Area Forecast Discussion
Issued by NWS Pittsburgh, PA

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FXUS61 KPBZ 091239

Area Forecast Discussion
National Weather Service Pittsburgh PA
839 AM EDT Fri Jun 9 2023

Isolated to scattered showers mainly north and east of
Pittsburgh this afternoon will offer little rain accumulation.
Dry weather and increasing temperature is expected Saturday into
Sunday before the next low pressure system provides widespread
rain chances by early next week.


Amid persistent northwest flow as the upper low sits over
Maine, a another shortwave will cross the Upper Ohio River
Valley today and create isolated to scattered showers. The
environment will be more favorable for shower and isolated
thunderstorm activity than Thursday as shear increases and
further cooling of mid- level air creates a small uptick in area
instability. That said, lack of strong sfc heating as daytime
highs remain seasonable cool will keep instability low while
column moisture will remain thin. This will limit QPF output and
ensembles agree by showing the probability for at least a tenth
of an inch of accumulation at less than 40 percent and for most
areas falling to less than 20 percent.

The potential for air quality issues remain a concern as the
pattern goes unchanged and can still draw wildfire smoke to the
region. Please see your local DEP for the latest information and
air quality alerts for you area.


Subsidence and sfc ridging will return dry weather forecasts to
the region Friday night into Saturday as the New England low
finally begins to shift east. Rising pressure heights aloft as
northwest flow weakens in response to the departing low will
promote temperature moderation as well for Saturday. Expect more
seasonable afternoon temperature amid increased insolation. This
pattern shift will also serve to cut off the wildfire smoke
fetch and likely end the current string of days with air quality

Quasi-zonal flow will develop by Saturday night over the region
as a developing trough/low deepens over the northern Mississippi
River Valley. A stream of cirrus connected to warm/moist
advection aloft in advance of this system will move over the
forecast area, moderating overnight temperature towards
seasonable levels.


The upper trough will continue to deepen over the western Great
Lakes Sunday, creating an upstream response of warm, moist
advection within southwesterly flow for the Upper Ohio River
Valley. Model trends continue to delay the arrival of the sfc
low and upper jet dynamics to late Sunday or even early Monday
morning, which aligns with the idea of slower eastward
progression as the upper low closes off. Surface ridging ahead
of this system should keep a majority of Sunday dry while
temperature rises a few degrees above normal.

Current thinking favors a shortwave pulse ahead of the main
trough axis pushing the surface low through the region late
Sunday into Monday. Timing of the front and coincident upper jet
dynamics in relation to diurnal heating will play in a role in
QPF production. More instability developing ahead of the line
and ideal jet positioning could push area QPF towards the 75th
percentile of 0.75 to 1.00 inches. On the other hand, faster
frontal push that prevents surface heating and sees the upper
forcing begin to split north/south of the forecast area could
push accumulations toward 25th percentile of around 0.25 inches.
Ensembles agree that dry slotting will quickly return dry
weather by Monday night behind the surface trough.

Thereafter, the upper low is favored to remain over the Great
Lakes through the late week period while sending weak
shortwaves through its trough base/backside NW flow. This
pattern favors intermittent rain chances with seasonable


Haze, from wildfire smoke directed south from Quebec, may
linger across the region but will likely be no lower than 6SM.

Iso/Sct showers will be possible today mainly east and north of
KPIT, however, any MVFR restrictions will be brief. Conditions
will quickly clear out by the evening and overnight.

Any lingering haze/smoke will likely clear from the region Saturday
with a chance in the upper level pattern. Restrictions in much-
needed widespread rainfall are possible by Sunday and Monday.


Prolonged dry conditions have resulted is sizable dry streaks
at some observing sites. The longest consecutive days without
measurable precip and current streaks are (as of June 7th):

Climate Site       Record Streak       Current Streak
Pittsburgh         26 days, 1874       19 days
DuBois             23 days, 1988       19 days
Zanesville         44 days, 1963       19 days
New Philadelphia   27 days, 1963       19 days
Wheeling           27 days, 1947/1884  19 days
Morgantown         36 days, 1908       5 days




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