Scientific Forecaster Discussion
fxus61 kpbz 221934 aaa
Area forecast discussion...updated
National Weather Service Pittsburgh PA
334 PM EDT sun Sep 22 2019
a cold front will bring shower chances to the region Monday. More
seasonable temperatures and mostly dry weather is expected through
the end of the week.
Near term /until 6 am Monday morning/...
dry and unseasonably warm weather continues this afternoon with
gusty winds from 15 to 20kts. Moderate boundary layer mixing with
higher gusts has helped to quickly reduce sfc moisture, so have
lowered forecast dew points somewhat to better reflect this.
The ridge will break down tonight as the upper level trough moves
over the Great Lakes. Clouds will slowly increase west to east
overnight as the trough pushes the upper level moisture plume into
the region, which should help mitigate morning River Valley fog
Short term /6 am Monday morning through Wednesday night/...
a pre-frontal sfc trough will push the first band of showers through
the region during the morning hours Monday. Showers along this front
will generally dissipate as they move west and outpace upper level
support, with the main upper level trough remaining over the western
Great Lakes. Thunder is unlikely as well given this lack of support
and no progged instability.
The main cold front will move through the region later in the day as
the upper level trough transitions east. A second line of showers
will be possible along this boundary, but the extent and intensity of
this new development will be dependent upon how quickly this pre-
frontal trough can exit east and the degree of heating that occurs
ahead of the front. The potential for heat recovery plus the cooling
temperature aloft may allow for enough instability for thunder, so
added a slight chance. However, the possibility remains that morning
showers stabilize the area enough to limit even shower development
along the cold front.
Increasing sfc high pressure and cool northwest flow to zonal flow will
fill in behind the exiting trough starting Monday night. Outside of a
chance for lake-enhanced showers developing north of I-80 Tuesday
afternoon within the northwest flow, this pattern will result in dry weather
and seasonable temperatures for the region.
Long term /Thursday through Sunday/...
a weak shortwave trough and its weak frontal boundary will clip the
region Thursday and provide shower chances. Thereafter, ridge
building will commence across the eastern U.S. Through the weekend as
a series of disturbances helps deepen the trough over the western
U.S. This will result in mostly dry weather with well above normal
Aviation /19z Sunday through Friday/...
VFR conditions continue through tonight in sw'ly flow ahead of an
approaching upper trough. Wind will gust from 15 to 20kts at times
this afternoon before waning this evening. Low-level wind shear is
possible overnight as 35 to 40kt wind blows just above the boundary
MVFR cigs are expected along and behind the frontal boundary Monday
morning/afternoon. However, vsby restrictions will remain isolated
drier air and building high pressure will return VFR conditions by