Flood Potential Outlook
Issued by NWS

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Winter/Spring Flood Potential Outlook
National Weather Service Pittsburgh PA
248 PM EST Fri Jan 19 2018

...WINTER SPRING FLOOD OUTLOOK THROUGH FEBRUARY 2ND...

The flood potential is above normal in the Upper Ohio Valley.

An above normal flood potential means that flooding could occur
with water levels having significant impacts.

For the long-range river outlooks and the probability of
exceeding flood stage or the chances of flooding relative to
normal at specific forecast points during the next 90 days...refer
to www.weather.gov/ohrfc and click on the 90-day river outlook on
the left hand side of the page. Click on flood chc vs normal to
view the risk of flooding with respect to normal.

Flood outlooks are issued bi-weekly by the national weather
service during winter and early spring to summarize basin
hydrometeorological conditions and to assess the potential for
winter/spring flooding. The outlooks are based on current and
forecast conditions during the outlook period.

In addition...a 90-day water resource outlook is issued monthly.

Factors considered in assessing flood potential are (1)
antecedent conditions (2) past precipitation (3) recent
streamflows and reservoir levels (4) soil moisture (5) water
content of the snow pack (6) ice conditions on the rivers and (7)
future precipitation.

Moderating temperatures last week after two weeks of temperatures
well below freezing created hydrologic problems in the Ohio
Valley. High flows were produced as a result of a combination of
heavy rains and snow melt, and high flows were exacerbated by the
breakup of ice in the rivers. Thus, resulting in ice jams. This
includes the mainstem of the Ohio River where a significant ice
jam was produced at Emsworth Dam, just below Pittsburgh. During
this time, Pittsburgh reached flood stage, which hasn`t happened
since 2011.

Following this brief warm-up, light snows have occurred producing
a 3 to 4 inch snowpack. Snow water equivalents in the snowpack
are one quarter to one third of an inch. A return of arctic air
maintained or produced additional ice on area rivers, with
significant ice still in place in the Beaver, Muskingum, and
Allegheny watersheds.

Flooding concerns remain elevated due to river ice in place, snow
melt, and the system projected for early next week.

$$

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