Area Forecast Discussion
Issued by NWS Burlington, VT

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976 FXUS61 KBTV 240429 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 1229 AM EDT TUE MAY 24 2016 .SYNOPSIS... High pressure will provide mainly clear and quiet weather tonight with seasonably cool temperatures expected. Moisture pivoting north and west around departing offshore low pressure will bring a renewed threat of scattered showers and a few thunderstorms Tuesday afternoon and early evening, mainly across Vermont. Thereafter, the first prolonged stretch of summerlike weather will build into the region for the remainder of the week and into the Memorial Day weekend with warm and increasingly humid conditions. While much of the period will be dry, there will be a daily threat of scattered showers and a few thunderstorms, mainly during the afternoon and early evening hours. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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As of 1229 AM EDT Tuesday...Going forecast in good shape with just some minor tweaks to the sky grids to match current pattern. Otherwise should just see a slow increase in clouds across Vermont over the next few hours. Lows will be in the 40s with some 30s in the mountains. On Tuesday short-term models continue to show good consistency showing a filling upper low will drift northeasterly along the northeastern seaboard through the day. While the system is essentially equivalent barotropic, weak deformation/moisture band rotating into our region on the system`s northwestern periphery should interact with some marginal instability and low level convergence to spark scattered showers and a few storms, mainly from the Champlain Valley east. Here solid chance to low-end likely pops (40-60%) will be maintained. Further west, a mainly dry and sunnier day is expected as this area will be removed from spoke of deeper moisture and convergence. High temperatures will be similar to today from the northern Champlain Valley west into northern New York (upper 70s to lower 80s) with slightly cooler readings (70s) further east where coverage of afternoon clouds and showers will be greater.
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&& .SHORT TERM /6 PM THIS EVENING 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/...
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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.
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&& .AVIATION /06Z Tuesday THROUGH Saturday/... Through 00Z 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. NOTE: KMSS ASOS seems to be reporting erroneous visibility/weather as low as 1/4SM HZ for the past several hours since about 21Z. Outlook 00Z Wednesday through Saturday... 18z Tue - 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...JMG NEAR TERM...Evenson/JMG SHORT TERM...Nash LONG TERM...Nash AVIATION...JMG

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