Area Forecast Discussion
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552 FXUS61 KPBZ 050131 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 831 PM EST Sun Dec 4 2016 .SYNOPSIS... Some locations in the higher elevations are expected to receive freezing rain tonight. An unsettled weather pattern will continue through the week, with much colder air arriving by Friday. && .NEAR TERM /THROUGH MONDAY/...
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A rather sharp short-wave trough is advancing eastward into the region this evening with widespread isentropic ascent allowing for a vast shield of stratiform precipitation to develop ahead of it, especially north of I-70 in Ohio. Along the southern edge of this precipitation shield, radar imagery has generally started to trend toward a more curious reflection of dynamical processes going on in the atmosphere. The striated depiction of echoes mostly from near Zanesville to Pittsburgh points toward CSI, as does the synoptic positioning relative to the upstream system with the upper jet curving overhead. Model cross sections do reveal an area of negative theta-e lapse rates with respect to geostrophic momentum in this area, so enhanced precipitation rates will be likely along the southern flank of the precipitation shield as a result. As this area moves northeastward, it is also starting to get into a slightly colder column. The 00z KPBZ sounding revealed an utter chasm in dewpoint depressions off the ground, which with varied precipitation rates due to more unstable processes going on has resulted in periods of sleet mixed in with the rain. Sleet was thus added to the grids with the unstable precipitation moving northeastward this evening. Farther north, model soundings reveal wet bulb temperature profiles that should be conducive to a period of snowfall for several hours tonight before warm advection gradually warms the lower portion of the profile too much to allow for continued snowfall. Additionally, mesonet observations especially in Forest and far northern Venango and Jefferson County reveal surface wet bulb temperatures straddling freezing. Thus, while the ground is not frozen, grassy surfaces now seem poised to pick up as much as a slushy inch in the aforementioned locations. While other areas south of here may see snow in the air, accumulation still seems unlikely. In the ridges, temperatures are trending from the mid 20s to mid 30s in Tucker and Garrett counties at this hour with some penchant for additional wet bulb cooling. However, due to a farther southward placement, warm advection off the deck should preclude much in the way of snowfall here. That said, freezing rain or even a touch of sleet will certainly be possible in these areas, thus the previously issued advisory has been left in effect for icing considerations. Temperatures will continue to be monitored over the Chestnut and Laurel Ridges to determine whether a headline expansion into these areas is warranted. Eventually by morning, flow should start to turn southwesterly, warming all areas including the stubbornly cold Garrett County to rainfall, however several hours of wintry precipitation will be likely before we reach that point. Fries
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&& .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/... Clouds will stream back in Monday night in advance of a low pressure system that will move across the region. As precipitation moves in Monday night and Tuesday morning, many places could have a brief period of freezing rain before warm advection changes all precipitation over to rain by Tuesday afternoon. Have continued with categorical pops through this time period, with rain changing over to snow as it wraps up late Tuesday night into Wednesday. High temperatures in the low to mid 40s on Tuesday will likely be the warmest readings of the 7 day forecast. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... Yet another system moves through Thursday, with a cold front bringing another chance for precip. Most of this precipitation would likely fall as snow, and behind the front temperatures will plunge into the teens by Thursday night. Cold advection should then prompt snow showers to continue through Saturday morning. Temperatures will struggle to recover, but another cold front will approach from the west Sunday. && .AVIATION /02Z MONDAY THROUGH FRIDAY/... A quick moving low pressure system will cross the area tonight spreading MVFR to IFR ceilings from west to east overnight. Despite temperatures currently in the mid to upper 30s, dewpoint depressions in the low-levels will allow temperatures to drop low enough to support some snow at least mixing in with rain at the onset of precipitation tonight. MVFR stratocu is then expected to persist into the afternoon given the cold flow off the Lakes in the wake of the surface front. At least some clearing should then take place late in the day Monday. .OUTLOOK... More restrictions are likely with, and in the wake of Tuesday low pressure. More restrictions will follow with a strong late week cold front. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...Winter Weather Advisory until 4 AM EST Monday FOR MDZ001. OH...None. PA...None. WV...Winter Weather Advisory until 4 AM EST Monday FOR WVZ514. && $$

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