Area Forecast Discussion
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FXUS61 KPBZ 212139 AAA
Area Forecast Discussion...UPDATED
National Weather Service Pittsburgh PA
539 PM EDT THU JUL 21 2016
Warm temperature, increased humidity, periodic thunderstorm
chances can be expected into early next week.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
-- Changed Discussion --540pm update...continue to monitor line of convection slowly
moving southeast toward the area. Latest satellite and radar
pictures continue to show a slow decay to the activity, which
falls in line with 18z operational model runs and the latest hires
data. This will be a situation where multiple updates may be
needed as the line evolves through the evening. Have lowered pops
this evening, attributed to the aforementioned model data, and
adjusted overnight lows in line with the latest blended hires
Changes for the near term period included precip probability
adjustments for the potential that ongoing convection over the
Great Lakes Region survives mid level warmth, or spawns outflow
that ploughes into the diurnally destabilizing airmass over the
area. An escalation through "chance" numbers was thus included for
the evening hours, and maintained tonight basically north of
Interstate 70 as isolated to scattered convection may accompany
the actual shortwave. Limitations include the aforementioned CAPE-
robbing mid level warmth, fading diurnal support, and lack of
Morning lows in the moderating airmass were progged close to the
previous forecast, i.e. about 5 degrees above the averages.
-- End Changed Discussion --
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY NIGHT/...
A better chance for rain is expected with another disturbance on
Friday. Improved boundary layer moisture and instability with a
marginally cooler mid level should be more conducive for showers
and storms, although limited deep layer shear should keep the
threat of severe isolated.
Thereafter, a shortwave ridge extending from the broad Central
CONUS high is forecast to continue the warmth and humidity over
the immediate area. Dewpoints in the upper 60s, to around 70 F
with temperature about 7 to 10 degrees above the averages will
generate heat indices in the 95 to 100 degree range for Saturday
and Sunday afternoons. A Hazardous Weather Outlook mention was
maintained for the Ohio counties as those heat indice projections
are flirting with the 100 degrees heat advisory criteria.
Convection in the warmth will be limited by warm mid levels and a
lack of forcing, so small PoPs will be the rule with hedges
dependant of weak disturbances and mesoscale effects.
.LONG TERM /MONDAY THROUGH THURSDAY/...
A stronger disturbance is forecast to carve the ridge over the
Upper Ohio early next week. That system will provide the next,
best chance of rain with a shortwave ridge quickly rebuilding in
its wake. The flatter flow pattern will moderate temperature in
this time frame, although readings are expected to remain above
.AVIATION /22Z THURSDAY THROUGH TUESDAY/...
High pressure should maintain VFR conditions through the evening.
Shower and thunderstorm chances are expected to increase tonight
with an approaching shortwave with local restrictions possible.
With uncertainty in timing/location of any precip, included only a
VCTS for ports north of I 80 where instability should be more
favorable, with VCSH mention south. Another weak wave should
result in additional scattered thunderstorms Friday afternoon.
.OUTLOOK /FRIDAY NIGHT THROUGH TUESDAY/...
Restrictions are possible in scattered thunderstorms Friday
evening, and again late Sunday and Monday with crossing