Scientific Forecaster Discussion
fxus61 kpbz 220915
Area forecast discussion
National Weather Service Pittsburgh PA
515 am EDT Sat Jul 22 2017
warm and humid through the weekend. Showers and storms are also
expected today and Sunday. Storms could be severe and produce
Near term /until 6 PM this evening/...
large mesoscale convective system over the western Great Lakes/upper Midwest will be
moving into my western counties around daybreak. 700 mb-500 mb lapse
rates approach 6.5ckm-1 while MUCAPES push 2.0kjkg-1. Wind shear
is impressive as well with nearly 40 knots of shear. All of
this will create an atmosphere that could yield strong to severe
storms, really at any time today. Atmosphere keeps its tropical
characteristics with precipitable waters around two inches and warm cloud
depths nearing 13kft. This will lead to heavy downpours with any
storm which will increase the flash flooding threat.
Limitations to the severe threat will be dependent on the amount
of cloud cover today, which in turn will keep temperatures down
and prevent the area from reaching forecasted convective
temperatures. Additionally, still have plenty of warm air aloft
and morning showers/storms will work to cool the lower levels
and increase atmospheric stabilization. All of this will need to
be monitored throughout the day.
Short term /6 PM this evening through Monday/...
the risk for showers and storms will continue overnight, with
the focus shifting southward as the surface boundary is pushed
toward West Virginia. Another shortwave, moving southeastward in
the northwest flow aloft, will work to move the boundary into
the mid-Atlantic region by dawn on Sunday.
Sunday confidence is lower in organized convection moving through
the region however we still remain in northwest flow with
disturbances riding through.
Activity wanes Sunday night with the loss of daytime heating, but
again expect a muggy night with temps well into the 60s and lower
Mid level trough sweeps through Monday afternoon so this will be the
last round of showers/storms before a welcome break occurs.
Long term /Monday night through Friday/...
- lower humidity
- active weather regime end of next week returns
500 mb heights build Tuesday into Wednesday offering a reprieve
from daily chance of storms. After Tuesday being the coolest day
of the week, temperatures ramp back up towards normal values in
the lower 80s.
A two Standard deviation below normal trough establishes across
eastern Canada Wednesday night through the balance of the week. This
will return passing shortwave troughs permitting the return of
precipitation under northwest flow. Much the case for this week,
thunderstorm complexes could traverse the region given we are on the
southern periphery of the trough, however confidence not high enough
to warrant anything greater than climo pops.
Aviation /09z Saturday through Wednesday/...
restrictions will continue this morning as showers and
thunderstorms cross the region. There is a chance of
thunderstorms to develop later in the afternoon but will
largely hinge on instability. At this time development looks
less likely in the absence of a trigger and cloud coverage
limiting surface- based instability.
periodic restrictions are expected on Sunday in morning fog and
daily rounds of thunderstorms.