Area Forecast Discussion
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664 FXUS61 KPBZ 181720 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 120 PM EDT Sun Mar 18 2018 .SYNOPSIS... High pressure will maintain dry weather and seasonal temperature into Monday. Low pressure then is likely to bring a wintry precipitation mix to the region Monday night and Tuesday. && .NEAR TERM /THROUGH TONIGHT/... No major changes needed. Based on the morning RAOB, maxima were lowered by just a couple of degrees for today into the upper 40s. Previous discussion follows... Brilliant sunshine today will lead to seasonable temperature amid high pressure. A few high clouds are possible tonight as the high moves ewd and flow aloft becomes more zonal. && .SHORT TERM /MONDAY THROUGH TUESDAY/... Models are in general agreement on a swd focus for precipitation Mon night and Tue, echoing the earlier swd deviation noted by the previous forecast. The reasoning noted by the previous shift seems in line with current model depictions, so little deviation from their process was made. Some combination of FZRA and snow will affect the higher elevations amid stronger warm air advection aloft, while rain and snow will affect the lowlands. Where snow does occur, snow ratios will be limited owing to the warm air aloft approaching 32F, especially in the ridges. Snow totals or FZRA are likely to warrant a Winter Weather Advisory in the ridge zones. Added Indiana County to the Hazardous Weather Outlook, as the higher terrain in the ern section of the county could be affected. Previous discussion follows... The advance of southern stream low pressure toward the Mid- Atlantic Region will increase precipitation chances for Mon night and Tue. Initial warm advection on the van of the low looks to support rain, then a wintry mix, as night falls and cooler air advects into the northern flank of an entrenching inverted trough over WV and MD. For the ridges, dynamic cooling via sely boundary-layer upslope wind, combined with the falling pressure associated with the crossing low in the predawn of Tue, may support more-decisive and deeper cooling in the higher elevations as per the NAM depiction. Freezing rain and eventually accumulating snow is likely in that scenario before mid-level support and moisture fade in the wake of the weakening mid-level low/shortwave trough. Shortwave ridging in advance of a digging Lower Ohio storm system should diminish POPs, at least for a spell on Tuesday, while temperature rises into the 40s on the strength of warm advection ahead of low pressure encroaching upon the Lower Ohio. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... ECMWF, GFS/ensemble are in general agreement on formation of a Eastern CONUS-to-coastal, southern stream trough for the mid to late week period. Given the projected weakness of the upper and mid level wind field, a damp, light snow/snow showery period is envisioned for Wednesday as cold advection in the low levels is intensified on the western flank of coastal low pressure. That unpleasantness looks to be followed by a dry, but cool period to close the work week as surface high pressure builds under northwest flow aloft. Only minor alterations were thus needed for the Superblend POP and cold temperature prognosis - which should modify as upper flow quasi-flattens by the weekend with low pressure digging over the Wrn U.S. && .AVIATION /17Z SUNDAY THROUGH THURSDAY/...
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VFR conditions will continue through the TAF period under high pressure. High clouds will begin to appear overnight and thicken somewhat on Monday. West to northwest wind of arund 10 knots will become light and variable tonight, and become light out of the northeast on Monday. OUTLOOK... Restriction potential returns with low pressure Mon night through Wed.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.