Area Forecast Discussion
Issued by NWS Burlington, VT

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442 FXUS61 KBTV 241833 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 133 PM EST Fri Nov 24 2017 .SYNOPSIS... High pressure over the mid-Atlantic states this morning will briefly build northward into the Northeast today allowing skies to clear and temperatures to rise into the low to mid 40s on increasing southerly flow. A low pressure system passing to our north on Saturday will bring a trailing cold front across the North Country accompanied by scattered rain and snow showers through Saturday night. Cloudy and dry conditions are expected for Sunday. && .NEAR TERM /THROUGH SATURDAY/... As of 1002 AM EST Friday...A quiet end to the work week is expected today as high pressure over the mid-Atlantic states builds northward into the Northeast, gradually scouring out low stratus deck across the region this morning. Have slowed the clearing trend based on current satellite trends with the mid- morning update. Also of note, are well-defined lee waves east of the Adirondacks/Green Mtns in the stable layer near ridgetop level. The wave clouds are most pronounced east of some of the higher summits across the spine of the Green Mtns, and appear even deeper east of the White Mtns in NH. In any event, outside of a few scattered snow showers and/or flurries across northern areas early this morning, it`ll be a dry, mild and increasingly windy day as a strengthening pressure gradient between the high and an approaching low to our west will develop southerly winds of 10-20 mph, with a few gusts to 30 mph in vicinity of Lake Champlain. Highs will touch 40 across the Adirondacks and Northeast Kingdom, while warming into the mid-40s elsewhere. Dry conditions continue through tonight as well as the North Country will be entrenched in a warm sector with a warm front to our north and a cold front to our west associated with low pressure passing well north of the border. South winds will remain brisk as the pressure gradient remains tight between the departing high and approaching low. This will keep overnight mins on the mild side in the mid/upper 30s across the deeper valleys, while the mid-slopes of the Adirondacks and eastern Vermont should drop off into the upper 20s to around 30. Aforementioned cold front approaches Saturday but really doesn`t swing through the forecast area until after sunset with a little pre- frontal trough and associated deep layer moisture producing some scattered showers through the day, mainly in the form of rain but a few snow showers are possible across the higher elevations during the morning hours. Overall QPF is very light, generally less than a tenth of an inch, so expect little to no snow accumulation and minor impacts to outdoor activities. Temps remain mild through the day, warming a couple degrees from Friday`s maxes in the low/mid 40s. && .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... As of 326 AM EST Friday...00Z guidance all still indicating a shortwave moving across the region Saturday night, but have backed off a bit on its intensity. Still looking at a period where scattered snow showers will increase in coverage, especially across the higher terrain of northern NY and northern Vermont. The primary tweak to the going forecast is to decrease the PoPs a few hours quicker on Sunday. Could still have a few high terrain snow showers Sunday morning, but think by noon those will be all gone. Still only expect minor accumulations, perhaps 1-2" at the higher elevations, and a dusting at low elevations. Once the snow showers across the north diminish, it will be a dry but rather cloudy afternoon with northwest winds occasionally gusting to 20 mph. Highs will be slightly below normal, generally low-mid 30s. Sunday night we should see another round of scattered snow showers or periods of light snow across the region as a weak Alberta Clipper and it`s associated upper level trough zips by just to our north. This system will also not have a lot of moisture to work with, basically what it can tap from the Great Lakes. So it looks like another situation where we have 1-2" at higher elevations, with a dusting at lower elevations. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 326 AM EST Friday...00Z guidance still pointing at a rather progressive synoptic pattern next week. We`ll start off with a brief shot of cooler northwest flow for Monday, but quickly transition to a westerly flow pattern that turns more southwest by mid/late week. So it looks like from Tuesday onward, temperatures will be above normal. 00Z GFS and ECMWF are in decent agreement with the overall pattern. The main "weather" features will be a weak front late Tuesday/early Wednesday, and then the next low pressure approaching late Thursday. A few notes on each day follow... Monday: Looks to be the coldest day of the week. Perhaps a few morning mountain snow showers, but some prospects for some sun by afternoon. 925mb temperatures drop to -8 to -10C, so expecting highs only in the upper 20s to lower 30s, with mid 30s in southern valley locations. Tuesday: Looks dry. Flow turns southwest ahead of an approaching front, with warmer air advecting in. 925mb temperatures should warm to about +5C by late in the day. This will support temperatures well into the 40s for most areas - perhaps a few places nearing 50F. Reasonably tight pressure gradient will support 40-50kts of wind around 850mb. So it will likely be a bit breezy (20-30 mph gusts) especially in the St Lawrence and Champlain Valleys. Did try to enhance the winds some in the gridded forecast as base model data that far in the future typically underestimates wind speeds. Weakening front comes through Tuesday night. Temperatures should be warm enough aloft and in the boundary layer that we are looking at light rain as the dominant precipitation type. Wednesday: 00z guidance is a little faster with previous model runs and suggests that it will be mostly dry for the day. However, given uncertainty in timing, maintained some PoPs in the event the front comes through during the morning. Temperature profiles would suggest rain showers ending as a little bit of higher elevation snow showers. Not a very robust front, so we aren`t talking about a lot of rain or snow. Also not a lot of cold air behind the front, so temperatures will still be above normal with highs in the lower 40s. Thursday: Uncertainty in the forecast increases as GFS and ECMWF have more significant timing differences. Both indicate high pressure moves off the coast with flow turning southwest ahead of the next low pressure system. However GFS is faster with bringing in moisture and precipitation by later in the day. ECMWF is about 12 hours slower. Do have some 15-25% PoPs in for Thursday and at the very least increasing clouds. In any event, highs will again be slightly above normal. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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Through 18Z Saturday...Stratus clouds continue to dissipate early this afternoon as S-SW winds increase 10-15kts with gusts 20-25kts resulting in increased low-level mixing. With the exception of MPV, all TAF locations have returned to VFR with just sct mid-upper level clouds. The 2-3kft clouds at MPV should move north of the area by 20Z or so. For tonight, developing low-level jet around 1500-2500ft AGL ahead of frontal system across the Great Lakes will bring LLWS to TAF locations at MSS/SLK/RUT/MPV. Expectation is that surface wind gusts of 20-25kts will keep BTV/PBG well-mixed to avoid LLWS criteria, but will see some potential low-level turbulence and bumpy airport approaches across the Champlain Valley throughout the night. The surface trough begins in move into nrn NY 15-18Z, and may see some scattered rain showers associated with this feature toward the end of the TAF period. Included VCSH in the TAFs at BTV/PBG/SLK/MSS mid-late morning for now, as activity should be scattered in areal coverage. Outlook... Saturday Night: Mainly VFR, with local MVFR possible. Chance SHRA, Slight chance SHSN. Sunday: Mainly VFR, with local MVFR possible. Slight chance SHSN. Sunday Night: MVFR. Chance SHSN. Monday: Mainly MVFR, with areas VFR possible. Slight chance SHSN. Monday Night: Mainly VFR, with local MVFR possible. NO SIG WX. Tuesday: VFR. Slight chance SHRA. Tuesday Night: Mainly VFR, with local MVFR possible. Chance SHRA. Wednesday: VFR/MVFR conditions possible. Chance SHRA, Chance SHSN.
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&& .MARINE...
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As of 125 PM EST Friday...A Lake Wind Advisory remains in effect for increasingly strong south winds over the open waters of Lake Champlain this afternoon through Saturday morning. South winds of 20 to 25 knots over the lake early this afternoon will increase markedly overnight, when south winds will likely top 30 knots with some gusts to 40 knots possible. This will produce very hazardous conditions with wave heights building to peak heights of 5 to 7 feet for a period tonight. Behind a cold front passage, winds will shift to the west and decrease during Saturday afternoon. Wave heights will gradually diminish Saturday afternoon but wave conditions will remain choppy.
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&& .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Lahiff NEAR TERM...Banacos/Lahiff SHORT TERM...Nash LONG TERM...Nash AVIATION...Banacos MARINE...Banacos

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