Area Forecast Discussion
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000 FXUS61 KPBZ 252145 AAA AFDPBZ Area Forecast Discussion...UPDATED National Weather Service Pittsburgh PA 445 PM EST Sat Feb 25 2017 .SYNOPSIS... Cooler temperatures will again be replaced by well above normal temperatures mid-week. More wintry conditions look to return late in the week. && .NEAR TERM /THROUGH SUNDAY/...
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445pm update...made some minor changes to evening PoPs in accordance with radar trends, latest hires guidance and latest model soundings. Once the shortwave trough moves through this evening, soundings are showing very dry air moving in aloft and near the surface. This will make it tough for precipitation to be produced, with the lack of lift to support a deepening of the saturated layer. Additionally, with such a thin layer of moisture, most soundings are showing the dendritic snow growth zone barely touching the saturated layer. Thinking through the evening and overnight will be to confine post shortwave precipitation to the north and ridges. The north will be reliant on any lake streamers that develop in the cold air and the ridges will likely take a little longer to see snow showers develop as the coldest air aloft does not really reach those locales until late this evening and after midnight. Temperatures have been modified with a blend of hires guidance. Previous discussion... Further upstream, a solid patch of clouds and scattered showers can be found over central Ohio to Indiana. These will shift eastward this evening as the upper- level low approaches. Expecting shower chances to increase through the evening, per latest hi- res model guidance. Scattered rain showers will changeover to snow showers as temperatures continue to descend through the evening. In general, less than an inch is expected across northern counties and into the mountains. Little to no accumulation is expected elsewhere. Building high pressure will end precipitation chances overnight with the ridges and locations along and north of I-80 the last holdouts. Winds and associated gusts are increasing, in the enhanced cold advection. Wind in the highest elevations could approach Advisory criteria towards dusk. This will bear further monitoring. Sunday will feature more docile weather as high pressure at the surface builds in. This will slowly erode cloud cover, leaving much sunnier conditions. Temperatures Sunday will moderate to near normal values.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... Surface high pressure will begin to shift eastward early in the short term period. This will mean dry and relatively clear conditions will quickly be replaced by increasing cloud cover on Sunday night. With a fairly linear jet streak parked directly overhead the CWA slowly beginning to migrate eastward into Monday, a weak H5 vort looks to traverse the Ohio Valley on Monday. Weak warm advection ahead of it may be just enough to generate a shower or two through the day Tuesday. Some soundings indicate that a brief window of snow may be possible at the onset due to wide surface dewpoint depressions and low wet bulb zero heights, however very light qpf expectations combined with warm advection and no support for below freezing temperatures should preclude any possibility of accumulation should this occur. With the northward migration of a warm front through the area on Tuesday, temperatures during the short term look to return to above normal yet again. Fries && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... A brief dry interlude follows th weak system from Tuesday before much higher PWATs follow for later Tuesday night into Wednesday night. A couple of successive waves look to pass the region in deep southwesterly flow. Some heavier rainfall may be possible with these given PWAT values running up toward 1.3 inches and a nicely couple jet structure to accentuate ascent. A trailing cold front will pass the area on Thursday. This will set temperatures into a free fall with model and ensemble consensus 850 mb temperatures falling into the negative teens Celsius. This should bring lake and upslope snows back into the picture. Additionally, some model indications exist of a weak system dropping through the Ohio Valley on Friday in the colder air. This could end up being a modest snow maker somewhere in the region depending upon its track. The extended forecast was generally favored colder than the SuperBlend guidance from Thursday night through Saturday due to the amplitude of the pattern and magnitude of cold air set to advect into the region. Fries && .AVIATION /22Z SATURDAY THROUGH THURSDAY/... Cold front and associated showers pushing east of the area, and strong westerly flow at the surface is taking hold. Winds will commonly gust 20-30kts this evening. Expecting little in the way of restrictions this afternoon as the increased mixing in the near-surface has raised ceilings on incoming stratocu to around 4kft. Scattered rain showers will transition to snow showers this evening, but coverage and intensity will be limited. MVFR CIGs are possible late tonight as the surface flow begins to weaken and ceilings lower. This will especially be true for FKL/DUJ where downlake moisture may be more prevalent. .OUTLOOK... Occasional restrictions are again possible as the unsettled weather pattern is maintained for the first half of the week. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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