Area Forecast Discussion
Issued by NWS Burlington, VT

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513 FXUS61 KBTV 181143 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 743 AM EDT Tue Jun 18 2024 .SYNOPSIS... Dangerous levels of heat begin this afternoon and will persist into Thursday. Highs will reach well into the 90s each day, and overnight temperatures will remain muggy and uncomfortable. Please be sure to take appropriate precautions to avoid heat stress through the remainder of this week. Isolated to scattered thunderstorm are expect this afternoon and Wednesday with potential for strong, gusty winds. Best chances for rain arrive late Thursday into Friday with a cold frontal passage. && .NEAR TERM /THROUGH WEDNESDAY/... As of 634 AM EDT Tuesday...A small mesoscale convective vortex, the leftover remnants of a large area of thunderstorms from yesterday, has ignited over the north end of Lake Ontario and is now moving through portions of northern New York. This feature will have implications for today`s heat, potential for localized heavy rainfall, and add additional forcing for thunderstorms to form. This feature has already produced 1-2 inches of rain in parts of Lewis County, NY where it has been training. It should weaken as it slowly travels eastward over northern New York and into Vermont, but it should be noted that models are not handling this feature well, but expect it to be a focal point for thunderstorm initiation through the afternoon. Given PWATs and other significant convective parameters are anomalously high, isolated strong storms are possible in addition to the lake breeze and terrain initiated storms. Heat-wise, locations that experience rain from this feature will likely see mitigation of the hottest conditions. Previous Discussion...Oppressive heat conditions remain on track to begin today and continue through Thursday. The one caveat will be for locations that end up getting a thunderstorm or remain under convective overhang for a decent portion of the afternoon. Best chances of thunderstorms today will be along the western shore of Lake Champlain as lake breeze initiates and pushes westward into prevailing southwesterly flow. Given the heat, lack of strong cape, and high levels of CAPE/DCAPE, gusty winds will be a threat. Steering flow aloft will be weak today favoring more of a pulse variety initiation, then transition to outflow boundary interactions. This isn`t the strongest trigger mechanism, but there should be a few thunderstorms given the high levels of instability and ample CAPE; SPC concurs and has included northern New York and portions of the Champlain Valley in a Marginal(5% chance) risk of a severe thunderstorm. Vermont locations will be spared the early thunderstorm chances, but prevailing flow and any outflows tracking east could trigger more storms along the slopes of the greens with maintenance parameters favoring a continued eastward propagation. Southern Vermont chances will be lower, generally less than a 20% chance. A weak trough could be the triggering mechanism for Wednesday as some models project a weak trough embedded in flow around the periphery of the ridge. Again, gust winds will be the primary threat. Otherwise, heat will build today with AM temperatures starting higher than previously expected. 90s will be readily achievable and may continue to warm until convection gets going in earnest. Champlain Valley locations may benefit the most from convective overhang clouds for the mid/late afternoon hours. Still, plan on dangerous heat conditions and have a plan to beat the heat. && .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY/... As of 332 AM EDT Tuesday...Thursday should be the last of the significant heat days. Lows in the morning will be incredibly mild with temperatures remaining in the upper 60s and 70s for most. During the day, temperatures will again reach the upper 80s and 90s and the humidity will remain high. Dew points will be in the upper 60s and low 70s. There will also be some afternoon convection, but the extent is still uncertain. With the warm moist airmass, there will be plentiful CAPE and it looks to be uncapped, so there will likely at least be a couple terrain and lake breeze induced storms. How much more forms depends on if there will be any other sources of lift. The deterministic Euro and some of the ensembles bring a weak shortwave through that is just enough to to form more organized convection, and some bring an MCS through the region from north to south. The other ensembles keep the storms scattered. The NAM has stronger forcing and also brings the 1000-500 mb wind shear above 30 KTs, which would indicate the possibility of a higher severe threat. For now, went chance PoPs for most areas as showers look likely, but there is the potential for more widespread convection. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 332 AM EDT Tuesday...A cold front moves through on Friday and ends the significant heat, though temperatures will remain above average and some humidity will remain, so it won`t exactly feel refreshing. The timing of the front is key on Friday. There should be adequate forcing and wind shear for severe storms, but the instability will depend on if it comes through earlier or later in the day. A majority of the Euro and GFS ensembles bring it to the south in the morning which would significantly reduce the instability and prevent much of a severe threat. Only around 40 percent even have 500 J/KG of CAPE for southern Vermont and only about 20 percent have higher than 1000 J/KG. In northern Vermont, these probabilities are much lower. Overall, the severe threat seems relatively low and limited to southern Vermont but it bears watching. Behind the front, drier weather should prevail through Saturday, before more widespread rainfall is possible Sunday into Monday as a low pressure moves in from the west. Despite looking cooler than this week, temperatures look to remain above normal and the ridge will sit ominously to the south, but far enough away to not directly impact the weather. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/...
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Through 12Z Wednesday...There is a line of showers and thunderstorms slowly moving eastward across northern New York. It will likely hold together and pass over MSS and SLK this morning. Whether it sticks together into PBG and Vermont is questionable but there will at least be scattered showers and thunderstorms around during the afternoon. Scattered storms will develop across northern New York as well in the afternoon, but due to their hit or miss nature it cannot be definitively determined if they will hit any of the airports or not. Besides being able to produce frequent lightning, the showers and storms will briefly lower visibilities at any terminal they reach to MVFR and possibly IFR. The storms should dissipate overnight before developing again tomorrow morning. Patchy fog will likely develop across the region tonight and there is a decent chance it develops at SLK and MSS. Winds are generally light and southerly during this period. LLWS is not a concern. Outlook... Wednesday: VFR. Slight chance SHRA, Slight chance TSRA. Wednesday Night: VFR. NO SIG WX. Thursday: VFR. Chance SHRA, Chance TSRA. Thursday Night: VFR. Chance SHRA, Slight chance TSRA. Friday: VFR. Chance SHRA, Slight chance TSRA. Friday Night: VFR. Slight chance SHRA. Saturday: VFR. Chance SHRA.
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&& .CLIMATE... Hot temperatures will result in values near records by the middle of next week. Below are some of the records under threat of being broken. Record High Temperatures: June 18: KBTV: 97/1994 Forecast 95 KMPV: 93/1994 Forecast 92 KPBG: 94/1994 Forecast 91 KMSS: 97/1994 Forecast 93 KSLK: 94/1907 Forecast 90 June 19: KBTV: 100/1995 Forecast 95 KMPV: 95/1995 Forecast 93 KPBG: 93/2001 Forecast 92 KMSS: 94/1955 Forecast 92 KSLK: 93/1994 Forecast 89 June 20: KBTV: 95/2012 Forecast 93 KMPV: 90/2020 Forecast 92 KPBG: 94/1964 Forecast 90 KMSS: 92/2012 Forecast 89 KSLK: 92/1995 Forecast 87 Record High Minimum Temperatures: June 18: KBTV: 73/1994 Forecast 74 June 19: KPBG: 70/1949 Forecast 74 June 20: KPBG: 70/1953 Forecast 74 KSLK: 68/2012 Forecast 65 && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Heat Advisory from noon today to 8 PM EDT Thursday for VTZ001>011-016>021. NY...Heat Advisory from noon today to 8 PM EDT Thursday for NYZ026>031-034-035-087. && $$ SYNOPSIS...Boyd NEAR TERM...Boyd/Myskowski SHORT TERM...Myskowski LONG TERM...Myskowski AVIATION...Myskowski CLIMATE...Team BTV