textproduct: Burlington

SYNOPSIS

Widespread snow arrives this evening and tonight, with most areas seeing 1 to 4 inches of snow by daybreak tomorrow, and 4 to 9 inches expected in the St. Lawrence Valley. Seasonably cold weather continues into the New Year along with occasional chances for mountain and lake effect snow showers. Moderating temperatures are expected for the middle of next week ahead of another weather system.

NEAR TERM /THROUGH THURSDAY/

As of 114 PM EST Wednesday...Winter Weather Advisories remain in effect, and for southwestern St. Lawrence County, the Winter Weather Advisory has been upgraded to a Winter Storm Warning - in effect through 7 AM/12Z.

Rapid refresh guidance and 12z high res guidance have trended towards more intense lake effect snow, especially across southwestern St. Lawrence County. Based on observations downwind of Lake Ontario, heavy snowfall rates of 1-2"/hr of snowfall appears likely along Gouverneur with the highest potential between about 5 PM and midnight. Given that breadth of time, reaching 7" should meet the 80% confidence bar for the warning. Lake effect snow will lift ahead of an approaching surface low. Deepening is expected as the 500mb upper low trends close to 500 dam, and an upper jet streak will nose in south of the region, placing northern New York very favorably within the left exit region of that jet. Sharp convergence along the surface low abutting the northwestern slopes of the Adirondacks will make that region most favored for snow as the low tracks overhead, which makes this event a bit of a hybrid case for St. Lawrence County.

Across Vermont, residual dry air and 850mb flow increasing to 30 to 40 knots will result in an initial drop of snow this evening that lifts north, followed by terrain shadowing. As the surface low tracks overhead overnight and northwest flow initiates, we'll see snow fill back in and then become terrain favored, leading to amounts mainly between 1-4", with locally lower patches in southern Vermont and on the New York side of the Champlain Valley.

One potential inhibiting factor will be how cold the air is. As the surface low shifts east, we cool below the dendritic growth zone. So we should go from a 20-25:1 SLR to something closer to 15:1 on the backside. Winds are expected to slacken as the surface low approaches. So squalls are not anticipated. However, on the backside, northwest flow will quickly allow for gusts 20-25 mph, locally up to 35 mph. So blowing/drifting snow is likely, especially with icy surfaces being a smooth frictionless surface and this snow leaning on the powdery side. This will probably also make measuring a little challenging too.

The main concern will be for holiday celebrations. The combination of blowing snow and locally heavy snow in parts of the St. Lawrence County may catch motorists off-guard with poor visibility within the moving target of heaviest snow. The initial lake effect band will be fairly transient, and will then merge with potential mesoscale banding on the northwest side of the strengthening surface low then sliding east. So for northern New York, be prepared for changeable weather, especially as wind chills fall towards -5 to -15 F. Temperatures have managed to warm nicely ahead of the surface low in the teens and mid 20s, but on the backside of the low, temperatures will quickly fall into the upper single digits to lower 10s across Vermont and near 0 over northern New York. Snow will taper off New Year's Day with continued chilly weather within northwest flow.

SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/

As of 114 PM EST Wednesday...Cold weather will continue Thursday night into Friday. Temperatures on Friday morning will be very chilly, with low temperatures near 0 to the single digits below zero. Winds will abate, though. So radiational cooling will at least have minimal wind chills. We don't moderate much on Friday with mainly 10s to near 20. A subtle trough will angle southeast late Friday into the overnight hours. This should lure some lake effect snow to our south northwards, and could also have a few showers of its own along the international border. At this time, amounts appear likely to be on the lighter side. Another cold night will pass Friday night into Saturday, with single digits to near 0 again.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

As of 114 PM EST Wednesday...Cold and dry conditions are expected for the most part on Saturday, with high temperatures well below normal, mainly in the teens. Some very light, isolated snow showers are possible (under 20% chance), especially in the Northeast Kingdom and mountains.

More interesting weather may follow Saturday night into Sunday, and again Monday afternoon - Monday night with more widespread light snow events in northwest flow. While it is likely to snow at some point through this period, the specific timeframe cannot be known in this pattern, so note precipitation chances currently are shown in six hour windows in the range of 10-40%. Signals for below normal temperatures are strong through Monday, then weaken Tuesday into Wednesday when there is some spread in the 500 millibar height fields after a long period of persistent troughing. Generally the cold will likely ease by midweek, although the degree of warming is unclear. Breaking it down by the most recent ensemble clusters, one multi-model cluster, especially in the GEPS, shows 850 millibar temperatures becoming above normal, while the mean in other clusters primarily from the GFS and ECMWF ensemble show near normal values. So at this time, near normal temperatures currently forecast (highs in the upper 20s to low 30s) is reasonable with the possibility for warmer conditions/thawing, with further warming possible for Wednesday.

At this time, a significant low pressure system is unlikely as the upper air pattern trends zonal midweek, but with some kind of frontal system approaching from the west we'll be monitoring for somewhat heavier precipitation with possibility of a rain/snow mix in the valleys. Stay tuned!

AVIATION /19Z WEDNESDAY THROUGH MONDAY/

Through 18Z Friday...An area of light snow is gradually blossoming over the airspace, a little faster than originally expected. With dry air in place, most precipitation will be flurries except at higher elevations such as at SLK where visibilities have already dropped under 3SM. Low chances of IFR conditions through 00Z elsewhere, although it would not be surprising if snow briefly was sufficiently heavy to do so at any site. After 00Z chances for steadier snow increase with the approach of a low pressure system from near Lake Ontario. As the low moves northeastward just east of MSS around 09Z and passing just north of BTV and EFK through 12Z, some snow showers are likely at most sites before dry air scatters out the cloud cover, with perhaps brief MVFR flight conditions trending VFR, in the wake of the front.

Currently winds are mainly westerly, with some gusts near 20 knots at most sites with steep low level lapse rates but winds aloft are not quite to the level to be concerned with LLWS. These winds will trend southerly, favoring BTV with regards to gusts while turning northeasterly at MSS, between about 00Z and 04Z. These conditions will continue until the aforementioned low pressure system and attendant front pass, with a sharp wind shift to northwesterly or westerly between 10Z and 14Z. Peak gusts will likely be 20-30 knots for a short time, then decrease gradually through the remainder of the period.

Outlook...

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

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.

The Newport AWOS has stopped reporting due to a communications failure likely at the site. TAF amendments will not be scheduled until this issue is resolved.

BTV WATCHES/WARNINGS/ADVISORIES

VT...None. NY...Winter Weather Advisory until 7 AM EST Thursday for NYZ026-027- 029-030. Winter Storm Warning until 7 AM EST Thursday for NYZ087.