Area Forecast Discussion
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033 FXUS61 KPBZ 211317 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 817 AM EST Tue Feb 21 2017 .SYNOPSIS... A weak system will pass the region late today with a chance of some showers, however warm conditions will continue through the week. && .NEAR TERM /THROUGH TONIGHT/...
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Refreshed hourly temp and dewpoint values for the morning. The forecast remains on track otherwise. Previous discussion follows... A fairly long fetch of elevated RH values in the layers generally above 300 mb extends across the entire CWA already very early this morning. This is well out in advance of a mid and upper level system currently splitting off from the upper flow in the Mississippi Valley. The vast majority of the moisture and lift will remain with the cut off low that will meander into the southeastern portions of the country. The remnant upper level wave in the northern stream will take its sweet time crossing the Great Lakes region on Tuesday, only to edge as far eastward as our area by very late in the day. Deep saturation with this system remains generally north of our area. In addition, as the H5 wave shears off to the north through Tuesday night, lift along the boundary as it shifts through the CWA on Tuesday night is looking fairly paltry. Beyond that, deep moisture is entirely lacking. That said, PoPs were trended back below likely threshold for the vast majority of the area with the boundary passage on Tuesday night. In fact, some guidance (the new 00z NAM) is trending toward a basically dry passage of the system. Regardless of the chances of rain, somewhat translucent high clouds will likely keep a lid on insolation driven upward temperature mobility on Tuesday, however warm advection will continue to do its thing. This warm advection combined with a notable uptick in boundary layer mixing as compared to yesterday should certainly result in a warmer Tuesday than Monday. Fries
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&& .SHORT TERM /WEDNESDAY THROUGH FRIDAY/... Nearly zonal/flat ridging will support fast moving shortwaves through the flow through Thursday. While most of the support for any precipitation should remain well north of the region, increasing moisture in w-sw flow may lead to widely scattered showers until the more amplified low pressure system ejects into the Plains and lifts a warm front across the upper Ohio Valley. Generally kept chance PoPs through the period based on the uncertainty in guidance and lack of deep moisture and lift. With little modification in 850hpa temperatures, expect values to remain 20+ degrees above seasonal averages. It still looks like one our warmest days this week will be Friday, as most ensemble guidance has over 70 degrees here at Pittsburgh. The only thing that could hamper this would be cloud cover and any shower coverage. && .LONG TERM /FRIDAY NIGHT THROUGH MONDAY/... Models continue to slow the progression of the strong cold front, with it`s current timing progged for early Saturday. Will continue with likely PoPs for this boundary, with a chance for thunder, though the overnight passage may be a bit of a limiting factor. Temperatures should return to near normal values, with snow showers as the system departs. Very broad troughing is then expected through the end of the forecast period, with another system progged for passage in the deterministic guidance. Seasonal temperatures will continue through the start of the work week. && .AVIATION /13Z TUESDAY THROUGH SATURDAY/... VFR can be expected through much of Tuesday although extensive high cloudiness will mar the sky. Sfc wind will veer to the south by daybreak as sfc high pressure gives way to an advancing trough. Some restrictions will start to edge in from the north on Tuesday night as a weak system shifts through the Great Lakes. High uncertainty exists on exactly how much shower activity will remain as it gets to our region as well as the degree to which ceilings and visibilities may fall as it passes. .OUTLOOK... Restrictions are likely with a Friday night/early Saturday cold front. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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