FGUS61 KRHA 102120 ESGRHA FLOOD POTENTIAL STATEMENT MIDDLE ATLANTIC RIVER FORECAST CENTER NATIONAL WEATHER SERVICE STATE COLLEGE PA 420 PM EST THU JAN 10 2008 WINTER/SPRING RIVER FLOOD POTENTIAL OUTLOOK MIDDLE ATLANTIC RIVER FORECAST CENTER OUTLOOK NUMBER 08-1 JANUARY 10, 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 10-24, 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 PERIOD FROM JANUARY 16-24, 2008 WILL MOST LIKELY BE NORMAL TO BELOW NORMAL, WHILE PRECIPITATION WILL MOST LIKELY END UP ABOUT 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 ABOUT AVERAGE EXCEPT IN VIRGINIA, WHERE IT IS BELOW AVERAGE. CURRENT FLOODING - NONE. RECENT PRECIPITATION - VARIABLE. DURING THE LAST 30 DAYS (12/10/07-01/08/08) PRECIPITATION HAS RANGED FROM ABOVE AVERAGE (AROUND 150 PERCENT OF NORMAL) ACROSS NORTHEASTERN PORTIONS OF THE MARFC SERVICE AREA TO BELOW AVERAGE (70 PERCENT OF NORMAL) ACROSS SOME SOUTHERN PORTIONS. STILL, MUCH OF THE MARFC REGION RECORDED NEAR AVERAGE PRECIPITATION (75-125 PERCENT OF NORMAL). WETTEST AREAS DURING THE LAST 30 DAYS INCLUDED PORTIONS OF NORTHEASTERN PA, SOUTHEASTERN NY AND NORTHERN NJ, WHILE CENTRAL VA WAS DRIEST. IN GENERAL, MOST LOCATIONS RECEIVED 2-5 INCHES OF PRECIPITATION DURING THE LAST 30-DAYS. VISIT WWW.ERH.NOAA.GOV/ER/MARFC TO VIEW PRECIPITATION DEPARTURE MAPS. SNOW CONDITIONS - AVERAGE TO MUCH BELOW AVERAGE. VERY LITTLE SNOW REMAINS ON THE GROUND ACROSS THE MARFC SERVICE AREA. FOR NORTHERN AND WESTERN AREAS, 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. WHERE PATCHES OF SNOW STILL EXIST, MAINLY ACROSS UPPER PORTIONS OF THE SUSQUEHANNA AND DELAWARE RIVER BASINS IN NY AND NORTHEAST PA, THE SNOW IS HYDROLOGICALLY INSIGNIFICANT WITH SNOW WATER EQUIVALENT VALUES OF ONLY AROUND A HALF INCH OR LESS. SNOW DATA AND INFORMATION CAN BE FOUND AT WWW.NOHRSC.NOAA.GOV AND AT WWW.ERH.NOAA.GOV/ER/MARFC. RIVER ICE - AVERAGE TO MUCH BELOW AVERAGE. THERE IS NO SIGNIFICANT RIVER ICE IN THE MARFC SERVICE AREA AT THE PRESENT TIME. FOR NORTHERN AREAS, INCLUDING NEW YORK AND THE NORTHERN HALF OF PENNSYLVANIA, RIVER ICE CONDITIONS ARE MUCH BELOW AVERAGE FOR EARLY JANUARY. FURTHER SOUTH, RIVER ICE CONDITIONS ARE BELOW AVERAGE ACROSS THE SOUTHERN HALF OF PA AND NORTHERN NJ AND ACROSS THE APPALACHIAN REGION. FINALLY, ACROSS MD AND VA, RIVER ICE CONDITIONS ARE CLOSER TO NORMAL SINCE THESE AREAS DO NOT TYPICALLY SEE AS MUCH RIVER ICE AS OTHER AREAS. STREAMFLOW CONDITIONS - VARIABLE. COMPARED TO MEDIAN FOR THIS TIME OF YEAR, STREAMFLOW IS HIGHEST ACROSS NY, NORTHERN PA AND NORTHWESTERN NJ WHERE IT IS CURRENTLY MUCH ABOVE MEDIAN. HEADING SOUTH, STREAMFLOW IS CLOSER TO MEDIAN FOR THE DATE ACROSS CENTRAL NJ, CENTRAL PA, NORTHEASTERN WV AND WESTERN MD. FINALLY, CURRENT STREAMFLOW CONDITIONS DECREASE FURTHER TO BELOW OR MUCH BELOW MEDIAN ACROSS SOUTHERN NJ, MUCH OF MD, AND MOST OF VA AND DE. 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 - MUCH ABOVE AVERAGE TO BELOW ABOVE AVERAGE. THE JANUARY 5, 2008, PALMER DROUGHT SEVERITY INDEX CHART (FOUND BY NAVIGATING THE WEBSITE: WWW.CPC.NOAA.GOV/PRODUCTS) IMPLIES VERY WET SOIL MOISTURE CONDITIONS ACROSS PORTIONS OF NY AND NORTHERN PA. MEANWHILE, ABOVE AVERAGE CONDITIONS EXIST ACROSS NORTHERN NJ AND MOST OF THE REMAINDER OF PA. ELSEWHERE, THE CHART SUGGESTS NEAR AVERAGE TO SOMEWHAT BELOW AVERAGE SOIL MOISTURE CONDITIONS FOR THIS TIME OF YEAR. HOWEVER, OTHER SOIL MOISTURE AND DROUGHT-RELATED DATA INDICATES PORTIONS OF VA 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 - ABOVE AVERAGE TO BELOW AVERAGE. CURRENT GROUND WATER LEVELS ARE GENERALLY IN THE RANGE OF AVERAGE TO ABOVE AVERAGE ACROSS THE NORTHERN TWO-THIRDS OF THE MARFC SERVICE AREA, AND AVERAGE TO BELOW AVERAGE ACROSS THE SOUTHERN THIRD. 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. RESERVOIR CONDITIONS ARE SOMEWHAT ABOVE AVERAGE ACROSS THE FAR NORTH, AND BELOW AVERAGE ACROSS PORTIONS OF VA. FUTURE WEATHER CONDITIONS - A STORM SYSTEM IS EXPECTED TO PRODUCE MOSTLY MODERATE RAINFALL ACROSS THE MARFC SERVICE AREA DURING THE NEXT 24 HOURS. MOST AREAS WILL RECEIVE A HALF INCH TO AN INCH OF RAIN WITH THE HEAVIEST AMOUNTS EXPECTED ACROSS PORTIONS OF PA, NY AND NJ. THIS AMOUNT OF RAIN COULD RESULT IN SOME MINOR FLOODING TO DEVELOP IN THE UPPER SUSQUEHANNA RIVER BASIN IN NEW YORK STATE. THEN, A COASTAL STORM MAY BRING MODERATE-HEAVY PRECIPITATION ACROSS PORTIONS OF THE MARFC SERVICE AREA AGAIN ON SUNDAY NIGHT AND MONDAY. EASTERN AREAS HAVE THE BEST CHANCE OF RECEIVING SIGNIFICANT PRECIPITATION FROM THIS POTENTIAL STORM. FINALLY, ANOTHER SIGNIFICANT STORM EVENT COULD OCCUR TOWARDS THE END OF NEXT WEEK. IN GENERAL, MORE SEASONABLE TEMPERATURES ARE ANTICIPATED DURING THE NEXT TWO WEEKS COMPARED TO THE VERY MILD WEATHER THAT HAS OCCURRED RECENTLY. REPEATING THE EXTENDED RANGE WEATHER OUTLOOK FOR THE NINE DAY PERIOD JANUARY 16-24: NORMAL TO BELOW NORMAL TEMPERATURES, AND NEAR NORMAL PRECIPITATION. AHPS FLOOD FORECASTS - NEAR AVERAGE TO BELOW 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 ABOUT THE SAME AS WHAT HAS BEEN HISTORICALLY OBSERVED FOR MOST OF THE MARFC SERVICE AREA. THE EXCEPTION IS IN VIRGINIA (INCLUDING THE POTOMAC BASIN), WHERE AHPS FORECASTS SUGGEST RIVER FLOODING DURING THE NEXT TWO WEEKS IS 10-15% LESS LIKELY THAN WHAT HAS OCCURRED HISTORICALLY. PLEASE VISIT WWW.WEATHER.GOV/AHPS/ FOR DETAILED AHPS INFORMATION. SUMMARY - THE RIVER FLOOD POTENTIAL FOR THE NEXT TWO WEEKS IS ABOUT AVERAGE FOR MOST OF THE MARFC SERVICE AREA. IN VIRGINIA, HOWEVER, RIVER FLOODING IS SOMEWHAT LESS LIKELY THAN NORMAL FOR THIS TIME OF YEAR. ACROSS THE NORTH, THE COMBINATION OF WET SOILS, HIGH STREAMFLOW CONDITIONS, AND SIGNIFICANT RAINFALL DURING THE NEXT 24 HOURS WILL POSSIBLY RESULT IN SOME SCATTERED MINOR FLOODING ACROSS PORTIONS OF THE UPPER SUSQUEHANNA RIVER BASIN IN NEW YORK STATE DURING THE NEXT COUPLE OF DAYS. BEYOND THIS SHORT-TERM THREAT, THE LACK OF SIGNIFICANT SNOW AND ICE ACROSS THE NORTH WILL KEEP THE RIVER FLOOD THREAT AROUND NORMAL FOR THE REMAINDER OF THIS OUTLOOK PERIOD. TO SUMMARIZE, HEAVY RAIN WOULD BE REQUIRED FOR WIDESPREAD SIGNIFICANT RIVER FLOODING TO DEVELOP ANYWHERE WITHIN THE MARFC SERVICE AREA. SEVERAL STORMS DURING THE NEXT WEEK OR SO DO HAVE THE POTENTIAL TO PRODUCE HEAVY RAIN AND WILL THEREFORE NEED TO BE MONITORED. WATER SUPPLY OUTLOOK - DROUGHT CONDITIONS LINGER ACROSS MUCH OF VIRGINIA. ALTHOUGH CONDITIONS HAVE GRADUALLY IMPROVED OVER THE LAST FEW MONTHS, THE DROUGHT HAS NOT BEEN ELIMINATED. WATER SUPPLY SHORTAGES ARE POSSIBLE IN THIS AREA DURING THE NEXT FEW MONTHS UNLESS PRECIPITATION AVERAGES ABOVE NORMAL. THE LATEST SEASONAL DROUGHT OUTLOOK (WWW.DROUGHT.GOV) RELEASED ON JANUARY 3, 2008, DOES SUGGEST CONTINUED SLOW IMPROVEMENT ACROSS VIRGINIA DURING THE NEXT TWO 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 JANUARY 24, 2008. $$ ....END MARFC.... NNNN