Area Forecast Discussion
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FXUS61 KPBZ 210512

Area Forecast Discussion
National Weather Service Pittsburgh PA
1212 AM EST Tue Feb 21 2017

Dry and warm weather will be briefly interrupted by some
showers late Tuesday as a weak front crosses the region.


A fairly long fetch of elevated RH values in the layers
generally above 300 mb extends across the entire CWA already
very early this morning. This is well out in advance of a mid
and upper level system currently splitting off from the upper
flow in the Mississippi Valley. The vast majority of the
moisture and lift will remain with the cut off low that will
meander into the southeastern portions of the country. The
remnant upper level wave in the northern stream will take its
sweet time crossing the Great Lakes region on Tuesday, only to
edge as far eastward as our area by very late in the day.

Deep saturation with this system remains generally north of our
area. In addition, as the H5 wave shears off to the north
through Tuesday night, lift along the boundary as it shifts
through the CWA on Tuesday night is looking fairly paltry.
Beyond that, deep moisture is entirely lacking. That said, PoPs
were trended back below likely threshold for the vast majority
of the area with the boundary passage on Tuesday night. In fact,
some guidance (the new 00z NAM) is trending toward a basically
dry passage of the system.

Regardless of the chances of rain, high clouds will likely keep
a lid on insolation driven upward temperature mobility on
Tuesday, however warm advection will continue to do its thing,
resulting in another day with highs straddling 60 across the
region. Fries


The front will enter the region Tuesday night, but it is
questionable whether it will survive the trek across as the
temperature gradient slackens with time. There is some modest
right entrance region support from the 300 mb jet overnight, but
much of the moisture remains to the south and there is little
isentropic help ahead of the front. Will continue with likely
PoPs with the expectation of a light QPF event. A few showers
may linger southeast of Pittsburgh after 12Z Wednesday before
ending by midday.

Flat ridging follows for Wednesday afternoon and evening, with a
dry interlude. By late Wednesday night, developing low level
southwest flow begins to induce isentropic lift and a slow
increase in moisture. This may be enough to produce a touch of
light rain or showers after 06Z Thursday, and have slight chance
PoPs for this.

Little change in airmass will result from the front, and have
continued with temperatures well above climatology.


Not sure how much precipitation will be across the region on
Thursday with a front north of the region. Have continued chance
pops through this period, as well as Thursday night along the
warm front associated with strong low pressure in the central
plains. As warm as this week will be, Friday will likely be the
warmest day of the week, with many locations possibly seeing 70
degrees. A cold front will bring showers along with a chance of
thunderstorms Friday night into Saturday morning, as well as
much more seasonable temperatures. Some scattered showers could
persist into Saturday night, and depending on the timing, may
end as a few snow showers. Expect dry and seasonable weather
Sunday before another chance of rain comes with a system racing
across the Tennessee Valley.


VFR can be expected through much of Tuesday although extensive
high cloudiness will mar the sky. Sfc wind will veer to the south
by daybreak as sfc high pressure gives way to an advancing
trough. Some restrictions will start to edge in from the north
on Tuesday night as a weak system shifts through the Great
Lakes. High uncertainty exists on exactly how much shower
activity will remain as it gets to our region as well as the
degree to which ceilings and visibilities may fall as it passes.

Restrictions are likely with a Friday night/early Saturday cold




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