Extended Streamflow Guidance
Issued by NWS Middle Atlantic RFC

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WINTER/SPRING RIVER FLOOD POTENTIAL OUTLOOK
MIDDLE ATLANTIC RIVER FORECAST CENTER
NATIONAL WEATHER SERVICE STATE COLLEGE PA
1235 PM EST THU JAN 18 2017

OUTLOOK NUMBER 17-02 - JANUARY 18, 2017

THIS WINTER/SPRING RIVER FLOOD POTENTIAL OUTLOOK IS VALID FOR THE
TWO-WEEK PERIOD JANUARY 19-FEBRUARY 2, 2017.

THIS OUTLOOK ESTIMATES THE POTENTIAL FOR RIVER FLOODING (NOT FLASH
FLOODING) TO DEVELOP DURING THE NEXT TWO WEEKS ACROSS THE MARFC AREA
OF RESPONSIBILITY (MID-ATLANTIC REGION) BASED ON A CURRENT
ASSESSMENT OF HYDROMETEOROLOGICAL FACTORS WHICH CAN CONTRIBUTE TO
RIVER FLOODING.  ACROSS THE MARFC AREA THESE FACTORS INCLUDE FUTURE
WEATHER CONDITIONS, RECENT PRECIPITATION, SOIL MOISTURE, SNOW COVER
AND SNOW WATER EQUIVALENT, RIVER ICE, STREAMFLOW, AND OTHERS.  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 - THE RIVER FLOOD POTENTIAL FOR MARFC
RIVERS IS AVERAGE/ABOVE AVERAGE FOR THE FIRST WEEK OF THIS OUTLOOK
PERIOD, THROUGH JANUARY 26, 2017.  DURING THE SECOND WEEK OF THIS
OUTLOOK PERIOD THE RIVER FLOOD POTENTIAL DECREASES TO BELOW
AVERAGE/AVERAGE.  FACTORS WHICH CONTRIBUTE TO THIS ASSESSMENT OF
RIVER FLOOD POTENTIAL ARE DISCUSSED IN SOME DETAIL BELOW.

CURRENT FLOODING - NONE.

RECENT PRECIPITATION - GENERALLY BELOW NORMAL.  DURING THE LAST 30
DAYS (DECEMBER 19, 2016-JANUARY 17, 2017) PRECIPITATION (LIQUID
EQUIVALENT) WAS BELOW NORMAL ACROSS MUCH OF THE MARFC REGION.  THE
DRIEST REGIONS RELATIVE TO NORMAL INCLUDED PORTIONS OF SOUTHEASTERN
NY, CENTRAL/EASTERN PA, NJ, DE, CENTRAL/EASTERN MD, PORTIONS OF
EASTERN WV AND CENTRAL/NORTHERN VA.  THESE AREAS RECEIVED 1.5-3.0
INCHES OF PRECIPITATION (WATER EQUIVALENT), WHICH WAS 10-50 PERCENT
BELOW NORMAL.  NEAR-NORMAL OR SOMEWHAT ABOVE-NORMAL PRECIPITATION
WAS OBSERVED ELSEWHERE, WITH AMOUNTS OF 2.0-4.5 INCHES WHICH WAS
ABOUT 10 PERCENT BELOW NORMAL TO ABOUT 30 PERCENT ABOVE.  PLEASE
VISIT WWW.WEATHER.GOV/MARFC, THEN CLICK ON WATER SUPPLY AND THEN ON
DEPARTURES FROM AVERAGE.

SNOW CONDITIONS - AVERAGE TO MUCH-BELOW AVERAGE.  CURRENTLY SNOW
CONDITIONS WITHIN THE MARFC SERVICE AREA ARE ESSENTIALLY
INSIGNIFICANT IN TERMS OF BEING A FACTOR CONTRIBUTING TO RIVER FLOOD
POTENTIAL.  SNOW IS GENERALLY CONFINED TO THE HIGHER ELEVATIONS OF
NY AND IS PATCHY IN NATURE.  FOR ABOUT THE NORTHWEST HALF OF THE
MARFC REGION, CURRENT SNOW CONDITIONS ARE BELOW AVERAGE TO MUCH-
BELOW AVERAGE.  ACROSS ABOUT THE SOUTHEAST HALF, WHERE SNOW ON THE
GROUND IS MUCH LESS COMMON, THE CURRENT LACK OF SNOW IS FAIRLY
TYPICAL.  SNOW INFORMATION CAN BE FOUND BY VISITING
WWW.WEATHER.GOV/MARFC/SNOW AND WWW.NOHRSC.NOAA.GOV.

RIVER ICE - AVERAGE TO MUCH-BELOW AVERAGE.  ALTHOUGH THERE HAS BEEN
SOME RIVER ICE THIS WINTER, CURRENTLY LITTLE IF ANY RIVER ICE IS
FOUND ON/IN MARFC RIVERS.  THIS IS QUITE UNUSUAL FOR MID JANUARY FOR
MOST OF THE SUSQUEHANNA AND DELAWARE RIVER BASINS, BUT IS NOT
UNCOMMON FOR MOST OTHER MARFC RIVER BASINS.  NO RIVER ICE FORMATION
IS EXPECTED DURING ABOUT THE FIRST WEEK OF THIS OUTLOOK PERIOD,
THROUGH AT LEAST JANUARY 25.

STREAMFLOW CONDITIONS - VARIABLE.  THE LATEST DATA FROM THE UNITED
STATES GEOLOGICAL SURVEY (USGS) INDICATE STREAMGAGES ACROSS ABOUT
THE NORTHERN HALF OF THE MARFC SERVICE AREA ARE SHOWING STREAMFLOWS
THAT ARE NEAR-TO-ABOVE MEDIAN FOR MID JANUARY DUE TO THE RECENT RAIN
EVENT.  ACROSS THE SOUTH STREAMFLOWS ARE NEAR-TO-BELOW MEDIAN.
PLEASE VISIT THE USGS WEB PAGES AT WWW.USGS.GOV/WATER FOR STREAMFLOW
DATA.

SOIL MOISTURE CONDITIONS - NORMAL TO BELOW NORMAL.  THE LONG-TERM
PALMER DROUGHT SEVERITY INDEX IS USED TO INFER DEEP SOIL MOISTURE
CONDITIONS.  THE JANUARY 14, 2017 CHART (FOUND AT
WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/ANALYSIS_MONITORING/
REGIONAL_MONITORING/PALMER.GIF) SUGGESTS DEEP SOILS ACROSS MUCH OF
THE MARFC SERVICE AREA CONTAIN MOISTURE THAT IS FAIRLY CLOSE TO
NORMAL FOR THIS TIME OF YEAR.  HOWEVER, OTHER SOIL MOISTURE
INFORMATION (GO TO WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/SOILMST_MONITORING
AND THEN CLICK ON THEN CLICK ON U.S. MONITORING) SHOWS CONSIDERABLE
SOIL MOISTURE DEFICITS REMAIN ACROSS LARGE PORTIONS OF THE MARFC
REGION.  THIS SUPPORTS THE MOST RECENT VERSION (JANUARY 10, 2017) OF
THE U.S. DROUGHT MONITOR CHART WHICH STILL SHOWS LARGE PORTIONS OF
THE MARFC REGION EXPERIENCING ABNORMALLY DRY TO SEVERE DROUGHT
CONDITIONS (HTTP://DROUGHTMONITOR.UNL.EDU).

GROUNDWATER - VARIABLE.  MANY USGS GROUNDWATER MONITORING WELLS
ACROSS THE MARFC REGION ARE CURRENTLY INDICATING GROUNDWATER LEVELS
THAT ARE BELOW OR EVEN MUCH-BELOW THEIR LONG-TERM NORMALS FOR THIS
TIME OF YEAR.  THERE ARE SOME WELLS SCATTERED ACROSS THE REGION WITH
NEAR NORMAL OR EVEN SOMEWHAT ABOVE-NORMAL WATER LEVELS, WITH NO
IDENTIFIABLE PATTERN.  VISIT HTTPS://GROUNDWATERWATCH.USGS.GOV.

RESERVOIR CONDITIONS - BELOW AVERAGE TO AVERAGE.  MOST MAJOR
RESERVOIRS WITHIN THE MARFC REGION ARE HOLDING STORAGES THAT ARE
BELOW AVERAGE/AVERAGE FOR THIS TIME OF YEAR.  RESERVOIR STORAGE IN
THE UPPER DELAWARE RIVER BASIN IS CURRENTLY CONSIDERABLY BELOW THE
LONG-TERM MEDIAN BUT CONTINUES TO SLOWLY IMPROVE.

FUTURE WEATHER CONDITIONS - ABOVE AVERAGE TEMPERATURES WITH LITTLE
CHANCE OF SNOW OR RIVER ICE FORMATION WILL CONTINUE FOR AT LEAST THE
NEXT WEEK FOLLOWED BY INCREASINGLY COLDER WEATHER THEREAFTER.  A
WIDESPREAD SIGNIFICANT RAIN EVENT IS POSSIBLE JANUARY 22-24, 2017.
THIS POTENTIAL RAIN EVENT REPRESENTS THE BIGGEST THREAT FOR RIVER
FLOODING TO DEVELOP DURING THE NEXT TWO WEEKS AND WILL NEED TO BE
MONITORED CLOSELY.  CHECK FOR UPDATES REGARDING THIS THREAT FROM
YOUR LOCAL NWS OFFICE LATER THIS WEEK AND WEEKEND.

AHPS RIVER FORECASTS - NEAR NORMAL TO BELOW NORMAL.  THE ADVANCED
HYDROLOGIC PREDICTION SERVICE (AHPS) GENERATES LONG-TERM (14 DAYS OR
GREATER) 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.  HOWEVER, IT IS IMPORTANT TO NOTE THAT AHPS
RIVER FORECASTS DO NOT TAKE INTO ACCOUNT ACTUAL FUTURE WEATHER
CONDITIONS WHEREAS ENSEMBLE RIVER FORECASTS (SEE NEXT SECTION) DO.
FOR THIS OUTLOOK PERIOD (THROUGH FEBRUARY 2, 2017) CURRENT AHPS
RIVER FORECASTS INDICATE A NEAR OR BELOW-NORMAL CHANCE OF RIVER
FLOODING FOR MOST MARFC RIVERS, DUE PRIMARILY TO THE LACK OF
SIGNIFICANT SNOW CONDITIONS.  THE GREATEST THREAT OF RIVER FLOODING
DEVELOPING DURING THIS OUTLOOK PERIOD IS ASSOCIATED WITH A POSSIBLE
FUTURE HEAVY RAIN EVENT, AND THIS FUTURE EVENT IS NOT INCLUDED IN
THE AHPS RIVER FORECASTS.

ENSEMBLE RIVER FORECASTS - A CONSIDERABLE THREAT OF RIVER FLOODING
DEVELOPING.  THE MOST RECENT RUNS (JANUARY 18, 2017) OF THE ENSEMBLE
RIVER FORECASTS DO SHOW A FAIRLY WIDESPREAD THREAT OF RIVER FLOODING
DEVELOPING AT NUMEROUS FORECAST LOCATIONS WITHIN THE MARFC SERVICE
AREA.  THIS THREAT IS CENTERED AROUND JANUARY 23-25, 2017 AND IS
ASSOCIATED WITH A POSSIBLY SIGNIFICANT RAIN EVENT JANUARY 22-24,
2017.  PLEASE VISIT WWW.WEATHER.GOV/ERH/MMEFS FOR ENSEMBLE RIVER
FORECASTS.

SUMMARY - THE RIVER FLOOD POTENTIAL FOR RIVERS IN THE MARFC REGION
IS AVERAGE TO ABOVE AVERAGE DURING THE FIRST WEEK, AND BELOW AVERAGE
TO AVERAGE THE SECOND WEEK.  HEAVY RAINFALL WOULD BE REQUIRED TO
CAUSE RIVER FLOODING.  A SIGNIFICANT RAIN EVENT IS QUITE POSSIBLE IN
THE SUNDAY-TUESDAY TIME FRAME NEXT WEEK, JANUARY 22-24, 2017.  THIS
RAIN EVENT WILL NEED TO BE MONITORED FOR HEAVY RAIN POTENTIAL THAT
COULD RESULT IN RIVER FLOODING DEVELOPING JANUARY 23-26, 2017.

WATER SUPPLY OUTLOOK - ACCORDING TO THE LATEST (JANUARY 10, 2017)
U.S. DROUGHT MONITOR (HTTP://DROUGHTMONITOR.UNL.EDU), LARGE PORTIONS
OF THE MARFC SERVICE AREA CONTINUE TO SHOW CONDITIONS THAT RANGE
FROM ABNORMALLY DRY TO SEVERE DROUGHT.  LATEST OUTLOOKS SUGGEST
THESE DRY CONDITIONS MAY PERSIST FOR A WHILE LONGER BUT SHOULD
GRADUALLY DIMINISH OVER THE COURSE OF THE NEXT FEW WEEKS.  SO FAR
ONLY ISOLATED AND GENERALLY LOW-IMPACT WATER SUPPLY ISSUES HAVE BEEN
NOTED WITHIN THE MARFC SERVICE AREA IN ASSOCIATION WITH THE DRY
CONDITIONS.  AT THIS TIME, ASSUMING NEAR-NORMAL PRECIPITATION DURING
THE NEXT FEW MONTHS, WIDESPREAD WATER SUPPLY PROBLEMS ARE NOT
ANTICIPATED.  VISIT WWW.DROUGHT.GOV, WWW.CPC.NCEP.NOAA.GOV AND
WWW.WEATHER.GOV/MARFC/WRO_UPDATE FOR ADDITIONAL DROUGHT AND WATER
SUPPLY INFORMATION.

PLEASE VISIT THE NWS MARFC HOMEPAGE AT WWW.WEATHER.GOV/MARFC OR FIND
US ON FACEBOOK AT WWW.FACEBOOK.COM/NWSMARFC/?REF=AYMT_HOMEPAGE_PANEL
AND ON TWITTER @NWSMARFC.

THE NEXT WINTER/SPRING FLOOD OUTLOOK WILL BE ISSUED BY THIS OFFICE
IN TWO WEEKS ON FEBRUARY 2, 2017.

SK
$$

....END MARFC....

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