Scientific Forecaster Discussion
fxus61 kpbz 200406
Area forecast discussion
National Weather Service Pittsburgh PA
1206 am EDT Fri Sep 20 2019
high pressure should maintain dry weather through the weekend. Rain
chances return Sunday night and Monday with a crossing cold front.
Near term /until 6 am this morning/...
high pressure will maintain dry conditions for tonight. Radiational
cooling should result in seasonably cool lows.
Short term /6 am this morning through 6 PM Saturday/...
mid- and upper-level ridging is expected to amplify across the upper
Ohio Valley through Sat as a sfc high drifts swd. Increasing mid/upr
heights and developing swly flow aloft should sustain the ongoing
Some models indicate showers developing Saturday with a brief
flattening of the upper ridge, but these seem to be driven by
moisture advection known to trip up model parameterization for
precipitation. Forecast soundings suggest a strong plume of warm air
at 850 mb, which likely will limit the depth of any convection
despite increasing low-level moisture. Chances for showers are
minimal, but non-zero, with greatest potential on Sat from zzv-ucp.
Long term /Saturday night through Thursday/...
the upper ridge will shift ewd thru the weekend ahead of a strong
trough in central Canada, but the timing and strength of the trough
remain uncertain. A slowing trend has been apparent in its arrival
over the last several model runs owing to potential for the trough to
close off, thus delaying arrival of its attendant cold front and
onset of precipitation.
Given this uncertainty, it is unclear precisely when the greatest
chance for rain will come, but it is likely to be somewhere in the
Sun night-Mon timeframe.
Thereafter, dry, cooler conditions are expected in the early half of
Aviation /04z Friday through Tuesday/...
high pres will maintain VFR and a light se, to S wind through
restrictions are likely with a Sun night/Mon cold front.