Area Forecast Discussion
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FXUS61 KPBZ 211942

Area Forecast Discussion
National Weather Service Pittsburgh PA
342 PM EDT Sun May 21 2017

Periods of rain and some thunderstorms will continue until the
passage of the cold front overnight. Rain chances will return
Tuesday with the approach of mid-atlantic low pressure.


Area of rain, associated with a shortwave ahead of the cold
front, will slowly move across the region through the afternoon.
Enhancement along the lifting surface warm front will support
heavier rain and a few embedded thunderstorms as is already
indicated by radar and progged by hi-res/mesoscale guidance.
Modest instability and 30kts of shear in the low levels may
support a few strong storms, especially in closer proximity to
the cold front this eve over Ohio but the more potent cells
crossing the warm front may also need to be watched, since
directional shear is greatest there.

Will continue to carry categorical PoPs for this first swath of
precipitation but carry likelies through tonight until the cold
front passes.  High PWAT values will support some efficient
rainfall but up to this point, very little training has
occurred. Thus, generally think water issues will be localized.

Front should be approaching the ridges by Monday morning, with
showers ending everywhere by midday. With expected cloud cover
and precipitation, temperatures both today and tonight should be
just around or slightly above seasonal averages.


Conditions should improve by Monday afternoon under building
high pressure and last through at least the start of Tuesday.
The models continue to differ on the evolution of low pressure
moving across the Tennessee valley on Tuesday. At this time,
have opted to bump PoPs up based on some of the newer guidance
and ensembles, as now the GFS seems to be the outlier. Departure
of this low will be quickly followed by yet another system,
again, which is being resolved a little differently between
deterministic models. Opted to stay close to a model blend for
midweek based on the uncertainty.

Temperatures are expected to be near seasonal averages through
the period.


Upper trough and embedded shortwaves will start to shift
eastward toward the end of the week, but it`s influence should
maintain at least low chances for precipitation through the
period based on model consensus. Temperatures will generally
stay just below seasonal averages through the start of the


Area of rain and embedded thunder will continue to move across
the upper Ohio Valley, bringing temporary MVFR and IFR
restrictions as heavier showers pass over a terminal. Some
improvement in cigs is expected before the cold front approaches
tonight. Coverage of showers and thunderstorms should increase
from what is currently being observed across western Ohio.
Expect deterioration in conditions where a thunderstorm passes,
with IFR conditions again possible.

Improvement is expected later tonight (west)and Monday morning
(east) as winds shift westerly and skies quickly clear.

The next chance for widespread restrictions and precipitation is
expected Wednesday night into Thursday.




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