FGUS61 KRHA 132030 ESGRHA FLOOD POTENTIAL STATEMENT MIDDLE ATLANTIC RIVER FORECAST CENTER NATIONAL WEATHER SERVICE STATE COLLEGE PA 430 PM EDT THU MAR 13 2008 WINTER/SPRING RIVER FLOOD POTENTIAL OUTLOOK MIDDLE ATLANTIC RIVER FORECAST CENTER OUTLOOK NUMBER 08-6 MARCH 13, 2008 INTRODUCTION - THE MIDDLE ATLANTIC RIVER FORECAST CENTER (MARFC) IS ONE OF 13 NATIONAL WEATHER SERVICE (NWS) RIVER FORECAST CENTERS LOCATED ACROSS THE CONTINENTAL UNITED STATES. MAJOR RIVER BASINS LOCATED WITHIN THE MARFC AREA OF RESPONSIBILITY INCLUDE THE SUSQUEHANNA, DELAWARE, RARITAN, PASSAIC, POTOMAC, SHENANDOAH, RAPPAHANNOCK, JAMES AND APPOMATTOX. STATES LOCATED WITHIN THE MARFC AREA OF RESPONSIBILITY INCLUDE ALL/PORTIONS OF NEW YORK, PENNSYLVANIA, NEW JERSEY, WEST VIRGINIA, MARYLAND, DELAWARE AND VIRGINIA. THE FOLLOWING OUTLOOK ESTIMATES THE POTENTIAL FOR RIVER FLOODING (NOT FLASH FLOODING) 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 DOES NOT ADDRESS THE SEVERITY/EXTENT OF ANY FUTURE RIVER FLOODING. THIS OUTLOOK IS VALID FOR THE ONE WEEK PERIOD MARCH 13-20, 2008, AND INCLUDES THE LATEST NWS EXTENDED-RANGE (6-10 DAY) WEATHER FORECAST. FOR THE MARFC SERVICE AREA, THIS FORECAST SUGGESTS THAT TEMPERATURES AVERAGED OVER THE FIVE-DAY PERIOD FROM MARCH 18-22, 2008 WILL LIKELY BE NORMAL TO BELOW NORMAL, WHILE PRECIPITATION AVERAGED OVER THE SAME FIVE DAYS WILL LIKELY BE ABOVE NORMAL. TO VIEW MEDIUM AND LONG-RANGE WEATHER OUTLOOKS, PLEASE VISIT WWW.CPC.NCEP.NOAA.GOV/. 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. CURRENT RIVER FLOOD POTENTIAL - VARIABLE. THE RIVER FLOOD POTENTIAL FOR THE NEXT WEEK IS SOMEWHAT ABOVE AVERAGE ACROSS THE NORTHERN TWO THIRDS OF THE MARFC SERVICE AREA, INCLUDING THE SUSQUEHANNA, DELAWARE, POTOMAC AND NEW JERSEY RIVER BASINS. ELSEWHERE, IT IS SOMEWHAT BELOW NORMAL. CURRENT FLOODING - NONE. RECENT PRECIPITATION - VARIABLE. WITHIN THE MARFC SERVICE AREA DURING THE LAST 30 DAYS, (02/12/08-03/12/08) PRECIPITATION WAS MUCH ABOVE NORMAL ACROSS PA, NY AND THE NORTHERN HALF OF NJ. HEADING SOUTH, PRECIPITATION WAS NORMAL TO ABOVE NORMAL ACROSS THE POTOMAC BASIN, THE DELMARVA PENINSULA AND THE SOUTHERN HALF OF NJ. FURTHER SOUTH PRECIPITATION WAS ABOUT NORMAL ACROSS THE RAPPAHANNOCK, SHENANDOAH AND APPOMATTOX BASINS, AND STILL SOMEWHAT BELOW NORMAL ACROSS THE JAMES BASIN. PRECIPITATION WAS GENERALLY IN THE 4-11 INCH RANGE ACROSS MOST OF PA, NY AND THE NORTHERN HALF OF NJ. HEAVIEST AMOUNTS OF 7-11 INCHES FELL ACROSS THE UPPER HALF OF THE DELAWARE RIVER BASIN. ELSEWHERE, PRECIPITATION WAS GENERALLY IN THE 2-7 INCH RANGE. THE JAMES BASIN IN CENTRAL VA ONCE AGAIN RECEIVED THE LEAST AMOUNT OF PRECIPITATION, 2-4 INCHES. PLEASE VISIT WWW.ERH.NOAA.GOV/ER/MARFC TO VIEW PRECIPITATION DEPARTURE MAPS. SNOW CONDITIONS - BELOW AVERAGE TO ABOUT AVERAGE. SNOW COVER IS PRESENTLY LIMITED TO JUST THE NORTHERN THIRD OF THE MARFC SERVICE AREA. EVEN HERE, THE SNOW COVER IS PATCHY AND FOUND MAINLY ACROSS THE HIGHER ELEVATIONS, WITH MANY VALLEYS NOW EXPOSED. WHERE SNOW DOES EXIST, SNOW WATER EQUIVALENT VALUES ARE GENERALLY IN THE 0-2 INCH RANGE, WITH SOME ISOLATED HIGH-ELEVATION AMOUNTS OF 2-3 INCHES. SNOW DEPTHS IN THIS SAME REGION ARE GENERALLY JUST A FEW INCHES, AGAIN WITH SOME ISOLATED HIGH ELEVATION DEPTHS OF 6-18 INCHES. WHERE SNOW EXISTS, THE CURRENT SNOW CONDITIONS ARE GENERALLY CONSIDERED TO BE BELOW AVERAGE TO ABOUT AVERAGE FOR MID MARCH. WHERE SNOW DOES NOT CURRENTLY EXIST (SOUTHERN TWO THIRDS OF THE REGION), SNOW CONDITIONS ARE CONSIDERED ABOUT AVERAGE FOR MOST AREAS FOR MID MARCH. BASIN-AVERAGE WATER EQUIVALENT ESTIMATES CAN BE SEEN AT WWW.ERH.NOAA.GOV/ER/MARFC OR AT WWW.NOHRSC.NOAA.GOV. RIVER ICE - BELOW AVERAGE TO AVERAGE. CURRENTLY, LITTLE OR NO RIVER ICE EXISTS WITHIN THE MARFC SERVICE AREA. FOR UPPER PORTIONS OF THE SUSQUEHANNA AND DELAWARE RIVER BASINS IN NEW YORK, RIVER ICE CONDITIONS ARE STILL SOMEWHAT BELOW AVERAGE FOR THIS TIME OF YEAR. ELSEWHERE, RIVER ICE CONDITIONS ARE ESSENTIALLY NORMAL. STREAMFLOW CONDITIONS - VARIABLE. COMPARED TO MEDIAN FOR THIS TIME OF YEAR, STREAMFLOW REMAINS HIGH ACROSS NY, MOST OF PA AND NORTHERN NJ. HEADING SOUTHWARD, STREAMFLOW DROPS OFF TO ABOUT NORMAL ACROSS THE POTOMAC BASIN, THEN TO BELOW NORMAL ACROSS MUCH OF VA. STREAMFLOW IS ALSO SOMEWHAT BELOW MEDIAN ACROSS MUCH OF THE CHESAPEAKE BAY REGION, ACROSS THE DELMARVA PENINSULA, AND IN PORTIONS OF SOUTHERN NJ. REAL-TIME WATER DATA CAN BE FOUND BY VISITING THE U.S. GEOLOGICAL SURVEY (USGS) WEB PAGES AT HTTP://WATER.USGS.GOV/. SOIL MOISTURE CONDITIONS - VARIABLE. THE MARCH 8, 2008, PALMER DROUGHT SEVERITY INDEX CHART (FOUND BY NAVIGATING THE WEBSITE: WWW.CPC.NOAA.GOV/PRODUCTS) CONTINUES TO INDICATE WET TO EXTREMELY WET SOIL MOISTURE CONDITIONS ACROSS NY, MOST OF PA AND THE NORTHERN HALF OF NJ. UNUSUALLY MOIST CONDITIONS HAVE EXPANDED A LITTLE FURTHER SOUTHWARD INTO NORTHEASTERN WV, MUCH OF MD, NORTHERN DE AND SOUTHERN NJ. ELSEWHERE THE CHART INDICATES NEAR AVERAGE SOIL MOISTURE CONDITIONS FOR THIS TIME OF YEAR. ACTUAL PALMER INDEX VALUES, HOWEVER, AS WELL AS OTHER SOIL MOISTURE AND DROUGHT-RELATED DATA INDICATES PORTIONS OF VA, MD AND A SMALL PORTION OF SOUTHERN DE STILL HAVE BELOW AVERAGE SOIL MOISTURE CONDITIONS FOR THIS TIME OF YEAR. SOIL MOISTURE AND DROUGHT RELATED DATA AND CHARTS CAN BE SEEN AT WWW.CPC.NCEP.NOAA.GOV/SOILMST/ AND WWW.DROUGHT.GOV. GROUND WATER - VARIABLE. SIMILAR TO OTHER CONDITIONS, CURRENT GROUND WATER LEVELS ARE ABOVE NORMAL ACROSS THE NORTH, NEAR NORMAL ACROSS THE CENTRAL REGION, AND BELOW NORMAL ACROSS THE SOUTH. RESERVOIR CONDITIONS - VARIABLE. RESERVOIR CONDITIONS ARE CURRENTLY ABOVE AVERAGE ACROSS THE FAR NORTH, AND BELOW AVERAGE ACROSS PORTIONS OF VA. FUTURE WEATHER CONDITIONS - THE WEATHER PATTERN DURING THE NEXT WEEK IS INDICATING THE POSSIBILITY OF THREE STORM SYSTEMS IMPACTING PORTIONS OF THE MARFC REGION. THE FIRST WILL BE A RATHER WEAK SYSTEM THAT TRACKS THROUGH THE VIRGINIAS FRIDAY AND FRIDAY NIGHT ACCOMPANIED BY MOSTLY LIGHT-MODERATE PRECIPITATION (MOSTLY RAIN). THE SECOND STRONGER SYSTEM TRACKS FURTHER SOUTH THAN THE FIRST AND COULD DROP MODERATE-HEAVY RAIN, ESPECIALLY ACROSS THE SOUTHERN HALF OF THE MARFC REGION AND ALONG THE COAST, OVER THIS WEEKEND. THE THIRD SYSTEM ALSO TRACKS RATHER FAR TO THE SOUTH AND COULD ALSO PRODUCE MODERATE-HEAVY RAIN BEGINNING TUESDAY AND PERSISTING INTO THURSDAY. AT THIS TIME SOUTHERN AND COASTAL REGIONS AGAIN SEEM TO STAND THE BEST CHANCE OF RECEIVING HEAVY RAIN FROM THIS THIRD SYSTEM. IN SUMMARY, A WET WEEK SEEMS LIKELY FOR PORTIONS OF THE MARFC REGION. AT THIS TIME THE HEAVIEST RAIN FOR THE WEEK SEEMS LIKELY TO FALL ACROSS SOUTHERN AND COASTAL REGIONS, BUT ANY CHANGE IN ANY OF THE STORM TRACKS COULD EASILY BRING THE HEAVY RAINS FURTHER NORTHWARD. REPEATING THE LATEST NWS EXTENDED-RANGE (6-10 DAY) WEATHER FORECAST FOR THE MARFC SERVICE AREA: TEMPERATURES AVERAGED OVER THE FIVE-DAY PERIOD FROM MARCH 18-22, 2008 WILL LIKELY BE NORMAL TO BELOW NORMAL, WHILE PRECIPITATION AVERAGED OVER THE SAME FIVE DAYS WILL LIKELY BE ABOVE NORMAL. AHPS FLOOD FORECASTS - VARIABLE. 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. FOR THE NEXT WEEK AHPS INDICATES THAT THE LIKELIHOOD OF RIVER FLOODING IS NEAR NORMAL TO ABOVE NORMAL ACROSS ABOUT THE NORTHERN HALF OF THE MARFC SERVICE AREA, AND SOMEWHAT BELOW NORMAL ACROSS THE SOUTHERN HALF. IT SHOULD BE NOTED THAT MID-MARCH IS, ACCORDING TO HISTORY, THE MOST FLOOD-PRONE TIME OF THE YEAR ACROSS MUCH OF THE MARFC SERVICE AREA, ON AVERAGE. PUT ANOTHER WAY, HISTORY SHOWS THAT RIVER FLOODING SOMEWHERE WITHIN THE MARFC REGION IS A FAIRLY COMMON OCCURRENCE IN MID MARCH. VERY WET SOILS AND HIGH STREAMFLOW ARE THE AHPS FACTORS CURRENTLY FAVORING FLOODING. THE SINGLE AHPS FACTOR THAT IS CURRENTLY DECREASING THE RIVER FLOOD POTENTIAL ACROSS THE NORTH IS THE CONTINUED LIMITED SNOW PACK. WHILE AHPS DOES TAKE INTO ACCOUNT PRECIPITATION THAT HAS OCCURRED IN HISTORY, IT DOES NOT TAKE INTO ACCOUNT FUTURE PRECIPITATION. HEAVY RAINFALL CAN RESULT IN FLOODING ANYWHERE WITHIN THE MARFC REGION, EVEN WHEN OVERALL RIVER FLOOD POTENTIAL IS CONSIDERED TO BE LOW OR BELOW AVERAGE. PLEASE VISIT WWW.WEATHER.GOV/AHPS/ FOR DETAILED AHPS INFORMATION. SUMMARY - THE RIVER FLOOD POTENTIAL FOR THE NEXT WEEK IS SOMEWHAT ABOVE NORMAL FOR THE SUSQUEHANNA, DELAWARE, POTOMAC AND NEW JERSEY RIVER BASINS. HIGH STREAMFLOW AND ABOVE-AVERAGE SOIL MOISTURE CONDITIONS ARE THE FACTORS CAUSING THE ELEVATED FLOOD RISK. IN ADDITION, AT LEAST TWO STORM SYSTEMS HAVE THE POTENTIAL TO PRODUCE SOME HEAVY RAIN DURING THE NEXT WEEK. WHILE THE SOUTHERN HALF OF THE MARFC REGION, ESPECIALLY THE POTOMAC RIVER BASIN, SEEMS TO HAVE THE BEST CHANCE OF RECEIVING HEAVY RAINFALL BASED ON TODAY'S DATA, ANY SHIFT IN INDIVIDUAL STORM TRACKS COULD EASILY BRING HEAVY RAINFALL FURTHER NORTHWARD INTO MORE VULNERABLE AREAS. THESE STORMS WILL NEED TO BE MONITORED CLOSELY. ACROSS CENTRAL AND SOUTHERN VA, THE RIVER FLOOD POTENTIAL FOR THE NEXT WEEK IS NORMAL TO SOMEWHAT BELOW NORMAL. WATER SUPPLY OUTLOOK - MILD-SEVERE DROUGHT CONDITIONS LINGER ACROSS MUCH OF VA, MD AND THE DELMARVA REGION. AS SUCH, WATER SUPPLY SHORTAGES REMAIN POSSIBLE FOR THE SOUTHERN THIRD OF THE MARFC REGION DURING THE NEXT FEW MONTHS UNLESS PRECIPITATION AVERAGES ABOVE NORMAL. THE LATEST SEASONAL DROUGHT OUTLOOK (WWW.DROUGHT.GOV) RELEASED ON MARCH 6, 2008, DOES SUGGEST CONTINUED SLOW IMPROVEMENT ACROSS THE DROUGHT AREA DURING THE NEXT THREE MONTHS. ELSEWHERE, ASSUMING NEAR NORMAL PRECIPITATION OCCURS, NO WATER SUPPLY SHORTAGES ARE ANTICIPATED ANYWHERE WITHIN THE MARFC REGION DURING THE NEXT FIVE MONTHS. THE NWS LONG-RANGE WEATHER OUTLOOK FOR THE MONTH OF MARCH SUGGESTS NORMAL TO ABOVE NORMAL TEMPERATURES AND PRECIPITATION FOR THE MARFC SERVICE AREA. PLEASE VISIT THE NWS MARFC HOMEPAGE AT WWW.ERH.NOAA.GOV/ER/MARFC FOR OTHER HYDROMETEOROLOGICAL INFORMATION. THE NEXT OUTLOOK WILL BE ISSUED BY MARFC IN ONE WEEK ON MARCH 20, 2008. SK $$ ....END MARFC.... NNNN