582 FXUS61 KPBZ 110931 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 531 AM EDT Thu Oct 11 2018 .SYNOPSIS... A crossing cold front will end rain showers from west to east today. Temperatures will become much cooler tonight, and remain below normal through the weekend. The next good chance of rain arrives with a Friday night disturbance. && .NEAR TERM /THROUGH TONIGHT/... At 530 AM, made some adjustments to PoPs based on radar and hi-res model trends, mainly to advance the back edge a little more quickly eastward this morning. The earlier gap in radar coverage across the CWA is filling in, although rain west of Pittsburgh is decidedly lighter than the activity to the east, which is in a more tropical air mass. Previous discussion... Our long-anticipated front currently resides in western Ohio. Bands of showers are currently organized in southeast Ohio and along the ridges, with lighter and more scattered activity in between. Coverage will continue to increase across the CWA over the next few hours as the front approaches and moisture continues to surge in from the southwest. The front should approach the Ohio River by 12Z, and cross the ridges by mid- afternoon. The heaviest rain will fall in the eastern CWA, with around an inch possible. Some brief downpours may be observed with high PWAT and deep warm cloud depths, but the overall progressive nature of the system will keep rainfall totals in check. The thunder threat will remain very marginal, but improving lapse rates may allow for a few rumbles, so kept a slight chance mention. Temperatures will steady out, or perhaps even fall a bit this afternoon behind the front, but the strongest cold advection will wait until the nighttime hours. Expecting the radar scope to be clear at 00Z Friday. However, as low-level flow turns northwest during the evening, cold advection ramps up and opens the door to our first round of subzero 850mb temperatures of the season. This with lingering low-level moisture will allow isolated showers to bloom, especially north of Pittsburgh and along the ridges. Model soundings come tantalizingly close to allowing for a few flakes, but the boundary layer should remain warm enough to keep precipitation liquid. Likewise, lingering clouds and a stirred boundary layer should keep frost possibilities in check across Ohio. Nevertheless, low temperatures Friday morning will end up 20 to 25 degrees colder than those this morning. && .SHORT TERM /FRIDAY THROUGH SATURDAY/... Subsidence and thinning moisture will shut off the isolated showers by midday Friday, although enough moisture will remain trapped underneath a stout inversion to keep clouds around for a while. Some locations will struggle to reach 50 degrees during the day. A fairly potent shortwave will cross Friday night into Saturday morning, bringing the next chance of rain showers. Precipitation will be light, but likely PoPs are appropriate. Model soundings are showing a bit more moisture in the dendritic growth layer, and sufficient depth of cold air, to allow for a few flakes to mix in across the higher ridges above 3000 feet. However, no accumulation will be mentioned. Precipitation departs with the shortwave by midday, and some sunshine should be seen areawide by afternoon as surface high pressure builds in. Much below normal temperatures will linger. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... A general troughing pattern will remain in place through this period, keeping temperatures below normal. If clear sky can linger Saturday night, Sunday morning may represent our best chance of seeing some frost. Temperatures may recover a bit Sunday afternoon as flow turns southwest around the departing high. However, a frontal boundary will bring renewed rain chances by Sunday night, with temperatures dropping back well below normal behind the front on Monday. Continued disturbances moving through the trough will keep some low shower chances going into midweek. && .AVIATION /10Z THURSDAY THROUGH MONDAY/... Deterioration to MVFR, with TEMPO IFR, is expected this morning in showers with an approaching cold front. The front should cross most ports this morning, with a WSHFT to the W after FROPA. CIGS should increase to VFR from W-E by late morning/aftn in dry advection behind the front. CIGS should lower to MVFR levels again Thu night with cool NW flow and an approaching upper trough. Outlook... Periodic restrictions are expected Fri/Sat with cool NW flow and a crossing trough. Restrictions potential returns with a late Sun/Mon cold front. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$