915 FXUS61 KPBZ 101146 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 746 AM EDT Wed Oct 10 2018 .SYNOPSIS... Today will be the last day of unseasonable warmth. Rain chances increase tonight ahead of a cold front, and continue through the passage of the boundary on Thursday. Much more fall-like temperatures will then take hold into the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... With 7:45am update, made some minor tweaks to hourly pops, temperatures, dewpoints, and sky cover. Cloud cover is a bit higher than forecast north and east of Pittsburgh, although skies are a bit clearer farther to the south. Previous discussion... The daylight hours will feature the continued erosion of the offshore upper high, as approaching Plains shortwave energy elicits downstream falling heights. This, plus the increase in clouds from the south through the day, will knock another couple of degrees off of afternoon high temperatures from yesterday. Still, many locations should reach the 80 degree level once again, perhaps for the final time this year. Expecting scattered showers to arrive in areas mainly south of Pittsburgh prior to 18Z, as the lower levels take a little time to moisten. Going to hold thunder out for now given the very meager instability and poor lapse rates noted on model soundings. && .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY/... The models are in general agreement overall with the timing of the well-advertised frontal boundary that will bring a stark pattern change. The front will be in the vicinity of the Ohio river by 12Z Thursday and swing across the ridges during the early to mid afternoon hours. Have PoPs ramping up to categorical areawide overnight with good southwesterly moisture feed, and then tapering behind the front on Thursday. Kept a slight chance of thunder ahead of the front as lapse rates aloft steepen enough for some modest elevated instability. Severe weather is not a threat. Some efficient rainfall production is possible for a time with with soundings saturated to 10-12kft, warm cloud depths to match, and precipitable water values briefly reaching or exceeding 2 inches in spots. Thankfully, the overall progressive nature of the system will keep rainfall totals in check, so flooding will not be anticipated either. After one last warm and humid night, temperatures will not rise much on Thursday as the front crosses, with perhaps a non-diurnal afternoon drop across Ohio. Only a few isolated showers will remain along the ridges and near/north of I-80 by 00Z Friday in northwest flow and lingering low level moisture. These will wane by sunrise as moisture becomes more scarce, but some clouds may linger for a bit on Friday as surface high pressure noses in. Dropped high temperatures a few degrees from the previous forecast for Friday given lingering clouds and subzero 850 mb temperatures in northwest flow. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... A general troughing pattern will linger through the extended period. Disturbances moving through this trough will provide some precipitation chances, but timing remains questionable. One such ripple moves through Friday night into Saturday, bringing some chilly rain showers. Better rain chances arrive with a frontal boundary, especially Sunday night into Monday. Things quiet down a bit by Tuesday. Temperatures will continue to run near or below normal through the extended period. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... VFR is expected through the afternoon under a high pressure ridge. A few showers are possible late this aftn as the ridge shifts E, and a weak shortwave in SW flow crosses the area. Widespread deterioration to MVFR and eventually IFR is expected tonight with the approach of a cold front. Outlook... Widespread restrictions are expected to continue Thu with FROPA. Restrictions are possible Thu night through Sat with cool NW flow and upper troughing, and again Sun with a crossing cold front. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$