Flood Potential Outlook
Issued by NWS Sterling, VA

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WINTER/SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
230 PM EST THU JAN 22 2015

...2015 WINTER/SPRING FLOOD POTENTIAL OUTLOOK...NUMBER 2

...River Flood Potential Outlook through February 5th...

Introduction:
Each winter and early spring, the National Weather Service office
serving the Baltimore/Washington area issues a series of routine
flood potential outlooks. These outlooks estimate the potential for
river flooding (not flash flooding) across the Baltimore/Washington
Hydrologic Service Area (HSA). This area includes the entire Potomac,
Shenandoah, and Rappahannock River basins, as well as drainage basins
west of, but not including, the Susquehanna in the Upper Chesapeake
Bay.

During this time of year, contributing factors to river flooding come
from recent precipitation, soil moisture conditions, snow cover and
snow water equivalent, river ice, antecedent streamflow, expected
weather conditions, and other factors. This outlook is valid for the
period through February 5th 2015.

In the Mid-Atlantic region, heavy rainfall is the primary factor
which leads to river flooding. Heavy rain can rapidly cause river
flooding at any time of the year, even when river flood potential is
considered to be low or below average.

Two week river flood potential outlook:
In the Baltimore/Washington HSA, the river flood potential is
near average through February 5th.

Current flooding:
None currently across the mid-Atlantic region.

Recent precipitation:
Over the last two weeks, precipitation has been above to well above
normal east of Interstate 95, and below normal west of Interstate
95. On one-month and two-month timescales, precipitation is generally
above normal everywhere except in the Potomac Highlands. On even
longer timescales, precipitation is generally near normal, except
below normal conditions in the Potomac Highlands still exist.

Snow conditions:
A small, but hydrologically insignificant, snowpack exists over much
of Northern Maryland and small portions of Northern Virginia and
Eastern West Virginia. The highest snow depths are along the
Allegheny Front, where depth is around a half foot. These snow
depths are below normal for this time of year.

River ice:
Most of the river ice that formed in early January across portions
of the service area has dissipated. However...river ice is very
likely to increase late this month into early February.

Streamflow conditions:
Rivers in the Baltimore/Washington HSA are generally near normal
levels for this time of year.

Soil moisture:
Soil moisture is near normal across most of the mid-Atlantic region.

Groundwater conditions:
Groundwater conditions are near normal across most of the hydrologic
service area.

Expected weather:
A series of storm systems will affect the region during the upcoming
week. Liquid-equivalent precipitation is expected to be between one
half inch and one inch for most of the area, with again some heavier
amounts possible mainly east of Interstate 95. Below normal
temperatures are very likely, perhaps the coldest of the season.

Probabilistic/Ensemble River Forecasts:
The ensemble river forecasts using the experimental short-term
hydrologic ensemble forecast indicate low flood potential.

The longer-term probabilistic forecasts on the Advanced Hydrologic
Prediction Service indicate a slightly below normal probability of
reaching flood stages through late February, 20 percent or less at
all river forecast points during the one month period.

Summary:
The river flood potential is near average through February 5th.

Water supply outlook:
Assuming near normal precipitation during the next few months, water
supply is expected to remain normal through the spring. No drought
conditions currently exist in the region. Development of drought
conditions is not expected.

Next issuance:
The next issuance of this product will be February 6th 2015.

For additional hydrologic or weather information, visit our website
at http://weather.gov/baltimore or http://weather.gov/washington.

$$

Elliott



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