Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 161429 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 929 AM EST Thu Nov 16 2017 .SYNOPSIS... Low pressure will move northwest of the region today while a secondary low develops on the New England coast then moves into the Gulf of Maine tonight. Precipitation may start as light snow mainly in the mountains and eastern Vermont, but will be mostly rain across northern New York and the Champlain Valley. A wintry mix will persist across central and eastern Vermont until about noon, producing light accumulations and slowing down the morning commute. Rain showers will change to snow showers tonight, with some accumulation primarily for the higher terrain and along the west slopes of the mountains of northern Vermont and New York. Dry weather returns for Friday as a weak area of high pressure moves in before the next low pressure system brings another round of rain and snow along with gusty winds for Saturday night and Sunday. && .NEAR TERM /THROUGH FRIDAY/... As of 929 AM EST Thursday...Overall the previous forecast remains in good shape for today with just a slight tweak needed to hourly temps and pops for the next few hours based on current trends. Precipitation east of the Greens is beginning to wane while transitioning to a rain/snow mix, while westward, lake effect rain showers are ramping up quickly on the Tug and into southern St. Lawrence County. Current forecast has this all covered well. Previous Discussion...A warm conveyor belt will bring a few hours of light precipitation this morning as it moves from west to east. Surface temperatures have risen into the 30s and 40s especially west of the Green mountains but even east of the mountains are warming but wet bulbs holding below freezing east. So this will limit much in the way of any mixed precip and have used the RAP profiles to drive derived ptype from the top down. Looking at perhaps less than an inch wet snow/sleet from the Green eastward this morning. Southerly winds will be gusting 25-35 mph, especially in the Champlain Valley as a low level jet continues this morning. Eventually warmer air aloft will win out as boundary layer temperatures warm enough that everywhere will turn to light rain this morning. Temperatures will push well into the 40s from the Champlain Valley westward. Some guidance suggests even near 50F in a few spots but all should get to 40 or above. As upper trof and cold air aloft moves overhead this afternoon and evening so character of precipitation will be mainly in the form of showers. Freezing level will be right at the mountain summits somewhere around 4000 ft during midday so no real snow accumulation much below 3000 ft. Tonight a cold front sweeps eastward through during the evening hours with winds shifting to the west/northwest. An upper level shortwave also drops down from the northwest just after the front. This feature will also bring a brief increase in deeper moisture. All the hi-res models continue show a roughly 6 hour period of time tonight with a strong orographic signal across the `Dacks and northern Green Mountains. Expecting snow/snow showers to increase across the higher terrain. Latest models suggest the flow will only be modestly blocked flow (per forecast Froude Numbers around 0.6 to 0.9), so expecting the highest chances of snow showers to be along and just west of the spine of the Green Mountains, but may just be blocked enough to back the moisture up enough that even Burlington gets in on some snow shower activity and perhaps a dusting to perhaps the first measurable snow of the season here at the airport. Looks like 1-3" of snow will fall at elevations above 1000ft in the northern Greens and into the northeast Kingdom. At the mountain summits above 3000 ft several more inches are possible. The northwest winds will also be a bit gusty at times, probably in the 20-25mph range. Temperatures will be falling below freezing everywhere by morning with lows mainly in the 20s perhaps near freezing on Lake Champlain so any snow that falls will be icing up especially in the higher terrain. The moisture and any lingering snow showers diminish quickly on Friday and expect some sun by afternoon. High temps will only go up a few degrees in the afternoon for highs in the upper 20s to mid 30s with gusty NW winds settling down as well. && .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY/... As of 350 AM EST Thursday...The changeable weather pattern then continues for the short term. We start the period with a narrow high pressure axis traversing the area Friday night with partly cloudy skies and light winds. Low temperatures generally in the 20s to locally around 30 in the Champlain Valley. By Saturday a larger storm system will evolve across the eastern portions of the midwest and begin to deepen rapidly as it tracks toward southwest Ontario in the Detroit/Toronto/Buffalo region by early evening. Models continue to slow the arrival of precipitation associated with this feature, not unreasonable given the increased amplification of the synoptic background flow and as such have held back bringing steadier rainfall into northern NY by late morning/early afternoon, and into VT from mid to late afternoon. Boundary layer thermal profiles support a brief mix with wet snow at time of precipitation onset across the Adirondacks and northern Greens, but this should be short lived as increasingly gusty southerly flow will boost temperatures into the upper 30s to mid 40s for most locales as the day progresses. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... As of 350 AM EST Thursday...Deepening surface low then takes a typical climo track into the St. Lawrence Valley Saturday night into Sunday with widespread light rains/snows along with breezy to windy conditions. Have discounted the 00Z NAM/GEM solutions showing an atypical track toward the Adirondacks. Given broad consensus among this morning`s ECMWF/GFS/UKMET in showing a potential sub-980 mb surface center a backside southwesterly jet in excess of 50 kts at 925 mb may evolve across the St. Lawrence Valley east along the northern slopes of the Adirondacks into extreme northwest VT by Sunday morning. A quick look at GFS sounding profiles during this period suggest these areas may approach or exceed wind advisory criteria. Time will tell. As colder air pushes into the region behind the system`s cold front later Saturday night into Sunday rainfall will change to wet snows or snow showers across the much of the area with some minor accumulations possible in higher elevations. Low temperatures mainly in the upper 20s to lower 30s with corresponding highs on Sunday in the upper 30s to lower 40s - typical November-type stuff. Mountain snow showers then continue Sunday night before waning on Monday as high pressure builds into the region. Looking further out, a general progressive flow pattern will continue across the northern tier of states through the remainder of next week along with a fairly seasonal temperature pattern. After dry weather Monday night into Tuesday, additional rain/snow shower activity enters the forecast again by Wednesday into Thursday as northern stream energy tracks east from the Great Lakes. && .AVIATION /15Z THURSDAY THROUGH MONDAY/... Through 12Z Friday...Mainly MVFR due to cigs this morning locally IFR vsby in -SN at MPV for another hour or two before changing to -SHRA as warmer air on south winds of 10-20kt pushes into the area. Trend toward a break in showers and perhaps brief VFR midday then back to MVFR with a cold frontal passage tonight. There is some chance of precipitation lingering longer into the afternoon at MPV with a coastal low forming near KBOS. Locally IFR vsby in snow and falling temperatures aft 23Z at KSLK with a cold front working its way east to MPV and BTV 03-06z with any rain showers changing to snow showers. Winds will shift to NW will increase with some gusts 20-25 kt by the end of the TAF period. Falling temps may lead to icy runways by morning. Outlook... Friday: VFR. Slight chance SHSN. Friday Night: VFR. NO SIG WX. Saturday: Mainly VFR, with local MVFR possible. Likely RA, Slight chance SN. Saturday Night: Mainly MVFR, with local IFR possible. Definite RA, Definite SN. Sunday: Mainly MVFR, with areas VFR possible. Windy with gusts to 35 kt. Chance SHRA, Chance SHSN. Sunday Night: Mainly VFR, with areas MVFR possible. Chance SHSN. Monday: VFR. Slight chance SHSN. && .MARINE... As of 648 AM Thursday...A Lake Wind Advisory is in effect. South winds near 30 knots will diminish this afternoon. However this evening a cold front will move across the region. Behind the front, winds will switch to the west/northwest and increase again to 25-30 knots. Anyone out boating will need to be aware of the rough conditions that will result from the strong winds. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Sisson NEAR TERM...Lahiff/Sisson SHORT TERM...JMG LONG TERM...JMG AVIATION...Sisson MARINE...Nash

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