Flood Potential Outlook
Issued by NWS Sterling, VA

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WINTER/SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
953 AM EST FRI FEB 5 2016

...2016 WINTER/SPRING FLOOD POTENTIAL OUTLOOK...NUMBER 3

...River Flood Potential Outlook through February 18th...

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 18th 2016.

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 18th.

Current flooding:
As of February 5th...flooding is still ongoing on the mainstem
Shenandoah River and a portion of the Potomac River near Whites
Ferry and Edwards Ferry. All streams and rivers should be below
flood stage within 18 hours.

Recent precipitation:
Precipitation for the last 30 days ranges from less than three
inches in portions of the Potomac Highlands and Virginia Piedmont
to over six inches in a corridor just east of the Blue Ridge and
Catoctin Mountains from Leesburg Virginia to Emmitsburg Maryland.
This is above normal almost everywhere...in some cases more than
twice the normal.

Snow conditions:
As of February 5th...snow conditions vary widely across the
Hydrologic Service Area. Much of the area...including almost the
entire Shenandoah and Rappahannock basins...has no snow cover at
all. Three inches or less is on the ground in portions of the
Potomac Highlands, and an inch or less is on the ground in lower
Southern Maryland. The most snow is in the core of where the
highest amounts were observed during the Blizzard of 2016,
extending from south of Cumberland Maryland to near Frederick
Maryland. In some of these areas, four or five inches of snow
is still on the ground, with around an inch of snow water
equivalent. Snowmelt is expected during the first week of the
outlook period.

River ice:
As of February 5th...most of the river ice broke up during the
recent higher flows. There are still some signals of river ice
on small streams in the eastern West Virginia Panhandle and
Western Maryland. However, these are likely only partial
blockages and temperatures will probably be warm enough to break
them up in the next several days.

Streamflow conditions:
As of February 5th...streamflow levels are much above normal, and
even the highest observed for this date on record in some spots.

Soil moisture:
Soil moisture is well above normal across most of our region.

Groundwater conditions:
Groundwater conditions are generally near normal.

Expected weather:
As of February 5th...seasonably mild temperatures are expected
through early Monday (February 8th) with no precipitation. A
storm system is expected to bring precipitation to the area later
Monday (February 8th) through Tuesday (February 9th). There is
currently uncertainty about precipitation type and amounts, but
there could be snowpack again across much of the area by the end
of the first week of this outlook period (February 11th).

For the second week of the outlook period, confidence is low but
it appears much of the second week will be normal or colder, which
would keep flood potential low. Milder weather might develop for
the final few days of the outlook period. Continue to monitor
forecasts for the latest information.

Probabilistic/Ensemble River Forecasts:
Ensemble River Forecasts from the Meteorological Model Ensemble
River Forecast (MMEFS) indicate little potential for new river
flooding through February 12th. Some renewed rises on rivers are
possible if precipitation early next week falls in the form of
rain for any period of time, but the rain would not be heavy
enough to cause flooding.

The longer range outlooks through early March indicate a near to
above normal flood risk...but this added risk is mainly due to
the current elevated water levels. The risk will decrease as
water levels drop.

Summary:
The river flood potential is near average through February 18th.

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 18th, unless
changing conditions dictate an earlier issuance.

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

$$

J Elliott



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