Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
529 am EDT sun Sep 21 2014
a cold front will bring showers and thunderstorms today. High
pressure will dominate the remainder of the week with dry weather.
Near term /until 6 PM this evening/...
still concerned over the potential for strong to severe storms
late today with the passage of a cold front. Wind field is
impressive and the atmosphere destabilizes ahead of the boundary.
NAM is clearly the strongest with mesoscale features compared to
other operational models. This leads ME to believe that the NAM
may be on its own with its depiction of the situation so will lean
away from it. Any convection this afternoon will have the
potential to produce gusty winds. With mixing heights rising ahead
of the front...could still see stronger wind gusts without
convection. Other limiting factors will be cloud cover and the
risk for scattered showers this morning. For a NAM solution to
come to fruition...would need to see convection fire and grow over
the Great Lakes along the front and then sustain itself...thanks
to the high shear values in its solution. The other operational
models are not in total agreement with this scenario. Forecast
will show showers this morning and then showers/storms this
afternoon right along the front. Have increased wind gusts during
Front will pick up speed late this afternoon as strong shortwave
trough will dig down from the western Great Lakes.
Short term /6 PM this evening through Tuesday/...
shower/storm chances with the front will end in the evening over
the South. Strong cold air advection will follow on the heels of the boundary as
the trough axis move through late Sunday night. 850 mb temperatures will
drop some 6-8 degrees Sunday night as the flow veers to the
northwest. Expect a large area of strtocu to quickly cover the
region. Its possible...with the colder air and northwest flow...
showers could redevelop...particularly over the north and ridges.
Heart of the cold air settles in over the region Monday. Expect
the stratocu deck to remain in place. Latest forecast soundings
are showing a thin layer of saturation which would likely prevent
additional shower activity on Monday. Noticeably colder 850 mb temperature
forecast Monday compared to previous runs. This will necessitate
the lowering of temperatures on Monday. If latest model output is
correct...highs Monday could be 15 to 20 degrees below normal.
Cold air will quickly retreat to the northeast Monday night as the
entire upper level system shifts toward the East Coast.
Warm air advection will kick in Monday night allowing skies to clear.
Surface high and ridging aloft will provide a sunny and comfortable
Long term /Tuesday night through Saturday/...
dry and seasonable pattern expected for the long term.
Aviation /09z Sunday through Thursday/...
line of showers with possibly a few isolated thunderstorms
preceding a cold front approaching from the west will quickly pass
across the region this morning. Upstream observations shows
several locations may briefly drop to MVFR ceilings as the line
passes but improve to VFR shortly thereafter. The actual cold
front will pass through this afternoon...and while latest model
consensus indicates only marginal lift for thunderstorms...there
is potential for strong wind gusts out of the west with either
showers or thunderstorms during frontal passage.
Outlook.../Monday through Friday/...
stratocumulus between 3-5kft above ground level will persist through
Monday...with VFR conditions expected through the week as the
region remains under a dry pattern.