FXUS61 KPBZ 162001
Area Forecast Discussion
National Weather Service Pittsburgh PA
301 PM EST Sun Dec 16 2018
Precipitation will taper off tonight and Monday, but some light
freezing rain will be possible in some locations. Dry
conditions are then expected through mid-week before the next
low pressure system begins to impact the region on Thursday.
.NEAR TERM /THROUGH MONDAY NIGHT/...
Precipitation types become tricky this evening. Looking at
model soundings, the NAM and GFS both show shallow warm clouds,
with temperatures nowhere near -10C, which is generally the
accepted temperature for when ice crystals begin to form in
clouds. With such warm clouds, this reduces the possibility of
precipitation types to drizzle and freezing drizzle. While no
precipitation is expected to the southwest of Pittsburgh,
precipitation will be possible in all other directions, and
surface temperatures do appear to fall low enough that this
could result in a widespread freezing drizzle/rain scenario.
This scenario continues to be highlighted in the HWO, but there
was not enough confidence in coverage of precipitation to issue
any advisories. Eventually by Monday afternoon cloud top
temperatures will begin to cool enough to produce ice crystals,
moving from north to south. However, some locations will still
have the chance of light freezing rain continuing all the way
into Monday night. Highs will be near normal on Monday, with
lows near normal tonight and about 5 degrees colder Monday
.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
The weather will be quiet during this period as high pressure
takes over across the eastern United States. The next upper
trough is expected to remain far enough west to keep conditions
dry through Wednesday night. Highs will rise above normal
Wednesday. Lows Tuesday night will be similar to those on Monday
night, and rise 5 to 10 degrees higher Wednesday night.
.LONG TERM /THURSDAY THROUGH SUNDAY/...
An upper trough that develops into an upper low still appears to
be the primary weather maker for the first part of the extended
forecast. While the chance for showers will increase Thursday,
have continued with likely pops Thursday night, Friday, and
Friday night. Temperatures should be warm enough Thursday night
and Friday for precipitation to remain all rain, then
temperatures will fall on Friday night with all precipitation
changing over to snow. Conditions should then begin to dry out
on Saturday, and there is some uncertainty as to whether winds
will be favorable to generate lake effect precipitation on
Sunday. After highs in the 40s and 50s on Thursday and Friday,
highs will fall back into the 30s for the weekend.
.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
MVFR conditions will persist across most of the terminals
through the period, though a brief return to VFR may occur where
some scattering of the cloud deck in anticipated in dry
advection behind the departing low. This will be most prevalent
at ZZV, though a window of clearing/scattered stratocu may make
it as far east as Pittsburgh. Confidence in this scenario is not
great, but there was enough model agreement to add it to the
sites mentioned above.
If this period of VFR occurs, it will be short-lived as NW
flow/cold advection resumes.
Cig restrictions are expected Monday in cold northwest flow
followed by a return to VFR through midweek. Restriction
potential returns with Thursday low pressure.
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