Area Forecast Discussion
Issued by NWS Burlington, VT

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798 FXUS61 KBTV 291142 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 742 AM EDT Mon May 29 2017 .SYNOPSIS... Moist low-level air mass across Pennsylvania and New York associated with a mid-level trough will lift northward into our region later this morning into this afternoon. Widespread showers will develop first across northern New York during the mid to late morning hours, and then across Vermont late this morning into this afternoon. A quarter to half inch of rain is generally expected, with the highest amounts across the northern Adirondacks and St. Lawrence Valley of New York. Overcast skies and showers will keep temperatures in the upper 50s to mid 60s today. The showers end by Monday evening. However, another round of showers and some thunderstorms will move across the area on Tuesday. A broad upper level low across Ontario and Quebec will maintain temperatures near to slightly below seasonal levels as we head into early June, along with daily chances for shower activity. && .NEAR TERM /THROUGH TUESDAY/...
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As of 738 AM EDT Monday...Relatively mild early this morning with combination of increasing mid-level cloudiness and increasing S-SE gradient flow keeping PBL well-mixed. Early AM temperatures generally in the 55-63F range, highest in the Champlain and St. Lawrence Valley areas. Have made just minor adjustments with the sunrise update, mainly to bring in higher PoPs a bit earlier with leading edge of rainfall across St. Lawrence County at 1130Z. Rich low-level moisture lurks not far away. RAP-based SPC Mesoanalysis shows PW values of 1.4" to 1.5" across central/wrn NY and PA, collocated with sfc-700mb trough extending from sern Ontario across srn NY/PA. As shortwave ridging across nrn New England moves away this morning, all guidance is consistent in lifting trough and associated moisture/WAA nnewd into the North Country. Should see developing rain showers across nrn NY zones 12-15Z, and eventually across VT 15-18Z. Axis of precipitation tied to the trough axis will shift newd thru the region relatively quickly - by 21Z rainfall should end in nrn NY and by 00z should lift out of the Northeast Kingdom of VT. Overall, looking for a quarter to half inch of rainfall falling over 3-6hr period, with the highest amts likely across nrn NY. Temperatures may fall several degrees this afternoon with onset of rainfall, with aftn readings mostly in the 50s. Gradient flow does increase in advance of the rainfall this morning, and may see a few gusts 20-30 mph across nrn NY and the Champlain Valley until the onset of steadier rainfall early this aftn. Relatively quiet conditions expected tonight, with variably cloudy conditions and redevelopment of south winds 10-15 mph. This should keep overnight temps from falling very much, with lows mostly in the mid 50s in the Champlain and St. Lawrence Valley areas, and upr 40s to lower 50s elsewhere where some decoupling is possible (especially east of the Green Mtns). Tuesday will feature deep-layer swly flow across the North Country, with an embedded mid-level vort max shifting newd from wrn NY into our region coincident with peak afternoon heating. Low 50s dewpoints will mitigate overall surface based instability, with SBCAPE values expected to remain below 1000 j/kg. That said, combination of synoptic forcing and sfc-6km bulk shear of 40-50kts should result in developing aftn convective showers and a few embedded thunderstorms, which may exhibit some organization. Can`t rule out a strong tstm or two, with brief heavy downpours and gusty winds/lightning, but activity should generally remain below severe limits owing to modest instability. Will continue to monitor. Highs on Tuesday mainly in the upr 60s to lower 70s. May again see some gusty winds for a time on Tuesday, especially in the St. Lawrence Valley with gusts to 30 mph possible with valley channeled flow.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 351 AM EDT Monday...Tuesday night should still see some activity east of Lake Champlain as an upper level shortwave will be moving through the North Country. There will be some marginal diurnal heating left over with some modest instability so there will be a slight chance into the evening for some rumbles of thunder, however as night falls expect the showers and any potential of thunder to diminish. None of the storms are expected to be severe although they could produce some gusty winds and locally moderate rainfall. There really isn`t much of a thermal gradient with the wind shift as the shortwave swings through, so temps overnight will only fall to the mid 50s. There is some potential for some fog development just before day break on Wednesday as the winds should be fairly light behind the precip and with dewpoints in the low 50s we could see at few patches of some light fog. Confidence isn`t really there yet especially with partly to mostly cloudy skies so I haven`t included any mention in the forecast. As we move into Wednesday afternoon another round of showers can be expected as another shortwave rounds the bottom of a persistent upper level low. Latest GFS and NAM continue to show modest surface instability on order of 500-1000 J/kg with some 0-6km shear in the 30-40kts range. Nothing to write home about but its enough to warrant the mention of chance thunder in the afternoon and early evening hours on Wednesday. Again none of these storms are anticipated to become severe but they could produce some 30+ mph winds with some locally moderate rainfall. The potential bigger item to note is that the 850mb jet axis will be oriented from southwest to northeast right up the Saint Lawrence valley and with decent mixing we could see 25-30kt gusts locally in the Saint Lawrence. Elsewhere there really isn`t much threat in the way of synoptically driven winds. Temps on Wednesday should warm into the upper 60s to low 70s with 925mb temps warming to 15C-16C by 21z. Then overnight there`s a slightly stronger thermal gradient as the Wednesday shortwave swings through. So we should cool Wednesday night into the upper 40s to low 50s putting us near normal for the first day of June. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 351 AM EDT Monday...The extended will be dominated by an upper level low that is blocked by a strong northern Atlantic low pressure system. So we`ll see several rounds of showers as shortwaves round the parent upper level low to end the weekend. Showery conditions will be the theme as the combination of relatively steep mid- level lapse rates and surface heating will result in shallow instability and shower development. The trends in the latest guidance point to potentially dry days on Thursday early Friday as we sit in between upper level shortwaves and Thursday looks to potentially be dry in- between shortwave troughs. Temps during the period look to be very seasonal, with daytime highs in the mid 60s to low 70s, and overnight lows in the mid 40s to low 50s. && .AVIATION /12Z MONDAY THROUGH FRIDAY/...
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Through 12Z Tuesday....VFR conditions with increasing mid-level cloudiness/ceilings from SW-NE early this morning. Will see increasing chances for showers beginning 12-14Z at MSS/SLK, and across PBG and VT terminals 14-17Z associated with rich low- level moisture and modest warm advection across PA/srn tier of NY lifting newd into our region. Should see intermittent periods of MVFR ceilings/vsby during the mid- day/afternoon hrs at our TAF locations, with HIR TRRN OBSCD and occasional moderate intensity to the rainfall. Some ceilings around 2500ft may linger east of the Green Mtns through tonight, including at MPV. Elsewhere, should see partial clearing and a return to VFR conditions toward 00Z Tuesday. As pressure gradient tightens, winds will be on the increase from the S-SE. Anticipate gusts 20-25kts at BTV/PBG/MPV/RUT between 12-18Z, with less gustiness once rain begins. Outlook... Tuesday: VFR. Breezy. Likely SHRA...Chance TSRA. Tuesday Night: VFR. Chance SHRA...Slight Chance TSRA. Wednesday: VFR. Breezy. Chance SHRA...Chance TSRA. Wednesday Night: VFR. Chance SHRA...Slight Chance TSRA. Thursday: VFR. Slight Chance SHRA. Thursday Night: VFR. Slight Chance SHRA. Friday: VFR. Chance SHRA.
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&& .MARINE... Lake Wind Advisory continues in effect. South winds will be on the increase reaching the 15-25 knot range toward daybreak Monday. These winds will create rather choppy conditions and the strongest winds (around 25kts) are expected during the midday hours. Should see south winds continuing in the 15-25 knot range right into Tuesday. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Banacos NEAR TERM...Banacos SHORT TERM...Deal LONG TERM...Deal AVIATION...Banacos MARINE...Evenson

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