Area Forecast Discussion
Issued by NWS Burlington, VT

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669 FXUS61 KBTV 212316 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 716 PM EDT Sun May 21 2017 .SYNOPSIS... Surface high pressure will translate east of New England this evening allowing a warm front to push into the North Country from the eastern Great Lakes region. We will see periods of rain developing this evening across northern New York, and during the overnight hours across central and northern Vermont. Lighter rain showers and overcast skies will linger during the day Monday, resulting in relatively cool temperatures. Rainfall amounts between one-third and one-half inch are generally expected across the North Country tonight into Monday morning. Dry conditions return on Tuesday with a brief period of surface high pressure. && .NEAR TERM /THROUGH MONDAY NIGHT/...
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As of 715 PM EDT Sunday...Overall little change to previous forecaster thinking for this update, but based on current radar and hi-res model trends decided to increase PoPs to 100% for tonight. Showers are finally beginning to reach the ground over the Tug Hill area and will be shifting into the St. Lawrence Valley within the hour, and eastward through the night with everyone seeing measurable precipitation. Previous Discussion... Mosaic composite radar reflectivity indicates axis of steady/moderate rainfall across sern Ontario swd across far wrn NY/wrn PA and ern OH at 1830Z. There are some leading echoes east of Lake Ontario into St. Lawrence County NY, which will bring a few light sprinkles or isold -SHRA across nrn NY late this afternoon/early this evening. However, bulk of steady precipitation doesn`t reach nrn NY until after 00Z, with onset of stronger 850-700mb WAA and isentropic ascent approaching from the SW. Mesoscale models, including the HRRR /BTV-4km WRF and NAM-Nest all show rainfall reaching the Champlain Valley by 03Z or so, and far ern VT by 05-06Z. Anticipate a 5-6hr period of rainfall, yielding amts generally between 0.33-0.50" thru early Monday morning. Will also see increasing P-gradient overnight. This will result in low-level channeling of winds in the Champlain Valley, with gusts locally up to 30 mph in the BTV area. A Lake Wind Advisory has been issued for Lake Champlain beginning at midnight as south winds increase to 15-25kts during the pre-dawn hrs. Overnight lows will generally be in the mid- upr 40s tonight. Best large-scale forcing slides to our east between 12-15Z Monday, but NAM RH profiles indicate continued saturated conditions in 950-850mb layer, and skies will generally remain cloudy with low overcast in place. The low-level inversion layer in place will keep sfc temps cool, despite 850mb thermal ridge in place (+10C to +11C) across nrn NY. Sfc high temps generally low- mid 50s east of the Greens, upr 50s in the Champlain Valley, and upr 50s to lower 60s across nrn NY. Maintained a chance of showers Monday afternoon. There is some indication of a trailing sfc trough/convergence line moving ewd across nrn NY into VT late in the afternoon, which may result in an additional period of (brief) rain shower activity. A weak sfc ridge builds newd into our region from western NY Monday night. This results in lowering inversion layer and light near-sfc winds. With moist soils, will see combination of abundant low clouds and patchy fog areawide. Moist layer is quite shallow, so not anticipating any precipitation. Lows Monday night mainly 43-48F.
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&& .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... As of 339 PM EDT Sunday...The short term looks to be the quiet intermission between the unsettled periods of the near and long term. After the passage of a cold front and associated trough, a weak ridge moves in, leaving Tuesday looking like a dry and fair day across the region. Winds will remain west-southwesterly behind the front so little change in the air mass leads to warmer temperatures than just prior to frontal passage with highs in the upper 60s and low 70s. Gradual increased cloud cover moving in from the west Tuesday night ahead of the next system will lead to low temperatures low 50s in the western counties and 40s in the eastern half. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... As of 339 PM EDT Sunday...The long term pics up again in activity as multiple systems will impact the area through to the weekend. A coastal low moves northeast into New England. The GFS and ECMWF still disagree on the inland advection of the precipitation with the GFS keeping it mostly offshore while the ECMWF being more aggressive and extended the precip into Southeast VT. For now have just kept chance PoPs east of the Greens for Wednesday. Thursday has a positively tilted upper trough associated surface low over Ohio Valley with a closed off upper low. The low progresses slowly to the northwest of the CWA before shifting west over the northern counties. This leads to and extended period of unsettled conditions and potential for precipitation from midday Thursday and through midday Friday as low pushes out to the coast. Lingering showers in the higher terrain remains in the resulting northwest flow through to early Saturday afternoon. The second half the weekend sees a high pressure ridge begin to build back in leading to a brief return to fair conditions. High temperatures in the long term will range from the upper 60s to upper 70s, while lows will be in the 40s to 50s. && .AVIATION /00Z MONDAY THROUGH FRIDAY/...
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Through 00Z Tuesday...Will see a gradual lowering of cloud ceilings through the evening with increasing chances for rain showers, especially during the overnight hrs. After midnight, should see development of MVFR ceilings (2-3kft) at SLK/MSS, along with HIR TRRN OBSCD areawide and vsby 4-5SM at times in showers and BR. There is a chance of MVFR ceilings at the remaining TAF locations, but anticipate predominantly 3-4kft ceiling heights for RUT/BTV/PBG. Should see MVFR developing at MPV by 14Z/Mon. Shower/rain activity diminishing in coverage but another possible focus area coming across from west to east late in the day. Otherwise, persistence with MVFR/VFR ceilings. Winds generally less than 10kts through 06Z. Thereafter, should see some gusts from the south approaching 20kts at BTV/PBG as gradient flow strengthens toward daybreak. Outlook... Monday Night: VFR/IFR. Chance SHRA...FG. Tuesday: VFR. NO SIG WX. Tuesday Night: VFR. NO SIG WX. Wednesday: VFR. Chance SHRA. Wednesday Night: VFR. Chance SHRA. Thursday: VFR. Chance SHRA. Thursday Night: VFR. Likely SHRA. Friday: VFR/MVFR. Likely SHRA.
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&& .MARINE...
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As of 231 PM EDT Sunday...A Lake Wind Advisory is in effect starting at midnight (04Z Monday). Gradient flow increases out of the south during the pre- dawn hours Monday, with sustained winds over Lake Champlain reaching 15-25kts after midnight and waves building to 2-4 feet. The highest waves are expected across the northern portion of the broad lake south of Grand Isle. South winds will remain generally in the 15-25kt range during the daylight hours on Monday, before diminishing Monday evening.
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&& .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Banacos NEAR TERM...Banacos/Lahiff SHORT TERM...MV LONG TERM...MV AVIATION...Banacos/SLW MARINE...Team BTV

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