Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 192234 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 634 PM EDT Thu Apr 19 2018 .SYNOPSIS... An upper level weather system will spark snow showers tonight into Friday. The snow showers will be most common across northern New York and the northern half of Vermont, with several inches of accumulation expected in higher elevations. A light coating of snow is expected on grassy surfaces in the Champlain and St Lawrence Valleys by Friday morning. Drier conditions will spread into the region for the weekend and early next week, with gradually warming temperatures each day such that we will see a return of highs in the 60s by Tuesday. Another storm will bring rain for the middle to end of next week. && .NEAR TERM /THROUGH FRIDAY NIGHT/...
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As of 634 PM EDT Thursday...Going forecast in real good shape and very little change needed at this time. Only tweak was adding some higher probabilities to the showers here in the Champlain Valley based on radar trends and the convective nature of the atmosphere...which still remains in place but should be changing to a more upslope pattern later tonight as flow aloft becomes more northwest with time. Previous Discussion... Visible satellite shows the convective nature of the clouds across the region with the lumpy texture. Radar also shows the scattered nature of the showers, most of which are in the form of light snow showers, though in the lowest elevations where temperatures have reached the lower 40s, a mix with some rain drops is possible as well. Given the convective nature, some graupel is not out of the question. The snow hasn`t been heavy, and looking at web cams, it`s been melting on contact with the ground and existing snow is still melting away. Expecting the convective snow showers to fade in the next few hours, however as the potent upper level shortwave responsible for the instability to produce the snow showers passes by to the east this evening, a deep northwest flow will set up. Plenty of moisture along with cooling temperatures aloft will transition the snow showers into a much more orographically locked situation. All the hi-res models show this clearly, and we`ve got a lot of strong signals for a pretty good upslope snow event. If this was the middle of winter we would be expecting some impressive totals. However it`s April and the marginally cold atmosphere won`t be able to support super high snow-liquid ratios. That said, cross sections in BUFKIT show a good overlap of the best omega (upward motion) within the best temperatures for dendritic growth. Tried to figure out what the snow-liquid ratios will be, and in the end came up with 14-17:1 above 1500 feet and more like 7-10:1 below 1000 feet. Precipitation amounts will also have a strong orographic signal, with 0.05" or less in the valleys, and more like 0.6" near the summits of the northern Greens and western slopes of the Adirondacks by Friday afternoon. Used a blend of hi-res models to get those values. Running the SLRs through the QPF, total snow by Friday afternoon should be 6-9" above 2500ft or so (especially the northern Greens) with 1/2" or less below 700ft elevation. Some tight gradients in the snowfall distribution. Have not raised any winter weather headlines for a couple of reasons: 1) The more significant snowfall amounts are going to be at the highest elevations and not impact too many people or that large of an area and 2) for the most part, there should be no significant travel impacts. Based on in-house road surface temperature model guidance, road surfaces in the lower elevations will only drop to around freezing later tonight, so it will be hard for snow to accumulate. At the higher elevations, above 1500ft or so, there could be a minor slushy accumulation. It should be noted that we do have a blocked flow situation overnight, with Froude number around 0.5, especially after midnight. This should result in the snow backing up more into the Champlain Valley, with a light accumulation (on grassy surfaces) even into the Burlington area. I, for one, am not happy about that prospect, but at least it will melt away by the afternoon. Snow showers will continue on and off during the day Friday, but primarily across higher elevations. Still fairly cold airmass for this time of year, so lots of 30s with lower elevations getting into the lower 40s. Similar to what we saw today. Friday night the snow showers become restricted to primarily high terrain across just far northern and northeast Vermont. Lows in the 20s to lower 30s in the warmer Champlain Valley.
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&& .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... As of 341 PM EDT Thursday...Northwest flow aloft will exist across the area Saturday and Saturday night. Most of the area will be dry during this time period...but there could be some lingering snow showers in the morning over the Northeast Kingdom of Vermont. Not expecting much in the way of any accumulating as moisture will be rather limited. Below normal temperatures will continue with highs in the upper 30s to upper 40s and lows Saturday night in the lower 20s to lower 30s. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 341 PM EDT Thursday...Upper ridge slowly builds into the region and should be centered over the area by Monday night. Upper ridge axis moves east on Tuesday and southwest flow aloft develops over the area through the remainder of the period. Eventually an upper trough moves into the region for Wednesday and Thursday. So based on the above scenario we will be looking at a warming and drying trend Sunday through next Tuesday with each day getting several degrees warmer. Highs on Sunday will be in the mid 40s to lower 50s...in the 50s on Monday...and mid 50s to lower 60s on Tuesday. We should be back in the 50s on Wednesday and Thursday as deeper moisture moves into the region and brings clouds and showers to the area. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... Through 18Z Friday...Mix of VFR and MVFR across the region this afternoon. Have scattered snow showers that have developed, and expect these to continue until early afternoon. Possibly very brief periods of IFR, but just like summer t-storms, trying to time when any snow shower affects a particular TAF site is tough. Have used "VCSH" in most TAFs. For BTV, any shower may end up being a rain shower. As we move into the evening, snow showers will become more locked to the higher terrain of the Adirondacks, the Green Mountains and northeast VT. Expecting some of these snow showers to back in from the mountains and affect BTV as well later tonight and early Friday. IFR conditions are expected for that reason at the sites that will be most affected. Snow showers will begin to abate by late Friday morning, with MVFR to VFR conditions across the region. Outlook... Friday Night: Mainly VFR, with local MVFR possible. Slight chance SHSN. Saturday: VFR. NO SIG WX. Saturday Night: VFR. NO SIG WX. Sunday: VFR. NO SIG WX. Sunday Night: VFR. NO SIG WX. Monday: VFR. NO SIG WX. Monday Night: VFR. NO SIG WX. Tuesday: VFR. NO SIG WX. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Nash NEAR TERM...Evenson/Nash SHORT TERM...Evenson LONG TERM...Evenson AVIATION...Nash

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