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Area Forecast Discussion
Issued by NWS Burlington, VT
Issued by NWS Burlington, VT
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085 FXUS61 KBTV 142348 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 748 PM EDT Sun Jul 14 2024 .SYNOPSIS... After a quiet end to the weekend, heat, humidity, and scattered showers and thunderstorms are forecast for Monday and Tuesday, followed by an additional chance for thunderstorms on Wednesday. Following a cold front passage Wednesday night, cooler and drier weather is expected for the end of the week and into next weekend. && .NEAR TERM /THROUGH MONDAY NIGHT/... As of 748 PM EDT Sunday...Not much needed updating at this time as forecast is good shape. Think upstream showers nearing Jefferson County, New York will hold together for very light rain in mainly western St. Lawrence County between 9 and 11 PM, with otherwise dry conditions until the early morning hours across the area. Didn`t fully drop PoPs, but may need to do so with the next update if radar trends diminish completely as rain enters the North Country. Previous Discussion... Surface high pressure and a weak ridge aloft provided a beautiful end to the weekend with warm temperatures in the 80s and slightly more comfortable dewpoints in the lower 60s. Tonight, a decaying mid-level shortwave trough will track eastward from the Great Lakes and bring a chance for showers and embedded thunder to portions of northern New York, but most of Vermont should remain dry. Clouds increase across the entire region through the overnight, helping to keep min temps mild in the mid-60s to low-70s. On Monday the remnant shortwave energy passes through the region and combined with increasing humidity and instability, we should see scattered showers and thunderstorms develop through the afternoon. A lack of any deep layer shear supports storms being more of the garden variety, but based on low flash flood guidance and PWATs surging back towards 2", any stronger cores will be capable of producing some isolated flash flooding if rainfall exceeds 1" in an hour, especially across central and northern Vermont. In addition, with high temps rising into the upper 80s to low 90s and dewpoints back into the upper 60s, heat indices are expected to rise into the mid/upper 90s for portions of central/southern Champlain Valley where a heat advisory has been issued. Afternoon convection should wane with the loss of surface heating after sunset, with some lingering isolated showers and thunderstorms through midnight. It should be another steamy overnight with lows only in the upper 60s to low 70s again, and dewpoints only a few degrees below for humidity close to 100%. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... As of 256 PM EDT Sunday...Tuesday is likely to be another warm and humid day. Heat indices are likely to climb into the 90s across the region as warm, moist air lifts northeast ahead of a cold front stretching out to our west. Interestingly, the source of moisture on Tuesday will be from a round about connection from the Pacific Ocean up through the Baja into the Intermountain West before making a beeline across the Plains. This leaves me slightly skeptical we can achieve truly oppressive dewpoints we can get out of the Gulf of Mexico, but almost all guidance has upper 60s to lower 70s. It`s hard to beat persistence. Heat Advisories are presently covering part of the Champlain Valley, and will likely be needed for the Connecticut River Valley as well. It will likely be added to the existing Heat Advisory tomorrow. The picture for thunderstorms is somewhat complicated. There are some timing discrepancies with the shortwave expected to cross the area Tuesday afternoon. It seems Monday night`s convection and trough will place some stable air across the region initially. This should allow the efficient warming expected on Tuesday, but the question is how much instability recovery can take place. If the shortwave is too early, we may be able to escape much impact, but if the shortwave is delayed until later in the afternoon, there will be upwards of 1500 J/kg of CAPE, 0-6km shear of 30 to 40 knots, and 1.50-2.00" PWATs. As noted before, the meso-beta vectors are slow, and so thunderstorms may not be in any real hurry or could backbuild despite some present flow. So the western half of Vermont and northern New York are in a marginal risk outlook for excessive rain, and we are in a marginal risk outlook for localized severe storms. Given the potential seems conditional, this all seems reasonable. Some lingering showers are expected overnight, followed by a prefrontal trough that shifts everything out, and that means a humid night in the mid 60s to lower 70s is anticipated. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... As of 256 PM EDT Sunday...The extended begins with a frontal boundary at our doorstep. The stretched out cold front to our west will only slowly shift east. However, a large upper trough begin to force it to make some eastward progress. The question is, exactly how fast will that be. A slower front means a warmer Wednesday with more chances to destabilize, while a faster front would result in activity limited to the Green Mountains eastwards. The upper trough is going to lag behind, but it will send cooler, less humid air eastwards. So if things don`t line up well, we could be on the drier side. Probabilistic guidance suggests one should not be too optimistic with the chance of exceeding 0.10" at greater than 50 percent. The clustering of drier ensembles are less than 20 percent too. To complicate matters, the 12z deterministic runs came in with a relatively dry Wednesday with a fast frontal progression, though. For now, the forecast changes little from the previous forecast. The focus is most likely to be the southern half of Vermont though, and so have stuck closely to blended data for rainfall forecasts for now which highlights that well enough. A few showers could develop on Thursday as the upper trough ambles east, but there will be a lot of happy people as temperatures trend slightly below normal! Dry high pressure sets up, and we`ll be looking at pleasant weather conditions through Saturday. Although temperatures will begin to climb back up above normal, there will not be the oppressive humidity. Then, there`s a reinforcing cold front sometime early next week. It will come with some showers, but nothing significant as it comes from the north without a tropical moisture feed. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... Through 00Z Tuesday...VFR conditions will prevail through the period. Temporary visibility reductions due to an unlikely direct hit of a heavier shower, especially late in the period, is possible at most sites. However, coverage of these variety of showers and thunderstorms looks isolated. In the 00Z to 02Z period, an area of light showers currently over eastern Lake Ontario may move through KMSS and KSLK overnight but shouldn`t flight conditions. Additional very light rain is possible there and possibly up through the northern Champlain Valley through 12Z. Towards 16Z, scattered showers and thunderstorms will develop with skies SCT-BKN. Winds overnight will be mainly <5kts, then south/southwest at 6-11kts after 14Z Monday. Outlook... Monday Night: VFR. Scattered SHRA, Scattered TSRA. Tuesday: Mainly VFR, with local MVFR possible. Chance SHRA, Slight chance TSRA. Tuesday Night: Mainly VFR, with local MVFR possible. Chance SHRA. Wednesday: Mainly VFR, with local MVFR possible. Chance SHRA, Slight chance TSRA. Wednesday Night: VFR. Chance SHRA. Thursday: Mainly VFR, with local MVFR possible. Chance SHRA, Slight chance TSRA. Thursday Night: VFR. Slight chance SHRA. Friday: VFR. NO SIG WX. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Heat Advisory from noon Monday to 8 PM EDT Tuesday for VTZ005- 009-011. NY...Heat Advisory from noon Monday to 8 PM EDT Tuesday for NYZ035. && $$ SYNOPSIS...Lahiff NEAR TERM...Kutikoff/Lahiff SHORT TERM...Haynes LONG TERM...Haynes AVIATION...Kutikoff/Lahiff