Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 231744 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 144 PM EDT Fri Jun 23 2017 .SYNOPSIS...
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Occasional showers and scattered thunderstorms associated with a cold front will continue through this evening before ending from northwest to southeast overnight. An upper level trough will then become established over the weekend with a brief shower or thunderstorm possible both days, but the majority of the time will be rain free. A better chance of showers will arrive Monday as the trough sharpens over the Great Lakes. Temperatures will drop to below normal over the weekend and early next week.
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&& .NEAR TERM /THROUGH SATURDAY/...
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Radar imagery showing numerous areas of showers crossing the region this afternoon as several weak convectively augmented vorticity maxima and associated small low level speed maxes cross the area, bringing periods of enhanced ascent and moisture convergence. This will continue to be the case through the late afternoon and early evening, with a few rounds of showers expected in most locations. There is been very little thunder so far given the extensive cloud cover and showers limiting destabilization. There may be some opportunity for limited instability to develop late this afternoon with a few breaks in the showers, and this may support a few widely scattered thunderstorms. PWAT is near 2 inches, so any storms that develop may produce brief heavy downpours. Severe weather risk is minimal given the anemic CAPE and poor lapse rates. Showers and widely scattered thunderstorms will continue into this evening along the pre-frontal trough and any remaining small scale mid level perturbations. The rain will then end from northwest to southeast overnight as the surface cold front crosses the area. The lake plains should see some clearing late tonight as a push of dry air arrives out of Canada and subsidence increases in the wake of the cold front. Low clouds will likely persist across the higher terrain of the Southern Tier and Tug Hill region in moist low level upslope flow. Cold advection will increase behind the cold front and allow lows to drop to drop into the lower 60s in most locations by daybreak. On Saturday a weak surface ridge will build into the Ohio Valley and eastern Great Lakes. Meanwhile, a broad/weak trough will become established in the mid/upper levels across the Great Lakes. A mid level shortwave will move through the mean longwave trough and cross the eastern Great Lakes during the afternoon. Meanwhile, mesoscale convergence zones will setup across our region as enhanced gradient onshore SW flow develops downstream of Lake Erie, with more westerly flow across Lake Ontario. This should allow a well defined surface convergence zone to develop from Niagara Falls east to Rochester, eventually building all the way east to Central NY. The convergence along this feature combined with the weak large scale ascent from the mid level shortwave may support a few widely scattered afternoon showers and thunderstorms, mainly in the corridor between the NYS Thruway and south shore of Lake Ontario. An isolated afternoon thunderstorm also cannot be ruled out across the higher terrain from the interior Southern Tier into the Finger Lakes. It will be less humid on Saturday, with highs in the mid 70s in most locations, and a few upper 70s from the Genesee Valley into Central NY.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
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Saturday night...The upper level pattern will feature a longwave trough centered over the Great Lakes region with an upstream intermountain ridge. At the surface...a weak ridge will be in place. Thus any leftover scattered evening convection on lake breezes, primarily S of Lake Ontario, should quickly dissipate during the evening with a dry and cool remainder of the night - low should be mostly in the 50s. Sunday and Sunday night...Sunday should start out nice, but expect the eventual development of scattered to possibly numerous showers and thunderstorms developing on lake breeze boundaries. Additional development may form along a weak cold front moving SE into WNY during the afternoon. Similar to Saturday night, expect convection to dissipate fairly quickly with the loss of daytime heating. Monday...The upstream cold pool aloft corresponding to the upper level trough will pass overhead. Strong insolation and resultant mixing, together with plenty of moisture and cool air aloft without any signs of a cap will result in fairly quick development of showers and some thunderstorms, although CAPE values will be unimpressive with a skinny profile seen in point forecast soundings. Still, with a freezing level somewhere near 8000-10000ft, cells could easily support small hail. As noted earlier, there may even be a hint of a lake response with a dry adabatic lapse rates over the 65-70+F waters. Once again, expect showers to be on the decrease during the evening with little or no showers late.
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&& .LONG TERM /TUESDAY THROUGH THURSDAY/...
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The longwave trough axis will quickly pivot across western and central NY through Tuesday. This pattern will continue to support cool temperatures with comfortable humidly. Daytime highs topping out in the 60s to perhaps about the 70 degree mark. The cool air aloft within the trough (again 850mb T around 6C) will support mainly a diurnal threat for showers and possibly some thunderstorms. Lake effect clouds/showers can also continue to be possible with steep low level lapse rates. Taller shower/storm cells in this cool environment may bring some small hail with a sub-10kft freezing level. Surface high pressure centered over the southern Appalachians will ridge north across the region Wednesday allowing for dry weather with mainly clear to partly cloudy skies and temps still a degree or two below normal. By Thursday, the high is forecast to shift off the Mid-Atlantic coast with southerly winds bringing a return of increasing moisture and warmth across western and central NY. Highs look to push into the upper 70s to around 80. This may also result in a few showers and thunderstorms later in the day Thursday.
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&& .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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Periods of showers and a few widely scattered thunderstorms will continue this afternoon and evening ahead of a cold front moving through the central Great Lakes. Some of the heavier showers will produce areas of MVFR VSBY, with local IFR in the heaviest downpours. MVFR CIGS Will become widespread this afternoon and evening, with pockets of IFR across higher terrain. The showers and scattered thunderstorms will end from northwest to southeast overnight with the passage of the cold front. VSBY will improve to mainly VFR as the rain ends. CIGS will improve to VFR across lower elevations overnight as clouds scatter out. MVFR and IFR CIGS will linger across higher terrain. On Saturday a weak/broad mid level trough will become established across the Great Lakes. While most of the time will be rain free, a few isolated showers and thunderstorms may develop along lake breeze boundaries, most notably along the KIAG to KROC corridor. Any lingering IFR CIGS across higher terrain will improve, leaving VFR to prevail Saturday outside of any isolated thunderstorms. Outlook... Sunday through Tuesday...Mainly VFR with a chance of mainly afternoon showers and isolated thunderstorms. Wednesday...Mainly VFR. Thursday...Mainly VFR with a chance of a shower or thunderstorm.
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&& .MARINE...
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Moderate west to southwest winds will develop on Lakes Erie and Ontario overnight and Saturday in the wake of a cold front crossing the area. This will bring choppy conditions with waves averaging 2-4 feet at the east end of both lakes, but conditions are expected to remain just below Small Craft Advisory levels. West to southwest winds are likely to increase on Sunday on Lake Erie as the pressure gradient increases ahead of a secondary cold front crossing the eastern Great Lakes. The increase in winds is less certain on Lake Ontario with considerable model differences showing up. At least moderate westerlies will continue with choppy conditions, and there is a chance of stronger Small Craft Advisory conditions if the stronger GFS based guidance verifies.
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&& .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...None. && $$ SYNOPSIS...HITCHCOCK NEAR TERM...HITCHCOCK SHORT TERM...ZAFF LONG TERM...SMITH AVIATION...HITCHCOCK MARINE...HITCHCOCK

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