Area Forecast Discussion
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015 FXUS61 KPBZ 231904 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 304 PM EDT Thu Mar 23 2017 .SYNOPSIS... A period of above-normal temperature and increasing chances for rain is expected through early next week. && .NEAR TERM /THROUGH TONIGHT/... A weak, low-amplitude disturbance will interact with the strengthening low-level jet overnight to generate light precipitation, particularly late tonight and early Fri morning. Although the focus will be in northern counties, latest hi-res models support broader PoP coverage across the forecast area. The strong warm air advection and increasing clouds tonight will inhibit the typical diurnal temperature cycle. Initial cooling and residual dry air may be enough to support wet-bulb values below freezing in very isolated locales for a brief window late tonight at the onset of any precipitation (e.g. a few of the coldest sheltered valleys in the ridge zones). In general, temperatures are expected to remain above freezing, but a brief period of light freezing rain may occur in those sheltered valleys before warm air advection wins the thermal battle. However, given the northern placement of the upper disturbance, there is a lower confidence in precipitation with southward extent, so it could be that little precipitation occurs in the areas most thermally-favorable for any freezing precipitation. This concern will be highlighted in the HWO until the conditional threat is abated with confidence. && .SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/... The disturbance responsible for overnight precipitation will move east Friday morning, leaving the remainder of the day mostly dry and relatively warmer. Another weak disturbance will affect primarily the northern zones Friday night, given the perseverance of an amplifying east-coast upper ridge. A series of compact shortwave troughs will develop in the swrn CONUS and eject newd beginning Saturday. As the first wave acquires a negative tilt, shortwave ridging will amplify over the Great Lakes region, leading to a likely-nwd displacement of precipitation on Saturday and Saturday night. Steady height falls will begin to spread across the region Sunday morning as the ejecting wave nears. By afternoon, the associated H5 jet maximum will cross the forecast area, likely invigorating deeper convection with its passage amid modest instability. This wave will be exiting the region by Monday morning, with a downward trend in precipitation expected by late Sunday night as shortwave ridging develops in its wake. && .LONG TERM /MONDAY THROUGH THURSDAY/... In the wake of the Sunday wave, a brief respite can be expected on Monday amid shortwave ridging before a second trough ejects from the Plains. This second wave will be favorable for widespread rain showers as it crosses on Tuesday as warm, moist air is drawn poleward ahead of the system. Behind the wave, seasonable air is expected to arrive mid-week with highs in the 50s and lows in the 30s. Given ensemble spread, there is considerable spread with the placement of the pattern of upper-level troughs and ridges across the country during this time, so the forecast details during this time remains lower-confidence. && .AVIATION /19Z THURSDAY THROUGH TUESDAY/... High pressure will keep a majority of clouds at bay through tonight. A shortwave trough crossing along a warm front will bring an increase in clouds and eventually light rain showers by Friday morning. Kept VCSH mention for Pittsburgh and south while northern ports stand the best chance to see borderline MVFR restrictions. Light wind will shift around to the south and gradually increase through the period. An increasing low-level jet will bring a chance for LLWS before mixing commences Friday morning. Outlook... The next chance for widespread restrictions is not expected until the approach of low pressure early on Sunday. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$ Kramar/TAX is the U.S. government's official web portal to all federal, state and local government web resources and services.