Scientific Forecaster Discussion
000 FXUS61 KPBZ 080852 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 352 AM EST Sun Dec 8 2019 .SYNOPSIS... High pressure will maintain dry weather today. Rain returns late tonight and Monday with approaching low pressure. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Weak warm advection today as 850 flow veers to the SW and surface winds veer to the S-SE. Moisture will increase with the warmer air, and clouds will move in from the southwest throughout the day. && .SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/... Warm air advection ramps up tonight as the zonal flow aloft is replaced by a southwest flow. Shortwave trough will swing through Ohio late tonight, behind a passing upper level jet. Large mid-level moisture plume will accompany the energy, deepening atmospheric moisture and increasing rain chances. Lower levels will take a bit longer to saturate, so widespread showers look to hold off until just before dawn. Strengthening upper level jet, in the southwest flow aloft, will continue to supply moisture and lift on Monday. Widespread, soaking rain, is a good bet on Monday. Rain rates look to increase Monday morning with the passage of a low-level jet and the aforementioned shortwave trough. Main swath of more significant rain will swing northeastward Monday afternoon trailing the upper level energy. Even with the clouds and rain, impressive warm air advection will promote well above normal temperatures. Models have lowered rainfall amounts, when compared to runs at this time yesterday. Generally it looks like 1 to 1.5 inches across the region by Tuesday morning, with a large chunk of that falling on Monday. There is still some disagreement of where the axis of heaviest rain will fall, this is likely due to differences in the placement of the jet axis. Given the time frame of precipitation accumulation, and the lack of convection, any possible water issues would be isolated. Main cold front finally passes through the area late Monday night. Widespread rain showers will continue until the front clears the region around dawn on Tuesday. Showers will be light as upper level support decreases and the deep moisture shifts southeastward. Strong cold air advection on Tuesday as the surface front shifts to the Mid-Atlantic region. The main moisture plume will get hung up south and east of Pittsburgh on Tuesday as the system fights against an impressive SE CONUS ridge. With the cold air pushing southeastward, light snow will develop within this plume of moisture Tuesday afternoon. Tuesday will feature falling temperatures throughout the day. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... Area of snow will drift southeastward Tuesday night, exiting the southeast ridges after midnight. Much colder air will remain in place through most of the week. A slow moderation is expected Friday and Saturday. The overall pattern looks dry until Saturday. && .AVIATION /09Z SUNDAY THROUGH THURSDAY/... Crossing high pressure will maintain VFR early this morning, but return flow after sunrise will result in stratus development with high MVFR cigs possible at most sites by this afternoon. Rain and related vis/cig restrictions are expected at the very end of the period (PIT) or after (elsewhere) with a crossing shortwave. .Outlook... Restrictions are likely to persist thru Wed with the advn and passage of a strong cdfnt. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None.