856 FXUS61 KBTV 100336 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 1036 PM EST Mon Dec 9 2019 .SYNOPSIS... Occasional showers with areas of patchy fog will persist overnight with temperatures holding steady in the upper 30s to mid 40s. After a warm start on Tuesday, a cold front will sweep across the region and bring cooler temperatures and scattered mountain snow showers. Temperatures start in the mid 40s to near 50, but drop back into the 30s by evening. Scattered snow showers and much cooler temperatures will prevail on Wednesday with highs in the 20s to lower 30s. && .NEAR TERM /THROUGH TUESDAY NIGHT/... As of 1034 PM EST Monday...Light rainfall amounts have played out close to forecast. Additional showers will move through based on upstream observations, but will mostly just clip southern Vermont, while some scattered showers persist in the Adirondacks for the rest of the night. Little additional rain is expected elsewhere and so we tapered POPs (probability of precipitation) a little more than previously forecast across much of eastern Vermont. Otherwise, we fine tuned the temperature/dew point trends leading up to and behind the passage of the cold front tomorrow. It will consist of a few hours of slightly lower dew point air preceding an increase in moisture just ahead of the front, which sweeps from west to east during the day on Tuesday. Timing of the colder/drier air in going forecast looks good. Previous Discussion... Water vapor shows progressive southwest flow aloft prevailing with enhanced deeper moisture advecting ahead of s/w energy from the Ohio Valley into the NE Conus. Radar shows expanding light rain showers acrs most of the fa, but as 925mb to 850mb wind fields continue to strengthen again this evening, expect downslope shadowing to prevail acrs the cpv. NAM 3km shows 925mb winds increasing to 40 to 50 knots with enhanced channeling in the valley, while 850mb low level jet couplet of 55 to 70 knots angles acrs central/southern VT btwn 21z- 03z. Soundings show much greater stability this evening, with limited mixing potential, so a few localized gusts in the 25 to 35 mph range is possible. The combination of snow pack and precip will limit mixing. Next question will bl stay well enough mixed to limit fog development as warm/moist air moves over relatively cold snow pack. Soundings profiles show more stratus type profiles over northern NY with 1000 to 2000 feet winds of 25 to 35 knots, while shallow inversion and saturated bl conditions will help with areas of fog/br development in central/eastern and northern VT zones. Lows generally remain steady or rise overnight with readings upper 30s to mid 40s most locations. Some locations in the CPV and SLV could be near 50f overnight into early Tues. QPF ranges from 0.10 PBG/BTV to 0.75 high peaks into eastern upslope regions of the central/southern Greens. Tuesday...Sharp cold front will be approaching the SLV by 12z, as deeper 850 to 500mb moisture fields are shifting into eastern New England. Any lingering showers should be confined mainly to our eastern CWA in the morning, with a brief period of scattered rain showers associated with fropa btwn 15z-21z Tues. Areal coverage/intensity of precip will be limited on Tues, due to the lack of deep moisture profiles. Temps will start out mild with readings in the mid 40s to lower 50s, but fall sharply during the aftn hours as moderate low level caa develops on brisk westerly winds. Sounding indicating better mixing profiles, especially slv, so have placed mention of localized gusts up to 30 knots in fcst, especially in favorable aligned flow. Tues night llvl caa continues with some trrn focused snow showers. Temps drop back into the teens and 20s. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... As of 400 PM EST Monday...An upper level short wave will pass the North Country on Wednesday, manifesting in a surface low to the north. As the low passes to the north, a weak cold front will cross the region during the afternoon and winds will shift from southerly to westerly - becoming favorable for lake effect snow. Though little synoptic ascent is present with this system, the surface front paired with lake moisture will support the development of snow showers during the afternoon and evening. Some high-res models indicate a narrow band of frontogenesis along with weak instability (CAPE values of 30-50 J/kg) across northern NY and some portions of northern VT. Therefore, snow squalls are a possibility late Wednesday afternoon and evening, especially across northern NY, with snow accumulations of 1-3 inches. Chances of precipitation will dwindle overnight as winds become northerly and cold, dry air moves in early Thursday morning ahead of an approaching surface high. High temperatures on Wednesday will be near 30 with overnight lows dropping to the teens and single digits. && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 400 PM EST Monday...A surface high will settle across the region on Thursday allowing for some sunshine, though temperatures will remain chilly with highs in the teens and 20s, and overnight lows dropping to single digits in some places. Friday morning, winds will increase and become southwesterly with the approach of a surface low from the west. The subsequent warm air advection will increase cloudiness and bump high temperatures up to the low 30s, but conditions will remain dry. A coastal low pressure system approaches the Northeast on Saturday, bringing the potential for numerous hazards. Widespread precip will begin as snow Saturday morning, but as temperatures increase throughout the day, accumulating mixed precipitation and rain are possible. Precipitation will continue through Sunday, becoming more scattered, though the threat of mixed precip remains. Downslope winds are also a concern along the western side of the Green Mountains on Saturday as breezy easterly winds are expected ahead of the approaching low. Because of the duration of the event, hydro-related concerns also exist for the weekend, and will be monitored more closely as the weekend approaches. Uncertainty remains regarding precip type for the weekend event and will be reassessed through the coming week. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... Through 00Z Wednesday...Low level wind shear will continue to be an issue through 12z with south winds at 2000 feet in the 35 to 45 knot range. Winds at the surface will be around 10 knots with some gusts to 20 knots. Areal coverage of precipitation is decreasing quickly across the area...but increasing across central New York and this will be moving northeast over the next several hours. Looking at MVFR to IFR visibilities with this precipitation through at least 06z before gradually improving back into the MVFR and VFR categories through 12z. There will be a general decrease in precipitation after 12z with visibilities returning back to VFR for much of the period after 12z. Ceilings will generally be in the MVFR category...but lower into the IFR category from time to time through 12z. After 12z ceilings will mainly be in the MVFR and VFR categories. Look for a wind shift to the west after 16z as a cold front moves across the area. Could see some 20 to 30 knot gusts after 18z...mainly across northern New York. Outlook... Tuesday Night: VFR. NO SIG WX. Wednesday: VFR. Slight chance SHSN. Wednesday Night: VFR. Slight chance SHSN. Thursday: VFR. NO SIG WX. Thursday Night: VFR. NO SIG WX. Friday: VFR. NO SIG WX. Friday Night: Mainly MVFR, with local IFR possible. Chance SN. Saturday: Mainly IFR, with areas MVFR possible. Likely RA, Chance SN. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Taber NEAR TERM...Kutikoff/Evenson/Taber SHORT TERM...Hammond LONG TERM...Hammond AVIATION...Evenson