Scientific Forecaster Discussion
fxus61 kpbz 141332
Area forecast discussion
National Weather Service Pittsburgh PA
832 am EST Sat Dec 14 2019
rain will mix with, and change to snow later today and tonight. Dry
weather returns Sunday with building high pressure.
Near term /through tonight/...
Adjustments have been made to total qpf; new snowfall totals
linger at the threshold for a Winter Weather Advisory in the ridges.
However, will hold off issuing a headline until confidence
Rain and fog should continue across the area this morning with an
approaching shortwave trough and its associated sfc low. The low is
progged to track across ern PA to New England this afternoon, with
backing wind and cold advection on the western side. Rain should mix
with and eventually change to snow later today in the cold advection,
though sfc and boundary layer temperatures should be warm enough to
preclude much accumulation outside of the higher terrain and areas
north of I 80.
Will mention 1-3 inches in the higher terrain, though there is a
potential for more if the rain transitions to snow faster in these
areas. Will include an hazardous weather outlook mention for this. An
increasing pressure gradient this afternoon between low pressure to
our east, and high pressure to our west, should result in gusty west-northwest
wind by this afternoon.
Short term /Sunday through Monday night/...
rain and snow should change to all snow this evening as the boundary
layer cools. The snow should taper off later this evening and
overnight for most locations as the main trough axis shifts east.
Limited lake and terrain enhancement should maintain a few snow
showers overnight, though less than optimal westerly wind direction
and a lack of decent moisture in the dendritic layer should limit
Dry weather should return by Sunday afternoon under building high
pressure. The high should move east of the region Sunday night, as a
digging central Continental U.S. Trough moves east. A developing sfc low in
response to the approaching trough, should track from the MS valley
to the Ohio Valley region late Sunday night and Monday, returning
precip to the forecast. Model soundings and critical thicknesses
indicate snow is likely initially Sunday night and Monday morning,
with a transition to mainly rain from S-N.
There could be a brief wintry mix during the transition. At this
time, it appears an inch or two of snow will be possible for some
areas before the transition. Some locally heavy rainfall is also
possible, but placement is in question with uncertainty in the exact
track of the low.
Long term /Tuesday through Friday/...
the central Continental U.S. Trough should maintain precipitation chances
through early Wednesday as it crosses. Mainly dry weather is then
expected through the end of the week under a building ridge. Colder
than average temperatures should return to seasonable levels by
Aviation /13z Saturday through Wednesday/...
widespread IFR/LIFR in rain is expected through much of the day as a
shortwave trough and associated low pressure track across the area.
The low is progged to be across New York this afternoon, with backing wind
and cold advection on the wrn side. Rain should mix with and
eventually change to snow this aftn/eve, with continued IFR. The
upper trough axis should shift east tonight, with scattered snow
showers and some improvement to low end MVFR.
A tightening pressure gradient on the wrn side of the low should
result in gusty west-northwest wind this afternoon and evening.
restrictions are likely again on Monday and Tuesday with The Crossing
of another low pressure system.