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 3:05 PM EST THU JAN 18 2018

OUTLOOK NUMBER 18-02 - JANUARY 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,
NOR THE LOCATION OR EXTENT OF LOCALIZED FLOODING DUE TO ICE JAMS.
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 - AVERAGE TO BELOW AVERAGE

THE RIVER FLOOD POTENTIAL FOR MARFC RIVERS DURING THE NEXT TWO WEEKS
(JANUARY 18-FEBRUARY 1, 2018) IS NEAR AVERAGE ACROSS ABOUT THE
NORTHERN HALF OF THE MARFC REGION, AND BELOW AVERAGE ACROSS THE
SOUTHERN HALF.  FACTORS WHICH CONTRIBUTE TO THIS ASSESSMENT OF RIVER
FLOOD POTENTIAL ARE DISCUSSED IN SOME DETAIL BELOW.

CURRENT FLOODING - NONE AT ANY MARFC FORECAST POINTS

NO MARFC FORECAST POINTS ARE CURRENTLY ABOVE FLOOD STAGE WITHIN THE
MARFC REGION. HOWEVER, IT IS POSSIBLE THAT SOME HIGHLY LOCALIZED
FLOODING DUE TO ICE JAMS IS STILL OCCURRING ALONG STRETCHES OF
STREAMS AND RIVERS IN BETWEEN OFFICIAL MARFC FORECAST POINTS.

RECENT PRECIPITATION - VARIABLE

DURING THE LAST 30 DAYS (DECEMBER 18, 2017 - JANUARY 16, 2018)
PRECIPITATION (LIQUID EQUIVALENT) WAS NEAR NORMAL TO ABOVE NORMAL
ACROSS ABOUT THE NORTHERN THIRD OF THE REGION.  FURTHER SOUTH,
PRECIPITATION WAS GENERALLY BELOW NORMAL ACROSS ABOUT THE CENTRAL
THIRD OF THE REGION.  FINALLY ACROSS THE SOUTHERN THIRD OF THE MARFC
REGION PRECIPITATION HAS GENERALLY BEEN MUCH BELOW AVERAGE DURING
THE LAST 30 DAYS.

SNOW CONDITIONS - BELOW AVERAGE TO AVERAGE

SNOW CURRENTLY COVERS THE GROUND ACROSS ABOUT THE NORTHWESTERN HALF
OF MARFC REGION, WHICH IS FAIRLY TYPICAL FOR MID-WINTER.  A FEW TO
SEVERAL INCHES OF SNOW IS ALSO FOUND ACROSS PORTIONS OF VA FROM
YESTERDAY`S SNOW EVENT. HOWEVER THE MOST HYDROLOGICALLY SIGNIFICANT
SNOW WITHIN THE MARFC SERVICE AREA IS FOUND NORTH OF A LINE FROM
ABOUT JOHNSTOWN TO ALLENTOWN, PA, THEN NORTHEASTWARD TO ABOUT
POUGHKEEPSIE, NY.  IN THIS REGION SNOW DEPTHS GENERALLY RANGE FROM 4-
12 INCHES WITH CORRESPONDING WATER EQUIVALENT VALUES OF GENERALLY
0.5-1.5 INCHES. LOCALLY HIGHER AMOUNTS ARE FOUND WITHIN THIS AREA.
IN THIS REGION SNOW CONDITIONS ARE CURRENTLY CONSIDERED PERHAPS A
LITTLE BELOW AVERAGE FOR MID-WINTER.  TO THE SOUTH AND EAST, SNOW
CONDITIONS ARE FAIRLY TYPICAL FOR THIS TIME OF YEAR, THOUGH THE
SEVERAL INCHES OF SNOW CURRENTLY ON THE GROUND IN VA IS A BIT
UNCOMMON.  SNOW INFORMATION CAN BE FOUND BY VISITING
HTTPS://WWW.WEATHER.GOV/MARFC/SNOW AND HTTPS://WWW.NOHRSC.NOAA.GOV.

RIVER ICE - SOMEWHAT ABOVE AVERAGE TO AVERAGE

UNUSUALLY COLD WEATHER FROM LATE DECEMBER THROUGH EARLY JANUARY
ALLOWED CONSIDERABLE RIVER ICE TO FORM ACROSS MUCH OF THE MARFC
REGION.  THEN A MILDER, WETTER WEATHER PATTERN DEVELOPED WHICH BROKE
UP MUCH OF THE RIVER ICE. NUMEROUS ICE JAMS FORMED THROUGHOUT THE
MARFC REGION AS A RESULT OF THE ICE BREAK-UP, LEADING TO ISOLATED
AREAS OF FLOODING.  THE RAIN AND MILDER TEMPERATURES DID NOT FLUSH
THE ICE FROM THE RIVERS COMPLETELY, AND IN FACT MUCH RIVER ICE
REMAINS, ESPECIALLY ACROSS THE NORTHWESTERN HALF OF THE MARFC
REGION.  RIVER ICE CONDITIONS IN THIS REGION REMAIN AVERAGE TO
SOMEWHAT ABOVE AVERAGE FOR MID-WINTER.  WITH A MILDER AND WETTER
WEATHER PATTERN LIKELY DURING THE NEXT WEEK AND PERHAPS LONGER,
ADDITIONAL ICE MOVEMENT IS ANTICIPATED.  AS SUCH, ADDITIONAL ICE
JAMS ARE POSSIBLE WHICH MAY RESULT IN LOCALIZED FLOODING, ESPECIALLY
ALONG STREAMS AND RIVERS IN THE SUSQUEHANNA AND DELAWARE RIVER
BASINS.  MEANWHILE, THERE IS MUCH LESS RIVER ICE REMAINING ACROSS
SOUTHERN AND EASTERN PORTIONS OF THE REGION THAN THERE WAS EVEN A
WEEK AGO, SO ICE CONDITIONS THERE ARE NOW ABOUT AVERAGE.

STREAMFLOW CONDITIONS - VARIABLE

WHILE MANY STREAM GAGES REMAIN AFFECTED BY ICE, THE LATEST
INFORMATION FROM THE UNITED STATES GEOLOGICAL SURVEY (USGS)
INDICATES BELOW-AVERAGE OR MUCH BELOW-AVERAGE STREAM FLOWS CONTINUE
ACROSS MUCH OF THE SOUTHEASTERN HALF OF THE MARFC AREA.  HOWEVER THE
MILD, WET WEATHER OF LAST WEEK ELEVATED STREAMFLOW CONDITIONS ACROSS
THE NORTHWESTERN HALF OF THE REGION BACK TO THE RANGE OF NORMAL TO
MUCH-ABOVE NORMAL.  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 LATEST CHART
(HTTP://WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/ANALYSIS_MONITORING/
REGIONAL_MONITORING/PALMER.GIF) ISSUED ON JANUARY 13, 2018 SUGGESTS
DEEP SOILS ACROSS MUCH OF THE MARFC SERVICE AREA CONTAIN MOISTURE
THAT IS FAIRLY CLOSE TO NORMAL FOR THIS TIME OF YEAR, THOUGH SOME
WETNESS HAS DEVELOPED ACROSS PORTIONS OF PA AND NY DUE TO THE
SNOWMELT AND RAINFALL OF LATE LAST WEEK.  HOWEVER, OTHER DETAILED
SOIL MOISTURE INFORMATION (GO TO
HTTP://WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/SOILMST_MONITORING AND THEN
CLICK ON U.S. MONITORING) INDICATES CONSIDERABLE SOIL MOISTURE
DEFICITS REMAIN ACROSS LARGE PORTIONS OF THE MARFC REGION,
ESPECIALLY EASTERN AND SOUTHERN REGIONS.

GROUNDWATER - NORMAL TO BELOW NORMAL

MOST USGS GROUNDWATER MONITORING WELLS WITHIN THE MARFC REGION ARE
CURRENTLY INDICATING GROUNDWATER LEVELS THAT ARE IN THE NORMAL TO
BELOW NORMAL RANGE. NOTICEABLE IMPROVEMENT HAS BEEN NOTED ACROSS
ABOUT THE NORTHERN HALF OF THE REGION DUE TO THE SNOWMELT/RAINFALL
EVENT IN THAT REGION LATE LAST WEEK.  PLEASE VISIT
HTTPS://GROUNDWATERWATCH.USGS.GOV.

RESERVOIR CONDITIONS - AVERAGE TO BELOW AVERAGE

MOST MAJOR RESERVOIRS WITHIN THE MARFC REGION ARE HOLDING STORAGES
THAT ARE AVERAGE/BELOW AVERAGE FOR THIS TIME OF YEAR.  FOR EXAMPLE,
RESERVOIR STORAGE IN THE UPPER DELAWARE RIVER BASIN IS BELOW THE
LONG-TERM MEDIAN BUT STILL WITHIN THE NORMAL RANGE.

FUTURE WEATHER CONDITIONS - MILDER AND WETTER

MODERATING TEMPERATURES ARE EXPECTED THIS WEEK, ALONG WITH GENERALLY
ONLY LIGHT PRECIPITATION FOR THE NEXT SEVERAL DAYS.  A STORM SYSTEM
AND ITS ASSOCIATED COLD FRONT MAY PRODUCE MODERATE-HEAVY
PRECIPITATION UFFFD MUCH OF WHICH MAY BE RAIN - AROUND NEXT TUESDAY-
WEDNESDAY, JANUARY 23-24.  THIS STORM SHOULD BE CLOSELY MONITORED
FOR ITS POTENTIAL TO CAUSE SNOWMELT AND HEAVY RAINFALL, ESPECIALLY
ACROSS THE NORTHERN HALF OF THE REGION WHERE THE MOST HYDROLOGICALLY
SIGNIFICANT SNOW IS FOUND.  ADDITIONALLY, RIVER ICE MOVEMENT IS
LIKELY AGAIN IN ASSOCIATION WITH THIS WEATHER SYSTEM, AND LOCALIZED
ICE JAM FLOODING IS POSSIBLE ESPECIALLY ALONG STREAMS AND RIVERS
WITHIN THE SUSQUEHANNA AND DELAWARE RIVER BASINS.  LONGER RANGE
WEATHER OUTLOOKS SUGGEST A PRETTY GOOD CHANCE THAT BOTH TEMPERATURES
AND PRECIPITATION MAY END UP ABOVE AVERAGE FOR THE SECOND WEEK OF
THIS TWO-WEEK OUTLOOK PERIOD AS WELL.  PLEASE VISIT
HTTP://WWW.CPC/NCEP.NOAA.GOV FOR LONGER RANGE WEATHER OUTLOOKS.

ENSEMBLE RIVER FORECASTS - NOT AVAILABLE DUE TO MARFC SOFTWARE
UPGRADES TODAY.  WE APOLOGIZE FOR ANY INCONVENIENCE. ENSEMBLE RIVER
FORECASTS CAN NORMALLY BE VIEWED AT
HTTPS://WWW.WEATHER.GOV/ERH/MMEFS.

AHPS RIVER FORECASTS - NOT AVAILABLE DUE TO MARFC SOFTWARE UPGRADES
TODAY.  AGAIN, WE APOLOGIZE FOR ANY INCONVENIENCE.

SUMMARY

FOR THE NEXT TWO WEEKS THE RIVER FLOOD POTENTIAL FOR RIVERS IN THE
MARFC REGION IS ABOUT AVERAGEACROSS ABOUT THE NORTHERN HALF OF THE
REGION, AND BELOW AVERAGE ACROSS THE SOUTHERN HALF.  THERE IS AN
INDICATION THAT A FAIRLY WARM AND WET WEATHER SYSTEM COULD CROSS THE
REGION AROUND NEXT TUESDAY-WEDNESDAY, JANUARY 23-24.  AS SUCH THIS
STORM COULD CAUSE SNOWMELT, MODERATE/HEAVY RAINFALL, AND RIVER ICE
MOVEMENT, ESPECIALLY ACROSS THE NORTHERN HALF OF THE MARFC SERVICE
AREA.  IT IS POSSIBLE THAT SOME RIVER FLOODING COULD RESULT FROM THE
EFFECTS OF THIS POTENTIAL STORM.  THE EVOLUTION OF THIS POTENTIAL
STORM SHOULD BE MONITORED DURING THE NEXT SEVERAL DAYS.

WATER SUPPLY OUTLOOK

ACCORDING TO THE LATEST (JANUARY 9, 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 IN THESE AREAS THIS WINTER WOULD BE
BENEFICIAL TO PREVENT MORE SERIOUS WATER SUPPLY PROBLEMS FROM
DEVELOPING THIS SPRING AND SUMMER. VISIT HTTPS://WWW.DROUGHT.GOV,
HTTP://WWW.CPC.NCEP.NOAA.GOV AND
HTTPS://WWW.WEATHER.GOV/MARFC/WRO_NORTH FOR ADDITIONAL DROUGHT AND
WATER SUPPLY INFORMATION.

PLEASE VISIT THE NWS MARFC HOMEPAGE AT HTTPS://WWW.WEATHER.GOV/MARFC
OR FIND US ON FACEBOOK AT
HTTPS://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/ABOUT FEBRUARY 1, 2018

MARFC/STK

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