Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 240816 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 416 AM EDT TUE MAY 24 2016 .SYNOPSIS...
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An upper level low pressure system just off the mid-Atlantic coast will move northeast today and reach eastern Maine tonight. This will bring clouds to the area along with the threat of showers across Vermont and parts of the northern Adirondacks. Dry weather is expected Wednesday morning...but then an upper level disturbance will move across the area Wednesday afternoon and bring a chance of showers and thunderstorms to the North Country. Above normal temperatures are expected today and Wednesday with highs in the mid 70s to lower 80s.
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&& .NEAR TERM /THROUGH WEDNESDAY/...
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As of 415 AM EDT Tuesday...We will see a gradual increase in clouds across most of the area today as an upper level low pressure system off the mid-Atlantic coast moves slowly northeast. There will be a sharp gradient of precipitation with this system across our area because of the track of the system. Looking at most of northern New York remaining dry today with a chance of showers across Essex County New York and most of Vermont. There could even be an isolated thunderstorm...mainly over southern and eastern Vermont. High temperatures today will be in the mid 70s east to lower 80s west. Upper level low continues to move northeast tonight and reach eastern Main by Wednesday morning. Still looking at some lingering showers over eastern Vermont tonight...but eventual dry conditions develop over the entire area later tonight through Wednesday morning. Eventually a shortwave trough moves across eastern Canada and the Northeast Wednesday afternoon. This will increase dynamic support over the area and bring a cold front into the region late Wednesday afternoon. Instability should also increase ahead of the front with highs getting into the mid 70s to lower 80s. Dew points will also be increasing...but feel model forecasts are doing their usual overforecast of dew points which in turns creates more instability. Feel CAPE values will be closer to 500 J/kg versus the model forecasts of 1000 J/kg. This should be sufficient to enhance the potential for convection and during this time of maximum instability...deep layer shear is increasing. Neither the instability or shear are strong...but enough to increase the potential for thunderstorms and have included in the forecast.
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY/... As of 355 PM EDT Monday... tuesday night: showers/isolated t-storms mainly for vermont will quickly fade by mid evening with the loss of heating. maybe a touch of patchy fog for late night, though confidence not high enough to include that in the forecast. wednesday: hi-res models are all pretty similar with overall scenario of a shortwave and associated weak surface front pushing into the region from the northwest. with temperatures well into the 70s, we`ll have some surface based instability. models suggest cape values of 500-1000 J/kg. nam also showing 0-6km shear of roughly 30-40kt developing during the afternoon especially across northern ny. looks like enough ingredients coming together for convection to develop during the afternoon -- perhaps with semi- organization to them. model radar reflectivity output from various hi-res models suggests a broken line of t-storms will rapidly develop mid-day across northern new york and push southeast and then quickly fade by early evening as they reach southern vermont where less instability will be available. have blended the reflectivity outputs to form the basis of the PoP forecast for the day. basically a 30-50% chance of t-storms for the afternoon, especially across northern ny and extending into northern vermont. thursday: will be a transition day. for most of us, it will be dry and fairly sunny. perhaps some showers or isolated t-storm across northern ny later in the day as a developing southwest flow sends a surge of moisture our way. stuck with the model blend with highs well into the 70s for the region. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 355 PM EDT Monday... looks like a summer pattern for the holiday weekend. that means warmth, moderately humid and the chance for thunderstorms each day. GFS and ECMWF are in "okay" agreement with the large scale synoptics, however there will be a "back-door" front setting up somewhere probably just to our east thanks to the still quite chilly atlantic ocean. depending on how far inland this front will push will greatly affect the weather we see. considerable differences in this subtle but important detail in the global models, so there is some bust potential in parts of the forecast. daily details: thursday night: southwest flow and associated moisture advection will lead to scattered showers. clouds and precipitation will keep it rather mild overnight, with lows in the 50s to lower 60s. friday: we`ll be solidly into a warmer and slightly more humid airmass. both GFS and ECMWF indicate a decent amount of surface based instability, with cape values likely topping out over 750 J/kg by the afternoon. not a lot of dynamic forcing, but the atmosphere will be fairly moist (precipitable water values over 1.25"). looks like a typical early August weather pattern, so I`ve gone ahead with a typical forecast for that part of the summer. 35-50% chance of afternoon thunderstorms looks good. will probably initially form over the higher terrain and then push east during the afternoon. with 850mb temperatures rising to around 15C, that would support support highs in the lower to mid 80s for the region. went a little warmer than the first guess model blends. saturday: looks a lot like friday, except the surface dewpoints are a little bit higher. i think this will be the first day that we`ll really start to notice the humidity. some differences in the overall temperature fields as denoted by the GFS and ECMWF. ECMWF wants to slide in slightly cooler air from the north, as it has the ridge axis suppressed slightly further south than the GFS. the GFS has 925mb temperatures rising to 20-23C, which would mean we could approach 90f in some valley areas. ECMWF is cooler (17C across the Canadian border to 22C in far southern vermont). took the blend of the models, but that still results in temperatures solidly into the 80s. based on those temperatures and a little higher humidity, afternoon thunderstorms will be a good bet once again. no strong focus other than terrain, so t-storms will be a hit and miss proposition. sunday & memorial day (monday): both GFS and ECMWF indicate that cooler atlantic airmass will pool to our east and try to make a westward push as a small high pressure develops east of new england. this "back door" front will be shallow, and just how much the terrain (white mountains and green mountains) restrict it`s westward movement is just a little beyond the resolution of the global models. for sunday, this backdoor front should still be to our east, so sunday looks to be a repeat of saturday (temperature wise and t-storm chance-wise). for monday, if anything, the models suggest a cooler airmass will push into eastern vermont. if this happens, we could see a pretty significant temperature variation (60s far east to mid 80s far west) across the forecast area. those specific details, as mentioned, are tough to pin down this far out. thus stuck with straight guidance blend for monday, which indicates an overall cooler day than sunday. still a rather moist airmass around, so will maintain 30-40% PoPs. given the cooler forecast, surface instability will be less, so probably not as many t-storms around for memorial day. still doesn`t look like a total washout of a day, so i think most outdoor activities/bar-b-ques should still be okay. && .AVIATION /08Z Tuesday THROUGH Saturday/... Through 06Z Wednesday...VFR through the forecast period. Winds variable less than 10 kts. After 15Z Tuesday, increasing moisture from the east/south will bring sct/bkn VFR cigs in the 050-100 AGL range with an increasing threat of a shower/isolated storm, especially at KMPV/KRUT terminals. Outlook 06Z Wednesday through Saturday... 06z Wed - 00z Thu: VFR with chance of afternoon/early evening showers and/or isolated thunderstorms each day. Activity generally scattered in nature with long periods of VFR/dry weather. Brief gusty winds and/or MVFR visibilities possible with any heavier activity. Thu: VFR under high pressure. Thu night-Fri: VFR/Chance MVFR in SHRA/TSRA with a warm front. Sat: Mainly VFR. SCT pm SHRA/TSRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Evenson NEAR TERM...Evenson SHORT TERM...Nash LONG TERM...Nash AVIATION...Neiles

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