Scientific Forecaster Discussion
fxus61 kpbz 170223
Area forecast discussion
National Weather Service Pittsburgh PA
923 PM EST Sat Nov 16 2019
dry and cool conditions will continue through Sunday.
Near term /until 6 am Sunday morning/...
no changes were needed for the late eve update.
very cool and dry air (dewpoint temp <10f) will continue to be
advected over the region tonight via easterly flow from northeastern
U.S. Surface high pressure under weak zonal flow aloft. Morning lows
5 to 10 degrees below average may thus be expected again.
Although the thermodynamic profile overnight appears favorable for a
Lee Mountain wave event amid llvl southeasterly flow ovr the ridges,
the balance between strong stability and wind speed does not appear
to be ideal with expected Froude number below 1.0. As a result, the
strength of the inversion above ridge top may be too great for the
wind to overcome, thus suppressing vertical propagation of mountain
waves and limiting stronger wind to the ridge tops.
Short term /6 am Sunday morning through Tuesday night/...
flow aloft will transition to sely on sun/Mon ahead of a trough
amplifying in the nrn plains. The net result will be increasing
warmth (though still remaining slightly below seasonal values) and
increasing chances for precipitation on Mon afternoon/night as a
deformation zone develops aloft to the north of the strengthening
mid-level low's trajectory.
If precipitation occurs (which itself is uncertain), several details
remain unclear with regard to precipitation phase. Although the
current expected track of the upper low appears sufficiently far
south to favor a colder temperature outcome, strong cold advection
is not expected, reinforcing surface high pressure is not
anticipated, and the presence of cloud ice is uncertain.
As a result, precipitation type (if any occurs) could be light snow,
drizzle/freezing drizzle, rain or a time-varying combination of all.
Regardless, at this time significant impacts are not expected from
Long term /Wednesday through Saturday/...
by Wed, the upper pattern will shift toward short-lived shortwave
ridging, suggesting dry conditions and a modest increase in warmth
during the middle part of the coming week.
A strong low will advance across the nrn Continental U.S. Late in the week,
leading to unsettled wx and possibly gusty wind by end of week.
Aviation /03z Sunday through Thursday/...
VFR is expected through the taf period as high pressure to the
northeast and weak shortwave ridging will dominant the region.
restrictions are likely early next week with the passage of a low