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Area forecast discussion 
National Weather Service Pittsburgh PA
522 am EDT Sat Jul 23 2016

Synopsis...
hot and humid weather is forecast for into early next week along
with intervals of scattered thunderstorms.

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Near term /through tonight/...
a bit of a weak surface wave will move across the northern
portions of the area today, bringing in a bit of drier boundary
layer air behind it. In general, even ahead of it, the atmosphere
outside of the boundary layer is rather moisture starved, so
shower and thunderstorm chances will remain very low and relegated
only to the southern half of the area during the maximum in
diurnal instability with only modest mid-cloud development
apparent at this hour.

Interestingly enough, increased mixing right along the surface
trough as well as locally increasing warm advection with it with
bring a corridor of warmer 850 mb air to the northern half of the
County Warning Area today. This combined with lowering dewpoints may allow for
actual higher temperatures across portions of the northern County Warning Area
than farther south. However, as dewpoints fall toward 60f, this
will not translate into heat index values. Farther south, a bit
more moisture in the column combined with some cumulus development
and more insolation being eaten up by latent heating should keep
temperatures from running up much above the lower 90s. However,
dewpoints will remain elevated throughout the day and likely into
the lower 70s during maximum heating. This will create a period of
the day with dewpoints in the upper 90s to near 100f, especially
in eastern Ohio. The heat advisory previous issued has been
continued for this.

As the surface boundary settles to the southwestern portion of the
area tonight, northeasterly flow should bring drier air deeper
into the County Warning Area. This should allow for a wider diurnal temperature
fall basically everywhere north of I-70 primarily due to a lower
dewpoint and strong radiational cooling. It does seem, though,
that this boundary layer drying will be fleeting as low level flow
will already be trending from northeasterly to southerly by
sunrise Sunday. Fries

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Short term /Sunday through Monday night/...
a passing shortwave ridge aloft will keep the forecast area mostly
dry through the afternoon Sunday. Only maintaining a slight chance
of showers/thunderstorms during the evening as the ridge axis shifts
east and flattens due to a weak wave passing through the southern
Great Lakes.

Ample low-level moisture will linger, keeping dewpoint temperatures
in the mid to upper 60s. This moisture, combined with hot
temperatures, will again have heat indices in the mid to upper 90s
for most locations west of the ridges. Only have a few counties
flirting with 100, and those counties already have a heat advisory
for Saturday, so opted to maintain the Sunday severe weather potential statement mention for now.

An upper-level trough will approach from the west Monday, dragging a
weak cold front behind it. This will be the impetus for the best
chance of rain over the next several days. Mid-level temperatures
will remain fairly homogeneous Sunday into Monday, but strong
warming at the surface and lingering high dewpoints will fuel
instability ahead of the trough Monday afternoon. This, along with
modest vertical shear, should be enough for a few strong
thunderstorms to develop, but a widespread severe threat is not
expected at this time. Model soundings do suggest efficient rain
production with any thunderstorms Monday as the warm cloud layer
will extend above 10kft and pwats approaching 2.0", which is well
above average. The boundary will sag south of the area Monday night,
with gradually declining rain chances into Tuesday morning. Tax

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Long term /Tuesday through Friday/...
a weakening surface boundary will stall just south of the forecast
area Tuesday. Models differ slightly on how far north afternoon
thunderstorms activate along the boundary Tuesday and Wednesday.
Kept slight chance pops relegated to south of the Mason-Dixon line
Tuesday afternoon, but high pressure building at the surface across
our north, results in a mostly dry forecast. Dry weather is expected
to last into Thursday morning, as upper-level flow GOES zonal. High
pressure will start to break down towards the end of next week as
broad troughing begins aloft. This will bring periodic showers and
thunderstorms back to the forecast through the early part of next
weekend. Tax

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Aviation /09z Saturday through Wednesday/...
some local MVFR fog is possible this morning, however a mid-cloud
deck seems to have developed over much of the area, resulting in
wider dewpoint depressions than even a few hours ago. This cloud
inhibit much in the way of fog development before sunrise, thus
the fog forecast is not confident. Whatever fog does develop
should rapidly clear with sunrise, allowing for VFR conditions at
all sites on Saturday. Fries

Outlook /Saturday through Wednesday/...
restrictions will be possible late Sunday and Monday with the
approach and passage of a weak cold front.

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Pbz watches/warnings/advisories...
Maryland...none.
Ohio...heat advisory from noon today to 8 PM EDT this evening for
ohz048-057>059-068-069.
PA...none.
WV...heat advisory from noon today to 8 PM EDT this evening for
wvz004-012.

&&

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