Area Forecast Discussion
Issued by NWS Burlington, VT

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567 FXUS61 KBTV 201940 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 340 PM EDT Sat Jul 20 2024 .SYNOPSIS...
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A weakening cold front will bring clouds and a few showers, especially across northern areas, overnight. Skies will trend sunny on Sunday with light north winds ushering in drier and cooler air. After an extended drier stretch, unsettled weather will begin by early Tuesday associated with a quasi-stationary front that will set up across New York and New England. Periods of rain are expected, with increased thunderstorm chances on Thursday.
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&& .NEAR TERM /THROUGH SUNDAY NIGHT/...
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As of 340 PM EDT Saturday...It`s been just about the most seasonable summer day possible, which makes it unusual given that we typically deviate from climatological normals. We are in a zone of weak high pressure with gradual pressure falls ahead of cold front shifting southward across southern Canada this evening. For this time of year it is a moderately strong front thermodynamically, as low level temperatures will drop several degrees along with lowering dew points. Refreshing dew points in the low to mid 40s are found on the cool side of the front and beyond the post-frontal clouds in southern Ontario/western Quebec this afternoon. The frontal zone, with regard to cloud cover, is relatively large and corresponds well with progged 700 millibar relative humidity exceeding 80%. This will be shifting southward over our region mainly in the nighttime hours, lingering into perhaps late morning. Based on satellite imagery today, mostly cloudy skies may linger in a particular location for upwards of seven hours. Solar heating and further weakening of the front will tend to reduce the cloudiness in central and southern Vermont during the morning, and these areas are most likely not to see any rainfall with the front. Farther north, while the intensity of the rain will be on a decreasing trend, some rain showers are likely, especially across the northern tier counties. Amounts still look to be mainly a few hundreths of an inch, with perhaps 0.1" in area like Swanton, Vermont. Behind the front, then the question is how low will afternoon relative humidity get? The NBM dew points are a little high relative to the HREF, and it remains to be seen how quickly the clouds dissipate/shift south during the day. The cool air advection will be battling strong heating, but overall temperatures have trended a touch cooler with this forecast with highs mainly in the low to mid 70s. An exception is over the lower Connecticut River Valley and lower elevations in the Taconic Foothills in Vermont, where weaker and later arrival of cool air advection will allow temperatures to reach near or above 80. Then tomorrow night, a dry air mass with light northwest winds aloft and climatological fog season should support localized dense fog in the favored locations mainly in central and southeastern Vermont and western Adirondacks. At our typical cold spot, Adirondack Regional Airport/Saranac Lake, MOS guidance suggests a low around 40 degrees, which would match the observed low on July 2nd when we last had a cool and dry air mass in the region. That would also suggest our broad valleys should see lows in the low and mid 50s, with many mid to upper 40s across central and northeastern Vermont as well as other portions of the Adirondacks.
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&& .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
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As of 335 PM EDT Saturday...Conditions remain dry Monday with temperatures generally running around to slightly above seasonal averages in the upper 70s to mid 80s. Synoptically, major features will be a large blocking ridge over the inter-mountain western US, a relative longwave trough across the Central Plains, and the Bermuda Ridge in the western Atlantic. While upper flow remains fast and zonal, a lifting migratory low will push a warm front through the North Country Monday night increasing chances of rain. With the track of the low south of Vermont, overrunning will favor spreading rain chances south to north overnight.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/...
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As of 335 PM EDT Saturday...Model consensus highly favors lingering a quasi-stationary boundary across portions of the Northeast Tuesday through Thursday night of next week building the Bermuda High northwestward. The actual placement will be key in determining which areas will receive heaviest rain, but the conceptual model for this setup points to potential for periods of moderate to heavy rainfall. Given the week of drying, flood potential will start lower early Tuesday across southern Vermont and likely be contingent on multiple rounds of thunderstorms (5-15% chance of flooding at this time). Moving forward, a couple of impulses are progged to move along the boundary Wednesday and Thursday bringing additional chances of moderate to heavy rainfall with some potential for localized flooding. Depending on where heaviest rain falls, some locations` susceptibility to flooding will likely increase from Tuesday to Thursday while precipitation chances become more widespread to include all locations to the Canadian border. While thunderstorm chances will be present Tuesday and Wednesday, the likely, most- active period for thunderstorms looks to be on Thursday when surface dew points will be highest and potential for increasing shear exists. Models suggest jet energy will be sufficient with the last impulse Thursday into Friday to push a surface front through the North Country allowing for a transition to relative ridging. However, thermal parameters along this proposed boundary will likely be weak, keeping temperatures in the mid/upper 80s heading into next weekend.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/... Through 18Z Sunday...VFR conditions are in place, with some MVFR ceilings expected for up to several hours between 06Z and 14Z, most likely at higher elevation sites of EFK, MPV, and SLK. At SLK, high-resolution ensemble forecast data suggests SLK in particular may see ceilings lower, such that chances of IFR conditions peak at 60% around 11Z. A cold front approaching from southern Quebec and southeast Ontario will bring increasing clouds tonight into tomorrow morning, pushing through MSS around 04Z, PBG, BTV, and EFK around 06Z, between 07Z and 08Z at SLK, and 09Z at MPV and RUT. Ceilings associated with these clouds will be mainly BKN-OVC 060-080, although embedded light showers will cause ceilings to dip close to 030 on the cool side of the front. Shower chances generally peak from 06Z to 11Z (in the 25 to 35% range) and are much lower at MPV and RUT compared to other sites. Winds will be light and variable behind the front, then increasingly N-NW around 5 knots by 12Z. Outlook... Sunday Night: VFR. NO SIG WX. Monday: VFR. NO SIG WX. Monday Night: VFR. Slight chance SHRA. Tuesday: VFR. Chance SHRA, Chance TSRA. Tuesday Night: VFR. Chance SHRA, Slight chance TSRA. Wednesday: Mainly MVFR, with local IFR possible. Chance SHRA. Wednesday Night: MVFR/IFR conditions possible. Chance SHRA. Thursday: Mainly VFR, with local IFR possible. Likely SHRA, Chance TSRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Kutikoff NEAR TERM...Kutikoff SHORT TERM...Boyd LONG TERM...Boyd AVIATION...Kutikoff