textproduct: Burlington

WHAT HAS CHANGED

As of 633 AM EST Tuesday...PoPs were slightly increased (up to 30-40%) along and near the spine of the Greens with additional forcing leading to isolated snow showers on Radar.

KEY MESSAGES

As of 140 AM EST Tuesday...

1. Lake effect snow shower chances will diminish this morning, but return this afternoon with continued cold conditions tonight.

2. Continued chances for light to moderate snow chances with possible embedded snow squalls and gusty winds Wednesday into Thursday as temperatures briefly increase back to seasonable norms.

3. A significant and dangerously cold arctic outbreak is expected late week into the upcoming weekend with wind chill values 20 to 40 degrees below zero possible.

DISCUSSION

As of 140 AM EST Tuesday...

.KEY MESSAGE 1: Chances for snow showers continue into mid week with a series of cold fronts associated with deepening low pressure systems traversing the region. Winds will become more westerly this morning into the afternoon which will help keep the lake effect band off Lake Ontario to our south for most of the day today. However, winds will once again turn southwesterly by late this evening pushing the lake effect band north back into the southern St. Lawrence County. Winds aloft will slacken today and this evening outside of the higher terrain lessening the northeast extent of the lake effect band. However, some isolated to scattered chances for snow showers enhanced by the lake can be expected downwind of the band in the Adirondacks and along the spine of the central and northern Greens this afternoon. Steep lapse rates and instability should be able to sustain at least some snowfall in the higher terrain. With limited coverage of the snow today, widespread travel concerns do not look likely, however, by Wednesday, a secondary system will bring more widespread chances of snow and gusty winds. Temperatures today and tonight will remain on the cold side with highs remaining in the teens and overnight lows into the single digits.

.KEY MESSAGE 2: Another deepening low pressure well north of us will drag along a warm front followed by a cold front with continued southwest flow Wednesday night into Thursday. Increased moisture with enhanced synoptic forcing will allow widespread warm advection snow showers to overspread northern New York and perhaps some snow showers along and east of the Greens in Vermont Wednesday night. The best forcing and moisture convergence will be over the St. Lawrence Valley, however, steepening lapse rates and orographic lift should be able to sustain some shower activity across the higher terrain of Vermont. Southwesterly flow aloft likely will limit the shower activity in the Champlain Valley. A dusting to an inch or two can be expected mainly across the Adirondacks and the St. Lawrence Valley. The main impact for Wednesday night will be increasing southerly surface winds in the Champlain Valley and the northern Adirondacks. South flow up to 30 to 40 mph will be channeled up the Champlain Valley Wednesday night into Thursday morning and along the northern periphery of the Adirondacks. These winds in areas of snow showers could lead to blowing snow with localized hazardous travel concerns. Southerly surface flow will also lead to non-diurnal temperatures Wednesday night with temperatures increasing overnight into the upper 20s to low 30s. Behind the warm front, southwest winds will enhance a reinvigorated lake effect band off Lake Ontario Thursday. A strong arctic cold will lead to enhanced forcing with localized heavy snow showers along with the lake effect snow showers Thursday afternoon. Instability will be near 100 J/kg, however, the convergence will limit the overall linearity of any squalls that develop. The NAM12 depicts snow squall parameter values 2 to 5. Snow showers will likely come in disorganized waves, however, these waves will be scattered to numerous.

KEY MESSAGE 3: A significant and dangerous arctic outbreak is looking more an more likely late week into the weekend as an extremely cold airmass moves into the region. Strong cold air advection is expected to occur across the forecast area on Friday and Friday night, then very cold 850mb temperatures -29 to -33 C crest over the forecast area late Friday night and early Saturday morning. Surface temperatures look to fall into the -20 to 0 F range during this period with wind chills as low as -10 to -35 F, even colder on mountaintops. Based on what we're seeing now, we'll likely need Cold Weather Advisories in place for most of the forecast area with potentially an Extreme Cold Warning for parts of northern New York where wind chills may be coldest.

Saturday will remain cold with highs only in the single digits above and below zero and high pressure taking hold of the region. Northwesterly surface flow is expected to continue throughout the day, making for MAXIMUM wind chills in the -15 to 5 F range, though most of the day should have wind chills around 5 below zero or lower. As is typical with high pressure, we anticipate light winds and breaks of clear sky throughout Saturday night, which would mean another very cold night with lows in the -20 to -5 F range. Wind chills Saturday night, though not quite as low as Friday night due to the calmer winds, will fall into the -30 to 0 F range. There remains some uncertainty on the longevity of the cold air as models show a storm system off the southeastern U.S. coast that may bring some milder air north into the forecast area late Saturday night and early Sunday morning. Overall, temperatures look to moderate into early next week but remain below seasonal averages.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

Through 12Z Wednesday...Lake effect snow is drifting south of the area this morning, but it is expected to return this afternoon with continued cold conditions tonight. SLK continues to report on and off snow showers this morning with ceilings varying from 1800-3300 feet above ground level and visibilities 1-3 miles in snow. About 40-60% chance of snow showers with IFR vis and MVFR cig continuing through 16Z Tuesday there, then chances decreasing further to 20-40% chance 16Z through 20Z Tuesday, more likely vis 3-5 miles, but IFR vis is not out of the question.

From 20Z onwards, VFR conditions are anticipated at SLK, but there remains the potential for the lake effect band to swing back through the area and cause degradations in conditions. MSS is another site that could have some on and off MVFR ceilings around 18Z through 22Z Tuesday as lake effect moisture angles towards it, though snow showers are also not out of the question at this site either. RUT is another site that just recently reported snow this morning, but this snow is not expected to be heavy or cause flight rule changes at this time.

Otherwise, VFR conditions and dry weather are the rule over the next 24 hours with winds out of the west and southwest gusting 15-30 knots through about 00Z-03Z Wednesday, but even after gusts diminish, conditions should remain fairly breezy with southwesterly sustained winds 5-15 knots. A briefly strong westerly to southwesterly low level jet looks to pass over SLK 03Z onwards, so as southwesterly surface winds decrease there, we could see a period of LLWS.

Outlook...

Wednesday: Mainly VFR, with local MVFR possible. Windy with gusts to 30 kt. Chance SHSN. Wednesday Night: Mainly VFR, with areas MVFR possible. Windy with gusts to 30 kt. Chance SHSN. Thursday: VFR. Chance SHSN. Thursday Night: VFR. Slight chance SHSN. Friday: VFR. Slight chance SHSN. Friday Night: VFR. NO SIG WX. Saturday: 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. 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.