Area Forecast Discussion
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000 FXUS61 KPBZ 151728 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1228 PM EST Mon Jan 15 2018 .SYNOPSIS... Low pressure will bring light snow to the region later today and into Tuesday. && .NEAR TERM /THROUGH TUESDAY/...
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As low pressure moves into the southern Great Lakes today, light snow will continue to spread through northwestern PA. The back edge of this initial band has reached the Pittsburgh metro area as of noon, and should continue pushing northeastward through the afternoon. The fine nature of these flakes are reducing visibility to 1 to 2 miles, but resulting in little more than a tenth of accumulation. Modest Warm air advection is moderating surface temperatures some, but highs are still expected to remain below normal. This evening, the trailing cold front will approach our Ohio counties, eventually bringing snow areawide overnight. Most models spread modest snow across the forecast area but some show an initial area of enhancement north of I-70 in an area of favorable upper-level jet dynamics. The outlier to this point is the 12z NAM which really slows the cold front, maintains a layer of dry air near the surface, which ultimately delays snow onset and cuts into accumulations. 12z GFS and a number of hi- res models show a little more consistency, and thus were relied on a little more. The more moderate snow north of I-70 associated with the surface trough will carry through the pre-dawn before dissipating and moving northeast out of the area. Near dawn Tuesday, the upper trough will pull moisture northward, focusing snow over more of our southern zones. This light snow is expected to continue well into Tuesday afternoon, before the dry slot can advance further. This will lengthen the residence time of snow over the Ridges, ultimately boosting their totals from previous forecasts. All told, kept forecast amounts a little general with 2-3" for most of the area over at least a 24hr period. The Ridges could push a little higher, but the period of snowfall will certainly be longer than the normal 12hr Advisory criteria window. For these reasons, will continue to hold off on a Winter Weather Advisory, although the potential for a short- fused one has now been included in the HWO.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
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Any remaining snow showers will continue to taper down Tuesday night in the wake of the cold front. The core of the cold air will pass through Wednesday morning, bringing the coldest temperatures of the work week. Current forecast has relatively light winds during this time, but this period will need to be monitored for potential Wind Chill Advisory headlines. Heights begin to build into Wednesday, but northwest flow through the mid-levels will keep clouds and the potential for light snow, especially north of I-80. Ridging, albeit brief, will carry into Thursday, bringing an increase in sunshine and helping to further moderate temperatures. Still highs will be several degrees off the averages.
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&& .LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/... Upper trough will be replaced with zonal flow through the end of the week before a trough builds over the western CONUS. New runs of the deterministic models have a fast-moving system passing across the region on Friday, but have opted to not make any major forecast changes based on this. Deepening western CONUS trough will support a return of seasonal or above temperature for next weekend. Timing differences between model guidance supports to use of a model blend through the period. && .AVIATION /17Z MONDAY THROUGH FRIDAY/... Prevailing VFR conditions are expected expected as upper level cloud coverage increases ahead of a clipper system set to arrive late this afternoon. Wave lifting ahead of the warm front has allowed for some light snow to develop over eastern OH already, which may allow for brief restrictions at ZZV early, but bulk of the restrictions will come later this afternoon as the cold front approaches. Once the snow arrives, deterioration to MVFR with intermittent IFR can be expected through the night. .OUTLOOK... Tuesday through the remainder of the week looks largely dry with VFR conditions. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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