Area Forecast Discussion
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000 FXUS61 KPBZ 221943 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 243 PM EST Sun Jan 22 2017 .SYNOPSIS... Low pressure will spread rain, and some snow over the region tonight through early Tuesday. && .NEAR TERM /THROUGH TONIGHT/... Adjustments for the late afternoon update included timing and coverage changes to precip probs given the latest radar trends as an area of showers continues to work northward toward the region. Deepening low pressure will emerge from the Lower Mississippi Valley tonight and spread widespread rain over the entire area. Escalating precip probs were adjusted for faster onset. && .SHORT TERM /MONDAY THROUGH TUESDAY/... Forecast confidence remains hampered as model depictions of the cutoff low pressure set to dig toward the Upper Ohio Region, have again deviated from previous days solutions with a southward track of the center. Nevertheless, increasing ascent via deformed flow and warm advection with increased moisture through the mid levels all support categorical precip probabilities into Monday, with a diminishment into Tuesday as the system exits. With the northern branch of split flow holding colder air north and west of the region, and with warm advection into the mid levels of the cutoff, this still looks to primarily remain a rain event for the Upper Ohio Region; however, the NAM, and to a much lesser extent the GFS, continue to develop sub-zero air over the region immediately above the boundary layer, probably due to dynamic cooling as the low deepens. Have decided to move toward this potential and have introduced a rain/snow mix-to snow mainly for the elevations and extreme northern zones on Monday and into Monday night, then more-so into Tuesday as colder air briefly wraps into the departing system. Should the low track and strengthening magnitude remain consistent and the cooling materialize, then an advisory for several inches of snow accumulation may be needed for the ridges and zones north of I 80. An HWO mention was included for this potential, although a warm boundary layer and dry advection into the maturing mid levels may hamper the possibility. QPF was progged using a RFC/WPC blend for the period. On the order of a half, to one inch of rainfall is anticipated. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... The long term period will feature a change to more seasonal weather a midweek cold front initiates a temperature reduction toward, and then below the averages during the latter half of the week. Tweaked, especially POPs, Superblend guidance was used in construction of the period. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... VFR conditions are expected through the evening with mid clouds ahead of approaching low pressure. The approaching low should result in a deterioration to MVFR, and eventual IFR, overnight and Monday with rain. Increasing E winds are expected tonight and Monday with an increasing pressure gradient. .OUTLOOK... Restrictions are likely through Tuesday as low pressure moves off the coast, and again late Wed through Fri with a crossing cold front and subsequent upper troughing. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$ 15/07

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