National Weather Service Text Product Display

Flood Potential Outlook
Issued by NWS Sterling, VA
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WINTER/SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1255 PM EDT THU MAR 21 2013

...2013 WINTER/SPRING FLOOD POTENTIAL OUTLOOK...NUMBER 7

...RIVER FLOOD POTENTIAL OUTLOOK THROUGH APRIL 4TH...

INTRODUCTION...
EACH WINTER AND EARLY SPRING...THE NATIONAL WEATHER SERVICE
OFFICE IN STERLING ISSUES A SERIES OF ROUTINE FLOOD POTENTIAL
OUTLOOKS. THESE OUTLOOKS ESTIMATE THE POTENTIAL FOR RIVER
FLOODING /NOT FLASH FLOODING/ ACROSS THE STERLING HYDROLOGIC
SERVICE AREA /HSA/. THE STERLING HSA 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 4TH 2013.

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 STERLING HSA...THE RIVER FLOOD POTENTIAL IS EXPECTED TO BE
NEAR AVERAGE THROUGH APRIL 4TH.

CURRENT FLOODING...
NONE CURRENTLY ACROSS THE MID-ATLANTIC REGION.

RECENT PRECIPITATION...
RAINFALL IN THE LAST SEVEN DAYS HAS BEEN AS LIGHT AS A QUARTER INCH
IN SOME SPOTS. A WEST-EAST BAND FROM GRANT COUNTY WEST VIRGINIA TO
SHENANDOAH COUNTY VIRGINIA TO FREDERICKSBURG VIRGINIA SAW OVER ONE
INCH OF LIQUID PRECIPITATION DURING THE LAST WEEK. THESE AMOUNTS...
EXCEPT FOR THE HEAVIEST PRECIPITATION...ARE BELOW NORMAL.
PRECIPITATION AT LONGER TIME PERIODS...30 TO 180 DAYS...IS GENERALLY
ABOVE NORMAL IN MOST OF THE MID-ATLANTIC REGION. A FEW SPOTS HAVE
SEEN OVER A FOOT OF RAIN IN THE LAST 90 DAYS.

SNOW CONDITIONS...
ALTHOUGH A LITTLE SNOW OCCURRED EARLIER TODAY...THIS WAS OVERALL
INSIGNIFICANT. HIGHER SNOW DEPTHS OF 4 TO 8 INCHES EXIST ATOP THE
UPPER PORTION OF THE BLUE RIDGE NEAR BIG MEADOWS...AND IN THE
HIGHLANDS WEST OF THE SOUTHERN SHENANDOAH VALLEY. ISOLATED SPOTS
ALONG THE ALLEGHENY FRONT MAY HAVE OVER A FOOT OF SNOW ON THE GROUND
AS OF THURSDAY MARCH 21ST. THESE AMOUNTS ARE ACTUALLY A LITTLE ABOVE
NORMAL FOR THIS LATE IN THE SEASON...BUT THE SNOWPACK IS SMALL
ENOUGH THAT THE REMAINING AMOUNTS WOULD NOT SIGNIFICANTLY CONTRIBUTE
TO A FLOOD SITUATION.

RIVER ICE...
THE RIVER ICE SEASON HAS ENDED.

STREAMFLOW CONDITIONS...
RIVERS IN THE STERLING HSA ARE NEAR NORMAL FOR THIS TIME OF YEAR.
SOME OBSERVED STREAMFLOWS AND LONG-TERM MEDIAN FLOWS FOR MARCH 21ST:

LOCATION                    OBSERVED          MEDIAN
NB POTOMAC/BARNUM           1140 CFS          975 CFS
NB POTOMAC/CUMBERLAND       2790 CFS         2290 CFS
SB POTOMAC/PETERSBURG       2130 CFS         1270 CFS
SB POTOMAC/SPRINGFIELD      4250 CFS         2280 CFS
CACAPON/GREAT CACAPON       1380 CFS          865 CFS
MONOCACY/FREDERICK I-70     1220 CFS         1300 CFS
POTOMAC/PAW PAW             8660 CFS         5950 CFS
POTOMAC/POINT OF ROCKS     18400 CFS        15000 CFS
POTOMAC/LITTLE FALLS       19200 CFS        17300 CFS
SF SHENANDOAH/FRONT ROYAL   3870 CFS         2010 CFS
NF SHENANDOAH/STRASBURG     2170 CFS          735 CFS
SHENANDOAH/MILLVILLE        7040 CFS         3340 CFS
OPEQUON/MARTINSBURG          298 CFS          389 CFS
RAPPAHANNOCK/REMINGTON      1350 CFS          914 CFS
RAPPAHANNOCK/FREDERICKSBG   3290 CFS         1860 CFS
RAPIDAN/CULPEPER            2025 CFS          607 CFS
PATUXENT/BOWIE               298 CFS          416 CFS

SOIL MOISTURE...
SOIL MOISTURE IS NEAR TO ABOVE NORMAL ACROSS THE ENTIRE MID-ATLANTIC
REGION.

GROUNDWATER CONDITIONS...
GROUNDWATER CONDITIONS ARE NEAR TO ABOVE NORMAL ACROSS THE AREA.
THERE ARE STILL A FEW SPOTS BELOW NORMAL BUT THOSE ARE IMPROVING
SOMEWHAT.

EXPECTED WEATHER...
A STORM SYSTEM IS FORECAST TO AFFECT THE AREA LATE THIS WEEKEND INTO
EARLY NEXT WEEK. HOWEVER...PRECIPITATION AMOUNTS ARE CURRENTLY
EXPECTED TO BE LIGHT...A HALF INCH OR LESS. NO SIGNIFICANT
PRECIPITATION IS EXPECTED AFTER THAT FOR SEVERAL DAYS.

THE OUTLOOK FOR WEEK TWO...MARCH 28 THROUGH APRIL 3...FAVORS BELOW
NORMAL PRECIPITATION AND STRONGLY FAVORS BELOW NORMAL TEMPERATURES.

PROBABILISTIC/ENSEMBLE RIVER FORECASTS...
ENSEMBLE RIVER FORECASTS USING THE EXPERIMENTAL SHORT-TERM
HYDROLOGIC ENSEMBLE FORECAST INDICATE THE CHANCE OF REACHING FLOOD
STAGE AT ANY OF THE RIVER FORECAST POINTS IN THE AREA DURING THE
NEXT WEEK IS EXTREMELY LOW...LESS THAN 5 PERCENT.

THE LONGER-TERM PROBABILISTIC FORECASTS ON THE ADVANCED HYDROLOGIC
PREDICTION SERVICE INDICATE A NEAR NORMAL CHANCE OF REACHING FLOOD
STAGE THROUGH MID APRIL. TYPICALLY...THE CHANCE OF REACHING FLOOD
STAGE AT OUR RIVER FORECAST POINTS THIS TIME OF YEAR IS 40 PERCENT
OR LESS AT ALL SITES...AND 25 PERCENT OR LESS AT MOST.

SUMMARY...
THE RIVER FLOOD POTENTIAL THROUGH APRIL 4TH 2013 IS NEAR AVERAGE.

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 LAST CURRENTLY SCHEDULED ISSUANCE OF THIS PRODUCT FOR
THE SPRING. SHOULD ADDITIONAL INFORMATION WARRANT FURTHER
ISSUANCES...THEY WILL BE ISSUED USING THIS PRODUCT IDENTIFIER ON OR
BEFORE MAY 2ND 2013.

FOR ADDITIONAL HYDROLOGIC OR WEATHER INFORMATION...VISIT OUR
WEBSITE AT WWW.WEATHER.GOV/BALTIMORE OR WEATHER.GOV/WASHINGTON.

$$

ELLIOTT
National Weather Service Weather Forecast Office
