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FXUS61 KBTV 070754 AFDBTV

Area Forecast Discussion National Weather Service Burlington VT 354 AM EDT Tue May 7 2024

SYNOPSIS
A beautiful day is on tap for today as high pressure settles over the region. Temperatures will warm into the mid 60s to mid 70s again under clear, blue skies. Rain and possibly a few thunderstorms are expected on Wednesday. Wet weather continues thereafter, and we'll trend cooler heading into the latter half of the week with temperatures struggling to rise above 60 by the weekend.

NEAR TERM /THROUGH WEDNESDAY/
As of 354 AM EDT Tuesday...With plentiful sunshine and temperatures warming well above normal, we're expecting a picture perfect day today. Once any patchy fog dissipates, there won't be much beyond a few passing clouds and highs will once again reach into the mid 60s to mid 70s. Low levels will become quite dry as lapse rates steepen under daytime mixing, and minimum relative humidity values will drop down into the 25 to 35 percent range. However, relatively light winds (though gusts to 20 mph are possible) and our recent rainfall will help to limit fire weather concerns. High pressure starts to move eastward tonight, making way for low pressure approaching from the midwest. Clouds will increase ahead of this system, but the bulk of any rain will hold off until early Wednesday. Winds will turn to the south/southeast, helping to keep temperatures a few degrees warmer than last night/this morning. Lows will be in the 40s areawide.

Things become more interesting on Wednesday as ridging breaks down, putting us in the interplay between an upper low centered near the Canadian Maritimes and another over the Upper Midwest. A shortwave trough will break off the latter feature and looks to wrap around the eastern trough, swinging directly across our region. Lift will be aided by an upper jet also moving overhead. PWATs surge toward an inch, and with favorable dynamics, expect a swath of showers will spread from west to east early Wednesday morning into the early afternoon hours. Some of the rain could be briefly heavy at times, and while better chances will remain to our south, can't rule out a rumble of thunder or two over our southern sections. Once this initial rain exits by mid afternoon or so, things become a little more questionable. Mid levels dry out while lapse rates steepen, allowing for elevated CAPE values of 300-600 J/kg. Shear will be ample, on the order of 50-60 kt. The question will be how much the atmosphere can recover after morning's precipitation, and whether the cap could be broken and storms become surface based. Note that most CAMs are indicating convection breaking out behind the main precipitation shield, keeping most of the stronger activity to our south. Still, there are some indications that there could be some discrete cells or multi-cell clusters that cross central/southern sections of our forecast area, some of which could be strong.
Main threats would be small hail and gusty winds. Note that the latest Day 2 Convective Outlook from the SPC does have the Marginal Risk area just barely intruding into our far southern CWA, namely far southern St Lawrence and Essex Counties in NY and southern Rutland and Windsor Counties in VT. Stay tuned to later forecasts, especially if you have outdoor plans.

SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY/
As of 354 AM EDT Tuesday...Challenging forecast for Wednesday night with changeable conditions as weak low pressure and a surface cold front passes by with trailing upper level boundaries following behind. The primary cold front poised to pass through at the start of this period looks to have shallow sharpness, as depicted by modeled 2 meter temperature gradients versus those higher up. Ahead of the boundary, forecast soundings in south central Vermont generally show low levels stabilizing quickly. However, with dew points in the 50s and moderately steep 700-800 mb lapse rates, meager elevated instability of about 150-350 J/kg per HRRR interquartile range supports keeping a slight chance of thunder going through early evening. Farther north, there are greater odds of low level winds having switched from southwesterly to northwesterly by this time indicative of loss of any remaining instability.

There may be enough shallow mixing behind the front that reduces the coverage of fog, but overall the combination of expected rainfall on Wednesday combined with additional forcing for ascent and loss of deep moisture suggests drizzle and patchy fog overnight. For now, have a mix of shower chances and fog/drizzle in locations favored to see low clouds, such as in the vicinity of the mountains. After sunrise, its unclear if low clouds will linger or if some partial sunshine may greet us as the upper level pattern looks rather unsettled and with only the weakest ridging building in behind Wednesday's system.

Overall, precipitation chances on Thursday have decreased a bit from the previous forecast and remain a bit higher as one goes southward.
However, the forcing for additional rainfall on Thursday looks bifurcated - it will be either non-existent in scenarios that keep our area under the influence of a northern jet stream, or substantial in a scenario with a quickly approaching shortwave from the southwest. In the coming days, the actual solution should become clear. Regardless, Thursday looks mostly cloudy and seasonably cool, and potentially chilly while low clouds in the morning hang around.

LONG TERM /THURSDAY NIGHT THROUGH MONDAY/
As of 354 AM EDT Tuesday...This period continues to look rather unsettled and potentially moderately wet. The beginning of the timeframe still looks most certain to be rainy (near 70% chance for most locations both Thursday night through Friday daybreak and during the day Friday). There is a consistent synoptic signal amongst model guidance for a slow moving low pressure system to approach from the southwest and produce isentropic lift in our region. Variations in the storm track provide uncertainty in both timing and intensity of precipitation, with odds of a heavier rainfall as you go into southern portions of our Adirondack region.
Several members of the GEFS are particularly wet such that the Otter Creek basin-average rainfall during this period could be around an inch; on top of the rainfall from Wednesday, the potential for minor flooding of this river remains low but non-zero. Otherwise, a wider flood threat is not foreseen with lack of tropical moisture or convective, intense precipitation with this system.

Beyond Friday, we will continue to see the influence of a longwave trough supporting occasional chances of showers. As a closed upper low to our west slowly crosses our region, precipitation should become more isolated in nature with increasing breaks in the clouds after an overcast start to the weekend. Probabilistic data shows no statistically significant change to our cool temperatures across the weekend even if each day trends warmer. By Monday, highs look to return to near seasonal norms in the middle 60s.

AVIATION /08Z TUESDAY THROUGH SATURDAY/
Through 06Z Wednesday...Mainly VFR conditions expected through the TAF period. Exception will be potential IFR in patchy fog 08z-12z this morning. Clouds will continue to decrease through the early morning hours, with FEW-SKC to prevail the remainder of the period. KMPV and KSLK have the best chances for any fog, though still uncertain as to how prevalent and dense it will be given most recent moisture profiles. Have kept with 2SM and a SCT IFR deck for now, but will need to watch trends closely for any IFR/LIFR potential. Regardless, fog threat would be over by 13z and VFR prevails thereafter. Light and mainly terrain-driven winds through 14z will trend north/northwest 5-10 kt during the daylight hours Tuesday, then light and variable again after 00z Wed.

Outlook...

Wednesday: Mainly MVFR, with areas VFR possible. Likely SHRA, Slight chance TSRA.
Wednesday Night: Mainly MVFR, with local IFR possible. Chance SHRA.
Thursday: Mainly VFR, with areas MVFR possible. Chance SHRA.
Thursday Night: Mainly VFR, with areas MVFR possible. Likely SHRA.
Friday: Mainly MVFR, with local IFR possible. Likely SHRA.
Friday Night: Mainly MVFR, with areas IFR possible. Chance SHRA.
Saturday: MVFR/IFR conditions possible. Chance SHRA.

BTV WATCHES/WARNINGS/ADVISORIES
VT...None.
NY...None.

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