Scientific Forecaster Discussion
fxus61 kpbz 181829
Area forecast discussion
National Weather Service Pittsburgh PA
229 PM EDT Fri Oct 18 2019
high pressure provides dry weather through Saturday. Low pressure may
bring rain to areas southeast of Pittsburgh Saturday night and Sunday
as low pressure passes by. A cold front will bring the next
widespread rainfall late Monday night.
Near term /through tonight/...
earlier low clouds have lifted into a scattered-broken cumulus deck.
These will dissipate later with the loss of diurnal heating and the
departure of subzero 850mb temperature.
With the arrival of surface high pressure and a mid-level ridge axis,
clear sky will continue through the night. With light wind and a dry
column, ideal radiational cooling conditions will set up. Frost is
likely areawide, and will issue an advisory for all areas where the
frost/freeze program is still active. Considered a freeze warning for
areas near zzv, but confidence in widespread freezing or below
values was not high enough. An upgrade to this area cannot be ruled
out. Frost will be less likely near the still-warm major rivers,
where steam fog will be prevalent.
Short term /Saturday through Sunday night/...
Saturday will feature plenty of sunshine as the surface high moves
across New England. Some high clouds will show up during the
afternoon on the outer fringes of the extra-tropical low moving into
the southeast Continental U.S.. low-level warm advection will help to push
afternoon high temperatures.
The aforementioned low will lift through the Carolinas with an
associated shortwave Saturday night and Sunday, moving offshore by
00z Monday. Models still have some minor disagreement on the
westward extent of the precipitation shield, with the GFS the least
aggressive with its coverage as compared to the NAM/ECMWF. Will
continue to follow the general model consensus, keeping pops mainly
to the south and east of Pittsburgh.
A return to surface high pressure/flat ridging aloft is then
pictured for Sunday afternoon and night, with dry weather and a
general lack of cloud cover. Southwest flow will become
reestablished, and above-normal temperature will continue.
Long term /Monday through Thursday/...
another deep upper low/trough will lift across the upper Midwest on
Monday, and into Ontario on Tuesday. Deep southwest flow will help to
push temperatures into the 70s for much of the area Monday afternoon.
The surface front is still timed for a Monday night/Tuesday passage,
with likely pops appropriate. While the 500mb trough may take on a
modest negative tilt as it passes, the surface low track and jet
positioning do not point to a strong wind threat. Also, mid-level
flow GOES zonal soon after frontal passage and low-level flow has more of a
westerly component. Thus, unlike the system earlier this week, a
period of low Clouds/Lake enhancement appears less likely.
Behind the system, a period of dry weather and seasonable
temperatures arrives with high pressure for Wednesday and Thursday. A
weak front may approach on Friday with a low rain chance.
Aviation /18z Friday through Wednesday/...
building sfc high pressure, ridge building aloft and the resulting
increased subsidence will slowly erode aftn strato cumulus from the SW to
the NE, and keep the area mostly cloud free through the day
Efficient radiational cooling combined with Warm River waters will
make River Valley steam fog possible Saturday morning. More
widespread fog is unlikely to develop due to the lack of near sfc
restrictions will be possible with a cold frontal passage early next
Ohio...frost advisory from 2 am to 10 am EDT Saturday for ohz039>041-
PA...frost advisory from 2 am to 10 am EDT Saturday for paz020-021-029-
WV...frost advisory from 2 am to 10 am EDT Saturday for wvz001>004-012-