Scientific Forecaster Discussion
fxus61 kpbz 182327
Area forecast discussion
National Weather Service Pittsburgh PA
627 PM EST Mon Nov 18 2019
broad upper-level low pressure will maintain cooler temperature
across the region. Sporadic patchy drizzle or light rain is possible
tonight and Tuesday.
Near term /until 6 am Tuesday morning/...
subsidence to the north of a closed mid-level low ovr WV has cleared
the sky of all but upper cloudiness this evening. Forcing for
ascent with this upper low will remain predominantly south of the
region as it crosses ewd through tonight. Precipitation chances are
thus minimal, although the nrn fringe of any rain showers may reach
Tucker and Garrett counties. Any accumulation will be quite limited.
Overnight lows under variable cloudiness and neutral advection were
projected near, or just a couple degrees under the averages.
Short term /6 am Tuesday morning through Wednesday night/...
a parade of shortwave troughs embedded in the broad ern-Continental U.S.
Longwave trough will maintain general cloudiness and cooler
temperature Tue and Wed, several degrees below seasonal average.
Low-level moisture will increase significantly below 850 mb on Tue
morning ahead of the first such wave. Forecast soundings suggest
moisture may be deep enough to fuel drizzle Tue morning as the wave
crosses. With air temperature hovering around 32f in the morning, it
is possible there is a brief window for patchy freezing drizzle.
However, reinforcing dry, cool air is non-existent, which will lead
this process to be self-limiting and brief. Given its brevity and
preceding warmer ground, little impact is expected from any freezing
Greater lift will be realized later Tue afternoon as a second trough
crosses. Nevertheless, only sparse and light precipitation coverage
is likely given lack of deep-layer moisture.
Nwly flow in the wake of the second trough will Supply Lake-hydrated
cool air to the region, promoting a broken stratocu deck and low-
end precip chances through the first half of Wed. For any showers in
the mountains or north of I-80, a changeover to snow is probable
late Tue night/Wed morning as thermal profiles will be almost
entirely sub-freezing. Given low-level air temps 32-34f, snow ratios
would be low, and any accumulation would be minimal.
Shortwave ridging in the wake of the mid-level trough will yield
backing wind and an end to any lake-enhanced showers as high pressure
builds into the region.
Long term /Thursday through Monday/...
a strong upper-level trough will move from the nrn plains into the
Great Lakes region on Thu. Ridging downstream from this trough will
limit onset of precipitation with this wave during the morning Thu,
but should be sufficiently east for rain to spread into ern Ohio by Thu
Although the strength of this trough varies among ensembles,
widespread rain is anticipated Thu night/Fri ahead of a cold front
as the wave crosses. Gusty wind may accompany this system given a
strong low-level jet and semi-favorable sfc low position. Gusty nwly
wind will persist in the ridges after the front crosses, given steep
lapse rates in the nwly flow in its wake.
A continued ern-Continental U.S. Trough is expected thereafter, maintaining a
progressive and active weather pattern into early next week.
Aviation /00z Tuesday through Saturday/...
despite crossing low pres, VFR is expected to be maintained until
weak cold advection ensures in the wake of the exiting system. MVFR,
to patchy IFR stratus and possibly some drizzle are anticipated
beginning in the peri-dawn hours of Tuesday. Llvl moisture under
upper troughing should maintain restrictions into Wednesday.
More widespread restrictions are expected with a late-week frontal