Flood Potential Outlook
Issued by NWS Sterling, VA

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FGUS71 KLWX 171835
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DCC001-MDC001-003-005-009-013-017-021-023-025-027-031-033-037-
043-510-PAC001-009-055-057-VAC013-015-033-043-047-059-061-069-
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027-031-037-057-065-071-312300-

WINTER/SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
235 PM EDT THU MAR 17 2016

...2015 WINTER/SPRING FLOOD POTENTIAL OUTLOOK...NUMBER 6

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.

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.

Short term river flood potential outlook:
In the Baltimore/Washington HSA, the river flood potential is
slightly below average through March 24th. Flood potential returns
to near average for March 25th through March 31st.

Long range river flood potential outlook:
In the Baltimore/Washington HSA, the river flood potential is
slightly below average through mid April.

Current flooding:
As of March 17th...no flooding is occurring in the Baltimore/
Washington HSA.

Recent precipitation:
As of March 17th...precipitation since the beginning of March has
been between a half inch and 1.5 inches in most of the HSA, with
slightly heavier amounts in the far eastern West Virginia
panhandle. This is below normal everywhere, but has served as a
reprieve from the wet conditions of February. Precipitation for
the last 30 days ranges from one to three inches in the rain
shadow regions just east of the Allegheny Front to over five
inches between Baltimore and Conowingo Dam. These amounts are
near to just above normal east of Interstate 81, but have dropped
below normal west of Interstate 81.

Snow conditions:
As of March 17th...there is no snow cover anywhere in the
Baltimore/Washington HSA. Although snow can still occur in the
spring, hydrologically significant snowfall is unlikely for the
remainder of the season.

River ice:
As of March 17th...river ice is no longer a concern and no river
ice of significance is expected for the remainder of the season.

Streamflow conditions:
As of March 17th...streamflow levels have recovered a bit and are
now near normal in most areas. Streamflow in the small tributary
streams to the tidal Potomac are below to well below normal.

Soil moisture:
As of March 17th...soil moisture is near normal across the region.

Groundwater conditions:
Groundwater conditions are generally near normal, though some
below normal conditions exist in the sandy soils of southern
Maryland.

Expected weather:
As of March 17th...light rain or snow is expected this weekend
(March 19th and 20th). Total liquid equivalent precipitation is
expected to be between one half inch and 1.5 inches. These
amounts will fall in a 24 to 36 hour period, and any snow would
melt later, so the precipitation is not expected to be of
enough hydrologic significance to cause anything other than
ponding of water and poor drainage flooding.

After this system, dry weather is expected through most of the
following work week. By Friday, March 25th, another cold front
is expected to approach, and the outlook from the Climate
Prediction Center for week two (March 25th through March 31st)
does favor above normal precipitation.

Probabilistic/Ensemble River Forecasts:
Ensemble River Forecasts from the Meteorological Model Ensemble
River Forecast (MMEFS) indicate almost no potential for river
flooding through March 24th.

The longer range outlooks through mid April indicate a near to
slightly below normal flood risk.

Summary:
The river flood potential is slightly below average through
March 24th. Flood potential returns to near average for March
25th through March 31st. The flood potential is near to
slightly below average through mid April.

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:
This is the final scheduled issuance of this product for spring
2016. If flood potential later this spring starts to appear higher
than normal, there would be an unscheduled issuance of this
outlook. Otherwise the next outlook will be issued in early
January 2017.

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

$$

J Elliott



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