Scientific Forecaster Discussion
fxus61 kpbz 270931
Area forecast discussion
National Weather Service Pittsburgh PA
531 am EDT Tue Jun 27 2017
upper low pressure will maintain cool temperatures and the risk
for showers or a storm today. Temperatures moderate the second
half of the week. Dry Wednesday, showers and storms return
Thursday and Friday.
Near term /until 6 PM this evening/...
expect the risk for showers to dissipate across the southern
half of the area during the morning hours, with the shortwave
trough rapidly moving into upstate New York. Behind the exiting
wave, winds will shift toward the northwest and there will be a brief
period of cold air advection. The main part of the cool pool
aloft will be across northern counties. This destabilization,
combined with a flow off of Lake Erie, and a third wave moving
across the Great Lakes, should allow for the redevelopment of
scattered showers and storms mainly across the north.
With the cooler air aloft, cu should have no problem developing
across most of the area, which will assist in keeping
temperatures below normal.
Short term /6 PM this evening through Thursday/...
upper level heights begin to rise tonight and broad high
pressure will move into the mid-Atlantic region on Wednesday
morning. As the surface high speeds eastward, and the upper
level ridge strengthens, flow in the lower and mid-levels will
turn toward the southwest and allow for a much warmer air-mass
to overspread the area. With lots of sun and warm air advection,
a return to more normal temperatures is expect on Wednesday.
The weak ridge will flatten Wednesday night, in response to the
next shortwave trough moving from the upper Midwest and then over
northern PA. Most of the energy from this wave will be used to
weaken the ridge. This loss of large scale ascent, combined with
the continued warming of temperatures aloft, will keep Wednesday
night dry. Do expect to see and increase in high and mid-level
clouds as the night progresses.
On Thursday, the next upper level system will dig into the
western Great Lakes and the surface reflection will be
positioned near the 500 low. A frontal boundary will extend
eastward from the surface low, stretching across New York and
into New England. In response to the Great Lakes system, heights
will rise over the upper Ohio Valley, which will keep energy
rotating around the 500 low to the north of the region. The
models are setting up an area of strong moisture convergence
over the north on Thursday, which will likely lead to the
development of showers and storms. Have included pops on
Thursday, generally north of pit, with likely pops over the far
Temperatures on Thursday will continue to moderate and would
expect gusty southwest winds as well.
Long term /Thursday night through Monday/...
great uncertainty in the long term portion of the forecast, as
models are still trying to work out the details of the next
large upper level system. With the system deepening over the
weekend, positioned near the western Great Lakes on Saturday,
the southeastward movement has slowed in relation to previous
model runs. Will rely heavily on blend of ensemble guidance to
compose the long term.
Aviation /10z Tuesday through Saturday/...
mainly VFR conditions are expected through the taf period,
through a crossing shortwave trough should result in scattered
showers through the day mainly north of pit. Mid level clouds should
be replaced by cumulus by mid morning as convective temps are
reached. A brief period of MVFR ceilings is possible for
fkl/duj in the morning, though mixing should lift heights to VFR
by afternoon. This mixing should also result in gusty west winds.
restriction potential returns mainly north of pit Thu/Fri with an
approaching cold front, with restrictions likely area wide Sat
as the front crosses.