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FXUS61 KBTV 011425 AFDBTV

Area Forecast Discussion National Weather Service Burlington VT 925 AM EST Fri Dec 1 2023

SYNOPSIS
Warm weather is expected today as a stalled cold front in New York and an incoming warm front allow temperatures to remain in the 40s to even lower 50s. Widespread rain will lift into the North Country late this afternoon, and transition at elevations above 1500 foot elevation to light snow accumulations expected, mainly above 2500 feet. Additional rounds of precipitation are likely Saturday. Saturday night into Sunday morning, freezing drizzle will be possible, and could result in slick travel.
Then, a larger scale system is expected Sunday afternoon into Monday, with the potential for several inches of heavy, wet snow across high terrain areas.

NEAR TERM /THROUGH SATURDAY/
As of 925 AM EST Friday...Forecast remains in very good shape.
Latest data suggests we have trended the right way towards more rain and less snow with the wave that will move through the region later today, with snow levels mainly above 3000 feet in northern New York and northern Vermont, and 4000 feet in central and southern Vermont. For now, main tweaks were to sky cover to bring in overcast skies areawide by 11 AM; satellite imagery shows clouds filling into southeastern portions of Vermont within the next hour, joining the rest of the region.
Precipitation chances were also slightly lowered over a strip of northern New York and far northern Vermont this morning, but a sprinkle cannot be ruled out in this area ahead of the primary rain event this afternoon.

Previous Discussion...

No major changes to the forecast this morning. A wet and dreary weekend is expected. For today, a weak frontal boundary is about to cross the St. Lawrence River. Some light returns are starting to show up on radar, with the first hint of rain now at Massena, NY. This front is not likely to drive much precipitation given the weak dynamics and most moisture being confined to the lower levels. This front will stall across northern New York and eventually dissipate as a warm front lifts north later this afternoon. The notable change to the forecast is that any guidance that was hinting at cold air remaining in place has largely turned towards the warmer solutions.
Probabilistic data suggested making a larger than normal upward adjustment in temperatures this afternoon from the previous forecast, such that some lower 50s are possible in south-central Vermont. Given the 50 observed at Massena overnight, this seems reasonable.

The forecast rainfall with the warm front is on track, but with the warmer temperatures, the area of snow has been tapered further up to the mountain summits. Rainfall amounts with the front generally range between 0.10" to 0.33". Snowfall could occur as low as 1500 ft agl, but most accumulations should remain at or above 2500 ft agl with this event.

This warm front also stalls across the region. So between Friday night and Saturday, there's not much of a diurnal range. Some spots will likely only see a difference in temperature of 2 to 4 degrees.
There will also be light winds, which could result in some lingering drizzle as PoPs briefly decrease Friday night into early Saturday.
However, an upper wave will eject northeast in channeled upper level winds and bring some more rain or snow early Saturday morning into the afternoon. The warm front shifts back to the south just a bit, and some cold air should start to filter back southwards. We'll be watching this closely, as we will likely be dealing with more drizzle and freezing drizzle heading into Saturday night. Additional QPF will be a few hundredths up to a tenth.

SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/
As of 345 AM EST Friday...Fairly active period of wx anticipated with several systems to impact our fa. First concern is potential for light freezing drizzle on Sat night, followed by a mix of rain and wet snow late Sunday aftn into Monday.

Confidence continues to increase for a period of light drizzle with areas of freezing drizzle on Sat night, as low level cold air drains down the SLV/CPV and parts of the northern mtns on north winds behind departing weak low pres. A sfc boundary wl remain draped acrs central NY into southern VT, while weak channeled 700-500mb vorticity and associated moisture wl remain acrs northern NY into central/northern VT on Sat night. Thermal soundings suggest plenty of moisture trapped below developing subsidence inversion with profiles indicating 90 to 100% rh proggs thru 800mb, while deep layer drying occurs btwn 800-300mb, supporting the idea of light precip. High res data from the HRRR/RAP and NAM3km indicates 2m temps dropping <0C as llvl caa develops on weak north winds behind departing low pres. It has been noted a rather cold air mass is lingering acrs central Canada this morning with single digit readings directly under high pres, which wl modify and slowly bleed into our fa. Attm the greatest potential for areas of freezing drizzle looks to be northern SLV/northern CPV and parts of the higher trrn of the northern Dacks/Green mtns. Always challenging to determine exact placement/areal coverage of light precip in this type of scenario. For temps have trended slightly cooler with lows hovering either side of freezing most locations.

Our next system quickly arrives Sunday aftn into Monday with another round of rain and snow. Still limited agreement among the guidance and their associated ensemble members, but confidence is growing for a period of measurable precip, so have increased pops to near 100%.
The ECMWF and associated ensemble members continue to be the coolest and most aggressive with potential for snowfall, even in the valleys locations, while the GFS and its ensemble members are warmer and show less potential for snow. Its interesting how the ECMWF is deeper/strong with closed 850-500mb circulation crossing our cwa, while axis of deep layer moisture extends from the Great Lakes into northern New England. Meanwhile, GFS shows initial surge of moisture/precip lifting quickly acrs our cwa on Sunday night, while mid lvl dry slot develops with better dynamics/moisture located acrs central/southern Canada by Monday.

The general synoptic scale pattern shows fast confluent flow acrs the Great Lakes into the NE CONUS, while digging s/w energy acrs the central Plains ejects toward the Ohio Valley on Sunday/Sunday Night.
This helps to enhance elongated double barrel sfc low structure, while a potent 170-190 knot jet at 250mb lifts acrs the MS/OH valleys, aiding in deep layer lift. The very fast 700 to 300mb flow aloft supports the idea of precip developing fast, but also exiting our region rather quickly on Monday, before a favorable period of upslope snow showers develop late Monday into Tues.

Thermal profiles are tricky once again, especially with limited cold air initially. The combination of dynamics and developing east/southeast upslope flow, helps to cool the 925mb to 850mb layer just enough acrs the upslope regions of the eastern/central Dacks and portions of the central/northern Green mtns to support the potential for a wet snowfall, while a cold rain occurs in the valleys. Current soundings would support snow levels near 1500-1800 ft for the event, with a sharp elevation dependent snowfall from the valley floors to summits. For my initial snowfall grids, integrated an elevation dependent snow ratio, which result in snowfall amounts thru 12z Monday at the summits of 6 to 8 inches, with 2 to 6 inches midslopes, and nothing to 2 inches 1000-1500 feet. WPC experimental winter storm outlook does have 30-50% chance of reaching criteria for portions of the northern Dacks and 10-30% for parts of northern VT and the SLV. Given the large spread in the upper level evolution, sfc low track, and associated thermal profiles, this fcst is definitely subject to change moving forward this weekend. For now have mention the potential for heavy wet snowfall acrs the mtns in the HWO and continue to monitor additional fcst this weekend for more details on accumulations and potential impacts.

LONG TERM /MONDAY NIGHT THROUGH THURSDAY/
As of 345 AM EST Friday...Through midweek expect mid/upper lvl trof to prevail, resulting in occasional upslope snow showers and below normal temps. Additional accumulating snowfall is likely in the northern Dacks and central/northern Greens Monday thru Weds of next week associated with favorable 925mb to 850mb caa and upslope flow.
The amount of lingering deep layer moisture and timing of embedded s/w energy in the flow aloft wl determine accumulating snowfall potential moving forward. Otherwise highs generally in the mid 20s to mid 30s and lows upper teens to mid 20s for early to middle of next week.

AVIATION /14Z FRIDAY THROUGH TUESDAY/
Through 12z Saturday...Mainly VFR conditions are present. A weak front is sliding across KMSS and KSLK, but with isolated rain showers. Winds are mainly south to southwest around 4 to 7 kts, but are still around 11 to 14 kts at KBTV, and winds should trend 5 kts or less today. Widespread rain will lift north around 18z-20z, and becoming moderate between 22z and 01z. It seems too warm for much snow, except KSLK around 00z. So expect gradual reductions in ceilings to 1500-2500 ft agl and visibilities in rain between 3-6SM and locally down to 1 1/2SM.
Low-level moisture stalls, resulting in ceilings trending to 700-1500 ft agl across the region with lingering drizzle, rain showers, a mix of rain and snow. Winds will trend light and variable, leaving these conditions to linger beyond 12z Saturday.

Outlook...

Saturday: Mainly IFR, with local MVFR possible. Chance SHRA, Chance SHSN.
Saturday Night: Mainly IFR, with local MVFR possible. Chance DZ, Chance FZDZ.
Sunday: Mainly IFR, with areas MVFR possible. Chance RA, Chance SHRA, Chance SHSN.
Sunday Night: Mainly MVFR, with areas IFR possible. Definite RA, Definite SN.
Monday: Mainly MVFR, with local IFR possible. Likely SHSN, Likely SHRA.
Monday Night: Mainly MVFR, with areas IFR possible. Chance SHSN.
Tuesday: Mainly MVFR, with local VFR possible. Slight chance SHSN.

BTV WATCHES/WARNINGS/ADVISORIES
VT...None.
NY...None.

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