FGUS61 KRHA 212031 ESGRHA FLOOD POTENTIAL STATEMENT MIDDLE ATLANTIC RIVER FORECAST CENTER NATIONAL WEATHER SERVICE STATE COLLEGE PA 331 PM EST THU FEB 21 2008 WINTER/SPRING RIVER FLOOD POTENTIAL OUTLOOK MIDDLE ATLANTIC RIVER FORECAST CENTER OUTLOOK NUMBER 08-4 FEBRUARY 21, 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 TWO WEEK PERIOD FEBRUARY 21-MARCH 6, 2008, AND INCLUDES THE LATEST NWS EXTENDED-RANGE (6-10 DAY AND 8-14 DAY) WEATHER FORECASTS. FOR THE MARFC SERVICE AREA, THESE FORECASTS SUGGEST THAT TEMPERATURES AVERAGED OVER THE NINE-DAY PERIOD FROM FEBRUARY 26-MARCH 5, 2008 WILL LIKELY BE BELOW NORMAL TO NORMAL, WHILE PRECIPITATION AVERAGED OVER THE SAME PERIOD WILL LIKELY BE NORMAL TO ABOVE NORMAL. PLEASE VISIT WWW.CPC.NCEP.NOAA.GOV/ TO VIEW MEDIUM AND LONG-RANGE WEATHER OUTLOOKS. 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 - AVERAGE TO SOMEWHAT ABOVE AVERAGE ACROSS THE NORTH, SOMEWHAT BELOW AVERAGE TO THE SOUTH. CURRENT FLOODING - NONE. RECENT PRECIPITATION - VARIABLE. DURING THE LAST 30 DAYS (01/21/08-02/19/08) PRECIPITATION WAS AGAIN BELOW NORMAL TO NORMAL ACROSS VA. PRECIPITATION AMOUNTS FURTHER NORTHWARD WERE NORMAL TO ABOVE NORMAL ACROSS MD, THE DELMARVA PENINSULA, SOUTHEASTERN PA AND SOUTHERN NJ. FINALLY, PRECIPITATION WAS ABOVE NORMAL TO MUCH ABOVE NORMAL ACROSS THE REST OF PA, NY, AND CENTRAL AND NORTHERN NJ. IN GENERAL, MOST LOCATIONS RECEIVED 2-7 INCHES OF PRECIPITATION DURING THE LAST 30-DAYS. THE JAMES BASIN IN CENTRAL VA RECEIVED THE LEAST AMOUNT OF PRECIPITATION (2-3 INCHES) COMPARED TO NORMAL, WHILE THE UPPER DELAWARE AND NEW JERSEY BASINS RECEIVED THE MOST (4-7 INCHES). VISIT WWW.ERH.NOAA.GOV/ER/MARFC TO VIEW PRECIPITATION DEPARTURE MAPS. SNOW CONDITIONS - MUCH BELOW AVERAGE TO ABOUT AVERAGE. ACROSS THE ENTIRE MARFC SERVICE AREA, SNOW CONDITIONS REMAIN RATHER LIMITED. WHILE SOME SNOW HAS FALLEN DURING THE LAST TWO WEEKS, PERIODS OF VERY MILD TEMPERATURES AND RAINFALL HAVE NOT ALLOWED THE SNOW TO PERSIST IN MOST AREAS. PRESENTLY, ALTHOUGH SNOW EXISTS ON THE GROUND ACROSS A FAIR PERCENTAGE OF THE SERVICE AREA, THE DEPTH OF THE SNOW IS GENERALLY ONLY IN THE 1-5 INCH RANGE. IN TERMS OF WATER EQUIVALENT, MOST OF THE SERVICE AREA HAS VALUES OF ABOUT A HALF INCH OR LESS, ALTHOUGH A FEW POCKETS OF 0.5-1.0 INCH WATER EQUIVALENTS EXIST ACROSS THE NORTHERN HALF OF PENNSYLVANIA AND IN THE CATSKILLS. FOR THE MOST PART, THE CURRENT SNOWPACK IS GENERALLY CONSIDERED TO BE HYDROLOGICALLY INSIGNIFICANT. FOR NORTHERN AND WESTERN PORTIONS OF THE MARFC SERVICE AREA, CURRENT SNOW CONDITIONS ARE MUCH BELOW AVERAGE FOR THIS TIME OF YEAR. FOR SOUTHERN AND EASTERN AREAS, SNOW CONDITIONS ARE CLOSER TO AVERAGE SINCE THESE AREAS DO NOT TYPICALLY RECEIVE OR KEEP AS MUCH SNOW ANYWAY. BASIN-AVERAGE WATER EQUIVALENT ESTIMATES CAN BE SEEN AT WWW.ERH.NOAA.GOV/ER/MARFC. IT SHOULD BE NOTED THAT MUCH OF THE CENTRAL THIRD OF THE SERVICE AREA WILL LIKELY RECEIVE A MODERATE SNOWFALL DURING THE NEXT TWO DAYS. RIVER ICE - MUCH BELOW AVERAGE TO AVERAGE. CURRENT RIVER ICE CONDITIONS ACROSS THE MARFC SERVICE AREA ARE AGAIN CONSIDERED MUCH BELOW AVERAGE FOR THIS TIME OF YEAR FOR NORTHERN AND WESTERN AREAS. FOR SOUTHERN AND EASTERN AREAS, RIVER ICE CONDITIONS ARE CLOSER TO NORMAL FOR THIS TIME OF YEAR SINCE THESE RIVERS DO NOT TYPICALLY DEVELOP OR KEEP AS MUCH ICE ANYWAY. PERIODS OF MILD TEMPERATURES, RAINFALL, AND HIGH STREAMFLOW DURING THE LAST TWO WEEKS HAVE ALL COMBINED TO ALLOW LITTLE IN THE WAY OF NEW RIVER ICE FORMATION. LIKE CURRENT SNOW CONDITIONS, AT THIS TIME RIVER ICE CONDITIONS ARE GENERALLY CONSIDERED TO BE HYDROLOGICALLY INSIGNIFICANT WITHIN THE MARFC SERVICE AREA. STREAMFLOW CONDITIONS - VARIABLE. COMPARED TO MEDIAN FOR THIS TIME OF YEAR, STREAMFLOW IS HIGHEST ACROSS NY, CENTRAL AND EASTERN PA AND NORTHERN NJ, WHERE IT IS CURRENTLY ABOVE NORMAL TO MUCH ABOVE NORMAL. MEANWHILE, STREAMFLOW IS BELOW MEDIAN TO MUCH BELOW MEDIAN ACROSS SOUTHERN NJ, SOUTHEASTERN PA, MOST OF MD, VA AND THE DELMARVA PENINSULA. 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 FEBRUARY 16, 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 MUCH OF NJ. ELSEWHERE WITHIN THE MARFC SERVICE AREA 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 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 GENERALLY ABOVE NORMAL ACROSS THE NORTH, NEAR NORMAL ACROSS THE CENTRAL REGION, AND BELOW NORMAL ACROSS THE SOUTH. RESERVOIR CONDITIONS - ABOVE AVERAGE TO BELOW AVERAGE. MOST LARGE WATER SUPPLY AND FLOOD CONTROL RESERVOIRS ARE HOLDING NEAR AVERAGE STORAGES FOR THIS TIME OF YEAR, ALTHOUGH RESERVOIR CONDITIONS ARE GENERALLY SOMEWHAT ABOVE AVERAGE ACROSS THE FAR NORTH, AND BELOW AVERAGE ACROSS PORTIONS OF VA. FUTURE WEATHER CONDITIONS - A STORM SYSTEM WILL BRING MOSTLY MODERATE PRECIPITATION OF UP TO ABOUT AN INCH (WATER EQUIVALENT) TO MUCH OF THE CENTRAL PORTION OF THE MARFC SERVICE AREA FRIDAY AND FRIDAY NIGHT. LIGHTER PRECIPITATION IS EXPECTED ACROSS THE FAR NORTH AND FAR SOUTH. ALL SNOW IS EXPECTED TO THE NORTH, MIXED PRECIPITATION WILL FALL ACROSS THE CENTRAL REGION, WHILE MOSTLY RAIN WILL FALL ACROSS THE SOUTH. MOSTLY DRY, SEASONABLE WEATHER ARRIVES OVER THE WEEKEND BEHIND THE STORM AND PERSISTS UNTIL A COLD FRONT CROSSES THE REGION TUESDAY INTO WEDNESDAY. THIS FRONT WILL ALSO BE ACCOMPANIED BY MOSTLY MODERATE PRECIPITATION WHICH PRESENTLY LOOKS LIKE RAIN FOR MOST AREAS. COLD WEATHER WITH ONLY LIGHT PRECIPITATION FINISHES THE WORK WEEK OUT NEXT WEEK, WITH PERHAPS ANOTHER WEATHER SYSTEM ARRIVING OVER THE WEEKEND OF MARCH 1-2, 2008. MILDER TEMPERATURES APPEAR POSSIBLE DURING AT LEAST THE EARLY PART OF THE WORK WEEK OF MARCH 3-7. AT THE PRESENT TIME THERE ARE NO STRONG INDICATIONS OF ANY WIDESPREAD HEAVY RAIN EVENTS FOR ABOUT THE NEXT WEEK OR SO. IN SUMMARY, FAIRLY TYPICAL WEATHER CONDITIONS ARE INDICATED DURING AT LEAST THE FIRST HALF OF THIS OUTLOOK PERIOD, WITH LITTLE CHANCE FOR FLOOD-PRODUCING RAINFALL. REPEATING THE EXTENDED RANGE WEATHER OUTLOOK FOR THE NINE-DAY PERIOD FEBRUARY 26-MARCH 5: NORMAL TO BELOW NORMAL TEMPERATURES AND NORMAL TO ABOVE-NORMAL PRECIPITATION. 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 TWO WEEKS AHPS INDICATES THAT THE LIKELIHOOD OF RIVER FLOODING IS HIGHEST ACROSS ABOUT THE NORTHERN HALF OF THE MARFC SERVICE AREA WHERE THE CHANCES ARE ABOUT NORMAL, OR A BIT ABOVE NORMAL IN SOME AREAS, FOR THIS TIME OF YEAR. THIS INCLUDES MOST OF THE SUSQUEHANNA BASIN, THE DELAWARE BASIN, AND THE CENTRAL AND NORTHERN NJ BASINS. ELSEWHERE, AHPS INDICATES THE CHANCES OF RIVER FLOODING DURING THE NEXT TWO WEEKS IS NEAR OR SLIGHTLY LESS THAN WHAT HAS BEEN HISTORICALLY OBSERVED. 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 TWO WEEKS WILL REMAIN NORMAL TO SOMEWHAT ABOVE NORMAL FOR THE SUSQUEHANNA, DELAWARE AND NEW JERSEY RIVER BASINS DUE TO HIGH STREAMFLOW AND VERY WET SOILS. BUT WITH LITTLE SNOW AND LITTLE RIVER ICE AT THE PRESENT TIME, THE RIVER FLOOD POTENTIAL IS NOT SIGNIFICANTLY HIGHER THAN NORMAL FOR LATE FEBRUARY. MORE HEAVY RAIN WOULD STILL BE REQUIRED FOR ADDITIONAL WIDESPREAD RIVER FLOODING TO DEVELOP, AND HEAVY RAIN DOES NOT SEEM LIKELY FOR AT LEAST THE NEXT WEEK. ELSEWHERE, THE RIVER FLOOD POTENTIAL DURING THE NEXT TWO WEEKS IS NEAR NORMAL TO BELOW NORMAL. THE SNOWPACK ACROSS THE NORTH WILL INCREASE SOME DURING THE NEXT TWO DAYS DUE TO THE NEXT STORM, BUT SHOULD STILL REMAIN BELOW NORMAL FOR THIS TIME OF YEAR. MILDER TEMPERATURES LATE IN THIS OUTLOOK PERIOD COULD BEGIN TO MELT THE SNOWPACK AGAIN. 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 FEBRUARY 21, 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 NORMAL 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 TWO WEEKS ON MARCH 6, 2008. SK $$ ....END MARFC.... NNNN