Area Forecast Discussion
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000 FXUS61 KPBZ 172151 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 551 PM EDT Sat Mar 17 2018 .SYNOPSIS...
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High pressure will result in dry weather into Monday, along with milder temperatures. Low pressure may bring accumulating snow to the ridges Monday night and Tuesday.
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Just a few light showers of flurries/sprinkles/mix remain as the supporting shortwave continues to lift out of the region. These will largely dissipate by mid-evening. The northern edge of the cloud shield will continue to erode with time, as weak subsidence dries out low level moisture from north to south. Temperatures have been challenging given the cloud cover gradient as well as wet-bulb effects from the earlier precipitation, but values below normal are expected across the area as clear skies and light wind take hold overnight. Previous discussion for Sunday... A splendid day Sunday with wall to wall sunshine area wide. With little mixing we won`t realize full sun temperatures. Most locations will make a run at 50 save for the higher elevations and north of I80.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... Its still winter on the calendar and in the forecast. Low pressure which in the past few runs has continued to trend a little farther south will bring accumulating snow to the mountains of West Virginia and western Maryland. There are still details to resolve with ptype. With inverted trough developing on windward side of the Appalachians, look for warm air to surge northward allowing column to climb above freezing for lower elevation locations in northern West Virginia. The big question with these setups is how far north will the warm air reach? Typically, higher resolution NAM does a good job but trends farther north with time. For this forecast package, brought rain into far southwestern Pennsylvania by 6Z Tuesday. Would not be surprised to see ptype to transition to all rain as far north as I-70 during the overnight hours. Farther to the east in the mountains, BUFR soundings point to a warm layer aloft which yields a short period of a wintry mix in the higher terrain. With southeast winds ushering in reinforcing shots of cooler air believe most of the time it will be snowing. Modest isentropic upglide between 290-300K and a column that is nearly saturated in the favored snow region support several inches of snow. The hazardous weather outlook has been maintained for potential winter weather advisories or winter storm watches. However since its 5th period the earliest a winter storm watch could be issued would be Sunday. Energy transfers to the coast rapidly Tuesday morning ending over locations outside the mountains by 15Z. With lingering northeasterly flow light snow will continue as the column will cool to support all snow. H8 temps by 0Z Wednesday collapse to -5C. With the trough continuing to dig clouds will hold through the day Tuesday into Wednesday. As winds switch around to the north- northwest expect snow showers to continue across West Virginia and Maryland most of Tuesday night into Wednesday. Any accumulation in this time frame will be a few inches at best. Temperatures will be below normal the entire short term with clouds and continued cold advection. Normal highs this time of year run in the upper 40s to lower 50s. Most will be lucky to reach the mid 40s with mid 30s well north of I-80 and in the mountains. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... - Where`s spring? - Below normal temperatures - Active weather regime persists Deep cyclonic flow aloft with full latitude trough in place across the eastern CONUS dominates the long term. Residual moisture in the mountains of West Virginia and Maryland could yield snow showers, but no significant accumulation expected Wednesday night. A brief break in the action Thursday through Friday night with surface high pressure in control. Mid level heights remain two standard deviations below normal and with a northerly low level trajectory, H8 temps continue to be subzero across the region. A transitory ridge crosses Friday before yielding to an approaching warm front Friday night. Would not be surprised if the timing holds for temps to rise during the overnight hours, especially in eastern Ohio due to increased cloud cover and pressure gradient. For the hollows of West Virginia and southwest Pennsylvania, a lower probability exists of that occurring. Precipitation type could be a concern at the onset Saturday morning if timing holds. Long range ensembles for the moment reside in good agreement. With the cyclone track well to our west, it won`t be a heavy QPF event so impacts should be minimal. Did not get to fancy in the grids at this juncture with just a rain/snow mix. Saturday will be the warmest day of the extended as southerly winds finally return, however it will be at the expense of clouds and precipitation thus it won`t be that much above normal. Overall for temps used the superblend with a little bit of the raw consensus guidance. && .AVIATION /22Z SATURDAY THROUGH THURSDAY/... Light wintry mix will continue, mainly south of I-70 through the early evening. Much drier air is ultimately winning, however, and the lower ceilings just are not materializing. If any terminal drops to MVFR this afternoon, it would likely be MGW as the deeper moisture pools there. Otherwise VFR conditions will be established through the duration of the forecast period. The one slight exception to this would be in some light patchy fog that could develop in FKL under clear skies. Winds will generally remain light and variable through the period. OUTLOOK... Restriction potential returns with low pressure Tue and Wed. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.