Area Forecast Discussion
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000 FXUS61 KPBZ 120108 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 808 PM EST Thu Jan 11 2018 .SYNOPSIS... Warm weather has dampened with rainfall and will become much colder with passage of a late Friday cold front. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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No major changes were needed for the eve update as POP adjustments were primarily cosmetic. Previous... Warm, moist advection on strong sly flow aloft is generating rainfall for areas along and west of I 79. Rain will continue to spread over the remainder of the area this evening, and continue through the night as broad ascent is maintained ahead of the high-amplitude trough sliding eastward. In addition, pockets of enhanced mid level frontogenesis via jet stream dynamics may result in periods of heavier rainfall. This in combination with snow melt and ice jamming is sufficient to maintain a flood watch for most of the Upper Ohio Region.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/... As the aforementioned trough slides eastward and ejects a vort center across the Upr OH on Friday night and Saturday, rain will transition to a wintry mix, and eventually snow. Winter storm warnings and advisories have been issued for the combinations of ice, and then snow accumulation. Questions remain on placement and magnitude of ice and snow amounts given the dispute between freezing rain supporting warm advection aloft, and the degradation of the dendrite-formation layer resulting from the warmth. At any rate, confidence is sufficient for the current headline package with surface cold air encroachment timed for late Friday afternoon over the northern tier of PBZ zones, with all precip changing to snow in the predawn of Saturday. By Saturday mrng, system departure will diminish the snow chances, with cold advection in its wake dropping temperature rapidly below the averages. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Upper troughing and below average temperature will persist across the eastern CONUS through the middle of next week. Sunday figures to be dry, but a shortwave may drop through the trough to bring snow chances by Monday, with snow showers lingering thereafter in northwest flow. && .AVIATION /01Z FRIDAY THROUGH TUESDAY/... VFR conditions will carry into tonight before condition deterioration is expected. Expect MVFR to IFR spreading west to east late tonight evening. IFR/low MVFR conditions will linger through midday Friday as precipitation temporarily eases. Colder air, and the resulting changeover to mixed precipitation and eventual snow will occur late in the TAF period. IFR conditions will be common by Friday evening. Winds will remain light out of the south overnight tonight before increasing and shifting northwesterly as the cold front passes Friday afternoon. .OUTLOOK... Restrictions can be expected through Saturday as a cold front changes rain to sleet and freezing rain, and then snow. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...Flood Watch through Saturday afternoon for OHZ039>041-048>050- 057>059-068-069. Winter Storm Warning from 4 PM Friday to 10 AM EST Saturday for OHZ039>041-049-050. Winter Weather Advisory from 7 PM Friday to 10 AM EST Saturday for OHZ059-068-069. Winter Weather Advisory from 4 PM Friday to 7 AM EST Saturday for OHZ048-057-058. PA...Flood Watch through Saturday afternoon for PAZ007>009-013>016- 020>023-029-031-073>076. Winter Storm Warning from 4 PM Friday to 10 AM EST Saturday for PAZ007>009-013>016-020>022-029. Winter Weather Advisory from 7 PM Friday to 10 AM EST Saturday for PAZ023-031-073>076. WV...Flood Watch through Saturday afternoon for WVZ001>004-012-021- 509>512. Winter Storm Warning from 4 PM Friday to 10 AM EST Saturday for WVZ001>003. Winter Weather Advisory from 7 PM Friday to 10 AM EST Saturday for WVZ004-012-021-509. && $$

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