesterly in New York, but winds will again trend light and variable tonight ahead of another trough. At the surface, high pressure will continue to build in from the west, so increasing subsidence will support some continued chances for MVFR ceilings especially at MSS, SLK, and EFK. As for precipitation, if it materializes there will be operational impacts with more light snow accumulation and lowering visibilities; therefore, have used PROB30 groups in the 06Z to 12Z period given low probabilities, and only at SLK, EFK, and BTV. The upper level trough that passes through in this timeframe will support upslope snow showers, with again favorable conditions for BTV in northwest blocked flow for these light snow showers.

Outlook...

Thursday Night: VFR. NO SIG WX. Friday: Mainly VFR, with local MVFR possible. Slight chance SHSN. Friday Night: Mainly MVFR and IFR, with local VFR possible. Definite SHSN. Saturday: Mainly VFR, with areas MVFR possible. Chance SHSN. Saturday Night: VFR. NO SIG WX. Sunday: VFR. NO SIG WX. Sunday Night: VFR. NO SIG WX. Monday: Mainly VFR, with areas MVFR possible. 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. 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...None. NY...None.