Flood Potential Outlook
Issued by NWS Sterling, VA

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WINTER/SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1100 AM EDT THU MAR 19 2015

...2015 WINTER/SPRING FLOOD POTENTIAL OUTLOOK...NUMBER 7

...River Flood Potential Outlook through April 2nd...

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 April 2nd 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 April 2nd.

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

Recent precipitation:
Over the last week, generally one quarter to three quarters of an
inch of rain has fallen across the area, with the heaviest amounts
north of Baltimore. Except north of Baltimore, these amounts are
below normal for a one-week period. However, heavier rain which
fell the prior week yields a two-week total that is near to above
average. On a one-month timescale, precipitation is generally above
normal except for a few areas in the Potomac Highlands and Nelson
County Virginia. On longer timescales, precipitation is generally
near to above normal, except for below normal conditions in the
Potomac Highlands.

Snow conditions:
There is no snow cover at the time of this report within the
Baltimore/Washington HSA.

River ice:
River ice is no longer a threat for the season. Water temperatures
have risen into the 40s in most areas.

Streamflow conditions:
Most streams in the Baltimore/Washington HSA are near normal for
this time of year.

Soil moisture:
Soil moisture is near to above normal, with the highest soil
moisture in the Potomac Highlands.

Groundwater conditions:
Groundwater levels have become steady but increased during
most of the month of March, and generally are near normal across
most of the hydrologic service area.

Expected weather:
Snow and rain are expected through Friday, March 20th. Total
liquid-equivalent precipitation is expected to be around a half
inch...with snow totals of 3 to 6 inches possible in the eastern
West Virginia panhandle and across much of northern Maryland. A
sharp warmup on Saturday should melt virtually all that snow,
and the relatively low liquid-equivalent should preclude a flood
threat.

There are additional chances for light rain or snow in the
Tuesday March 24th through Thursday March 26th timeframe.
Amounts with these potential systems look to be light at this
time and would not pose a flood threat.

Even though flooding is unlikely in week one of this outlook,
the outlook for week two...March 26th through April 1st...
favors below normal temperatures and above normal precipitation.
It is for this reason that the outlook for the next two weeks
is kept at average.

Probabilistic/Ensemble River Forecasts:
The ensemble river forecasts using the experimental short-term
hydrologic ensemble forecast indicate river rises are possible
during week one of the outlook period (through March 26th), but
flood potential is very low.

The longer-range outlook from the Advanced Hydrologic Prediction
Service indicates near average flood potential, generally 30
percent or less, through mid-April.

Summary:
The river flood potential is near average through April 2nd.

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 currently expected.

Next issuance:
This is the final regularly scheduled issuance of the flood
potential outlook for the season. However, if a higher than average
threat of flooding is anticipated between now and the end of April,
this product could be updated at any time. Outside of the winter
and spring season, information on flood potential out to 7 days is
routinely contained within the Hazardous Weather Outlook (HWO)
product, which is linked from our website below.

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

$$

JE



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