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513 FXUS61 KPBZ 211017 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 617 AM EDT THU JUL 21 2016 .SYNOPSIS... Hot temperatures are expected today, but humidity will be tolerable. A more steamy airmass is forecast for Friday and the weekend, along with periodic thunderstorm chances. && .NEAR TERM /THROUGH TONIGHT/... Other than updating near-term hourly temperatures, no updates were needed at 615 AM. Previous discussion... Surface high pressure will slide to our south during the day. 500 mb heights will reach their peak during the day, and with still low dewpoints and dry soil, today will likely feature the highest temperatures out of the next several days. The difference in later periods will be higher dewpoints, resulting in higher heat index/apparent temperature values than today. Given the pattern and favorable antecedent conditions, kept the idea of temperatures higher than most models would suggest. Tonight, an approaching shortwave will start the process of locally mitigating the upper ridge. Expect at least a few showers and thunderstorms to reach the forecast area prior to sunrise, although the initially dry airmass may hinder the southward progress of rain. PoPs may need to be lowered in subsequent updates. Kept low temperatures on the warm side given slow cloud increase and better mixing than tonight. && .SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/... A weak upper-level wave will pass north of the area Friday morning, with a chance of showers and thunderstorms, mainly north. The main shortwave timing has been consistent, passing by 12z, but a transition to a northwest upper-level flow regime will open the door for additional showers and thunderstorms through Friday. Fueled by high dewpoints nearing 70, instability will increase through the afternoon. If thunderstorms can develop under mesoscale influences, Friday afternoon, a few could be strong. The marginal risk has been maintained. A bit of model divergence heading into the weekend, as most guidance shows high pressure re-gaining control of the area by Saturday. The 00z NAM continues to hold the surface high back to the northwest, ultimately streaming additional upper-level waves across our north. Will continue to monitor this trend in the NAM, but for now, opting to carry a drier forecast with temperatures soaring well above average. Hot temperatures and dewpoints nearing 70s will lead bring uncomfortably warm conditions for the weekend. && .LONG TERM /MONDAY THROUGH WEDNESDAY/... Ridge of high pressure will temporarily break down beginning of next week as a system dives into the Great Lakes. This will bring rain chances back to the area Monday, but the progressive nature of this system will limit overall precipitation. High pressure re-establishes by middle of next week with drier weather again expected. Zonal flow aloft will bring the next disturbance back to the area by the latter part of next week. After the hot weekend, temperatures will moderate some, but will remain above average through the extended period. && .AVIATION /10Z THURSDAY THROUGH MONDAY/... VFR conditions were maintained through the TAF period, although restrictions cannot be ruled out towards the end north of PIT. No issues today with few clouds and light winds. A shortwave will start to approach late tonight and bring an increase in clouds, and possibly spread a few showers or storms into the area after 06Z. Handled with VCTS mention for now. Any ceilings towards the end of the period should remain around 5000 feet. .OUTLOOK /FRIDAY THROUGH MONDAY/... Scattered restrictions in thunderstorms are possible Friday through Monday. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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