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Area Forecast Discussion
Issued by NWS Burlington, VT
Issued by NWS Burlington, VT
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204 FXUS61 KBTV 160541 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 141 AM EDT Tue Jul 16 2024 .SYNOPSIS... Heat will remain the rule for a few more days until a cold front reaches the area on Wednesday afternoon. Intervals of showers and storms, a few strong, will move through the region late this evening into tonight, and then redeveloping Tuesday afternoon. The higher chances for stronger storms will be Tuesday afternoon.. Following one last round of showers with a cold front Wednesday evening, cooler and drier weather is expected for the end of the week and into next weekend. && .NEAR TERM /THROUGH WEDNESDAY/... As of 1139 PM EDT Monday...Issued a quick update to match PoPs/Wx up to current conditions. Large swath of moderate to heavy rain with embedded thunder is lifting across VT at this hour. The heaviest activity is moving into the northern Champlain Valley, with another stronger cell down across south- central VT. This activity is all pushing to the north and east, and will produce heavy rainfall as it does so. Winds will become a little gusty with the more robust cells, but nothing severe anticipated as storms should remain elevated. Other than the above, the forecast is in good shape and no other changes were needed. Previous discussion...It was a chain reaction once the first thunderstorm developed in west-central St. Lawrence County, with several storms quickly pulsing up across northern New York and far western Vermont between 8 and 10 PM. Activity has finally waned a bit outside of the northern Lake Champlain area. However, the cluster of thunderstorms entering Rutland County is expected to help trigger more storms across Vermont, with activity finally exiting northeastern Vermont after 2 AM. We have had isolated areas of 1-1.5" of rain in northern New York in 1 to 2 hours time, so we cannot rule out an instance of flash flooding through this evening. That being said, instability will gradually be diminishing out ahead of the upstream convection such that intensity of rain/thunderstorms should be weakening. Other than revising the current six hour QPF to better reflect observations and latest model guidance, no significant changes made. It`s a hot day across the forecast area. Mid 80s to lower 90s with dewpoints in the mid 60s to lower 70s is causing heat indices in the upper 80s to mid 90s across the region. Satellite suggests fair weather cumulus remains quiescent. A few showers have popped up along the Addison- Rutland county line, but there`s dry subsidence still hanging over the region from this morning`s activity. Upstream, we`re monitoring a weakening upper shortwave across western New York State presently producing strong to severe storms near Buffalo. Convective processes are expected to briefly reverse the shortwave`s weakening trend, with strong 850hPa southwesterly flow pivoting just up to upstate New York. Strong low-level convergence and elevated instability should allow showers and storms to continue propagating northeast overnight. The lack of surface instability should keep this sub-severe, but parts of southern St. Lawrence County, the Adirondacks, and the far southern half of Vermont may have to remain watchful for gusty winds if outflows can maintain themselves into our region. We will track its progress to see how well it holds together as the threat for strong to locally severe storms is non-zero. A marginal risk outlook (Level 1 of 5) is present for that region), and a small portion of St. Lawrence County in a Slight Risk (Level 2 of 5). Overnight lows will remain warm given the south flow. Rain may cool things off somewhat, but still expecting temperatures in the mid 60s to lower 70s. For Tuesday, we could see some lingering clouds as this shortwave is somewhat slow to move out. There could be a few pockets of showers still in the Northeast Kingdom early in the morning. Dry, subsident air behind the shortwave should produce sufficient heating, but this may be tempered by initial cloud covers. Eastern Windsor has been added into the Heat Advisory tomorrow as increasing dewpoints will counter the somewhat cooler daytime highs. Heat indices should again reach the mid to upper 90s across the Champlain Valley and in the Connecticut River Valley. Thunderstorms will again fire as the result of a mesoscale vortex from convection in the Plains. This one appears more likely to hold itself together and arrives a bit earlier than today`s. So a Slight Risk for severe thunderstorms (Level 2 of 5) covers much of the region due to the higher shear and better time of day for convection. This also appears more capable of producing heavy rainfall. Grounds will be primed by tonight`s activity. So it will not take much to result in flash flooding in common trouble spots. && .SHORT TERM /WEDNESDAY NIGHT/... As of 308 PM EDT Monday...There remains considerable spread amongst the guidance what we can expect weather wise here in the North Country on Wednesday. Global ensemble guidance shows a general consensus of members with low pressure centers tracking along the St Lawrence River valley from eastern Ontario into western Quebec. That does favor the development of scattered thunderstorms on Wednesday out ahead of a surface cold front. SPC currently has the eastern two-thirds of our CWA in a Day 3 marginal severe risk. On the other hand, WPC has Day 3 marginal excessive rainfall outlook (ERO) to our south. The thinking is that what kinds of hazardous weather we get on Wednesday will depend on where the boundary sets up, which at this point could range from the Adirondacks to the Connecticut River valley. With Mesoscale Convective Systems (MCSs) setup, it is not uncommon for higher-resolution guidance to not get a good handle on until 6- 12 hours prior to their development. In plain language, if the Midwest gets a long-lasting MCS to form and come through our region in the overnight hours, there could be little convective activity during the daylight hours. PWATs still do look elevated, although not extreme on Wednesday, generally in the 75-90th percentile range of SPC sounding climatology for the Albany, NY upper air site. If we do get convection to come through on Tuesday night, then it is certainly plausible that Wednesday might well turn out to be a relatively benign day with drier air starting to make its way into the region. Looking at deterministic guidance, it does look like the CAPE/shear combination is not nearly as robust as on Tuesday. So it is reasonable to wager that storms, if they do become strong or severe, would be much more isolated or scattered in coverage. But then again, a lot hinges on the convective development and evolution on Tuesday into Tuesday night. Long story short, it is prudent to utilize a bit of a wait and see approach at this time. Given the considerable uncertainty, largely stuck to a blend of guidance for this forecast period. The best chance for locally heavy rainfall, or a few stronger storms, would be across the southeast portion of our CWA. But for those tired of the seemingly relentless heat and humidity, relief is coming. Cold air advection should begin in earnest by overnight Wednesday, with gusty northwest winds sending PWATs from the 75-90th percentile range of SPC sounding climatology to the 10-25th percentile range by Thursday morning. Refer to the long term discussion for details. && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 308 PM EDT Monday...Overall, the long term portion of the forecast would feature delightful weather for mid July standards in the North Country. The main question for Thursday would be whether we get isolated to scattered shower activity as the upper low builds in or we get mainly dry weather. For now, have only had slight chance PoPs for parts of the region on Thursday with only at worst isolated to widely scattered showers. Either way, no adverse weather impacts are anticipated as it is just a question of we start a stretch of much- deserved break from the recent heat and humidity heading into the weekend. Expect dew points in the 50s (with 40s in spots) Friday into the weekend. Daytime temperatures would trend near to even slightly below climatological normal with mid 70s to low 80s on tap. 50s would return to the forecast for overnight lows, with 40s in the colder hollows and low 60s in the urban centers. Indeed, the CPC 6- 10 day outlook does indicate a trend towards near to just above normal temperatures for our region. It would be music to the ears to see the 6-10 day outlook indicate below normal rainfall for the period. After a wet first third of July, the dry stretch will be much welcome. Overall, largely stuck to blended guidance for this portion of the forecast but the main take home message is to look forward to a pleasant if not absolutely delightful stretch of weather heading into the weekend. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... Through 06Z Wednesday...Showers coming to an end early this morning will keep a mix of conditions through 08z. Trending toward MVFR ceilings thereafter, but IFR in patchy fog will be possible 08z-12z, especially at KMSS/KSLK/KMPV. Skies scatter to VFR at all terminals 14-16z. Another round of showers/thunderstorms will move from west to east 22z-03z, with skies and visibilities prevailing MVFR in any precipitation, though brief IFR will be possible in heavy thunderstorms. Precipitation ends late in the period, but MVFR ceilings will likely persist through 06z Wednesday. Light and variable winds through early this morning will pick up to 5-10 kt out of S/SW after 14z and remain so through the remainder of the forecast period, though some storms will be capable of producing gusty winds. Outlook... Wednesday: VFR. Chance SHRA, Slight chance TSRA. Wednesday Night: VFR. Slight chance SHRA. Thursday: VFR. Slight chance SHRA. Thursday Night: VFR. NO SIG WX. Friday: VFR. NO SIG WX. Friday Night: VFR. NO SIG WX. Saturday: VFR. NO SIG WX. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Heat Advisory until 8 PM EDT this evening for VTZ005-009-011. Heat Advisory from noon today to 8 PM EDT this evening for VTZ021. NY...Heat Advisory until 8 PM EDT this evening for NYZ035. && $$ SYNOPSIS...Haynes NEAR TERM...Hastings/Haynes SHORT TERM...Chai LONG TERM...Chai AVIATION...Hastings/Neiles