FGUS61 KRHA 241852 ESGRHA FLOOD POTENTIAL STATEMENT MIDDLE ATLANTIC RIVER FORECAST CENTER NATIONAL WEATHER SERVICE STATE COLLEGE PA 152 PM EST THU JAN 24 2008 WINTER/SPRING RIVER FLOOD POTENTIAL OUTLOOK MIDDLE ATLANTIC RIVER FORECAST CENTER OUTLOOK NUMBER 08-2 JANUARY 24, 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 JANUARY 24-FEBRUARY 7, 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 BOTH TEMPERATURES AND PRECIPITATION AVERAGED OVER THE NINE-DAY PERIOD FROM JANUARY 29-FEBRUARY 6, 2008 WILL MOST LIKELY BE ABOVE NORMAL TO 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 - GENERALLY SOMEWHAT BELOW AVERAGE. CURRENT FLOODING - NONE. RECENT PRECIPITATION - BELOW NORMAL TO NEAR NORMAL. DURING THE LAST 30 DAYS (12/25/07-01/23/08) PRECIPITATION HAS GENERALLY BEEN BELOW NORMAL (50-90% OF NORMAL) ACROSS MOST OF THE MARFC SERVICE AREA. FAR EASTERN AND COASTAL REGIONS, AS WELL AS PORTIONS OF THE POCONO/CATSKILL MOUNTAINS, HAVE FARED BETTER WITH NORMAL OR EVEN SLIGHTLY ABOVE NORMAL PRECIPITATION (100-130% OF NORMAL). CONVERSELY MUCH OF CENTRAL VIRGINIA HAS SEEN ONLY 40-75% OF NORMAL PRECIPITATION DURING THE LAST 30 DAYS. IN GENERAL, MOST LOCATIONS RECEIVED 1-4 INCHES OF PRECIPITATION DURING THE LAST 30-DAYS, WITH SOME ISOLATED 4-5 INCH AMOUNTS ALONG THE COAST. VISIT WWW.ERH.NOAA.GOV/ER/MARFC TO VIEW PRECIPITATION DEPARTURE MAPS. SNOW CONDITIONS - MUCH BELOW AVERAGE TO NEAR AVERAGE. ACROSS MOST OF THE MARFC SERVICE AREA, SNOW COVER IS PRESENTLY MINIMAL AND CAN GENERALLY BE DESCRIBED AS HYDROLOGICALLY INSIGNIFICANT. MOST LOCATIONS HAVE LESS THAN A FEW INCHES OF SNOW ON THE GROUND WHICH CORRESPONDS TO LESS THAN A HALF INCH OF SNOW WATER EQUIVALENT. ISOLATED WATER EQUIVALENT VALUES OF 0.5-1.0 INCHES EXIST IN THE CENTRAL APPALACHIANS. MORE WIDESPREAD 0.5-1.0 INCH VALUES EXIST ACROSS THE POCONOS/CATSKILLS (WITH ISOLATED VALUES OF 1.5 INCHES) AND ACROSS PORTIONS OF THE UPPER SUSQUEHANNA RIVER BASIN IN NEW YORK. 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. SNOW DATA AND INFORMATION SOURCES INCLUDE THE NOAA/NWS NATIONAL OPERATIONAL HYDROLOGIC REMOTE SENSING CENTER (WWW.NOHRSC.NOAA.GOV), THE U.S. ARMY CORPS OF ENGINEERS, NWS COOPERATIVE OBSERVERS, THE COMMUNITY COLLABORATIVE RAIN, HAIL AND SNOW NETWORK (COCORAHS), THE NEW YORK CITY DEPT. OF ENVIRONMENTAL PROTECTION, AND OTHERS. BASIN-AVERAGE WATER EQUIVALENT ESTIMATES CAN BE SEEN AT WWW.ERH.NOAA.GOV/ER/MARFC. RIVER ICE - BELOW AVERAGE TO AVERAGE. COLDER TEMPERATURES SINCE THE FIRST OUTLOOK TWO WEEKS AGO HAVE ALLOWED FOR SOME RIVER ICE FORMATION IN TYPICAL REGIONS ACROSS THE MARFC SERVICE AREA. AT LEAST SOME ICE IS NOW BEING OBSERVED IN MOST STREAMS AND RIVERS WITHIN THE MARFC SERVICE AREA, EXCEPT FOR THOSE IN PORTIONS OF VIRGINIA AND NEAR THE COAST. THE MOST WIDESPREAD RIVER ICE CONDITIONS ARE FOUND ACROSS NORTHERN AREAS, INCLUDING NEW YORK AND THE NORTHERN HALF OF PENNSYLVANIA. ALTHOUGH THERE IS WIDESPREAD RIVER ICE IN THIS REGION, SOME OF IT SIGNIFICANT, ICE CONDITIONS ARE STILL CONSIDERED GENERALLY BELOW AVERAGE FOR THIS TIME OF YEAR. ELSEWHERE WITHIN THE MARFC REGION, RIVER ICE CONDITIONS ARE CLOSER TO NORMAL FOR THIS TIME OF YEAR, MEANING SOME RIVER ICE EXISTS BUT IT IS GENERALLY NOT EXTENSIVE ENOUGH TO BE CONSIDERED HYDROLOGICALLY SIGNIFICANT. STREAMFLOW CONDITIONS - GENERALLY BELOW MEDIAN TO NEAR MEDIAN. COMPARED TO MEDIAN FOR THIS TIME OF YEAR, STREAMFLOW IS HIGHEST ACROSS NY, MOST OF PA AND NJ, AND ACROSS UPPER PORTIONS OF THE POTOMAC BASIN WHERE IT IS CURRENTLY NEAR MEDIAN. HEADING SOUTH, STREAMFLOW DROPS OFF QUICKLY TO BELOW OR EVEN MUCH BELOW MEDIAN ACROSS SOUTHEASTERN PA AND ALL OF MD, DE AND VA. 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 JANUARY 19, 2008, PALMER DROUGHT SEVERITY INDEX CHART (FOUND BY NAVIGATING THE WEBSITE: WWW.CPC.NOAA.GOV/PRODUCTS) IMPLIES WET TO VERY WET SOIL MOISTURE CONDITIONS ACROSS NY, PORTIONS OF PA AND NORTHERN NJ. ELSEWHERE WITHIN THE MARFC SERVICE AREA THE CHART INDICATES NEAR AVERAGE SOIL MOISTURE CONDITIONS FOR THIS TIME OF YEAR, EXCEPT FOR A PORTION OF THE DELMARVA PENINSULA WHERE MODERATE DROUGHT CONDITIONS ARE INDICATED. 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 - MUCH BELOW AVERAGE TO AVERAGE. CURRENT GROUND WATER LEVELS ARE GENERALLY IN THE RANGE OF MUCH BELOW AVERAGE TO AVERAGE ACROSS THE SOUTHERN THIRD OF THE MARFC SERVICE AREA, AND AROUND AVERAGE ACROSS THE NORTHERN TWO-THIRDS. 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 - THE WEATHER DURING THE NEXT WEEK WILL START OUT COLD. WHAT PRESENTLY LOOKS TO BE LIGHT PRECIPITATION WILL CROSS THE REGION THIS WEEKEND WHILE A DEVELOPING OCEANIC STORM OFF THE MID-ATLANTIC COAST SHOULD STAY TOO FAR EAST TO STRONGLY IMPACT THE MARFC REGION. DRY AND GRADUALLY WARMER WEATHER IS EXPECTED EARLY NEXT WEEK UNTIL A COLD FRONT ACCOMPANIED BY LIGHT/MODERATE PRECIPITATION CROSSES THE REGION DURING MIDWEEK. FOLLOWING THE FRONT, DRY AND SEASONABLE WEATHER WILL PRECEDE A POSSIBLE STORM SYSTEM LATE IN THE WEEK NEXT WEEK, WHICH COULD BE ACCOMPANIED BY SOME MODERATE/HEAVY PRECIPITATION. ANOTHER STORM SYSTEM COULD AFFECT THE MARFC REGION FEBRUARY 4-6. IN GENERAL, QUITE CHANGEABLE WEATHER IS ANTICIPATED DURING THE NEXT WEEK OR SO WITH NO STRONG INDICATIONS OF ANY HEAVY RAIN EVENTS BEFORE LATE NEXT WEEK. REPEATING THE EXTENDED RANGE WEATHER OUTLOOK FOR THE NINE DAY PERIOD JANUARY 29-FEBRUARY 6: NORMAL TO ABOVE NORMAL TEMPERATURES AND PRECIPITATION. AHPS FLOOD FORECASTS - BELOW AVERAGE TO AVERAGE. 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 THIS OUTLOOK PERIOD AHPS INDICATES THAT THE LIKELIHOOD OF RIVER FLOODING IS NEAR OR LESS THAN WHAT HAS BEEN HISTORICALLY OBSERVED FOR MOST OF THE MARFC SERVICE AREA. IN GENERAL, THE AHPS INDICATES THAT THE LIKELIHOOD OF RIVER FLOODING DURING THE NEXT TWO WEEKS WITHIN THE MARFC SERVICE AREA IS 0-10% LESS LIKELY THAN WHAT HAS OCCURRED HISTORICALLY DURING THIS TWO-WEEK PERIOD. IT SHOULD BE NOTED THAT, ACCORDING TO HISTORY, RIVER FLOODING DURING THIS TWO-WEEK PERIOD IS NOT LIKELY TO OCCUR TO BEGIN WITH. HISTORY DOES SHOW THAT THE CHANCES OF RIVER FLOODING WITHIN THE MARFC SERVICE AREA DO INCREASE LATER IN FEBRUARY AND MARCH. PLEASE VISIT WWW.WEATHER.GOV/AHPS/ FOR DETAILED AHPS INFORMATION. SUMMARY - THE RIVER FLOOD POTENTIAL FOR THE NEXT TWO WEEKS IS SOMEWHAT BELOW AVERAGE FOR MOST OF THE MARFC SERVICE AREA. EVEN ACROSS THE NORTH, HEAVY RAIN WOULD BE REQUIRED FOR WIDESPREAD SIGNIFICANT RIVER FLOODING TO DEVELOP DUE TO THE CURRENT LIMITED SNOW PACK AND BELOW AVERAGE RIVER ICE CONDITIONS. ONE STORM SYSTEM LATE NEXT WEEK SEEMS TO HAVE SOME POTENTIAL TO PRODUCE SOME HEAVY RAIN. LIKEWISE, LONGER-RANGE WEATHER OUTLOOKS CURRENTLY SUGGEST THAT THE WEATHER CONDITIONS DURING THE SECOND WEEK OF THIS OUTLOOK PERIOD COULD BE WETTER THAN NORMAL. WATER SUPPLY OUTLOOK - MILD-MODERATE DROUGHT CONDITIONS LINGER ACROSS MUCH OF VIRGINIA INTO THE DELMARVA REGION. ALTHOUGH CONDITIONS HAVE GRADUALLY IMPROVED OVER THE LAST FEW MONTHS, THE DROUGHT HAS NOT BEEN ELIMINATED, AND THE LAST 30 DAYS HAS BEEN QUITE DRY FOR MUCH OF CENTRAL VIRGINIA. 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 JANUARY 17, 2008, DOES SUGGEST CONTINUED SLOW IMPROVEMENT ACROSS VIRGINIA DURING THE NEXT TWO-THREE MONTHS. ELSEWHERE, ASSUMING NEAR NORMAL PRECIPITATION OCCURS, NO WATER SUPPLY SHORTAGES ARE ANTICIPATED ANYWHERE WITHIN THE MARFC REGION DURING THE NEXT FIVE MONTHS. 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 FEBRUARY 7, 2008. $$ ....END MARFC.... NNNN