Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 230029 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 729 PM EST Mon Jan 22 2018 .SYNOPSIS... A storm system will bring mixed precipitation and rainfall to the region tonight into Tuesday along with milder temperatures. Colder air returns by Tuesday night with lingering light snows tapering off. Seasonably cold air persists into Friday before another substantial warmup and mixed precipitation return by next weekend. && .NEAR TERM /THROUGH TUESDAY NIGHT/... As of 532 PM EST Monday...Update to expand winter weather advisory for the Champlain Valley as quick walk upstairs showed a mixture of snow/sleet and freezing rain here at btv with a light glaze already developing. Given the band of moderate mixed precip lifting across the cpv and our urban areas during the peak evening commute, expecting areas of difficult travel. Thinking ice accumulation up to a tenth or so is possible here across the CPV and up to two tenths or so in the SLV and parts of eastern/central VT. Temps with northwest winds continue to struggle in the mid 20s, but all guidance suggests as warm front lifts north winds will shift to the south and temps will warm into the mid 30s by midnight in most locations. Have adjusted pops/temps and precip type accordingly. Expecting band of light to moderate precip to be along the international border area by midnight with just spotty rain and pockets of freezing rain as upper level dynamics and better moisture is either north or west of our cwa. Better moisture and lift arrives with surface cold front on Tuesday for another 2 to 4 hour window of mainly moderate rainfall. Previous discussion below: Only minor changes to our current forecast through the evening and overnight hours as low pressure near KDSM tracks toward Lake Huron by sunrise Tuesday. We`re still looking at a period of mixed precipitation along it`s accompanying warm front this evening with light snow and ice accumulations expected. Latest trends in the models have been to reduce the overall icing threat across the southern and eastern portions of the forecast area and showing more in the way of sleet. Quite a bit of uncertainty exists in the exact thermal profiles however and this leads to a low confidence forecast on eventual accretions in these areas. As a result all Winter Weather Advisories remain in place with this package. The warm frontal precipitation should be rather brief (3-6 hours) so the ice amounts should be generally on the light side, ranging from a few hundredths to perhaps a quarter inch in the far northern SLV near KMSS. Some snow and sleet will also be prevalent in the first few hours of precipitation onset, especially across northern and eastern VT, though again accumulations should be light and mainly from a dusting to perhaps 2 inches. As the warm front pushes northward, the low to mid level flow trends south/southeasterly by mid to late evening in all areas save the far northern SLV. This will foster steadily rising temperatures into the overnight hours and morning hours on Tuesday as we firmly enter a pronounced warm sector. During this time frame p-type should transition to mostly spotty areas of light rain or showers with many areas seeing a period of dry weather. By Tuesday the system`s cold front marches steadily east through time, crossing through northern NY in the mid to late morning, and across VT during the afternoon. A period of steadier rainfall will occur for several hours ahead of this boundary as temperatures climb into the upper 30s to mid 40s for most spots. Contemplated adding an outside shot of thunder as a narrow pre-frontal band of steeper mid- level lapse rates and slightly negative Showalter values crosses the area. Confidence is low enough however to preclude mention at this point. Behind the front temperatures steadily fall Tuesday night as lingering precipitation transitions to light snows/snow showers and takes on a more orographic character with synoptic flow trending northwesterly. Some light backside accumulations of a dusting to 2 inches will be possible in these areas with some spot totals slightly higher at the higher summits. Lows by Wednesday morning to generally bottom out in the 15 to 25 range - coolest north and west. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 351 PM EST Monday...After the cold front pushes through Tuesday night, temperatures will fall throughout the day Wednesday. Expect some residual snow showers lingering through the day Wednesday. Additional accumulations during the day will be restricted to under an inch in the northern Greens, with other areas only seeing a dusting if anything. Behind the frontal passage, the lower atmosphere will become better mixed and winds could become gusty at times. The combination of the colder air mass and the gusty winds will make for cold wind chills Wednesday lasting through Thursday night. Wednesday night, a surface high will build in from the northwest. This will allow cloud cover to decrease and overnight temperatures to bottom out in the single digits above to single digits below zero. Thursday through Thursday night will be the coldest day of the week (highs generally in the teens and lows near or below zero) before warm air advection commences Friday. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 351 PM EST Monday...The temperature swings will continue through the longterm with a warming trend starting Friday and precipitation returning over the weekend. After the system moves through, expect early next week to be drier with temperatures returning down to seasonal norms of 20s to low 30s by Monday. Details...As the surface high shifts off the Atlantic Coast by Friday evening, southerly return flow along the Eastern Seaboard will transport warmer air northward. Meanwhile further west, a surface low will form in the lee of the Canadian Rockies Thursday night. Between the surface high to our east and the strengthening lee low to the west, a southwesterly jet will transport Gulf moisture northeastward. There is still some question as to the extent of the amplification of the longwave trough associated with this system, and the resulting extent of the moisture transport/warm air advection ahead of the trough. This is leading to greater uncertainty with the temperatures, precipitation amounts, precipitation type, and precise timing through the weekend. The trend of the 00Z ECMWF and the 06Z and 12Z operational runs of the GFS is towards a lesser amplified trough and more progressive system, resulting in less moisture transport into the North Country. However, a look at the GFS ensembles reveals substantial spread among different ensemble members with regards to the amplification of the upper-level flow and the subsequent low-level baroclinicity associated with the amplification of the flow. For this reason, not ready to bite off completely yet on the deterministic trend towards a slightly colder, drier system. With complex thermal profiles, current thinking is we`ll see a fairly quick shot of mainly rain sometime Saturday night through Sunday with the possibility of some mixed precipitation on the front end and back end of the system. If the warmer solutions do verify, the system could provide some renewed hydro concerns. Will continue to monitor trends in numerical guidance closely as models begin converge on a better consensus for this storm. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/...
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Through 00Z Wednesday...Widespread mvfr cigs and vis prevailing across our taf sites this evening, with localized icing having major impacts on the aviation community. Expecting conditions to slowly improve at slk/rut/btv and pbg as temperatures warm above freezing and steadier precip lifts north of terminals. However...northeast winds and surface temps below 0c...will result in additional icing at mss overnight and pockets of icing at mpv. Thinking with developing southeast flow...areas of ifr cigs are likely at mpv...while cigs lift to mvfr/vfr across the CPV. Localized wind gusts btwn 25 and 30 knots possible this evening at rutland from the southeast...with areas of moderate low level wind shear and turbulence possible at all sites. A band of moderate rain with additional mvfr and period of ifr vis possible on Tuesday. Outlook... Tuesday Night: Mainly VFR, with areas MVFR possible. Likely RA, Chance SHRA, Chance SHSN. Wednesday: VFR. Slight chance SHSN. Wednesday Night: Mainly VFR, with local MVFR possible. NO SIG WX. Thursday: Mainly VFR, with local MVFR possible. NO SIG WX. Thursday Night: Mainly VFR, with local MVFR possible. NO SIG WX. Friday: VFR. NO SIG WX. Friday Night: VFR. NO SIG WX. Saturday: Mainly VFR, with areas MVFR possible. Slight chance RA, Slight chance SHSN.
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&& .HYDROLOGY... As of 320 PM EST Monday...Widespread rainfall is expected across the area late tonight and especially on Tuesday. Current data suggests 24 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 36 hours and will be updated if later information suggests a different scenario than current thinking. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Winter Weather Advisory until 7 AM EST Tuesday for VTZ001-002- 005-009-011-016-017. Winter Weather Advisory until 10 AM EST Tuesday for VTZ003-004- 006>008-010-012-018-019. NY...Winter Weather Advisory until 7 AM EST Tuesday for NYZ026>028- 030-031-034-035-087. && $$ SYNOPSIS...JMG NEAR TERM...JMG/Neiles/Taber SHORT TERM...RSD LONG TERM...RSD AVIATION...Taber HYDROLOGY...JMG/Evenson

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