Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 292254 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 654 PM EDT Fri Jul 29 2016 .SYNOPSIS... Canadian high pressure will bring dry weather tonight through Saturday. High temperatures on Saturday will range from the upper 70s to lower 80s, with pleasantly low humidity levels. The next upper level disturbance approaching from the Great Lakes will bring the next chance for showers for Sunday into Monday, possibly lingering into Tuesday along with cooler temperatures. High pressure Wednesday through Friday will bring warming temperatures and mainly dry weather. && .NEAR TERM /THROUGH SATURDAY/...
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As of 654 PM EDT Friday...Forecast looks to be in great shape this evening as ridge of high pressure is nosing into the northern St. Lawrence Valley promoting clearing skies. Associated surface-850 mb northerly flow helping to drop dewpoints into the 50s from north to south. Temps may not fall too sharply at first but as winds go light and variable expect sizable temperature falls given the dry air advecting in. Radiational fog in the typical river valleys as well, all of which is handled well in the going forecast. Projected lows look on track in the 50s to near 60, a more comfortable night than has been experienced in the past couple for sure. Previous near-term discussion issued at 415 PM Friday follows... Quiet weather conditions tonight with light N-NW winds and mostly clear skies. Should see min temps a bit cooler than recent days with advection of lower dewpoints/clear skies/good radiative cooling. Lows mainly in the 50s to around 60 near relatively warm Lake Champlain. Looks like a good night for radiation fog to develop around midnight in the favored river valleys of central and eastern VT, and also across the valley locations within the northern Adirondack region. Pleasantly dry conditions for Saturday with weak surface high pressure across southern Quebec providing light north winds and sfc dewpoints in the low-mid 50s. Model RH, cloud fields, and simulated satellite all show some areas of high clouds from time to time through Saturday so skies will partly to mostly sunny. 850mb temperatures of +11 to +14C depending on the model of choice but all should translate to afternoon highs in the upper 70s to lower 80s. Winds light and variable.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... As of 415 PM EDT Friday...12z guidance not all that consistent, but consistent enough to indicate that there will be period of showers (perhaps a steady moderate rain) sometime between late Sunday into Monday, all in association with a trough swinging through. That trough and associated energy is currently back across Nebraska. Timing differences between the models, with ECMWF being the fastest (showers by Sunday morning), the GFS with it`s showers coming in during the afternoon, and NAM the slowest with nothing really until early evening. Stuck a little closer to the GFS as it seemed like a good compromise. Thus painting in increasing chances of showers from southwest to northeast during the day. Some interesting signals in the models for late Sunday/Sunday night. All models show some precipitation "bullseyes" where they indicate a small area of locally heavy rain. Doesn`t appear to be convective feedback, as models keep instability very minimal during the period. However over the course of 18 hours or so, QPF adds up in the models. GFS has a swath of 2-3" from south-central VT back across central NY. ECMWF has 2-3" almost everywhere across VT, with lesser totals west. NAM has 1-2" from central VT extending southwestward. Great variability in the model depiction. Think this is due to how each model handles the shortwave energy, which appears to come through in pieces, combined with convergence aloft around the 700mb level. Soundings do indicate a fairly juiced atmosphere, with Precipitable Water values around 1.5", fairly deep warm cloud depth (11-12k ft) along with rather weak winds, with 850mb trending southeasterly (hint of atlantic moisture tap). Bottom line, could see some downpours, perhaps Sunday night. For precip totals in the forecast, I went with an overall model blend including output from 00z model suite. End up with rainfall totals of 1-1.25" across South-Central VT. Lower amounts the further north you go -- just 0.25-0.33" or so up along the Canadian border. At this point don`t expect any flood issues. Ground in that part of the state is very dry (borderline moderate drought), and as long as the rain falls over several hours, the ground will absorb it. However, something that will need to be watched in later forecasts. As mentioned above, instability is very minimal, so primarily rain showers with only isolated rumble of thunder expected. Precipitation will be slow to end on Monday, with lots of clouds around. Temperatures Sunday 70s to perhaps lower 80s (depends on how quick the showers get in). Will be on the cool side Monday with all the clouds, just 70s. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 415 PM EDT Friday...okay agreement between 12z suite of GFS and ECMWF. Both show a weak shortwave moving across early on Tuesday that should result in a few showers first thing in the day. Ridging aloft develops mid/late week, though ECMWF is much more pronounced with it. GFS is, like the 00z run, showing a flatter ridge. Even so, it should be dry Wednesday and Thursday. Perhaps an isolated shower in some of the higher terrain, but have PoPs less than 20% both days. A front will be approaching on Friday, though at this point the 12z runs keep us dry. With 00z runs having a slightly faster timing, have kept some 20-30 PoPs in for Friday, in the event later models speed up again. Probably the most noticeable aspect of the weather next week will be the increasing heat. GFS has 925mb temperatures of 20-22C on Wednesday and increases it to 24-26C by Friday. ECMWF is a little cooler. Thus looking at highs well into the 80s to even lower 90s by Thursday and Friday. 25C at 925mb typically translates to 35C (95F) at lower elevations. Not ready to go that warm yet, but followed the previous forecasters idea of upping high temperatures a few degrees from the base model blend. && .AVIATION /00Z Saturday THROUGH Wednesday/... Through 18Z Saturday...Mainly VFR except local LIFR/VLIFR in FG at KMPV/KSLK 06-12z Sat. Threat of showers across s-central VT/KRUT will continue to diminish this afternoon as cold front with drier air pushes south of the region. Dry weather elsewhere will continue through the rest of the TAF period. Still looking for locally dense radiation fog at KMPV/KSLK by about 06z and should be gone by 12-14Z Sat. Some cumulus at 3500-4500 ft aft 14z Sat with some high clouds moving in from the southwest in advance of a warm front aloft. Winds generally N 5-10 kts through the afternoon. Mostly clear with light winds tonight. Outlook 18z Saturday through Tuesday... Sat: VFR/mainly clear Saturday with light winds under high pressure. Sun: Mainly VFR, possible MVFR in evening showers with approaching weak low pressure. Mon: Areas of MVFR in showers. Local IFR possible with weak low pressure. Tue: Becoming VFR with building high pressure. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Sisson NEAR TERM...Loconto/Sisson SHORT TERM...Nash LONG TERM...Nash AVIATION...Sisson

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