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
2:13 PM EST THU JAN 04 2018

OUTLOOK NUMBER 18-01 - JANUARY 4, 2018 - CORRECTED FOR SUMMARY
SECTION

THIS WINTER/SPRING RIVER FLOOD POTENTIAL OUTLOOK IS VALID FOR THE
TWO-WEEK PERIOD JANUARY 4-18, 2018.

THIS OUTLOOK ESTIMATES THE POTENTIAL FOR RIVER FLOODING (NOT FLASH
FLOODING) TO DEVELOP DURING THE NEXT TWO WEEKS ACROSS THE MIDDLE
ATLANTIC RIVER FORECAST CENTER`S (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 DURING THE NEXT TWO WEEKS IS BELOW AVERAGE.  FACTORS WHICH
CONTRIBUTE TO THIS ASSESSMENT OF RIVER FLOOD POTENTIAL ARE DISCUSSED
IN SOME DETAIL BELOW.

CURRENT FLOODING - NONE.

RECENT PRECIPITATION - VARIABLE.  DURING THE LAST 30 DAYS (DECEMBER
5-JANUARY 3, 2018) PRECIPITATION (LIQUID EQUIVALENT) WAS BELOW
NORMAL TO MUCH-BELOW NORMAL ACROSS ALL OF THE MARFC SERVICE AREA.

SNOW CONDITIONS - BELOW AVERAGE TO AVERAGE.  SNOW COVERS THE GROUND
ACROSS MOST OF THE MARFC REGION AS OF THIS MORNING, DUE IN PART TO
THE SNOWSTORM CURRENTLY AFFECTING EASTERN PORTIONS OF THE SERVICE
AREA.  ACROSS MOST OF THE AREA SNOW DEPTHS ARE LESS THAN 6 INCHES
AND SNOW WATER EQUIVALENTS ARE LESS THAN A HALF INCH.  OF COURSE
ISOLATED LOCATIONS HAVE SOMEWHAT HIGHER VALUES.  ACROSS EASTERN
PORTIONS OF THE AREA, THE CURRENT SNOWSTORM IS EXPECTED TO DEPOSIT 6-
12+ INCHES OF SNOW, WITH UP TO AN INCH OF WATER EQUIVALENT.  MOST OF
THIS SNOW WILL ACCUMULATE EAST OF MARFC`S RIVER BASINS.  HOWEVER,
RIVER BASINS IN NJ, SOUTHEAST PA AND NORTHERN DE WILL SEE SOME
SIGNIFICANT SNOW FROM THIS STORM.  SNOW CONDITIONS ARE CURRENTLY
CONSIDERED BELOW AVERAGE TO AVERAGE FOR MOST OF THE REGION, AND IN
FACT ARE GENERALLY HYDROLOGICALLY INSIGNIFICANT. WHILE THE CURRENT
SNOWSTORM WILL CREATE ABOVE-AVERAGE SNOW CONDITIONS FOR EXTREME
EASTERN PORTIONS OF THE AREA, THE SIGNIFICANT SNOW WILL BE EAST OF
MOST OF OUR RIVER BASINS.  SNOW INFORMATION CAN BE FOUND BY VISITING
WWW.WEATHER.GOV/MARFC/SNOW AND WWW.NOHRSC.NOAA.GOV.

RIVER ICE - SOMEWHAT ABOVE AVERAGE.  THE UNUSUALLY COLD WEATHER
RECENTLY HAS ALLOWED RIVER ICE TO FORM ACROSS MUCH OF THE MARFC
REGION. BOTH THE EXTENT AND THICKNESS OF THE RIVER ICE IS CONSIDERED
SOMEWHAT ABOVE AVERAGE AT THIS TIME.  AFTER AN EXTREMELY COLD
WEEKEND, MILDER TEMPERATURES ARE ANTICIPATED NEXT WEEK WHICH WILL
BEGIN TO ERODE RIVER ICE ACROSS SOUTHERN AND EASTERN PORTIONS OF THE
REGION.

STREAMFLOW CONDITIONS - BELOW TO MUCH-BELOW AVERAGE.  WHILE MANY
STREAMGAGES ARE CURRENTLY AFFECTED BY ICE, THE LATEST DATA FROM THE
UNITED STATES GEOLOGICAL SURVEY (USGS) INDICATE BELOW-AVERAGE OR
MUCH BELOW-AVERAGE STREAMFLOWS ACROSS THE MARFC AREA.  PLEASE VISIT
THE USGS WEB PAGES AT HTTPS://WATERDATA.USGS.GOV/NWIS/RT FOR CURRENT
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 DECEMBER 30, 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 DETAILED SOIL MOISTURE
INFORMATION (GO TO WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/SOILMST_MONITORING
AND THEN CLICK ON U.S. MONITORING) INDICATES CONSIDERABLE SOIL
MOISTURE DEFICITS ACROSS LARGE PORTIONS OF THE MARFC REGION,
ESPECIALLY EASTERN AND SOUTHERN REGIONS.

GROUNDWATER - MOSTLY BELOW NORMAL.  MOST USGS GROUNDWATER MONITORING
WELLS WITHIN THE MARFC REGION ARE CURRENTLY INDICATING GROUNDWATER
LEVELS THAT ARE BELOW OR MUCH-BELOW THEIR LONG-TERM NORMALS FOR THIS
TIME OF YEAR.  PLEASE 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 BELOW THE LONG-TERM MEDIAN BUT
STILL WITHIN THE NORMAL RANGE.

FUTURE WEATHER CONDITIONS - TODAY`S COASTAL SNOWSTORM WILL MOVE AWAY
FROM THE REGION TONIGHT.  BITTER COLD BUT DRY WEATHER IS EXPECTED
THIS WEEKEND, WITH SOME LAKE EFFECT SNOW IN THE USUAL REGIONS.
MILDER WEATHER, COMPARED TO RECENTLY, IS EXPECTED FOR MUCH OF NEXT
WEEK.  A STORM SYSTEM EARLY NEXT WEEK WILL PRODUCE LIGHT-MODERATE
PRECIPITATION, AS WILL A LATE WEEK STORM SYSTEM.  AT THIS TIME THERE
ARE NO STRONG INDICATIONS OF ANY WIDESPREAD HEAVY RAIN EVENTS FOR AT
LEAST THE NEXT WEEK. LONGER-RANGE WEATHER OUTLOOKS SUGGEST
TEMPERATUHES WILL STAY PRETTY CLOSE TO NORMAL FOR JANUARY, WITH
NORMAL OR ABOVE NORMAL PRECIPITATION.

ENSEMBLE RIVER FORECASTS - NO THREAT OF RIVER FLOODING DEVELOPING.
THE MOST RECENT RUNS (JANUARY 3, 2018) OF THE ENSEMBLE RIVER
FORECASTS, WHICH TAKE INTO ACCOUNT ANTICIPATED FUTURE WEATHER
CONDITIONS INCLUDING PRECIPITATION AND TEMPERATURES, SHOW NO RIVER
FLOODING DEVELOPING WITHIN THE MARFC REGION FOR AT LEAST THE NEXT
WEEK.  NO WIDESPREAD HEAVY RAIN EVENTS ARE ANTICIPATED FOR AT LEAST
THE NEXT WEEK.  PLEASE VISIT WWW.WEATHER.GOV/ERH/MMEFS FOR ENSEMBLE
RIVER FORECASTS.

AHPS RIVER FORECASTS - NEAR 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 PREVIOUS SECTION)
DO.  FOR THIS OUTLOOK PERIOD (THROUGH JANUARY 18, 2018) CURRENT AHPS
RIVER FORECASTS INDICATE BELOW-NORMAL TO NORMAL CHANCES OF RIVER
FLOODING ACROSS THE MARFC REGION.

SUMMARY - FOR THE NEXT TWO WEEKS THE RIVER FLOOD POTENTIAL FOR
RIVERS IN THE MARFC REGION IS BELOW AVERAGE.   AT THIS TIME NO
WIDESPREAD SIGNIFICANT RAIN EVENTS ARE INDICATED FOR AT LEAST THE
NEXT WEEK.  LOW STREAMFLOWS, DRY SOILS AND LIMITED SNOW CONDITIONS
ARE ALSO HELPING CREATE THE BELOW AVERAGE RIVER FLOOD THREAT.

WATER SUPPLY OUTLOOK - ACCORDING TO THE LATEST (JANUARY 4, 2018)
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 MODERATE DROUGHT.  DRIEST REGIONS ARE ACROSS
THE SOUTH AND EAST.  ABOVE-AVERAGE PRECIPITATION THIS WINTER WOULD
BE BENEFICIAL ACROSS MOST OF THE MARFC REGION TO PREVENT MORE
SERIOUS WATER SUPPLY PROBLEMS FROM DEVELOPING THIS SPRING AND
SUMMER.  VISIT WWW.DROUGHT.GOV, WWW.CPC.NCEP.NOAA.GOV AND
WWW.WEATHER.GOV/MARFC/WRO_NORTH 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 JANUARY 18, 2018.

SK
$$

....END MARFC....

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