Area Forecast Discussion
Issued by NWS Pittsburgh, PA

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000 FXUS61 KPBZ 161528 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1128 AM EDT Sat Mar 16 2024 .SYNOPSIS...
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The first in a series of cold fronts will cross the region tonight into Sunday morning, creating a line of mainly light rain showers. Additional cold fronts and upper disturbances will create periodic precipitation chances again Sunday night through Tuesday morning that may lead to limited snowfall accumulation.
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&& .NEAR TERM /THROUGH TONIGHT/...
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KEY MESSAGES: - Warm advection and insolation will raise area temperature about 10 degrees above the daily average. - A cold front arrives late tonight with mainly light rain showers and introduction of a cooler air mass. ------------------------------------------------------------------- Dry advection aloft plus subsidence ahead of the next upper level trough is aiding rapid stratocu erosion across western PA and northern WV approaching the noon area. With clearing skies and weak warm advection, area temperature is expected to remain approximately 10 degrees above the daily average. The passage of an upper level trough and surface low into Quebec will push a well-defined cold front southeast through the region tonight. Rain showers ahead of the boundary are likely to be light (most locations see less than 20% chance of exceeding 0.25" total), with decreasing expected amounts from NE to SW due to farther removal from stronger upper forcing. Ensembles favor fairly rapid drying post-frontal passage as the dry westerlies develop aloft with the main upper trough axis hanging to the NW.
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&& .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
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KEY MESSAGES: - Cold advection plus weak lake fetch will support isolated to scattered showers favoring northwest PA and the higher terrain. - Precipitation type will be a mix of rain and snow during daylight hours before switching to snow. ------------------------------------------------------------------- In the post-frontal environment, the Upper Ohio River Valley will be positioned within general westerly flow as the upper trough axis remains over the Western Great Lakes. There is some discrepancies among hi-res and global models on angle of the boundary layer flow, which will play out in one of two scenarios for the afternoon (forecast more closely tied with scenario 1). Scenario 1: A more W-E to WSW-ENE orientation should maintain dry slotting over the region and create little to no fetch of lake moisture to support afternoon showers. Temperature will be near to slightly above average, though gusty wind will keep `feel-like` temperature down. Scenario 2: A more WNW-ESE orientation would allow for some lake moisture influx to the boundary layer, combining with broad ascent to foster isolated/scattered afternoon showers. Cold advection aloft would remain limited and thus still see a mix of rain/snow with no accumulations. Temperature is closer to average while wind remains gusty. Overnight, a shift of the upper trough axis towards Lake Erie will send a secondary cold front towards the region while cooling 850mb temperature. A slight increase in boundary layer moisture while maintain broad ascent (though losing diurnal heating) will enable a continuation of isolated light snow showers. Lack of deeper moisture and stronger forcing will ensure any snowfall accumulations during this period will be light (if any, given warmer grounds).
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&& .LONG TERM /MONDAY THROUGH FRIDAY/... KEY MESSAGES: - Cold temperatures are expected to linger through Tuesday - Lake enhanced snow is expected Sunday night into Tuesday. - Wind chill values will be abnormally cold early Tuesday (teens in the lower elevations/single digits to below zero in the higher terrain). - Above average temperatures return mid-week. ---------------------------------------------------------------- Long range ensemble models continue to favor a cold pattern across the Ohio River Valley late Sunday into Tuesday across the Great Lakes. Arctic air will drive high and low temperatures to be below average by 5 to 10 degrees Monday and Tuesday. Probability of low temperatures below 25F Tuesday morning is 55% or higher near I-80 and in the ridges. As a large upper-lvl low pivots out of the Great Lakes and enters New England, flow off of Lake Erie will shift from the west to northwest. Therefore, snow shower potential will drift further south of I-80 Monday afternoon into Tuesday. Probability of one inch of snow for both days ranges between 50% to 70% north of I-80/eastern Tucker County. Probability of >= 0.1 inches of snow is elevated (above 90%) within the ridges due to upsloping and confided along I-80 (in close proximity to the lake). Accumulation will likely be focused during the overnight time period, when sfc temperature fall near or below freezing. With a strong gradient wind associated with the low and cold advection, expected wind chill values to be abnormally cold early Tuesday. Teens in the lower terrain, single digits to below freezing in the ridges of PA/WV. Increase fetch over the lake with a new shortwave may keep snow showers in the region into Wednesday. However, accumulation will likely be very little given a building ridge to the west. Near to above average temperatures are expected to mid-week into Friday. However, precipitation chances may return as a trough advances across the Southeast and tracks north along the East Coast. && .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/... A bit of patchy fog and low stratus will finally dissipate by 14Z or 15Z at the latest under high pressure. Mid and high level clouds are expected to increase later today as a cold front approaches from the Upper Great Lakes region. This front will cross the Upper Ohio Valley region tonight through early Sunday, with showers and MVFR restrictions expected. In addition, SW wind gusts to 20kt are expected with mixing and a tightening pressure gradient ahead of the front. A WSHFT to the NW, with additional gusts to 20kt are expected after the late Saturday night FROPA. .Outlook... Gusty NW wind is expected Sunday behind the exiting cold front. Restrictions and scattered snow showers return Monday night and Tuesday with a reinforcing cold front and subsequent upper troughing. VFR returns Wednesday as a ridge of high pressure builds in. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...Frazier NEAR TERM...Frazier SHORT TERM...Frazier LONG TERM...Hefferan AVIATION...WM/Shallenberger

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