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FXUS61 KBTV 090929 AFDBTV

Area Forecast Discussion National Weather Service Burlington VT 429 AM EST Sat Dec 9 2023

SYNOPSIS
Warming trend continues today with increasingly breezy conditions. A strong storm will impact the region Sunday through Monday, bringing initially heavy rainfall that will transition to a heavy wet snowfall. Travel could be very difficult, especially Sunday night into Monday, including the Monday morning commute. Scattered power outages are possible especially over higher elevations. In addition, rivers are expected to rise sharply Sunday night, with several rivers forecast to crest in Minor Flood Stage Monday. Mostly quiet weather returns for rest of the work week.

NEAR TERM /THROUGH SUNDAY/
As of 424 AM EST Saturday...We have quite a temperature spread across North Country this morning. While 925mb and 850mb temperature analysis shows the warm air aloft overspreading the region from southwest to northeast, surface high pressure to our east means that the St Lawrence valley remains in a cool northeast flow regime.
Locations east of the Green Mountain spine will also take a good part of today to mix out the low-level cold air. While Massena and Lyndonville remain in the mid 20s, Burlington has seen its temperature steadily climb through the night into the low 40s. So daytime highs forecast is rather tricky, but overall idea is that the coolest spots are across northern St Lawrence county as well as east of the Greens. These locations should only top out in the upper 30s to low 40s. On the other hand, southern St Lawrence county and the Champlain valley should see highs in the mid 40s to near 50.
Southerly wind gusts between 15 and 25 mph are expected over the Adirondacks and Champlain Valley during the afternoon hours. Expect broken to overcast skies through the day as clouds spread into the area ahead of the approaching system.

Tonight's weather is relatively quiet compared to what is in store for the region later Sunday into Monday. Overnight lows on Saturday stay rather mild generally in the upper 30s to low 40s except low to mid 30s for northern St Lawrence valley as well as sheltered locations east of the Greens. Aside from a few scattered rain showers, most of the rain will come after daybreak on Sunday.

SHORT TERM /SUNDAY NIGHT THROUGH MONDAY/
As of 424 AM EST Saturday...A strong storm system approaches the Northeast US on Sunday. Initially, the H5 trough is positively tilted with a weak low pressure developing near the St Lawrence valley. Temperatures on Sunday afternoon will be unseasonably mild in the mid 40s to low 50s, with mid 50s possible across southern portions of the CWA. Southerly winds will also make for a breezy, if not blustery day with wind-driven rain. Expect 0.25 to 0.75 inch of rain to fall by early Sunday evening. With dew points surging into the 40s, there will be rather significant snowmelt leading to the loss of snowpack. The combination of rainfall and snowmelt runoff will eventually lead to area river rises by Sunday night into Monday. More details in the hydrology discussion.

Model guidance has come into better consensus that a coastal low would develop over the Mid Atlantic and track over central/eastern MA overnight Sunday into Monday morning, before deepening as it lifts northeastwards into Maine. Individual members of the 00z GFS and ECMWF continue to show remarkable consistency and clustering as we now move into 48 hours of the onset time. While the overall upper level flow is still fairly progressive with a neutral to slightly positive NAO regime, models are indicating that the H5 trough does go negatively tilted for a time, greatly increasing the odds of colder air arriving in time for a 6 to 12 hour window of heavy, wet snow. While the threat for pre-frontal strong to damaging winds has diminished, concern is increasing for 35 to 40 mph post-front northwest winds leading to power outage concerns due to snow loading. Expect the sub-freezing 925mb isotherm to approach Champlain valley by the pre-dawn hours on Monday before sweeping across our entire CWA by early Monday afternoon. Expect surface temperatures to fall into the 32-34 range for points along and west of the Adirondacks through the pre-dawn hours, and then for areas east of the immediate Champlain Valley by the morning commute.

Temperatures are expected to remain constant or fall slightly during the day as strong cold air advection continues, with 925mb temperatures falling to -6 to -8C range regionwide by sundown. The main change with this forecast package is the expansion of the Winter Storm Watches to northern St Lawrence county as well as northern Champlain Valley, including Burlington. With a coastal low tracking over east MA, this favors accumulating snow across the Champlain valley. The 00z NAM 3km and 12km both show the potential for heavy rain to flip over to heavy snow during the pre-dawn into the early morning hours. Strong dynamical cooling should limit the mixed precipitation phase. 1 inch per hour snowfall rates during the Monday morning hours will lead to a hazardous morning commute across the densely populated northern Champlain valley. Southern St Lawrence county looks to be just a little too far to the west of the northwest quadrant of the best deformation associated with the deepening coastal low. With higher confidence in the coastal low being the dominant surface feature, flooding threat across northern NY has also decreased although Flood Watches remain in effect for now. Our southeastern zones including Windsor county should see mostly rain, thereby increasing the risk for localized urban poor drainage flooding. This is also the area where WPC has highlighted a slight risk in their Day 3 excessive rainfall outlook.

By Monday late afternoon into evening, as the low pressure center lifts further north and east into northern Maine and maritime Canada, stratiform precipitation will quickly come to an end across northern NY and then VT, transitioning into upslope snow showers.
But as mentioned earlier, with heavy wet snow clinging onto the trees and continued northwest gusts in the 25 to 35 mph range, expect lingering power outages and difficult recovery efforts by utility crew. A silver lining is that the model guidance has trended colder, so SLRs should increase to above 10:1 for most locations across VT by the afternoon hours, which might mitigate the snow loading adverse impacts.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
As of 424 AM EST Saturday...Some lingering snow showers expected for the first half of Monday night, mainly across terrain, the international border, the Northeast Kingdom, and perhaps western slopes. These snow showers are expected to taper off throughout the night as temperatures drop to seasonal averages in the teens to lower 20s under a gradually clearing sky. Generally an inch or under of additional snow is expected, except for Jay Peak, which could gain a couple inches. Gusty winds will also drop off during the night, though still perhaps 15-20 mph at times.

Quieter weather to return Tuesday onward, with highs in the 20s and 30s for much of the rest of the week, around or just below average.
Lows in the teens and 20s. A brief cold shot from an upper trough could bring some scattered terrain-focused snow showers Tues night- Weds night. Friday, a warming trend will begin into the weekend, with highs in the 30s and 40s as mid/upper level ridging builds into the region. Lows will also begin to increase into the 20s and 30s.

AVIATION /10Z SATURDAY THROUGH WEDNESDAY/
Through 06Z Sunday...Cloud deck 4,000-8,000 feet AGL early this morning, though there's an IFR cloud layer out in the Ottawa- Ogdensburg-Potsdam area that could threaten to lower site MSS from VFR or IFR periodically for the next few hours. Otherwise, VFR conditions for all sites at the moment. Some IFR fog and low clouds are possible for MPV over the next few hours as well, but most guidance is showing the site to remain VFR or MVFR through at least 22Z Saturday, at which point low clouds and fog return.
00-06Z Sunday forecast is least certain at this time, but thinking MPV will gradually drop to MVFR and then IFR conditions in fog and low clouds. This is currently the only site that is expected to be affected, but other sites like RUT and BTV show hints of MVFR vis at this later time period 00-06Z Sunday. Winds are expected to pick up at BTV around 17Z Saturday out of the south with gusts 20-25 knots. Other sites could have sustained southerly/southeasterly winds 5-10 knots. Any brief and isolated LLWS this morning around MSS is anticipated to drop off quickly.

Outlook...

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

HYDROLOGY
A Flood Watch remains in effect from Sunday afternoon through Monday afternoon for the eastern Adirondacks eastward into most of central and northern Vermont, including the Champlain Valley.

A strong storm system will bring widespread 1.0 to 2.5 inches of precipitation Sunday into Monday, with locally higher amounts of over 3 inches possible. Dew points surging well into the 40s on Sunday afternoon into evening will lead to significant snowmelt. NOHRSC analysis shows widespread 1-3 inches of Snow Water Equivalent outside of the immediate valleys. The combination of rainfall and snowmelt runoff will lead to sharp river rises Sunday night into Monday. Latest River Forecast Center forecasts have several rivers cresting in Minor Flood Stage Monday morning into Monday afternoon. These rivers are the Winooski River at Essex Junction and Waterbury, the Mad River at Moretown, East Branch of the Ausable at Ausable Forks, and the Otter Creek at Center Rutland.

Strong cold air advection will change rain into heavy, wet snow by Monday morning, with even the valleys changing to snow by mid day Monday. This will help mitigate the snowmelt runoff contribution. Rivers are forecast to recede late Monday through Monday night.

CLIMATE
Record daily precipitation is possible on both Sunday and Monday. Below are current daily records that may be broken based on the current forecast:

December 10: KBTV: 1.10/1938 KMPV: 0.93/1957 KPBG: 0.69/2004 KMSS: 0.86/1953 KSLK: 0.73/1953

December 11: KBTV: 1.43/1952 KMPV: 0.96/1952 KPBG: 0.81/1952

EQUIPMENT
The Burke Mountain NOAA Weather Radio, WWG-50, broadcasting on a frequency of 162.425 MHz is experiencing technical difficulties and is currently off the air. Technicians have advised that parts are needed to conduct repairs, with an estimated return to service on Tuesday, December 12th.

Please refer to local media and commercial radio for the latest weather information. The following nearby NOAA Weather Radio transmitters that can be used include Mount Ascutney on a frequency of 162.475 MHz and Mount Mansfield broadcasting on a frequency of 162.400 MHZ.

BTV WATCHES/WARNINGS/ADVISORIES
VT...Winter Storm Watch from Sunday evening through Monday evening for VTZ001>008-010-016>019.
Flood Watch from Sunday afternoon through Monday afternoon for VTZ001>011-016>021.
NY...Winter Storm Watch from Sunday evening through Monday evening for NYZ026>031-034.
Flood Watch from Sunday afternoon through Monday afternoon for NYZ028-031-034-035.

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