Area Forecast Discussion
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000 FXUS61 KPBZ 201606 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1106 AM EST Sat Jan 20 2018 .SYNOPSIS... High pressure will maintain dry and warmer weather through today. Light rain chances return with the new week. && .NEAR TERM /THROUGH TONIGHT/...
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Main change to the afternoon forecast was to go more optimistic on cloud cover per satellite trends. Earlier low clouds in the southeast ridges have faded, and generally cirrus is expected for most of the afternoon. Thicker clouds will arrive later with increasingly moist isentropic lift. Nudged afternoon highs up a degree or so as well. Previous... SE CONUS surface high pressure and Nrn Great Lakes low under zonal flow aloft will maintain dry weather, warm advection, and moderating temperature through tonight. That temperature moderation will not be compromised by increasing cloud cover as per escalating boundary layer moisture; on the contrary, the increase in surface dewpoints will hasten the snow melt later in the day and into eve. Much of the area has the water equivalent of an inch (up to 2 inches over I 80 zones) of snow still on the ground. Weekend weather will thus provide ideal conditions for a gradual snow melt and ice rot, without the complications of heavy rainfall. Ice jam and backwater flooding will remain a localized hydrologic possibility; hence, no headlines are anticipated.
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&& .SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/... Intensifying warm advection under building upper high pressure in advance of a Cntrl Rockies-to-Plains low will drive Upper Ohio temperature well above the averages for the start of the new week. Rain chances will be initially be limited to light precip with the low level warm frontal moisture surge on Sunday and Monday. The continued advance of that low toward, and across the Great Lakes on Monday and early Tuesday will provide the next likely chance for measurable rain as that system pulls a cold front across the region. Low pressure track, rapid progression, and projections of a narrow moisture plume should preclude widespread flood issues as per QPF expectations of a half inch or less, especially as snow melt will be complete. That cold front will also interrupt the January flaw by heralding more seasonal temperature for mid week. && .LONG TERM /WEDNESDAY THROUGH FRIDAY/... Late week weather is expected to feature another temperature moderation and generally dry weather as another trough digs over the Wrn U.S., with warm advection for points east. Rain chances will increase again as that trough emerges from the Cntrl U.S. && .AVIATION /16Z SATURDAY THROUGH WEDNESDAY/... VFR will be marred for the first half of the TAF period by llvl wind shear and eventual gusts of 20 to 25 kts due to the tight pressure gradient between SE CONUS high pressure and Nrn Great Lakes low. Otherwise, VFR conditions are expected to deteriorate this afternoon and evening as primarily MVFR stratus develops in the intensifying warm, relatively moist advection regime. .OUTLOOK... Restriction potential continues for the first half of the week with the approach and passage of a frontal system. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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