Area Forecast Discussion
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306 FXUS61 KPBZ 222256 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 556 PM EST Sun Jan 22 2017 .SYNOPSIS... Low pressure will spread rain, and some snow over the region tonight through early Tuesday. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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A very slow northward ejection of an upper level system currently over the lower Mississippi Valley looks to be in the cards for tonight. As has been the case for the past several cycles, the SuperBlend guidance has been utterly useless and far, far too fast with the northward spread of PoPs into the region this evening. As a result, chances of precipitation have been curtailed greatly and with significantly longevity across the northern half of the CWA. The preponderance of current model guidance just simply does not jive with the SuperBlend guidance, which is both too fast spreading rainfall into the area and far too quick moving it out of the area as well going into the new week. As such, a substantial shift to a later time interval with a long-lived deformation zone overhead has been favored in the forecast update. That said, one band of deformation precipiation will likely have a glancing blow across the southern half of the area this evening befor the main upper system and deeper deformation enters the picture overnight into Monday. Otherwise, most breaks in the clouds from earlier in the day have already been closed up, and generally overcast/warm conditions should continue into Monday. Fries
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&& .SHORT TERM /6 AM MONDAY MORNING 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 /22Z SUNDAY THROUGH FRIDAY/...
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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. The easterly flow may keep cigs up a bit around KMGW and KLBE until the upper level system moves overhead on Monday. .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.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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