Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 181900 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 300 PM EDT Fri Jun 18 2021 .SYNOPSIS...
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While our more humid airmass will support scattered showers and even a few thunderstorms early tonight and again on Saturday...the bulk of the time will be rainfree. Sunday should prove to be the nicer of the two days with only a minimal chance for afternoon showers across the SOuthern Tier.
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&& .NEAR TERM /THROUGH SATURDAY NIGHT/...
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While most of the area will be rainfree this evening...a few showers and thunderstorms will re-develop ahead of a warm front. This will especially be the case across the Southern Tier...where it is still not out of the question that a strong thunderstorm could form between 23 and 03z. Scattered showers will then taper off in coverage during the overnight. After a dry start on Saturday...a few showers and thunderstorms could develop during the midday and afternoon in advance of an approaching shortwave. Again...the bulk of any activity should be focused on the Southern Tier. Weak low level ridging and nocturnal stability will kill off any convection early Saturday evening...leaving the rest of the night pcpn free.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
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Low amplitude ridging works overhead Sunday, allowing for mostly dry conditions. Deterministic guidance has been indicating a very weak upper level shortwave crossing the area in the afternoon, which combined with diurnal instability could kick up a few showers/thunderstorms. For now, added low chance PoPs for Sunday afternoon mainly from the Southern Tier east to the Finger Lakes region, which looks to be in closer proximity to the passing shortwave. Though the first half of Sunday night will likely remain dry, rain chances will gradually increase from west to east moving closer to Monday morning ahead of an approaching upper-level longwave trough. A warm front moving in from the south the area will help moderate overnight temperatures, with lows only dipping into the upper 60s and low 70s, lower 60s across the western Adirondacks. The aforementioned large upper level trough will dig across the upper Midwest/upper Great Lakes on Monday while the strengthening main surface low pressure pivots northeast just south of James Bay. A strong trailing cold front will approach from the west on Monday, providing the larger scale forcing and bringing widespread shower and thunderstorm chances to the area. Though model guidance continues to keep any remnants of the tropical system currently moving towards the Gulf Coast away from the Great Lakes region, strengthening SW flow out ahead of the front will still allow GOMEX moisture to surge northeast across the area. This, combined with a 50kt+ 850mb jet passing overhead and surface trough axis swinging through the area, should lead to the likelihood for showers and thunderstorms to break out across the area by Monday afternoon, some of which could be on the stronger side. PWATS nearing 2" will bring the potential for locally heavy rainfall. At the same time, a strengthening upper level jet over the upper Great Lakes will aid in the development of low pressure on the cold front under the right entrance region of the jet, acting to slow the eastward progression of the surface boundary. This will allow showers and storms to linger into Monday night, though decreasing amounts of instability should help limit overnight thunderstorm coverage. The cold front will slowly cross the area sometime closer to Tuesday morning, as surface low pressure rides northeast along the boundary.
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&& .LONG TERM /TUESDAY THROUGH THURSDAY/...
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Plentiful moisture will still be in place and right entrance region of the upper jet overhead, continuing to support the likelihood of showers right into the day on Tuesday, with lessening chances for thunder as the day progresses owed to instability getting shoved east of the area with the boundary. Main upper trough axis crosses the area Tuesday night with the chance for a few lingering showers. A much cooler and drier airmass is then set to move into our area for Wednesday and Thursday as high pressure builds across the area from the west. Upper troughing will remain overhead which will keep the cooler air locked in over the Northeast and Mid Atlantic. Despite any diurnal instability that develops with the cool airmass overhead, limited moisture will preclude much in the way of any shower development either day, with much of the time remaining dry. Otherwise, above normal temperatures and high humidity levels on Monday will trend downward, with below average temperatures by Wednesday and Thursday and much more comfortable humidity levels.
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&& .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
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VFR conditions will be in place regionwide today...despite the cloud cover from a convective complex over Ohio. The increased clouds will yield some showers but true convection will hold off until after 22z and should be generally confined to the Southern Tier. Any site that receives a storm could experience MVFR conditions for a brief time. The rain and thunder chances will slowly taper off from west to east overnight. While most sites will maintain VFR conditions...IFR to MVFR cigs are expected to develop across the Southern Tier. Any low cigs from the overnight will improve to VFR by 13z on Saturday. The remainder of Saturday should feature VFR weather. Outlook... Sunday...Mainly VFR...but MVFR cigs possible in scattered showers and thunderstorms across the Southern Tier during the afternoon. Monday and Monday night...VFR to MVFR conditions with showers and thunderstorms likely. Tuesday...Mainly VFR...but MVFR conditions possible east of Lake ONtario where some lingering showers and thunderstorms will be likely. Wednesday...VFR.
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&& .MARINE... Southwest winds in the 10-15 knot range will bring choppy conditions to Lake Erie and the northeast end of Lake Ontario today through Saturday, but winds and waves are expected to remain below Small Craft Advisory criteria. A few scattered thunderstorms may produce gusty winds and locally higher waves late this afternoon and evening, and possibly again Saturday afternoon and evening. Relatively light winds will return Sunday as weak high pressure moves into the eastern Great Lakes. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...None. && $$ SYNOPSIS...RSH NEAR TERM...RSH SHORT TERM...PP/AA LONG TERM...JM AVIATION...RSH MARINE...Hitchcock

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