Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 182004 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 404 PM EDT Fri Aug 18 2017 .SYNOPSIS... The weekend will feature slightly unsettled weather Saturday and Saturday night with a few light showers. Sunday will be mostly sunny, dry and warm. That sunny and warm weather will continue Monday, allowing for perfect conditions to view the solar eclipse. Increasing chances for showers and thunderstorms return for late Tuesday and into Wednesday. && .NEAR TERM /THROUGH SATURDAY NIGHT/... As of 350 PM EDT Friday... Now-This Evening: As expected, most of the area has had a lull in shower activity since mid/late morning (excepting southern VT). Skies have cleared enough from the Champlain Valley westward to push temperatures into the lower 80s. Low clouds have remained stubborn east of the Green Mountains, and temperatures are only in the mid 60s. With the warmer temperatures west -- along with some relatively high dewpoints (upper 60s-lower 70s), we are seeing some pretty significant surface based instability develop. CAPE values are in excess of 2000J/kg across much of northern NY. However, that moisture is pretty shallow -- both mid-level and low-level GOES 16 water vapor imagery shows extremely dry airmass across northern NY. Precipitable water value observations show this difference as well -- 1.46" precipitable water currently in Burlington, with 1.10" in Watertown NY. Meanwhile, east of the Green Mtns, instability is nil, even though moisture is deeper. So the ingredients for deep/widespread convection are not coming together all that well. Again, this was expected. End result, we should still see a few showers/isolated thunderstorm develop into the evening hours, but they shouldn`t be too much to worry about. I like how the HRRR models depict this. As such, I`ve removed the "heavy downpour" enhanced wording that we were carrying in the forecast. PoPs for the evening are generally in the 25-35% range. Tonight: Otherwise it`s going to be a yucky sleeping night if you don`t have AC. Dewpoints will remain in the mid-upper 60s, so thats about as cold as it will get and it will feel muggy. With the high humidity, we may see a light fog/haze develop in most areas overnight. Perhaps a few patches of denser fog in eastern Vermont. Saturday: Another day that will be on the slightly warm and humid side, but not an uncommon mid-summer day. At upper levels, there will be a trough off to our west, putting us in deep southwest flow. However the mid/upper levels will still be relatively dry, so this will limit the potential for convective activity. Hi-res models do indicate a few hit or miss (but mostly miss) showers developing during the day. As such, have some 20-35% PoPs, highest across the higher terrain of northern Vermont. High temperatures will be a few degrees above normal, with upper 70s to lower 80s. Saturday Night: models all indicate the upper trough will be passing overhead, and this passage will be accompanied by clouds and a few light showers. Kept PoPs in the 25-35% range. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... As of 350 PM EDT Friday...If you love outdoor summer activities, Sunday will definately be a day to take advantage of it. Plenty of sunshine, temperatures in the mid 70s to lower 80s, and most importantly lower dewpoints -- all thanks to high pressure ridging and a west/northwest flow bringing in the drier air. && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 350 PM EDT Friday...First...ECLIPSE. Partial for CWA...basically 58-65 percent. Sky conditions looking very favorable. Patial begins at BTV around 1725 UTC and ends around 1953 UTC according to NASA Eclipse sight. Zonal flow across area on Monday with surface high south of area, this will eventually allow for some increased humidity and clouds but really not til Tuesday. A pretty nice eclipse day with Highs in the 80s and sunshine. The next system has been delayed as its awaiting a sharp, deep shortwave from central Canada to drop across the Northern Plains Tuesday and then rotate across the Great Lakes Tuesday night and lift NE into Ontario/Quebec on Wednesday. The timing looking like more of a Tue ngt-Wed feature. However...surface temps in the M-U80s with rich dewpoints in the 60s and PWATs approaching 1.75 inches should produce SFC based CAPES in the 1000-1500 range at least. Also...despite the main dynamics and surface front still across the Great Lakes, there are falling heights...diffluent flow aloft and indications of some pre-fntl trof, thus chance for t-storms will increase toward evening...esp NY and Intl border. Wind dynamics don`t look too favorable and timing may just be too late but still worth watching as they will increase Tue ngt. Leading, strong shortwave and surface front move through Tue ngt- midday Wed. By Wed aftn...front should be just east of CWA. Trof axis still west of CWA Wed ngt-Thu with surface high still west as well. Therefore, some unstable flow but PWATs fall to around 0.50 inches on Thu. Current thinking is largely mountain upslope shower/sprinkle. Highs on Thu L-M70s. Thu ngt-Fri deep trof axis passes area with surface high pressure building into region thus primarly dry and cooler temperatures. Highs in U60s-L-M70s. A cool start with lows in the 40s/50s and some possible upper 30s. Friday ngt-Sat morning should be as cool or cooler. && .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/... Through 18Z Saturday...a mix of conditions across the region, with VFR across most of northern NY, and MVFR across eastern/southern Vermont. A few showers are also near RUT as I type. Trends should be toward VFR, except eastern Vermont where MVFR ceilings will likely hang on. During the evening we expect scattered showers to redevelop and move across the region. However the confidence in exact timing and location are such that "VCSH" is the best that can be placed into the TAFs right now. Expect MVFR ceilings to also redevelop across much of the area, along with at least a "light" (4-6sm) fog. Guidance suggests that IFR due to visibilities of 1-2sm and ceilings under 1000ft will develop in locations east of the Green Mountains (eg: MPV), with some as well across the `Dacks. Conditions will start to improve after 13z Saturday. Outlook... Saturday Night: VFR. Chance SHRA. Sunday: VFR. NO SIG WX. Sunday Night: VFR. NO SIG WX. Monday: VFR. NO SIG WX. Monday Night: VFR. NO SIG WX. Tuesday: VFR. Chance SHRA...Slight Chance TSRA. Tuesday Night: VFR. Chance SHRA...Slight Chance TSRA. Wednesday: VFR/MVFR. Likely SHRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Nash NEAR TERM...Nash SHORT TERM...Nash LONG TERM...SLW AVIATION...Nash

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