Area Forecast Discussion
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000 FXUS61 KPBZ 120914 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 414 AM EST Fri Jan 12 2018 .SYNOPSIS... Rain, changes to sleet and freezing rain late today, then eventually snow tonight. Much colder through the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... For the overnight period, have made some changes to PoPs in line with latest radar trends and hires model guidance. It appears the swath of steady rain will slowly drift to the west and north overnight. Increasing low-level southeasterly flow will push the rain shield back toward the eastward moving surface front. At the same time, main shortwave will move quickly northeastward in the strong southwest flow aloft. Cold front will reach my far western counties around dawn and most of what is left of the band of rain will be situated just ahead of the surface boundary. Cold front will reach PIT by early afternoon, and as surface wave deepens along the boundary low-level winds will rapidly increase behind the front. This will eventually increase the cold air advection at the surface. Rainfall rates and coverage are expected to decrease late this morning and into the afternoon as a dry slot develops ahead of the next shortwave which reaches Eastern Ohio by this evening. Much colder surface temps begin to dive southward late this afternoon as the cold front reaches my southeastern ridge counties. So with the expected wind direction, and the timing of the colder air aloft, it appears a mix of freezing rain and sleet will develop over NE Ohio and NW PA late this afternoon and move south- southeastward. The late afternoon and evening precipitation type is solely dependent upon how strong the near surface cold air advection is and how long it takes for the mid-level low to move eastward. Latest forecast soundings are indicating that the surface temps will cool much faster then those above 2000 ft. So until the temps aloft can also cool, an extended period of sleet and freezing rain is expected from NW to SE, beginning late this afternoon and carrying into the evening hours. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/... As the trough slides eastward and ejects a vort center across the Upr OH tonight and Saturday, the transition to a wintry mix, will continue during the evening and then comes the snow. Entire CWA is expected to be all snow after 06z. The last place to completely change over will be the ridge counties of N WV and W MD. Winter storm warnings and advisories remain in place for the combinations of ice, and 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. System departs quickly late Friday night and Saturday morning, with snow fall expected to end over the eastern third of the area by mid-morning. The rest of Saturday looks mainly dry with some sunshine possible late in the morning and through a large chunk of the afternoon. Very strong cold advection will keep it very cold on Saturday, and as this arctic air crosses Lake Erie some lake snow is possible. Winds at 850mbs remain northerly through most of Saturday, so any band that does develop would have trouble making much headway southward and would be confined to the western half of my area. Steady or slowly falling temps are expected on Saturday. Heart of the arctic air will depart Sunday morning, so a mix of sun and clouds is expected. Temperatures on Sunday will remain very cold, 15 to 20 degrees below normal. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Upper troughing and below average temperature will persist across the eastern CONUS through the middle of next week. Light snow chances return late Monday with the passage of another arctic front. && .AVIATION /09Z FRIDAY THROUGH TUESDAY/...
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IFR/low MVFR conditions will linger through the day as precipitation temporarily eases. Colder air, and the resulting changeover to mixed precipitation and eventual snow will occur later in the TAF period. IFR conditions areawide by late afternoon. 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.
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MD...Winter Weather Advisory from 7 PM this evening to 10 AM EST Saturday for MDZ001. OH...Flood Watch through Saturday afternoon for OHZ039>041-048>050- 057>059-068-069. Winter Storm Warning from 4 PM this afternoon to 10 AM EST Saturday for OHZ039>041-049-050. Winter Weather Advisory from 7 PM this evening to 10 AM EST Saturday for OHZ059-068-069. Winter Weather Advisory from 4 PM this afternoon 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 this afternoon to 10 AM EST Saturday for PAZ007>009-013>016-020>022-029. Winter Weather Advisory from 7 PM this evening 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 this afternoon to 10 AM EST Saturday for WVZ001>003. Winter Weather Advisory from 7 PM this evening to 10 AM EST Saturday for WVZ004-012-021-509>514.
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