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NWS Area Weather Forecast Discussion
County Warning Area [CWA]: PBZ
Regional NWS Weather Office: Pittsburgh, PA

FXUS61 KPBZ 201522

Area Forecast Discussion
National Weather Service Pittsburgh PA
1122 AM EDT Thu Jul 20 2017

Thunderstorm chances will escalate today with severe storms
possible. Active weather remains in place through the weekend,
with the risk of severe weather returning Saturday.


Two thunderstorm over southern Ontario and
another dropping across northern Indiana...are connected by a
wavy frontal boundary near the southern Great Lakes shores.
Neither of these MCSs are expected to impact our area, but
additional thunderstorms are expected to fire along and ahead of
the front later this afternoon and evening, with the bulk of the
activity forming after 20-21Z. They will form in an air mass
northwest of PIT with perhaps 1000-2000 J/kg of CAPE and 30-40
knots of effective bulk shear. This should be sufficient for a
few strong to severe thunderstorms. Wind will be the primary
threat, as wet bulb zero heights are too high, and CAPE aloft is
too low, for much of a hail threat. An isolated tornado remains
possible as well. Have continued with likely PoPs across the
northern half of the CWA. Coverage and intensity should slowly
fade after sunset, with a few scattered showers and storms
remaining in the vicinity of the Mason/Dixon line by sunrise as
the boundary slowly advances.

Temperatures/dewpoints on track for now and made only minimal


The latest deterministic model trends are that this evenings
convection and frontal passage will be decisive enough to drive
the boundary south of the region for Friday. POPs for Friday
were thus reduced, then revamped for the approach of another
strong shortwave on Friday night, which may spawn more severe
storms given the projected wind profile. Current timing does not
favor that scenario, hence the marginal SPC outlook for the time

Models indicate a repetitive pattern for Saturday and cold
frontal passage for Sunday. Likely POPs were thus maintained for
the weekend along with the beginning of a downward temperature


The pattern of shortwaves crossing in zonal/northwest flow is
expected to give way to Great Lakes-to-Northeastern-CONUS
troughing during the first half of next week. Temperature will
thus moderate back toward, and a few degrees under the average
and rain chances will decline into mid week.


High confidence forecast save for the onset and duration of
thunderstorms this afternoon and early evening. These times
could vary by 2-3 hours and flight category between 6-12Z

An upper level disturbance crossing this afternoon will bring a
line of strong to severe storms moving from north to south
affecting likely all terminals if it develops like many of the
high resolution models indicate. Inserted VCTS for all terminals
starting around 20Z north and 0Z south of the mason dixon line.
Brief restrictions to IFR vis can be expected if an airport is
impacted by a storm. In wake of the storms, last 6-9 hours of
forecast its hard to tell if MVFR fog will develop or will there
be a canopy of stratocu or just VFR? For now, rolled with an
optimistic forecast no cigs below 030.

Additional rounds of storms are expected through the weekend,
and morning fog is possible as well.





Forecast Discussion from: NOAA-NWS Script developed by: El Dorado Weather