Area Forecast Discussion
Issued by NWS Burlington, VT

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501 FXUS61 KBTV 272104 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 504 PM EDT Thu Jul 27 2017 .SYNOPSIS... Scattered showers and isolated thunderstorms across the region this afternoon will end after sunset as a cold front sweeps southeastward through the region and is replaced by high pressure. Cloudy skies for most areas will begin the day on Friday, with a trend towards sunny and clear skies by the afternoon and evening. High pressure remains in control through the weekend with dry weather and seasonably cool temperatures expected. && .NEAR TERM /THROUGH FRIDAY NIGHT/... As of 322 PM EDT Thursday...Forecast is playing out well with a surface cold front pushing into the Ottawa Valley this afternoon, sparking a line of showers across northern New York. As we move through the later afternoon into the early evening, continued clearing across central and northern areas will aid in some modest surface instability spreading eastward across central/northern Vermont on order of 500-1000 J/kg which will be sufficient to sustain scattered showers and isolated thunderstorms through late evening. Not looking at anything becoming severe, but certainly brief heavy showers are possible in any stronger cores along with a few strikes of lightning. With the loss of insolational heating after sunset, instability weakens as the front drops into the region and any ongoing convective activity will diminish to a mainly dry night. Forecast challenge for tonight then becomes the potential for widespread low clouds and fog. High pressure building in behind the aforementioned front begins aloft with forecast modeled soundings showing a strong subsidence inversion developing during the pre-dawn hours. Increasing northerly and strongly blocked flow combined with the inversion looks to trap abundant moisture in the low levels so while breaks in the clouds become more abundant across the region this afternoon, feel that clouds will increase markedly again after sunset as the inversion sets up. Only exception will be the St. Lawrence Valley where clearer skies will prevail, along with the higher summits which will likely be above the clouds come sunrise Friday. With abundant clouds around, temps tonight won`t fall off too much, and expect lows to mainly be in the mid 50s to low 60s. Overall, Friday and Friday night will be dry with high pressure firmly in control, and cloud cover continuing to be the main forecast challenge. Through the day the subsidence inversion will eventually break up so cloudy skies in the morning will trend towards clearing by mid-day, but heading into the afternoon and overnight hours, upper level low pressure digging southeastward from the Great Lakes into the mid-Atlantic will spread some mid/high clouds northward into the North Country. Shouldn`t have an impact on the forecast highs or lows, and might even make for a pretty sunset across northern areas. Cool northerly flow will limit afternoon highs to the low/mid 70s north and mid/upper 70s south, and lows Friday night will be seasonally cool in the mid 50s valleys to mid 40s mountains with the climo favored valleys likely seeing some dense fog. && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
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As of 502 PM EDT Thursday...The weekend the weather will be rather quiet as a 500mb low dives south of the North Country through the DELMARVA region. That leaves us with weak cold air advection and high pressure building in through the day Saturday. What little clouds will see will be decreasing from northeast to southwest as the day progresses to mostly clear by the evening. Temps will be seasonally cool with highs in the lower 70s and overnight lows in the upper 40s to low 50s.
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&& .LONG TERM /SUNDAY THROUGH THURSDAY/...
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As of 502 PM EDT Thursday...Sunday sees the high pressure crests overhead conditions should be favourable for some fog development in the protected river valleys in the early morning. Temperatures will start to be on the rise with another fair day of dry weather to end the weekend. The next chance for precipitation comes mid week as a coastal low pressure system tracks up towards New England. Models differ on whether the low crosses the benchmark but in either case, merges with energy from a far northern stream system and brings a frontal system with a chance for some scattered showers across the North Country Tuesday afternoon/evening. As stated before, the models don`t paint areal clear picture so have continued to opt with continuity of prior forecasts and keep just a mention of chance showers for Tuesday, with the higher terrain being most likely to see activity. Temperatures continue the warming trend with highs reaching mid 80s by midweek and overnight lows in the mid 50s to low 60s.
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&& .AVIATION /21Z THURSDAY THROUGH TUESDAY/... Through 18Z Friday...Some isolated showers remaining across the area this afternoon. Along with that a mix of MVFR/VFR which should transition to all VFR by 21Z. Showers should be ending by about 00z across the area as well. Overnight, ceilings at all locations except KMSS will lower to MVFR with the ample low- level moisture as well as northerly flow through the overnight hours. Furthermore, KMPV/KSLK will see blocking flow leading to IFR/LIFR ceilings after 06Z until mid morning on Friday at which point, all stations should improve to VFR. Southerly winds at 05-15 knots will go light and variable overnight before swinging around the north-northwest after 13Z at 05-10 knots. Outlook... Friday Night: VFR. NO SIG WX. Saturday: VFR. NO SIG WX. Saturday Night: VFR. NO SIG WX. Sunday: VFR. NO SIG WX. Sunday Night: VFR. NO SIG WX. Monday: VFR. Slight Chance SHRA. Monday Night: VFR. Slight Chance SHRA. Tuesday: VFR. Slight Chance SHRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Lahiff NEAR TERM...Lahiff SHORT TERM...Verasamy LONG TERM...Verasamy AVIATION...Verasamy

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