Area Forecast Discussion
Issued by NWS Burlington, VT

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797 FXUS61 KBTV 170238 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 938 PM EST Fri Feb 16 2018 .SYNOPSIS... A cold front moving southeastward across the North Country early this afternoon will bring a period of snow to the region, with a dusting to a half inch in most areas. The front will eventually usher in colder and drier air on northwest winds this evening. As an area of surface high pressure builds across from the Ohio Valley and Great Lakes, clearing skies and lighter winds overnight will result in lows in the single digits to low teens for early morning Saturday. High pressure will maintain tranquil weather conditions throughout the day Saturday, with highs in the low to mid 30s. Thereafter, an area of low pressure moving from the Delmarva peninsula eastward well south of New England will bring a chance for light snow Saturday night, mainly across central and south-central Vermont. A light snow accumulation is possible. A significant warming trend is expected Monday through Wednesday of next week, along with increasing chances for rain. Near record high temperatures are possible Tuesday into Wednesday, with highs well into the 50s and possibly lower 60s. && .NEAR TERM /UNTIL 10 AM SATURDAY MORNING/... As of 933 PM EST Friday...Overall forecast is on track and only made some minor edits to reflect current observations. Clouds have struggled to break along the Green Mountains this evening but it finally looks as if the clouds are beginning to break up thanks to the influx of dry air behind the cold front that came through earlier this afternoon. Also tweaked the Temp/RH trends but overnight low still looks good as long as winds across the Champlain Valley decouple between 04Z and 06Z. Previous Discussion...Secondary cold front continues to translate southeastward across central VT at 1930Z. Have seen temperatures south of the front in the upr 30s to 44F or so across Rutland and Windsor counties. Meanwhile, temperatures are falling through the lower 30s across nwrn VT and into the upr 20s for nrn NY with moderately strong low- level CAA ongoing. There is an axis of frontogenetic precipitation within the frontal zone, generally lasting 1-3 hrs in any one location as it moves sewd from the sfc boundary. Precipitation has been initially starting as rain, before changing to wet snow as vertical temperature profiles cool to near freezing. May see a dusting to an inch or so with the front next couple of hours across central/s-central VT, especially across the higher terrain areas before drier air moves in from the NW. Snow is about ended at KMSS, and GOES-16 visible imagery shows rapid clearing upstream across the Ottawa Valley...which will shift into the North Country this evening. With the falling temperatures to below freezing next few hours, may see a few icy spots develop on the roads into this evening, but not expecting any widespread impact from black ice formation. Will experience some moderate NW winds 10-15kt, with gusts to 20kt this evening with steep low-level lapse rates in place. However, P-gradient weakens considerably toward midnight as high pressure begins moving in from the Ohio Valley and ern Great Lakes region. Should set up good radiational cooling conditions late with diminishing winds and clearing skies. Have indicated overnight low temperatures generally in the upr single digits to lower teens, except near zero across the Adirondacks and far nern VT. Surface anticyclone remains in control on Saturday as it crests across NY/New England during the morning hours, and shifts into the Gulf of Maine Saturday afternoon. Will see a southerly return flow 5-10kt develop by aftn, with daytime highs in the low-mid 30s. PoPs NIL. && .SHORT TERM /10 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/... As of 250 PM EST Friday...The 12Z NWP guidance suite generally trended south with next shortwave trough and associated sfc cyclogenesis off the Delmarva Peninsula Saturday night. Mid- level flow pattern is quite progressive, and anticipate the sfc low to track quickly out to sea south of the benchmark. The North Country will be on the far northern fringe of associated precipitation, and anticipate just an inch or so across central/s-central VT, with perhaps up to 2" of snowfall for the srn Greens Mtns based on current indications. Highest PoPs 60-70% across s-central VT, with just a chance of light snow (40% PoPs) across nwrn VT into far nrn NY based on guidance trends. Best chance for light snow will be 06-12Z Sunday. Lows early Sunday morning generally in the low-mid 20s with prevailing mid- level overcast much of the night. High pressure is back in control Sunday and Sunday night with seasonable conditions for mid-February. Highs Sunday expected in the mid-upr 30s, and back into the low-mid 20s for lows Sunday night. && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 256 PM EST Friday...12z guidance still showing a big pattern change for next week with a strong upper ridge building off the SE US coast, basically a large summer-time bermuda high type pattern. As a result, very warm air will get transported up the entire east coast for at least the first half of the week. A series of low pressure systems will ride along the convergent boundary between the warm air moving north and colder air across Canada. Although this boundary will be a little to our north, we will be close enough to the track of the low pressure that periods of rain are expected. Although the GFS, Canadian and ECMWF are in agreement with the synoptic scale features, there remain differences in actual location and timing of the lows and the frontal zone such that it gets pretty tricky to pin down some important specifics that will ultimately affect our weather. Stayed pretty close to a blend of the models, though with a slight lean toward the GFS and Canadian output, especially as it relates to temperatures and precip chances. The warmth will result in a good deal of snow melt which in turn will cause rivers to rise which in turn could be problematic with a number of ice jams in place. Please see the Hydrology section toward the bottom of this discussion for more details on that aspect of the forecast. A few notes regarding each day follow... Monday: Should see clouds and light rain spread across the region by late in the afternoon. This is due to developing strong warm air advection. 925mb temperatures start the day about -2C and by late Monday will be +3 to +4C. Afternoon temperatures should top out in the 40s. Strengthening southerly 850mb winds of 35-45 knots should make for breezy conditions in the Champlain Valley. Periods of rain overspread the region overnight. Temperatures will continue to slowly rise all night and most everywhere should be near 50F(!!) first thing Tuesday. Tuesday: Very warm and wet. Again, see the hydro section below for those concerns. 925mb temperatures will be in the +9 to +11 range, which if we had sunshine would support surface temperatures into the 60s. At this point think the clouds and periods of rain will keep highs "only" in the mid to upper 50s, which is still approaching daily record high territory. We should see much of our snowpack gone by the end of the day. Those extremely warm temperatures continue Tuesday night. Rainfall amounts will likely take on a strongly orographic look as we`ll have a 50-55kt west/southwest 850mb jet overhead, so that would probably mean enhanced rainfall on the west side of the Adirondacks and across the Greens, with minimum amounts in the Champlain Valley and eastern Vermont. Wednesday: big differences in timing amongst models with the passage of a strong cold front. GFS is quickest, basically having the front through the entire region by mid-afternoon. Canadian is a bit slower. Euro is much slower, and holds the front off until Wednesday night. Makes for a very tricky temperature forecast. If the Euro is right, Wednesday will be into the 60s here in Burlington! As comparison, GFS has the high in the upper 40s first thing and falling from there for Burlington. The blend I ended up with has the front cutting the region during the day. Highs would range from near 40F in the St Lawrence Valley to around 60F in southeast VT. With the front, expecting some rain showers, perhaps ending as a touch of snow showers. Thursday: Looking like seasonable and dry as high pressure builds in. Friday: bit uncertain at this point. Could see clouds and perhaps light precipitation return as high pressure moves off the coast, allowing a return to southwest flow and some warm air advection. Didn`t deviate at all from the model blend guidance. && .AVIATION /03Z SATURDAY THROUGH WEDNESDAY/... Through 00Z Sunday...Conditions will quickly improve across all TAF sites by 02Z as satellite imagery shows the low clouds quickly moving toward the SE and drier air moving into the region. A few snow showers remain along the higher peaks of the Adirondack and Green Mountains with KRUT/KMPV/KSLK showing some light snow. The drier air should bring an end to this by 02Z as well. VFR conditions will prevail from 02Z onwards with some gusty winds redeveloping across KBTV and KMPB late Saturday morning. Outlook... Saturday Night: Mainly VFR, with local MVFR possible. Chance SN. Sunday: Mainly VFR, with local MVFR possible. Chance SHSN. Sunday Night: VFR. NO SIG WX. Washingtons Birthday: Mainly VFR, with local MVFR possible. Chance SHRA. Monday Night: Mainly MVFR, with local IFR possible. Definite RA. Tuesday: Mainly MVFR, with local IFR possible. Likely RA. Tuesday Night: Mainly MVFR, with local IFR possible. Likely RA. Wednesday: Mainly MVFR, with local IFR possible. Likely SHRA. && .HYDROLOGY... As of 255 PM Friday...12z guidance still indicating an extended period of warm temperatures, with temperatures remaining well above freezing from Monday through much of the day Wednesday. The warm air won`t be just near the surface, but even across the higher elevations. Adding to the warmth, it looks like we`ll have some wind and relatively high dewpoints. That is usually a good combo to really help ripen and melt snowpack across all elevations. Long range MMEFS guidance indicates that we could have about about 2" of liquid melt out of the snowpack. Even with no rain, that amount of water will result in rises on all streams and rivers. And the bad news is that there will be some rain as well. Quite a wide spread in model QPF outputs, but we could see 1/2 to 1" in many areas, though we`ll be fine tuning that aspect of the forecast in the coming days. Still any rain will only add to the river rises. Given we`ve got a number of ice jams still in place from the January thaw event, it`s a growing concern for us that we could see flooding issues again in areas where ice jams are in place. We may also end up enough rises to cause the ice jams to also move downstream, bringing any problems with them. Whether or not we see more widespread minor river flooding is still tough to pin down at this point. However the MMEFS guidance based upon 06z Friday GEFS ensembles have 30-50% probability of reaching minor flood stage at several river points. Bottom line, definitely stay tuned to later forecasts. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Clay NEAR TERM...Banacos SHORT TERM...Banacos LONG TERM...Nash AVIATION...Clay HYDROLOGY...Nash

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