Area Forecast Discussion
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000 FXUS61 KPBZ 162346 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 646 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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Deep moisture has already departed the southeastern fringes of the CWA. This has brought rain to an end virtually simultaneously with the arrival of cold air. As such, even in the terrain, just a few trace reports of snow accumulation have been reported prior to the ending of the snowfall. Boundary layer moisture erodes within a few hours after the departure of the deeper moisture on northwesterly flow per GOES-16 imagery and regional observations, thus sky cover goes nearly clear for a short period from northwest to southeast overnight. 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/...
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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, if not warnings. Headline coordination with neighboring offices is ongoing at the moment, and they will be issued shortly. 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.
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&& .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 /00Z SATURDAY THROUGH WEDNESDAY/...
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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.
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&& .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...
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MD...None. OH...None. PA...None. WV...None.
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&& $$

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