KBTV issues Area Forecast Discussion (AFD) valid 2019-12-10T22:54:00Z 536 FXUS61 KBTV 102254 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 554 PM EST Tue Dec 10 2019 .SYNOPSIS... A cold front crossing the North Country this evening will result in rapidly falling temperatures. As temperatures plummet below freezing, any standing water or slush will rapidly freeze, and a few icy spots are possible tonight and into the morning commute on Wednesday. High temperatures on Wednesday will generally be in the 20s to near 30. Another trough approaching from the Great Lakes will bring the potential for additional snow showers during Wednesday afternoon. The next chance for widespread precipitation will occur Saturday, with moderate rain generally expected across the North Country. && .NEAR TERM /THROUGH WEDNESDAY NIGHT/... As of 553 PM EST Tuesday...Overall in forecast in good shape with only some minor tweaks. Pronounced southwest flow aloft over the region is helping to keep plenty of clouds and some rain around. Rain is mainly south of Montpelier, Vermont and with plenty of rain moving up from the mid-Atlantic region have held onto the rain a bit longer in southern Vermont. The cold front associated with colder air is slowly moving into the Saint Lawrence Valley and portions of the northern Adirondacks. Because of the slower timing of the colder air have adjusted hourly temperatures and dew points to account for the slower drop. Still looking at the potential for some black ice as the lower dew points remain west of the Saint Lawrence River Valley. Rest of forecast in real good shape and no other changes needed at this time. Previous Discussion... Slow-moving deep-layer frontal zone continues to bring light rain across central/s-central VT this afternoon. A shallow/secondary cold front shifting into the St. Lawrence Valley will sweep eastward this evening. This secondary front will come through generally dry, but strong low-level CAA is expected, along with a W-NW wind shift. Briefly gusty winds of 20-30 mph are possible through this evening with good low-level mixing. As temperatures fall, the main concern is a rapid refreeze of any slush or standing water from today's snowmelt. Some surfaces will sufficiently dry out first, but patchy black ice may occur on untreated surfaces that are initially wet through this evening. Have issued a Special Weather Statement to address for this evening into the overnight hours. Temperatures by daybreak expected to fall into the teens, except locally in the lower 20s across the valleys of s-central VT. On Wednesday, narrow surface ridge axis brings dry/partly sunny conditions during the morning hours. This ridge axis shifts out quickly as next shortwave approaches from the Great Lakes region. Flow quickly shifts back swly by afternoon, and lake enhanced snow showers will begin developing across St. Lawrence and Franklin counties by 18Z. Have a period of 70-80 PoPs across the Adirondacks mid-late afternoon, with chances for late afternoon and evening snow showers elsewhere as trough axis shifts across the region. Snow accumulations of 1-3" are possible from swrn St. Lawrence County into the Adirondacks, with generally an inch or less elsewhere across the North Country. Wednesday's highs generally 25-30F. Wednesday night will feature brisk conditions early, with NWLY gusts 25-35 mph possible in the wake of the surface trough passage. Clearing skies and diminishing winds after midnight should allow temperatures to fall into the low-mid teens, except locally in the single digits across the Adirondacks and far nern VT. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 329 PM EST Tuesday...No real changes for Thursday through Friday night with high pressure in control of the sensible weather across the North Country. Below normal temperatures are expected on Thursday as Canadian high briefly settles in. Breezy winds Thursday morning will diminish towards afternoon and although it'll be chilly, a dry airmass will be in place allowing for plenty of sunshine during the day. High temperatures should generally be around 20 for the Northeast Kingdom and higher terrain of the Adirondack and Green Mountains, and low to mid 20s elsewhere. High pressure will begin to slide eastward Thursday night as winds aloft turn out of the southwest ahead of our next approaching system for Saturday. Temperatures on Friday will moderate to near seasonable norms in the low to mid 30s. Despite warming temperatures it will still feel chilly Friday as southerly winds increase around 10-15 knots with gusts upwards of 20 knots at times during the afternoon. Warm air advection will continue overnight Friday with low temperatures generally remaining steady in the low to mid 30s. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 329 PM EST Tuesday...The main story for the extended will be the "nor'easter" for Saturday. Overall, model guidance is in relatively good agreement on the evolution of this system however there are some differences on upper level structure and placement of the surface low with slight variations on the timing/placement of phasing shortwaves aloft. There is still plenty of time to hammer out the details on this system, especially in regard to placement of heaviest QPF. One thing of note, while highest PWATs remain well to our south and east, sounding climatology for ALY at 12z Dec 14 show PWATs around 1" near the daily maximums for the day. Currently, guidance indicates around 0.75" across northern New York and northwestern Vermont with amounts increasing to around 1.50" across southeastern Vermont. Unfortunately, one trend which has been covered well by all guidance is the likelihood that this event will be primarily rain, expect for maybe the highest peaks. At this time, have run with rain/snow based on surface temperatures due to strength of warm nose aloft, however there is the potential for pockets of freezing rain for the deeper hollows across eastern Vermont and the Connecticut River Valley at the onset of precipitation early Saturday morning. Soundings indicate the best potential at typical location such as Springfield & St. Johnsbury. Additionally, we will be watching the potential for gusty east-southeasterly downsloping winds late Saturday morning as soundings indicate 40-45 knot low level jet developing around 925- 900 mb. Soundings indicate a stable layer in place as this coincides with precipitation, but given dry slot development across this location Saturday afternoon a few locations could see brief gusts up to 30 kt. Colder air finally works its way in the region Sunday afternoon with some lingering snow showers. The pattern for active weather continues with another deepening system developing across the Central Plains poised to impact the region by early next week with uncertainty regarding where the low will track. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... Through 18Z Wednesday...An axis of light rain extending from e-central NY into s-central VT will bring periods of light rain through 21Z at MPV and RUT. Aviation wx conditions will primarily be VFR, but intervals of MVFR ceilings are possible. Meanwhile, a secondary cold front is shifting ewd from sern Ontario. Southwesterly low-level flow in advance of the front is resulting in upslope cloudiness and MVFR ceilings at SLK through 00Z. Generally VFR ceilings in advance of the front at MSS/PBG/BTV. The front itself will pass through dry in most locations. Main impacts (for ground ops) will be a W-NW wind shift and possibly the formation of some patchy ice...as temperatures plummet below freezing 21-00Z at MSS/SLK, and 00-03Z at PBG/BTV/MPV, any standing water will quickly freeze. NW winds remain near 10kt overnight, but should see ceilings lifting with some breaks in the overcast after 04Z and into Wednesday morning. As another low-mid level trough moves eastward through the Great Lakes, will see low-level winds quickly return to S-SW at 6-10kts from 13Z right through the early afternoon hours Wednesday. A few snow showers are possible at KSLK toward 18Z Wednesday, but the bulk of snow shower activity is expected to hold off until mid-late afternoon across the North Country. Outlook... Wednesday Night: VFR. Chance SHSN. Thursday: VFR. NO SIG WX. Thursday Night: VFR. NO SIG WX. Friday: Mainly VFR, with local MVFR possible. NO SIG WX. Friday Night: Mainly MVFR, with local IFR possible. Chance SN, Chance RA. Saturday: Mainly IFR, with areas MVFR possible. Likely RA. Saturday Night: Mainly IFR, with areas MVFR possible. Chance RA, Chance SN. Sunday: Mainly MVFR, with local IFR possible. Likely SHSN, Chance SHRA. && .MARINE... A Lake Wind Advisory continues into tonight. A cold front crossing the North Country will maintain good low-level mixing, with westerly winds 20-30 kts for a time this evening. Should see winds trend downward to 10-15 kts after midnight. Waves initially 2 to 4 feet should subside to 1 to 2 feet after midnight. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Banacos NEAR TERM...Evenson/Banacos SHORT TERM...LaRocca LONG TERM...LaRocca AVIATION...Banacos MARINE...Hastings