378 FXUS61 KBTV 200935 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 435 AM EST Sun Dec 20 2020 .SYNOPSIS... Some light snow showers are expected today as a weak upper-level disturbance moves through. Monday will be dry, but unsettled and showery conditions return for Tuesday. The next notable weather system looks to impact the North Country Thursday and Friday, potentially bringing some heavy rainfall and gusty winds. As temperatures rapidly fall behind the system, a flash freeze is possible towards the end of the week. && .NEAR TERM /THROUGH MONDAY/... As of 403 AM EST Sunday...So far this has been a relatively mild morning for the North Country compared to the previous few nights, thanks to ongoing warm air advection overnight. An upstream shortwave can clearly be seen on morning water vapor satellite imagery over southern Ontario, which will move eastward into our forecast area through the day today. This will prompt thickening and lowering cloud cover, along with some lighter snow showers. Radar imagery already showing light returns over the North Country, but with observations showing plenty of dry air still at the surface, most of what is seen on radar is evaporating before reaching the surface. Expect lower- levels to fully saturate and spotty snow showers to generally start reaching the surface mid to late morning. There is limited moisture associated with the wave, thus snow accumulations will be light today. Looking at generally under an inch for most locations, with 1-3 inches expected over higher terrain of the Green Mountains. In addition to the light snow showers, will see increasing southerly winds today becoming 10-20 mph by this afternoon. The spotty snow showers will come to an end this evening for most of the area, although they may linger over the northern Adirondacks a little longer through the night tonight. May even see some spotty freezing drizzle overnight with forecast soundings indicating drying of mid-levels with lots of low-level moisture stuck near the surface. Any freezing drizzle would be very localized however, thus impacts would be very limited. Overnight lows will be in the mid to upper 20s. Monday will be a quiet weather day with mainly dry conditions. Will see some low clouds lingering for much of the morning, but may see some breaks in the clouds develop by afternoon. Highs will be in the 30s. && .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... As of 435 AM EST Sunday...Mid/upper lvl trof continues acrs the ne conus for Monday night into Tuesday with light snow showers possible mainly in the mtns. The combination of a weak secondary boundary, embedded 5h vort, good mid lvl moisture and favorable upslope flow, expect some snow shower activity acrs the northern dacks and green mtns on Monday Night into Tuesday. The forcing is weak and moisture limited as northwest flow prevails, but a few inches of snowfall is possible in the mountains. Valleys will see minimal accumulation, especially with bl temps in the l/m 30s on Tues. Weak sfc high and associated building mid/upper lvl heights, result in decreasing pops on Tues Night with some clearing possible. Have trended temps lower for Tues night based on clearing skies and light winds associated with ridge axis overhead. Lows generally single digits slk/nek to mid teens Tues Night, while highs range from the upper 20s to mid 30s. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 435 AM EST Sunday...A significant storm will impact the region late week with the potential for multiple hazards. These hazards include heavy rainfall/potential flooding, gusty winds, and flash freeze associated with tumbling temps on the backside of the system. Large scale pattern amplification develops late week, as strong ridge develops acrs the inter-mountain west, while deep full latitude trof evolves over the eastern conus. This full latitude trof and associated deep/strong southerly flow will advect rich sub- tropical moisture into the ne conus, as pw values surge btwn 0.75 and 1.0, which is 3 to 5 std above normal. A strong 250h dual jet couplet is progged to enhanced favorable upper lvl divergence, while anomalously strong southerly 850mb jet of 60 to 75 knots is progged to develop ahead of approaching trof. Many ingredient coming together to support the idea of heavy rainfall potential along sharp boundary with favorable fgen forcing and llvl convergence. Furthermore, as wave of low pres develops along boundary and mid/upper lvl trof becomes negatively titled and closed off, forward propagation of boundary and associated axis of potential heavy rainfall. The next question will be how warm temps get with strong southerly waa signature and associated ripening/melting of deep/cold snowpack acrs central/southern VT. Crnt forecast suggest temps well into the 40s on Thurs and continue to hold steady Thurs Night, before falling sharply late Friday/Friday Night, but not before reaching the upper 40s to mid 50s, with dwpts climbing into the 40s. Thinking this will cause snow melt to occur, along with the probability of heavy rainfall increasing, the potential for flooding moving forward will need to be watched closely. Have mention the idea of heavy rainfall possible in HWO for now and will fine tune messaging as event becomes better defined/resolved by guidance. Another concern will be potential for some gusty south/southeast winds late week. Latest guidance is slightly more southerly with progged 850mb jet of 60 to 75 knots, and co-located with heaviest precip/best forcing. Plenty of questions with regards to angle/direction of llvl wind fields, along with amount of mixing of higher winds to sfc, especially over cold snow pack. The evolution of sfc low pres development and eventually track will ultimately determine the wind potential acrs portions of our fa. Have also mention this potential upcoming hazard in the HWO for now. Finally, guidance continues with the idea of a very sharp boundary swinging acrs our fa on the backside of this system late Friday/Friday Night time frame. This time frame has been delayed by 6 to 12 hours, as boundary parallels flow aloft and eastward movement is delayed. However, still noticing a sharp thermal gradient with fropa and the potential for lingering precip behind the boundary with rain changing to snow. This moisture and falling temps, could result in a flash freeze type scenario. However, these events are very challenging to predicted this far in advance, just be advised some parameters are looking favorable for this to occur late week. Very warm temps are likely on Thurs into Friday, as progged 925mb temps surge btwn 8-10c by 12z Friday associated with strong llvl waa on southerly flow. Have mentioned highs well into the 40s on Thurs, holding steady on Thurs Night, and climbing back into the upper 40s to lower 50s on Friday, before falling sharply behind boundary late Friday/Friday Night. If trends are slower with fropa arrival, highs on Friday, given llvl thermal profiles could be well into the 50s to near 60F, but if fropa is faster, highs could also be falling quickly into the 20s and 30s. Large spread is shown in the latest guidance and we will need to utilize model blend for now. && .AVIATION /10Z SUNDAY THROUGH THURSDAY/... Through 06Z Monday...Starting off the TAF period with just some mid-level clouds streaming over the area in advance of an approaching upper-level shortwave. Will see lower-level clouds spread over the area today, with widespread MVFR level ceilings expected by around 20Z. Will also see some snow showers, especially between 18Z and 06Z, which will be accompanied by predominantly IFR visibilities. Snow showers will end right towards the end of the 24 hour TAF period, allowing for visibilities to improve but MVFR level ceilings to linger through 06Z. Winds will trend generally south 5-12 knots for the next 24 hours. Outlook... Monday: Mainly VFR, with local IFR possible. NO SIG WX. Monday Night: Mainly MVFR, with local IFR possible. Chance SHSN. Tuesday: Mainly MVFR, with local IFR possible. Chance SHSN. Tuesday Night: Mainly VFR, with local MVFR possible. Slight chance SHSN. Wednesday: VFR. NO SIG WX. Wednesday Night: VFR. NO SIG WX. Thursday: Mainly VFR, with areas MVFR possible. Chance RA, Chance SN. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Duell NEAR TERM...Duell SHORT TERM...Taber LONG TERM...Taber AVIATION...Duell