Area Forecast Discussion
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000 FXUS61 KPBZ 170213 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 913 PM EST Fri Feb 16 2018 .SYNOPSIS... A brief period of dry weather is expected tonight before a quick moving system brings snow to most locations Saturday afternoon and evening. Next week should be warm and wet. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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Stratocumulus is remaining rather pervasive late this evening as drier air below it and above it works into the region. Subsidence is starting to erode the edges near Franklin and Zanesville, and it would seem with dry air moving in and subsidence, that the rest of in should start to more rapidly erode from northwest to southeast in the next few hours. With cold advection underway, temperatures have been falling all day. Cold advection will continue into the evening hours before pressure gradients relax and flow drops to almost nil. This will occur as skies clear, which should allow temperatures to fall back at least to seasonal averages overnight. Fries
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/... Moisture starts to increase from the southwest again on Saturday as cold air will have settled into the region by that time. This should allow for mid and high clouds to start to increase from the southwest near or shortly after sunrise. This will allow for temperatures to remain in check going into the latter half of the day as deeper moisture again increases. A potent short wave trough looks to shift through the lower Great Lakes by the end of the day with the right entrance region of the upper jet set to track straight through the area. A bifurcated frontogenetical maxima field suggest one weakening areas of 850-700 mb frontogenesis translates northeastward across the eastern CWA through the late afternoon and early evening hours while a second and much stronger one follows the redeveloping surface low across the Appalachians. This results in a heavier swath of QPF across the far southeastern portion of the CWA. It is in this area that the forecast gets the trickiest and thermal profiles come into play quite strongly. NAM and GFS thermal profiles aren`t a lot different going into the afternoon and evening hours. They would suggest that enough warm air creeps into the boundary layer west of the terrain to at least mix with rain in places like Morgantown, Uniontown, and Parsons. However, farther west and in the terrain itself, precipitation would be mostly snow. That said, the ground isn`t that cold anymore after all of the rain, and temperatures will be marginal. Snow ratios have been adjusted accordingly, and accumulation potential, especially during the daytime hours, has been held back significantly other than in the highest terrain. Even with that in mind, snow amounts from Saturday afternoon into the evening will likely yield at least widespread advisory accumulation in the terrain. With this in mind and taking into consideration the corridor of best ascent/qpf, have opted to issue Winter Weather Advisories for the ridges north of the Mason-Dixon line as well as the Coopers Rock zone and go with a Winter Storm Watch for the highest terrain, where around six inches will be most likely. Deeper moisture departs to the east overnight Friday night. This yields a questionable moisture profile as the dendritic layer dries out, upslope flow remains, and precipitation is still probable to be falling. This may yield a period of freezing drizzle, however given the proximity of the lifting profile to the bottom of the dendritic layer, it would seem poorly formed flakes are more likely in the terrain than freezing drizzle at the moment. Fries Previous discussion for beyond Saturday night...Dry weather is forecast for Sunday and most of Sunday night, with the bulk of precipitation waiting until Monday to move into the area from the west. Temperatures will be on the rise through the period, with highs in the 40s on Sunday and 50s/60s on Monday. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... Upper level pattern should allow for the chance of precipitation to continue through much of the week. The warmest temperatures should occur on Tuesday before a cold front moves through on Wednesday, with locations from Pittsburgh south likely to reach 70 degrees ahead of the front. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... As the low-level lapse rate steepens amid cold air advection, the widespread clouds will give way to broken stratocu before subsidence helps erode all low clouds this evening. Ongoing restrictions will ease by early evening, with light wind and scattered cirrus expected overnight amid building high pressure. Clouds will increase late Saturday afternoon as moisture surges nwd ahead of an approaching disturbance. Snow will impact many terminals by afternoon with some rain possible around MGW. OUTLOOK...MVFR conditions will continue Saturday night and again Monday into Tuesday. && .HYDROLOGY... Although heavy rain is winding down, runoff will lead to continued river flooding beyond the period of rain. River Flood Warnings have been issued along much of the Monongahela and Ohio Rivers. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...Winter Storm Watch from Saturday afternoon through late Saturday night for MDZ001. OH...None. PA...Winter Weather Advisory from 2 PM Saturday to 4 AM EST Sunday for PAZ074-076. WV...Winter Weather Advisory from 2 PM Saturday to 4 AM EST Sunday for WVZ510. Winter Storm Watch from Saturday afternoon through late Saturday night for WVZ512-514. && $$

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