FGUS61 KRHA 102042
ESGRHA

FLOOD POTENTIAL STATEMENT
MIDDLE ATLANTIC RIVER FORECAST CENTER (MARFC)
NATIONAL WEATHER SERVICE STATE COLLEGE PA
 342 PM EST THU JAN 10 2013 

WINTER/SPRING RIVER FLOOD POTENTIAL OUTLOOK
NWS MIDDLE ATLANTIC RIVER FORECAST CENTER

OUTLOOK NUMBER 13-01 - JANUARY 10, 2013

THIS OUTLOOK IS VALID FOR THE TWO-WEEK PERIOD JANUARY 10-24, 2013.

THIS OUTLOOK ESTIMATES THE POTENTIAL FOR RIVER FLOODING (NOT FLASH
FLOODING) TO DEVELOP ACROSS THE MARFC AREA OF RESPONSIBILITY
(MID-ATLANTIC REGION) BASED ON A CURRENT ASSESSMENT OF
HYDROMETEOROLOGICAL FACTORS WHICH CONTRIBUTE TO RIVER FLOODING.
ACROSS THE MARFC AREA, THESE FACTORS INCLUDE RECENT PRECIPITATION,
SOIL MOISTURE, SNOW COVER AND SNOW WATER EQUIVALENT, RIVER ICE,
STREAMFLOW, FUTURE WEATHER CONDITIONS, AND OTHERS.  THIS OUTLOOK
INCLUDES THE LATEST NWS EXTENDED-RANGE (6-10 AND 8-14 DAY) WEATHER
FORECASTS DISCUSSED BELOW IN THE FUTURE WEATHER CONDITIONS SECTION.
THIS OUTLOOK DOES NOT ADDRESS THE SEVERITY/EXTENT OF ANY FUTURE RIVER
FLOODING.

REMEMBER, IN THE MID-ATLANTIC REGION HEAVY RAINFALL IS THE PRIMARY
FACTOR WHICH LEADS TO RIVER FLOODING.  HEAVY RAINFALL CAN RAPIDLY
CAUSE RIVER FLOODING ANY TIME OF THE YEAR, EVEN WHEN OVERALL RIVER
FLOOD POTENTIAL IS CONSIDERED TO BE LOW OR BELOW AVERAGE.

TWO-WEEK RIVER FLOOD POTENTIAL OUTLOOK - SOMEWHAT ABOVE AVERAGE TO
BELOW AVERAGE.  THE RIVER FLOOD POTENTIAL ACROSS THE MARFC SERVICE
AREA FOR THE NEXT TWO WEEKS THROUGH JANUARY 24, 2013 IS SOMEWHAT ABOVE
AVERAGE ACROSS PORTIONS OF THE SUSQUEHANNA AND DELAWARE BASINS, MAINLY
JUST DURING THE NEXT 5-6 DAYS.  ELSEWHERE, THE RIVER FLOOD POTENTIAL
IS MOSTLY AVERAGE, EXCEPT BELOW AVERAGE IN THE JAMES AND APPOMATTOX
RIVER BASINS IN VIRGINIA.  FACTORS WHICH CONTRIBUTE TO RIVER FLOOD
POTENTIAL ARE ADDRESSED INDIVIDUALLY BELOW.

CURRENT FLOODING - NONE.

RECENT PRECIPITATION - VARIABLE.  PRECIPITATION WITHIN THE MARFC
SERVICE AREA DURING THE LAST 30 DAYS (DECEMBER 12, 2012-JANUARY 8,
2013) RANGED FROM BELOW AVERAGE (50 PERCENT OF NORMAL) ACROSS PORTIONS
OF VIRGINA TO MUCH ABOVE AVERAGE (150-200 PERCENT OF NORMAL) ACROSS
SMALL PORTIONS OF PENNSYLVANIA AND NEW YORK.  IN GENERAL, DURING THE
LAST 30 DAYS NORTHERN AREAS HAVE RECEIVED MORE PRECIPITATION RELATIVE
TO NORMAL THAN SOUTHERN AREAS.  NOTEWORTHY IS THE STATE OF VIRGINIA,
WHERE RATHER DRY CONDITIONS HAVE PERSISTED FOR SEVERAL MONTHS NOW,
ESPECIALLY IN THE JAMES RIVER BASIN.  PLEASE VISIT
WWW.ERH.NOAA.GOV/ER/MARFC FOR ADDITIONAL PRECIPITATION INFORMATION.

SNOW CONDITIONS - NEAR AVERAGE.  CURRENTLY WITHIN THE MARFC SERVICE
AREA THERE IS SNOW ON THE GROUND ACROSS THE HIGHER ELEVATIONS OF THE
APPALACHIANS, ACROSS ABOUT THE NORTHERN TWO-THIRDS OF PA, AND IN NY
AND NORTHWESTERN NJ.  THE AREA COVERED BY SNOW IS FAIRLY TYPICAL FOR
THIS TIME OF YEAR.  WHERE SNOW EXISTS, WATER EQUIVALENT VALUES ARE
GENERALLY IN THE 0.5-2.0 INCH RANGE, WITH HIGHER VALUES LIMITED TO THE
HIGHER ELEVATIONS IN THE APPALACHIANS AND ACROSS THE NORTHERN HALF OF
PA AND NY.  SCATTERED VALUES OF 2.5 INCHES EXIST IN THESE REGIONS.
SNOW DEPTHS ARE GENERALLY IN THE 1-12 INCH RANGE, AGAIN WITH SOME
ISOLATED HIGHER AMOUNTS.  AT THIS TIME SNOW CONDITIONS WITHIN THE
MARFC SERVICE AREA ARE CONSIDERED TO BE REASONABLY CLOSE TO AVERAGE,
BOTH IN TERMS OF THE AREAL EXTENT OF THE SNOWPACK AS WELL AS THE
AMOUNT OF WATER CONTAINED WITHIN IT.  PLEASE VISIT WWW.NOHRSC.NOAA.GOV
AND WWW.ERH.NOAA.GOV/ER/MARFC FOR SPECIFICS ON SNOW CONDITIONS.

RIVER ICE - BELOW AVERAGE TO AVERAGE.  LITTLE SIGNIFICANT RIVER ICE
EXISTS WITHIN THE MARFC SERVICE AREA.  THESE CONDITIONS ARE BELOW
AVERAGE FOR JANUARY ACROSS NORTHERN PA AND NY, BUT CLOSER TO AVERAGE
ELSEWHERE, WHERE SIGNIFICANT RIVER ICE OCCURS LESS FREQUENTLY.

STREAMFLOW CONDITIONS - MUCH BELOW MEDIAN TO MEDIAN.  ACCORDING TO THE
U.S. GEOLOGICAL SURVEY (USGS) STREAMFLOW FOR RIVERS WITHIN THE MARFC
REGION CURRENTLY RANGES FROM MUCH BELOW MEDIAN ACROSS PORTIONS OF VA
TO ABOUT MEDIAN ACROSS MOST OF PA, NJ AND NY.  REAL-TIME WATER DATA
CAN BE FOUND BY VISITING THE USGS WEB PAGES AT HTTP://WATER.USGS.GOV/.

SOIL MOISTURE CONDITIONS - VARIABLE.  THE LONG-TERM PALMER DROUGHT
SEVERITY INDEX IS WIDELY USED TO INFER DEEP SOIL MOISTURE CONDITIONS.
THE JANUARY 5, 2013 INDEX CHART (WWW.CPC.NOAA.GOV/PRODUCTS WEBSITE)
INDICATES UNUSUALLY MOIST TO VERY MOIST SOILS ACROSS PORTIONS OF PA,
NY AND AROUND THE CHESAPEAKE BAY REGION.  MEANWHILE, THE CHART SHOWS
MODERATE DROUGHT CONDITIONS ACROSS PORTIONS OF VA.  ELSEWHERE, NEAR
NORMAL SOIL CONDITIONS ARE INDICATED.  FOR ADDITIONAL SOIL MOISTURE
INFORMATION VISIT WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/SOILMST_MONITORING.

GROUND WATER - NORMAL TO BELOW NORMAL.  MOST USGS GROUND WATER
MONITORING WELLS WITHIN THE MARFC REGION ARE INDICATING NEAR NORMAL
LEVELS.  HOWEVER, MANY MONITORING WELLS LOCATED IN THE CHESAPEAKE BAY
REGION AND IN VA ARE SHOWING BELOW NORMAL LEVELS.  PLEASE VISIT
HTTP://GROUNDWATERWATCH.USGS.GOV FOR CURRENT GROUNDWATER LEVELS.

RESERVOIR CONDITIONS - ABOUT AVERAGE.  IN GENERAL, MOST MAJOR
RESERVOIRS WITHIN THE MARFC REGION ARE HOLDING NEAR NORMAL STORAGES
FOR THIS TIME OF YEAR.

FUTURE WEATHER CONDITIONS - UNSEASONABLY MILD WEATHER IS PREDICTED FOR
ALL OF THE MARFC REGION FOR THE NEXT FEW DAYS.  GENERALLY ONLY LIGHT
TO MODERATE PRECIPITATION, MOSTLY RAIN, IS EXPECTED FOR THE NEXT THREE
DAYS, MOSTLY ACROSS THE NORTH.  HOWEVER, SNOWMELT IS ALSO ANTICIPATED.
THEN A SLOW MOVING COLD FRONT ACCOMPANIED BY SEVERAL WAVES OF LOW
PRESSURE WILL PRESS SOUTHEASTWARD THROUGH THE MARFC REGION FROM SUNDAY
(JANUARY 12) THROUGH TUESDAY (JANUARY 15).  RAINFALL WILL ACCOMPANY
THIS SLOW-MOVING WEATHER SYSTEM.  THIS SYSTEM MAY PRODUCE A GENERAL
1-2 INCHES OF RAIN ACROSS MUCH OF THE MARFC REGION, MOSTLY DURING THE
SUNDAY-TUESDAY TIME FRAME.  ONCE THE COLD FRONT FINALLY CLEARS THE
MID-ATLANTIC REGION, A COLDER AND DRIER PATTERN MORE TYPICAL OF
JANUARY LOOKS LIKELY FOR MOST OF THE SECOND WEEK OF THIS OUTLOOK
PERIOD.  THE LATEST (JANUARY 9, 2013) NWS 6-10 DAY AND 8-14 DAY
WEATHER FORECASTS FOR THE MARFC REGION SUGGEST NORMAL TO BELOW NORMAL
TEMPERATURES WHEN AVERAGED OVER THE NINE-DAY PERIOD JANUARY 15-23,
2013.  MEANWHILE, PRECIPITATION WILL MOST LIKELY BE ABOVE NORMAL FOR
THE SAME PERIOD.  PLEASE VISIT WWW.CPC.NCEP.NOAA.GOV.

AHPS RIVER FORECASTS - ABOUT NORMAL.  THE ADVANCED HYDROLOGIC
PREDICTION SERVICE (AHPS) GENERATES PROBABILISTIC RIVER FORECASTS
BASED ON CURRENT BASIN CONDITIONS (RIVER LEVELS, SOIL MOISTURE, EXTENT
AND CONDITION OF ANY SNOWPACK) ALONG WITH 50 YEARS OF HISTORIC
TEMPERATURE AND PRECIPITATION DATA.  REMEMBER, AHPS RIVER FORECASTS DO
NOT TAKE INTO ACCOUNT ACTUAL FUTURE WEATHER CONDITIONS.  FOR THE NEXT
TWO WEEKS (JANUARY 10-14, 2013) AHPS RIVER FORECASTS INDICATE THAT THE
LIKELIHOOD OF RIVER FLOODING WITHIN THE MARFC SERVICE AREA IS
GENERALLY ABOUT AVERAGE.  PLEASE VISIT WWW.WEATHER.GOV/AHPS/ FOR
ADDITIONAL INFORMATION.

ENSEMBLE RIVER FORECASTS - LIMITED RIVER FLOOD THREAT DURING THE NEXT
WEEK ACROSS PORTIONS OF THE SUSQUEHANNA BASIN.  A RELATIVELY NEW TOOL
DEVELOPED BY THE NWS NOW AIDS IN ASSESSING LONGER TERM RIVER FLOOD
POTENTIAL.  THE PROCESS USES PRECIPITATION AND TEMPERATURE DATA
DERIVED FROM NUMEROUS NUMERICAL WEATHER PREDICTION MODELS DIRECTLY AS
INPUT INTO HYDROLOGIC MODELS TO GENERATE RIVER FORECASTS FOR UP TO ONE
WEEK INTO THE FUTURE FOR LOCATIONS WITHIN THE MARFC SERVICE AREA.  THE
RIVER FORECASTS ARE AUTOMATICALLY GENERATED FROM COMPUTER MODELS
WITHOUT THE ADDED EXPERTISE AND EXPERIENCE OF HUMAN FORECASTERS, AND
SEVERAL ASSUMPTIONS ARE MADE IN THE GENERATION OF THE FORECASTS.
SINCE EACH NEW RUN OF WEATHER PREDICTION MODELS CAN GENERATE
DRASTICALLY DIFFERENT FORECASTS OF PRECIPITATION AND TEMPERATURES, THE
RESULTANT RIVER FORECASTS MAY ALSO SHOW DRAMATIC RUN-TO-RUN
VARIABILITY, AS WELL AS VERY WIDE RANGES OF POSSIBILITIES.  THESE
LONG-RANGE FORECASTS SHOULD BE USED WITH CAUTION AND UTILIZED AS
ANOTHER TOOL TO ASSESS RIVER FLOOD POTENTIAL FOR UP TO ONE WEEK INTO
THE FUTURE.  WITH THIS IN MIND, THE MOST RECENT RUNS (JANUARY 10,
2013) OF THE ENSEMBLE RIVER FORECASTS DO INDICATE A MINIMAL THREAT OF
MOSTLY MINOR RIVER FLOODING WITHIN THE SUSQUEHANNA RIVER BASIN DURING
THE NEXT SEVEN DAYS (THROUGH JANUARY 17, 2013).  PLEASE VISIT
WWW.ERH.NOAA.GOV/MMEFS TO VIEW THESE ENSEMBLE RIVER FORECASTS.

SUMMARY - THE RIVER FLOOD POTENTIAL DURING THE NEXT TWO WEEKS THROUGH
JANUARY 24, 2013 VARIES ACROSS THE MARFC REGION.  DURING THE NEXT FIVE
DAYS, MELTING SNOW COMBINED WITH THE POSSIBILITY OF SIGNIFICANT
RAINFALL LEADS TO A SOMEWHAT ABOVE-AVERAGE RIVER FLOOD POTENTIAL FOR
PORTIONS OF THE SUSQUEHANNA AND UPPER DELAWARE RIVER BASINS.  THIS
THREAT WILL DIMINISH BY MID-WEEK NEXT WEEK AS MUCH COLDER TEMPERATURES
RETURN TO THE REGION.  MEANWHILE, THE RIVER FLOOD POTENTIAL ACROSS THE
REMAINDER OF THE MARFC REGION DURING THE NEXT TWO WEEKS IS NEAR
NORMAL, EXCEPT FOR THE JAMES AND APPOMATTOX BASINS IN VIRGINIA WHERE
IT IS SOMEWHAT BELOW NORMAL DUE TO THE EXISTING DRY CONDITIONS.

WATER SUPPLY OUTLOOK - ACCORDING TO THE LATEST (JANUARY 8, 2013)
U.S. DROUGHT MONITOR, MODERATE DROUGHT CONDITIONS ARE FOUND WITHIN THE
MARFC SERVICE AREA IN PORTIONS OF CENTRAL AND SOUTHERN VIRGINIA.  THIS
AREA INCLUDES MUCH OF THE JAMES AND APPOMATTOX RIVER BASINS.  A
DROUGHT WATCH HAS BEEN POSTED BY THE STATE OF VIRGINIA FOR PORTIONS OF
THIS REGION.  STILL, ASSUMING NEAR NORMAL PRECIPITATION DURING THE
NEXT FEW MONTHS, NO WATER SUPPLY SHORTAGES ARE EXPECTED ANYWHERE
WITHIN THE MARFC REGION THROUGH AT LEAST APRIL, 2013.  THE LATEST
(JANUARY 3, 2013) NOAA U.S. SEASONAL DROUGHT OUTLOOK SUGGESTS THE
MODERATE DROUGHT CONDITIONS ACROSS PORTIONS OF VIRGINIA MAY IMPROVE
DURING THE NEXT THREE MONTHS.  PLEASE VISIT WWW.CPC.NCEP.NOAA.GOV AND
WWW.DROUGHT.GOV FOR DROUGHT-RELATED DATA AND CHARTS.

PLEASE VISIT THE NWS MARFC HOMEPAGE AT WWW.ERH.NOAA.GOV/ER/MARFC FOR
OTHER HYDROMETEOROLOGICAL INFORMATION.

THE NEXT WINTER/SPRING FLOOD OUTLOOK WILL BE ISSUED BY THIS OFFICE IN
TWO WEEKS, ON JANUARY 24, 2013.

SK
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