Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 250546 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 146 AM EDT Wed Apr 25 2018 .SYNOPSIS... High pressure will give way to low pressure tracking through the region from Wednesday onward into the first part of the upcoming weekend. Plenty of clouds along with a periodic threat of showers or light rain are expected during this period as temperatures trend cooler. Behind this system, confidence is increasing for a substantial warm-up by the early to middle portions of next week as high pressure returns to the northeast. && .NEAR TERM /UNTIL 2 PM THIS AFTERNOON/...
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As of 146 AM EDT Wednesday...Going forecast in good shape with just some minor tweaks to temperatures and dew points based on current conditions. Temperatures should not fall much more with cloud cover over the region and deeper moisture/light rain moving up into the region...which going forecast has handled well. Previous discussion below: Another outstanding day continues to unfold across the area as departing high pressure, ample sun and modest southerly return flow have boosted afternoon temperatures well into the 60s to lower 70s. Humidity levels remain on the low side, but not as extreme as we saw yesterday as southerly trajectories are transporting a slightly higher dewpoints into the forecast area on the back side of the surface high. For tonight into Wednesday we continue to watch low pressure and associated moisture lifting slowly northward from the Ohio Valley/Mid Atlantic states. High clouds will slowly thicken and lower over time with chances of showers increasing late across the southern and western portions of the forecast area. Low temperatures to run somewhat milder and more uniform as longwave radiative processes become minimized later tonight - mainly 40s with a few 30s in favored northern mountain hollows. Models remain consistent in showing the aforementioned moisture phasing with a digging northern stream upper trough approaching from the Great Lakes and southern Canada tomorrow, and our current idea for increasing clouds and the threat of light rainfall still looks good as we progress into the daylight hours on Wednesday. The devil lies in the more discrete details in regard to how "steady" this rainfall will eventually be through the day with most recent hi-res guidance now suggesting a more showery regime with orographic influences as the nose of a modest southeasterly 30 kt jet lifts through the region. As such, overall QPF was lowered slightly with p-type characterized as more showery than a steady all-day rainfall. PoPs will remain high however, so any outdoor recreational interests should be planned accordingly. Given the abundance of clouds and light precipitation around highs will trend cooler and range mainly through the 50s. Showers then continue on and off for Wednesday night as the parent upper trough tightens atop our area. Good PVA and moisture convergence is associated with this feature, and combined with relatively cool 700-500 mb thermal profiles high PoPs will be maintained. There could be a few wet snowflakes mixed in at the highest summit levels later at night but precipitation will be largely characterized as light rain or showers. Given a near neutral thermal advection regime in the lower levels minimum temperatures should run quite similar to tonight - mainly upper 30s to mid 40s or so.
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&& .SHORT TERM /2 PM THIS AFTERNOON THROUGH FRIDAY/... As of 321 PM EDT Tuesday...The surface low will exit to our northeast Thursday, allowing for Wednesday`s precipitation to further taper off into more orographically-focused showers throughout the day Thursday. With the surface low departing towards the Canadian Maritimes, the predominant flow over the forecast area will be northwesterly/westerly. While wrap-around moisture will be decreasing throughout the day as the low pulls away further into eastern Canada, enough moisture will still be present during the day to support an additional tenth to two tenths of an inch of rain in favorable upslope areas of the western slopes of the northern Adirondacks and Green Mountains. Other areas, including the Champlain Valley, will be more prone to downsloping and pick up lower accumulations on the back end of the system Thursday. Thursday night will be drier as shortwave ridging builds in. Friday the forecast turns tricky as models struggle to come to a consensus on the interaction of two shortwave features. The longwave pattern will feature a broad trough digging over the eastern half of the country, containing multiple pieces of embedded energy with questionable interactions. A southern stream cutoff low will lift out of the Southeast Friday just ahead of a potent northern stream wave digging into the Great Lakes Region. Initially, thinking was that the southern stream low would go out to sea, leaving the North Country dry in between features Friday. However, subsequent model runs continue to trend slower with the northern wave, which would open the door for the cutoff low to our south to lift into the northeastern US and bring us some rain Friday. Both the 12Z runs of the GFS and NAM are favoring this solution, while the 00Z ECMWF and 12Z GEM model runs continue to keep the North Country drier Friday with the low tracking to our east. Current thinking for this forecast package is that the track of the low will lie somewhere in the middle of the two extremes, so discounted the outlier 00Z ECMWF solution and favored more of a 12Z GFS/NAM/GEM blend in handling this system. The main changes to the forecast that this supports is increasing our PoPs Friday, particularly during the afternoon/evening hours, and lowering our daytime temperatures slightly for Friday. Stay tuned for future forecasts as uncertainty is fairly high during this time frame. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... As of 321 PM EDT Tuesday...The weekend will start off cooler and showery on the back end of the departing system. After the passage of a cold front, flow will become increasingly northwesterly Saturday, advecting in cooler, drier air from Canada. The good news is the coldest air will remain well to our north, so the cool down behind the front won`t be anything extreme. Surface temperatures will be generally in the 50s Saturday, then fall into the 30s Saturday night as northwesterly flow continues. Any lingering precipitation from the upper trough will end Saturday night. Sunday will be drier, albeit cooler, with highs in the 40s to low 50s. After a slightly colder than average weekend, Monday will feature a pattern shift that will usher in much warmer weather. High pressure over the Ohio River Valley Sunday will shift to the East Coast by Monday, putting our forecast area in southwesterly return flow to start the work week. Both the deterministic ECMWF and GFS are in agreement with keeping the high pressure anchored off the southeastern US Coast through midweek. A quick look at the GEFS ensembles also shows fairly good support for anomalously high heights building over the East Coast next week. For us here in the North Country, that means sunshine and temperatures well above normal are looking increasingly likely by midweek. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
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Through 06z Thursday...Deeper moisture moving up into the region early this morning from the south will allow for VFR ceilings to lower into the MVFR category after about 14z and remain there through about 02z when some periods of IFR ceilings may develop...especially across northern New York. Despite increasing chances for rain this morning visibilities will remain in the VFR category and will eventually lower into the MVFR category after about 21z when precipitation becomes a bit more steady. Winds will generally be 10 knots or less through the period. Outlook... Thursday: Mainly MVFR, with areas IFR possible. Chance SHRA. Thursday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA. Friday: VFR. Chance SHRA. Friday Night: MVFR/IFR conditions possible. Chance SHRA. Saturday: Mainly VFR, with areas MVFR possible. Chance SHRA. Saturday Night: Mainly VFR, with areas MVFR possible. Chance SHRA, Chance SHSN. Sunday: Mainly MVFR, with areas VFR possible. Slight chance SHRA.
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&& .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...JMG NEAR TERM...Evenson/JMG SHORT TERM...RSD LONG TERM...RSD AVIATION...Evenson

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