FGUS61 KRHA 191901
ESGRHA

FLOOD POTENTIAL STATEMENT
MIDDLE ATLANTIC RIVER FORECAST CENTER (MARFC)
NATIONAL WEATHER SERVICE STATE COLLEGE PA
 201 PM EST THU JAN 19 2012 

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

OUTLOOK NUMBER 12-02 - JANUARY 19, 2012

THIS OUTLOOK IS VALID FOR THE TWO-WEEK PERIOD JANUARY 19-FEBRUARY 2,
2012.

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 - GENERALLY ABOUT AVERAGE.  THE
RIVER FLOOD POTENTIAL FOR THE NEXT TWO WEEKS (THROUGH FEBRUARY 2,
2012) IS ABOUT AVERAGE FOR MID WINTER ACROSS THE MARFC SERVICE AREA.
FACTORS WHICH CONTRIBUTE TO RIVER FLOOD POTENTIAL ARE ADDRESSED
INDIVIDUALLY BELOW.

CURRENT FLOODING - NONE.

RECENT PRECIPITATION - GENERALLY ABOUT AVERAGE.  PRECIPITATION WITHIN
THE MARFC SERVICE AREA DURING THE LAST 30 DAYS (DECEMBER 20,
2011-JANUARY 18, 2012) WAS MOSTLY AROUND AVERAGE (80-120 PERCENT OF
NORMAL).  PORTIONS OF PA AND NY WERE SOMEWHAT WETTER THAN AVERAGE
(100-150 PERCENT OF NORMAL), WHILE SOUTHEASTERN VA AND THE LOWER
DELMARVA PENINSULA WERE SOMEWHAT DRIER THAN NORMAL (50-100 PERCENT OF
NORMAL).  PLEASE VISIT WWW.ERH.NOAA.GOV/ER/MARFC FOR PRECIPITATION
INFORMATION.

SNOW CONDITIONS - MUCH BELOW AVERAGE TO NEAR AVERAGE.  WITH WINTER
ESSENTIALLY HALF OVER, STILL NO HYDROLOGICALLY SIGNIFICANT SNOW EXISTS
ON THE GROUND WITHIN THE MARFC SERVICE AREA.  THIS IS QUITE UNUSUAL
FOR THIS TIME OF YEAR ACROSS ABOUT THE NORTHWESTERN HALF OF THE MARFC
SERVICE AREA WHERE CURRENT SNOW CONDITIONS ARE BELOW AVERAGE TO MUCH
BELOW AVERAGE.  MEANWHILE, FURTHER SOUTH AND EAST CURRENT SNOW
CONDITIONS MAY BE CONSIDERED CLOSER TO AVERAGE AS THIS AREA OFTEN HAS
LITTLE OR NO SNOW ON THE GROUND, EVEN IN MID WINTER.  PLEASE VISIT
WWW.NOHRSC.NOAA.GOV AND WWW.ERH.NOAA.GOV/ER/MARFC FOR SPECIFICS ON
SNOW CONDITIONS.

RIVER ICE - MUCH BELOW AVERAGE TO NEAR AVERAGE.  NO HYDROLOGICALLY
SIGNIFICANT RIVER ICE EXISTS WITHIN THE MARFC SERVICE AREA.  THE LACK
OF SIGNIFICANT RIVER ICE ACROSS THE NORTHWESTERN HALF OF THE MARFC
SERVICE AREA IS AGAIN RATHER UNUSUAL FOR THIS TIME OF YEAR, HENCE
CURRENT RIVER ICE CONDITIONS THERE ARE MUCH BELOW AVERAGE.  FURTHER
SOUTH AND EAST, CURRENT RIVER ICE CONDITIONS ARE CLOSER TO AVERAGE AS
THIS AREA OFTEN HAS LITTLE OR NO RIVER ICE, EVEN IN MID WINTER.
STREAMFLOW CONDITIONS - NEAR MEDIAN TO ABOVE MEDIAN.  STREAMFLOW IS
CURRENTLY IN THE MEDIAN TO ABOVE MEDIAN RANGE ACROSS MUCH OF THE MARFC
REGION.  ACCORDING TO THE U.S. GEOLOGICAL SURVEY (USGS) MOST
STREAMGAGES ACROSS THE MARFC REGION ARE REPORTING FLOWS THAT ARE
80-500 PERCENT OF MEDIAN FOR THIS TIME OF YEAR.  STREAMFLOW IS HIGHEST
WITH RESPECT TO MEDIAN ACROSS THE NORTHERN HALF OF THE MARFC SERVICE
AREA, WHILE FURTHER SOUTH STREAMFLOW IS LOWER WITH RESPECT TO MEDIAN.
SOMEWHAT BELOW MEDIAN FLOW CURRENTLY EXISTS ACROSS THE APPOMATTOX
BASIN IN VA AND ACROSS LOWER PORTIONS OF THE DELMARVA PENINSULA.
REAL-TIME WATER DATA CAN BE FOUND BY VISITING THE USGS WEB PAGES AT
HTTP://WATER.USGS.GOV/.

SOIL MOISTURE CONDITIONS - ABOVE TO MUCH ABOVE NORMAL.  THE LONG-TERM
PALMER DROUGHT SEVERITY INDEX IS WIDELY USED TO INFER DEEP SOIL
MOISTURE CONDITIONS.  THE JANUARY 14, 2012 INDEX CHART
(WWW.CPC.NOAA.GOV/PRODUCTS WEBSITE) INDICATES EXTREMELY MOIST SOILS
ACROSS THE NORTH, WITH UNUSUALLY MOIST TO VERY MOIST SOILS ACROSS THE
SOUTH.  ESPECIALLY ACROSS THE NORTH, THE WET SOILS REFLECT TO SOME
DEGREE THE FACT THAT MUCH OF THE PRECIPITATION SO FAR THIS WINTER HAS
FALLEN AS RAIN INSTEAD OF SNOW.  PLEASE REFER TO
WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/SOILMST_MONITORING FOR INFORMATION.
GROUND WATER - GENERALLY NORMAL TO ABOVE NORMAL.  MOST USGS GROUND
WATER MONITORING WELLS ARE INDICATING ABOVE NORMAL (IN SOME AREAS MUCH
ABOVE NORMAL) LEVELS ACROSS THE NORTHERN TWO-THIRDS OF THE MARFC
SERVICE AREA, WHILE FURTHER SOUTH GROUND WATER CONDITIONS ARE CLOSER
TO NORMAL.  HOWEVER, SOME MONITORING WELLS ACROSS PORTIONS OF THE
CHESAPEAKE BAY REGION ARE SHOWING BELOW NORMAL LEVELS.  PLEASE VISIT
HTTP://GROUNDWATERWATCH.USGS.GOV/.

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

FUTURE WEATHER CONDITIONS - FAIRLY TYPICAL WINTER WEATHER WITH EVEN
SOME SNOW THIS WEEKEND UP NORTH WILL AGAIN LEAN TOWARDS MILD NEXT
WEEK.  SOME LIGHT TO MODERATE RAIN SEEMS LIKELY EARLY NEXT WEEK WITH
SOME INDICATIONS OF A POSSIBLE SIGNIFICANT RAIN EVENT LATE NEXT WEEK,
JANUARY 26-27.  THE LATEST (JANUARY 18, 2012) NWS 6-10 DAY AND 8-14
DAY WEATHER FORECASTS FOR THE MARFC REGION SUGGEST BOTH TEMPERATURES
AND PRECIPITATION WILL BE ABOVE NORMAL WHEN AVERAGED OVER THE NINE-DAY
PERIOD JANUARY 24-FEBRUARY 1, 2012.  THE NWS OUTLOOK FOR THE MARFC
REGION FOR THE REST OF THE WINTER AND INTO EARLY SPRING (THROUGH
APRIL, 2012) SUGGESTS NORMAL TO ABOVE NORMAL TEMPERATURES AND
PRECIPITATION.  PLEASE VISIT WWW.CPC.NCEP.NOAA.GOV.

AHPS RIVER FORECASTS - 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 19-FEBRUARY 2, 2012) AHPS RIVER FORECASTS INDICATE THAT THE
LIKELIHOOD OF RIVER FLOODING IS NEAR AVERAGE FOR THE ENTIRE MARFC
REGION.  PLEASE VISIT WWW.WEATHER.GOV/AHPS/.

EXPERIMENTAL ENSEMBLE RIVER FORECASTS - NO RIVER FLOOD THREAT DURING
ABOUT THE NEXT WEEK ACROSS THE MARFC SERVICE AREA.  A RELATIVELY NEW
TOOL IS CURRENTLY BEING TESTED BY THE NWS TO AID 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 EXPERIMENTAL FORECASTS SHOULD BE USED WITH CAUTION AND TREATED
AS ANOTHER TOOL TO TRY TO ASSESS RIVER FLOOD POTENTIAL FOR UP TO ONE
WEEK INTO THE FUTURE.  WITH THIS IN MIND, THE MOST RECENT RUNS
(JANUARY 19, 2012) OF THE EXPERIMENTAL ENSEMBLE RIVER FORECASTS
INDICATE VIRTUALLY NO THREAT OF RIVER FLOODING WITHIN THE MARFC
SERVICE AREA DURING THE NEXT 6-7 DAYS (THROUGH JANUARY 25, 2012).
PLEASE VISIT WWW.ERH.NOAA.GOV/MMEFS TO VIEW THESE EXPERIMENTAL
FORECASTS.

SUMMARY - WHILE SIXTEEN YEARS AGO TODAY (JANUARY 19, 1996) MUCH OF THE
MARFC REGION WAS IN THE MIDST OF A RECORD-BREAKING MID-WINTER RIVER
FLOOD EVENT, THE RIVER FLOOD POTENTIAL DURING THE NEXT TWO WEEKS
THROUGH FEBRUARY 2, 2012 IS PRETTY CLOSE TO NORMAL.  ALTHOUGH THERE IS
STILL NO SIGNIFICANT SNOW ON THE GROUND AT THIS TIME WITHIN THE MARFC
REGION, SOILS ARE WET AND STREAMFLOW CONDITIONS ARE STILL ELEVATED
ACROSS MOST AREAS.  WHILE PRESENTLY THERE ARE NO STRONG INDICATIONS OF
ANY WIDESPREAD HEAVY RAIN EVENTS FOR THE MARFC SERVICE AREA DURING
ABOUT THE NEXT WEEK OR SO, LONGER RANGE WEATHER OUTLOOKS CONTINUE TO
SUGGEST GENERALLY WARMER AND WETTER THAN NORMAL CONDITIONS DURING THE
NEXT TWO WEEKS.  ADDITIONALLY THERE IS A SUGGESTION OF A SIGNIFICANT
RAIN EVENT SOMETIME AROUND JANUARY 26-27, THOUGH MUCH CAN CHANGE
BEFORE THEN.  TAKEN ALL TOGETHER, DURING THE NEXT TWO WEEKS RIVERS
WITHIN THE MARFC SERVICE AREA WILL CONTINUE TO HAVE ABOUT A NORMAL
CHANCE OF FLOODING FOR THIS TIME OF YEAR.

WATER SUPPLY OUTLOOK - NO DROUGHT CONDITIONS CURRENTLY EXIST WITHIN
THE MARFC REGION, AND ASSUMING NEAR NORMAL PRECIPITATION DURING THE
NEXT FEW MONTHS, NO WATER SUPPLY SHORTAGES ARE EXPECTED ANYWHERE
WITHIN THE MARFC REGION THROUGH AT LEAST APRIL, 2012.  HOWEVER,
ABNORMALLY DRY CONDITIONS DO EXIST ACROSS SOUTHEAST VA AND PORTIONS OF
THE DELMARVA PENINSULA, AND IF BELOW AVERAGE RAINFALL CONTINUES IN
THIS REGION SOME DROUGHT CONDITIONS COULD DEVELOP THERE IN THE NEXT
COUPLE OF MONTHS.  THIS CONCLUSION IS SUPPORTED BY THE LATEST (JANUARY
19, 2012) NOAA U.S. SEASONAL DROUGHT OUTLOOK.  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 ON
THURSDAY, FEBRUARY 2, 2012.

SK
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