Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 211858 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 258 PM EDT Sun May 21 2017 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH MONDAY NIGHT/...
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As of 231 PM EDT Sunday...At 18Z, strong sfc anticyclone extended from the Gulf of St. Lawrence southward across ern New England. This system tilts westward with height, and have seen building 700-500mb heights throughout the afternoon across nrn NY and VT. That said, there is abundant mid-upper level moisture entrained in anticyclonically curved flow aloft, which will yield mostly cloudy skies/filtered sunshine through the remainder of the daylight hrs late this aftn/early this evening. Temperatures have risen into the upper 60s to lower 70s, with dry low-level air mass in place (2-m dewpoints in the low-mid 30s). Composite 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 WEDNESDAY/... As of 325 AM EDT Sunday...Broad southwesterly upper level flow across the region during the short term period with high pressure giving way to a coastal low on Wednesday. Monday night lingering chance pops in Vermont will trend downward to nil by midnight as weak front departs the region. Little airmass change behind the boundary, and low level winds return to southerly by mid day Tuesday. Tuesday weak surface high pressure will keep precipitation at bay, however periodic vort maxes eject out of base of 500 mb trough to west will traverse the area keeping scattered to broken sky cover. One shortwave trough moving up in the southwest flow will spin up a surface low Wednesday morning along the Delmarva coast and move it northeast to southern New England coast Wednesday evening. Chance pops across the region...ECMWF spreads precip shield further west than GFS, and expect to further refine this part of the forecast in coming days. Southwesterly flow will also keep seasonable temperature in place with highs in the 70s and lows in the 40s to lower 50s. && .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... As of 325 AM EDT Sunday...Long term period becomes more active as the upper trough to the west shifts east, spreading precipitation into the area. Model differences seen last night are starting to coalesce into a common solution. Mean upper level trough over eastern US will move east in two phases. First is southern low moving out of Gulf states will swing northeast Thursday, spreading more showers up the east coast. The northern portion of the trough will hang back over the Great Lakes, then move east and merge with the southern low remnants over the gulf of Maine on Friday. The result is a prolonged period of likely pops for rain Thursday and Friday. With all the pieces in motion there should be some breaks at some point in there, but difficult to tease out those details this far out. For Saturday the low finally kicks out with building high pressure. Some lingering showers especially in Vermont in the mountains, but trend will be to salvage at least part of the Memorial Day weekend. Plenty of cloud cover and rain cooled air to keep temperatures a few degrees below normal but still seasonable. Overall flow through this period is southwesterly as well, and no real temperature changes. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... Through 18z Monday...Mid-level cloud cover (BKN-OVC100-150) will spread ewd across the TAF locations this afternoon and early this evening. 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. 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. Chance SHRA. Tuesday: VFR. NO SIG WX. Tuesday Night: VFR. NO SIG WX. Wednesday: VFR. Chance SHRA. Wednesday Night: VFR. Chance SHRA. Thursday: VFR/MVFR. Likely SHRA. Thursday Night: VFR. Likely SHRA. Friday: MVFR. Likely SHRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Banacos NEAR TERM...Banacos SHORT TERM...Hanson LONG TERM...Hanson AVIATION...Banacos

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