textproduct: Burlington

WHAT HAS CHANGED

As of 321 PM EDT Saturday...

Potential for snowfall into lower elevations has increased for Sunday. Additional snow showers also are expected on Monday with unseasonably cold air and trough moving through.

KEY MESSAGES

As of 321 PM EDT Saturday...

1. Gusty winds will continue ahead of an approaching cold front, with the strongest gusts across northern New York and near the International Border this evening.

2. Widespread rain will change to snow before ending during the day on Sunday. Minor snow accumulations and slushy, slippery travel is possible during the day.

3. Unseasonably cold conditions Sunday night into Monday night will be accompanied by a chance of snow showers, especially Monday morning.

4. Temperatures are favored to warm back to seasonal averages through the week with some potential for showers late next week.

DISCUSSION

As of 321 PM EDT Saturday...

KEY MESSAGE 1: A Wind Advisory remains in effect for Franklin and Clinton Counties in northern New York from 5 PM today to midnight tonight for wind gusts between 40 to 50 MPH. The strongest gusts will primarily be along the US Route 11 corridor from Moira, NY to Ellenburg Depot, New York, generally from 6 to 9 PM tonight. A few power outages and downed tree limbs may result.

This afternoon we have seen breezy south to southeast winds across the region, with gusts mostly in the 30 to 40 MPH range. The gustiness, associated with sunshine and warm dry air near the ground, is resulting in steep low level lapse rates. Those lapse rates support mixing of modestly strong winds aloft and further drying us out, as relative humidities locally have fallen as low as 30-40% but mainly 40-60%. With low level winds ramping up tonight and continued dry air mass present, the mixing will tap into more significant winds aloft. 925 millibar winds of 45 to 55 knots continue to be modeled across the northern fringes of the Adirondacks, particularly along US Route 11 such as in Malone, NY. Enhancement from downsloping will lead to gusts up to 40 to 50 MPH with a localized gust to 55 MPH possible. The southerly flow also will lead to channeled winds in the Champlain Valley, which appear to be localized once again to the western side of the lake due to a slight easterly component to the near surface flow. The magnitude of the low level jet does not look concerningly strong, so potential for downed tree limbs may be enhanced more due to recent wet weather than due to the winds alone.

KEY MESSAGE 2: A large, highly amplified longwave trough is supporting a large area of precipitation along a cold fronts steadily approaching from the west tonight. A strong thermal gradient will be present and likely increasing with time as the front moves into our region. The upper level jet configuration, with jet streaks to our north and south by midday Sunday, will be favorable for widespread precipitation behind the surface front. As such, confidence in a (very) late season snowfall is increasing. Precipitation rates may be heavy enough even for localized 1" per hour snowfall at times, with moderate snowfall intensity (>0.05" of liquid in an hour) likely during the daytime hours from the Adirondacks and points eastward. The strongest frontogenesis and the more intense precipitation rates should largely slide eastward such that Advisory level snowfall amounts are unlikely, but Probability Matched Mean HREF accumulations are currently in the 1 to 4 inch range for much of Vermont and northern New York above about 500 feet elevation.

Have nudged temperatures closer to some of the raw model guidance away from the National Blend to get snow and accumulations more consistent with the expected cold air spilling into the region during the day after the cold front passes through. Given initially marginally cold temperatures, a wet snow can be expected. However, snow ratios should trend towards a more average snow density with time; impressively cold cloud temperatures in the snow growth zone within 10,000 feet of the surface are expected before snow tapers off.

KEY MESSAGE 3: Main focus for early in the week will be the unusual cold. While we typically have a final wintry period before the warm season truly gets underway, Monday does look potentially within daily record territory, especially for low temperatures Monday night as high pressure builds in. These temperatures currently are forecast in the range of 15 to 25, but clear skies and light winds could support a frigid night, with temperatures more typical of winter in the single digits to low teens.

Before skies trend clear, a couple of boundaries will move across the area Sunday night through Monday to support snow shower chances. Of most note, the snow squall parameter shows some favorable ingredients for a minor, scattered type of event for Monday morning as a secondary cold front/wind shift boundary moves southward across our region. There will be some instability, lingering low level moisture, and convergence along this front to support at least some shower activity. For now have just a coating of snow indicated over a large area and have increased the chances of precipitation a bit, as the forcing looks fairly consistent amongst model guidance. Will add detail as confidence grows, but overall not looking like a significant event other than the fact that it is late in the season for winter weather.

KEY MESSAGE 4: Long wave ridging is expected to displace troughing through next week, shunting the polar front jet and main storm track northeastward into eastern Canada. This pattern favors slowly warming temperatures despite a continued northwest flow pattern. Highs are projected to warm from low/mid 50s midweek into the 60s heading into the weekend while lows correspondingly warm from the 30s into the 40s. Models diverge late next week, but the consensus shows an amplification to the ridge axis which may allow for a backdoor cold front to drop through the region promoting some shower chances by Friday night.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Through 18Z Sunday...Ongoing southerly will remain gusty (25-35kts) into the overnight hours ahead of rainfall. As surface speeds drop, LLWS will ramp up with faster flow aloft outpacing surface speeds; some slight directional shear is likely as well with 850mb flow turning predominantly 200-220 degrees. LLjet will exit by 12Z with LLWS diminishing west to east after 05Z. CIGs will lower in earnest overnight as surface speeds drop, primarily MVFR then IFR increasing in coverage 12-18Z behind the front as winds turn westerly. Some RASN chances increase after 15Z for lower elevations with snow levels dropping and likely seeing a period of snow after 18Z.

Outlook...

Sunday Night: VFR. Chance SHSN. Monday: VFR. NO SIG WX. Monday Night: VFR. NO SIG WX. Tuesday: VFR. Slight chance SHRA. Tuesday Night: Mainly VFR, with areas MVFR possible. Slight chance SHRA, Slight chance SHSN. Wednesday: Mainly MVFR, with local IFR possible. Slight chance SHRA. Wednesday Night: Mainly VFR, with local IFR possible. NO SIG WX. Thursday: Mainly VFR, with local MVFR possible. NO SIG WX.

BTV WATCHES/WARNINGS/ADVISORIES

VT...None. NY...Wind Advisory until midnight EDT tonight for NYZ027-028-030- 031.