Area Forecast Discussion
Issued by NWS Burlington, VT

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065 FXUS61 KBTV 221147 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 647 AM EST Mon Jan 22 2018 .SYNOPSIS... A warm front will lift northeast into the region this afternoon and evening. Widespread precipitation is expected to develop as a result. The precipitation will begin as a wintry mix this afternoon and tonight before changing over to rain during the morning hours on Tuesday. Light ice accumulations are expected... especially across portions of northern New York and areas east of the Green Mountains in Vermont. The warm front moves north of the area early on Tuesday and rain is expected for all areas as highs climb into the 40s. && .NEAR TERM /THROUGH TUESDAY/... As of 647 AM EST Monday...Noticing some colder air from Canada making a push southward this morning...especially across the Saint Lawrence Valley...northeast New York...and the northern third of Vermont. Flow aloft will be backing to the southwest as the morning wears on so at some point the flow of shallow cold air will stop...but this helps set the stage for mixed precipitation at the onset of the warm air advection event and places like the northern Champlain Valley may hold onto mixed precipitation an hour or two longer before changing over to rain. This subtle change does not change the overall ice forecast as the warm nose aloft does not really have an impact until after 00z. But some areas could see just a bit more snow before the changeover...generally up to an inch. Rest of forecast remains unchanged. Previous Discussion... Winter Weather Advisory remains in effect for portions of northern New York and eastern Vermont. Light ice accumulations are expected to have an impact in these areas. Weather starts off quiet this morning before a warm front lifts northeast into the region later in the day and into the first half of the night. Precipitation really gets going around mid- afternoon through about midnight before the warm front lifts north of the border and areas gets into the warm sector. Thermal profile still supports the idea of mixed precipitation over much of the area. The only exceptions being southeast Saint Lawrence County and a good portion of the Champlain Valley where a brief period of mixed precipitation develops before changing over the rain as temperatures warm above freezing and remain above freezing through the night. The real areas of concern are across the Saint Lawrence Valley...the northern portions of the northern Adirondacks...and Clinton county in New York and areas east of the spine of the Green Mountains in Vermont. Low level cold air holds on in northern New York in response to northeast winds...but strongest push of the warm layer aloft moves into this region and thus we continue to expected one to two tenths of ice accumulation across this areas. A bit more of mixed precipitation will occur over eastern Vermont and it will not be until later tonight that more icing develops as thermal profile becomes more favorable for freezing rain. However...this is all taking place as warm front lifts north of the border and that is why we are expecting lower ice accumulation numbers in eastern Vermont...generally up to a tenth of an inch of ice. Still enough to cause problems. Once warm front lifts north of the border after midnight tonight...area gets in the warm sector and precipitation will shut down for a bit...especially from the Champlain Valley eastward. A cold front is still expected to move into the region on Tuesday and enhance the potential for rain as temperatures should warm into the 40s across the entire area. Most areas will see at least a quarter to half inch of rain with higher amounts possible over southern Vermont. See hydrologic section below for details on how this will affect river levels and ice jam potential. && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY/... As of 409 AM EST Monday...As the aforementioned surface low pressure continues to lift northeast from the St. Lawrence Valley into southern Quebec and the parent upper trough swings in behind it, the attending cold front will sweep across the forecast area Tuesday night with rain changing to snow from west to east through the pre-dawn hours of Wednesday. Behind the front west-northwest flow will aid in some lingering snow showers across the upslope regions of the Adirondacks and northern Greens through early afternoon, but the deeper valleys will trend towards drier conditions. A dusting to perhaps 2 inches is possible through Wednesday in the valleys, with 2-5" across the higher peaks, especially in northern Vermont. Temps fall sharply behind the front, running in the mid-30s to low-40s before midnight Wednesday, then plummeting into the teens and 20s by sunrise, and steadily falling further through the day to widespread low/mid teens by sunset. In addition, a brisk northwest wind Wednesday will make for wind chills in the single digits above and below zero. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... As of 409 AM EST Monday...Quieter yet unseasonably colder conditions develop for the latter half of the work week as surface high pressure builds in behind the departing low pressure system, yet the upper trough remains aloft. No precipitation is expected for Wednesday night through Friday night, but high temps will be widespread in the teens Thursday, and struggle to hit the low 20s for Friday. Both Wednesday and Thursday nights will see a return of single digit lows above and below zero. Heading into the weekend the pattern continues to look more active as we continue to monitor model trends which indicate the potential for another warmup and mixed precipitation event. The combination of strong high pressure exiting off the eastern seaboard and a clipper low moving through southern Ontario will develop strong south/southwesterly flow across the Appalachian mountains tapping into rich Gulf moisture ahead of a cold front. Timing continues to be uncertain in regards to the frontal passage, but trends are towards a more progressive system with thermal profiles supporting mainly rain Saturday night through Sunday, possible starting as a wintry mix, before ending rapidly Sunday night as a mix of rain and snow. We`ll certainly be ironing out the finer details as the week goes on so stay tuned. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... Through 12Z Tuesday...VFR conditions to start this morning but as a warm front approaches the area from the southwest ceilings will lower into the MVFR and IFR categories...especially this afternoon and tonight. Visibilities will also be lowering after about 22z as widespread mixed precipitation moves into the area. The precipitation will last through about 06z then lift north of the Canadian Border. Improving conditions will develop after 06z with ceilings and visibilities returning into the MVFR and VFR categories as winds begin to increase from the south and southeast. The only exception to this will be at KMSS where winds will remain from the northeast and be rather gusty this afternoon and tonight. There may also be some low level wind shear that develops at KSLK after 06z as strong low level southwesterly jet develops over the area. Outlook... Tuesday: Mainly MVFR, with areas IFR possible. Definite RA, Chance FZRA. Tuesday Night: Mainly MVFR, with local IFR possible. Chance RA, Chance SN. Wednesday: Mainly VFR, with areas MVFR possible. Slight chance SHSN. Wednesday Night: VFR. Slight chance SHSN. Thursday: Mainly VFR, with local MVFR possible. NO SIG WX. Thursday Night: Mainly VFR, with areas MVFR possible. NO SIG WX. Friday: VFR. NO SIG WX. && .HYDROLOGY... As of 409 AM EST Monday...Widespread rainfall is expected across the area late Monday night and especially on Tuesday. Current data suggests 36 hour rainfall totals ending at 700 pm Tuesday will range from 0.50 to 1.00 inch across the area. Given the substantial loss of snowpack across lower elevations during last week`s storm, and the fact that the warm-up will be of lesser magnitude we are not expecting significant ice movement or water rises on area rivers at this time. This is in close agreement with NERFC guidance and our latest river forecasts. Conditions will continue to be monitored closely over the next 48 hours and will be updated if later information suggests a different scenario than current thinking. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Winter Weather Advisory from 4 PM this afternoon to 10 AM EST Tuesday for VTZ003-004-006>008-010-012-018-019. NY...Winter Weather Advisory from 1 PM this afternoon to 7 AM EST Tuesday for NYZ026>028-030-031-034-087. && $$ SYNOPSIS...Evenson NEAR TERM...Evenson SHORT TERM...Lahiff LONG TERM...Lahiff AVIATION...Evenson HYDROLOGY...Evenson/JMG

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