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 IN THE POTOMAC HIGHLANDS.

SNOW CONDITIONS...
A SMALL...BUT HYDROLOGICALLY INSIGNIFCANT...SNOWPACK EXISTS OVER
MUCH OF NORTHERN MARYLAND AND SMAL PORTIONS OF NORTHERN VIRGINIA AND
EASTERN WEST VIRGINIA. THE HIGHEST SNOW DEPTHS ARE ALONG THE
ALLEGHENY FRONT...WHERE DEPTH IS NEARLY A HALF A FOOT. THESE SNOW
DEPTHS ARE BELOW NORMAL.

RIVER ICE...
MOST OF THE RIVER ICE THAT FORMED IN EARLY JANUARY ACROSS PORTIONS
OF THE SERVICE AREA HAS DISSIPATED. RIVER ICE IS EXPECTED TO
INCREASE LATE THIS MONTH AND EARLY IN FEBRUARY.

STREAMFLOW CONDITIONS...
RIVERS IN THE BALTIMORE/WASHINGTON HSA ARE GENERALLY BELOW NORMAL
FOR THIS TIME OF YEAR SOUTH AND WEST OF THE WASHINGTON METRO
AREA...AND NEAR NORMAL ELSEWHERE.

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 MAINLY EAST OF INTERSTATE 95. A MIXTURE OF RAIN...
SLEET...FREEZING RAIN...AND SNOW...IS EXPECTED FRIDAY NIGHT INTO
SATURDAY...AND AGAIN SUNDAY NIGHT INTO MONDAY. EACH SYSTEM COULD
PRODUCE ACCUMULATING SNOW FOR AT LEAST A PORTION OF THE AREA.

THE OUTLOOK FOR WEEK TWO...JANUARY 29 THROUGH FEBRUARY 4...STRONGLY
FAVORS BELOW NORMAL TEMPERATURES. NEAR NORMAL PRECIPITATION IS
FAVORED ACROSS MOST OF THE AREA...THOUGH AREAS CLOSEST TO THE BAY
ARE MOST LIKELY TO SEE ABOVE NORMAL PRECIPITATION.

PROBABILISTIC/ENSEMBLE RIVER FORECASTS...
THE ENSEMBLE RIVER FORECASTS USING THE EXPERIMENTAL SHORT-TERM
HYDROLOGIC ENSEMBLE FORECAST INDICATE LOW FLOOD POTENTIAL THROUGH
JANUARY 29TH.

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 WWW.WEATHER.GOV/BALTIMORE OR WEATHER.GOV/WASHINGTON.

$$

ELLIOTT






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