HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE BLACKSBURG VA
550 PM EDT THU APR 24 2008
...DROUGHT/WATER RESOURCES STATEMENT NUMBER 2008-9...
...DROUGHT CONDITIONS LINGER DESPITE NEAR NORMAL APRIL RAINFALL
SO FAR...
SUMMARY...
THE LAST TWO WEEKS HAVE SEEN LITTLE OVERALL CHANGE IN THE INTENSITY
AND AREAL EXTENT OF DROUGHT ACROSS THE BLACKSBURG HYDROLOGIC SERVICE
AREA (HSA). MODERATE DROUGHT CONDITIONS STILL EXIST OVER THE
MAJORITY OF THE HSA...WITH SEVERE DROUGHT BARELY INTO THE HSA IN
NORTH CAROLINA.
THE BLACKSBURG HSA COVERS 27 COUNTIES IN SOUTHWEST VIRGINIA...4 IN
EXTREME SOUTHEAST WEST VIRGINIA AND 9 IN NORTHWEST NORTH CAROLINA
AND INCLUDES PORTIONS OF THE FOLLOWING RIVER BASINS:
JAMES...ROANOKE...NEW...GREENBRIER...DAN...YADKIN...CLINCH AND
HOLSTON.
THE U.S. DROUGHT MONITOR (USDM)...
THE USDM ISSUED TODAY AND REFLECTING CONDITIONS THROUGH 7 AM ON
APRIL 22 SHOWED NO SUBSTANTIAL CHANGES IN THE OVERALL DEPICTION OF
DROUGHT IN OUR AREA. SEVERE DROUGHT (D2) IS STILL PRESENT OVER A
SMALL PORTION OF THE SOUTHERN HSA IN NORTH CAROLINA BUT THERE
IS NO D2 IN VIRGINIA. MODERATE DROUGHT (D1) STILL EXISTS OVER A
BROAD AREA OF THE CENTRAL HSA...COVERING MUCH OF THE NEW AND
ROANOKE RIVER VALLEYS. AN AREA OF D0 OR ABNORMALLY DRY EXISTS
NORTHWEST OF ROANOKE TO THE WEST VIRGINIA BORDER.
IT SHOULD BE POINTED OUT THAT THE CATEGORIES ON THE DROUGHT
MONITOR ARE GENERALIZED AND THE LOCAL IMPACTS OF DROUGHT MAY BE MORE
OR LESS THAN WHAT IS DEPICTED ON THE MAP.
THE U.S. DROUGHT MONITOR IS A JOINT EFFORT OF THE U.S. DEPARTMENT OF
AGRICULTURE...THE NATIONAL DROUGHT MITIGATION CENTER...THE NATIONAL
WEATHER SERVICE AND THE NATIONAL CLIMATIC DATA CENTER. THE WEBSITE
FOR THE U.S. DROUGHT MONITOR IS HTTP://WWW.DROUGHT.UNL.EDU/DM.
THE CATEGORIES OF DROUGHT ARE EXPLAINED BELOW:
D0 IS THE LEAST INTENSE INDICATOR OF DROUGHT ON A SCALE THAT RANGES
FROM D0 THROUGH D4. IT IS BASICALLY A DROUGHT WATCH THAT INDICATES A
REGION GOING INTO OR COMING OUT OF DROUGHT.
D1 IS MODERATE DROUGHT...CONDITIONS THAT MAY BE ASSOCIATED WITH D1
INCLUDE SOME CROP DAMAGE...INCREASED FIRE RISK...FALLING RIVER...
STREAM...AND RESERVOIR LEVELS AND SOME WATER SHORTAGES.
D2 IS SEVERE DROUGHT...CROP OR PASTURE DAMAGE IS LIKELY. FIRE RISK IS
POTENTIALLY HIGH...ALONG WITH WATER SHORTAGES AND POSSIBLE WATER
RESTRICTIONS.
D3 IS EXTREME DROUGHT...MAJOR CROP AND PASTURE LOSSES AND WIDESPREAD
WATER SHORTAGES AND RESTRICTIONS.
D4 IS EXCEPTIONAL DROUGHT...WIDESPREAD CROP AND PASTURE LOSSES...
WATER SHORTAGES AND WATER EMERGENCIES. MAY BE THOUGHT OF AS THE
50-YEAR DROUGHT OR THE 2 PERCENT ANNUAL CHANCE OF OCCURRENCE.
THE CATEGORIES ARE BASED ON A NUMBER OF KEY INDICATORS: 1) PALMER
DROUGHT INDEX (PDSI) 2) CPC SOIL MOISTURE MODEL 3) USGS WEEKLY
STREAMFLOW PRECENTILES 4) THE STANDARDIZED PRECIPITATION INDEX AND
5) THE SATELLITE VEGETATION INDEX.
RECENT PRECIPITATION...
RAINFALL SO FAR IN APRIL IS RUNNING SLIGHTLY ABOVE NORMAL IN THE
EASTERN HSA AND SOMEWHAT BELOW NORMAL OVER NORTHWEST NORTH CAROLINA
AND THE SOUTHWEST COUNTIES OF IN VIRGINIA.
LONGER TERM PRECIPITATION...(FROM NWS COOPERATIVE NETWORK)
MONTH OR SEASON PRECIPITATION NORMAL % OF NORMAL
MARCH 2008 3.42 4.14 83
FEBRUARY 2008 2.42 3.22 75
JANUARY 2008 1.48 3.65 41
DECEMBER 2007 3.28 3.12 105
WINTER 07-08 (DEC-FEB) 7.19 9.99 72
FALL 2007 (SEP-NOV) 8.49 10.51 81
SUMMER 2007 (JUN-AUG) 9.42 11.79 80
SPRING 2007 (MAR-MAY) 9.75 12.28 79
ALL OF 2007 36.72 44.15 82
PALMER DROUGHT SEVERITY INDEX (PDSI)...
THE PALMER INDEX IS CALCULATED WEEKLY AND INDICATES THE RELATIVE
DRYNESS OR WETNESS AFFECTING AN AREA. THERE ARE SEVEN PDSI
CATEGORIES DEFINING WET AND DRY CONDITIONS AS SHOWN IN THE TABLE
BELOW:
-4.0 OR LESS - EXTREME DROUGHT
-3.0 TO -3.9 - SEVERE DROUGHT
-2.0 TO -2.9 - MODERATE DROUGHT
-1.9 TO +1.9 - NEAR NORMAL
+2.0 TO +2.9 - UNUSUAL MOIST SPELL
+3.0 TO +3.9 - VERY MOIST SPELL
+4.0 OR ABOVE - EXTREMELY MOIST
THE TABLE BELOW SHOWS THE APRIL 19 2008 PDSI FOR THE SIX CLIMATE
ZONES WHICH COVER THE BLACKSBURG HSA. ALL AREAS HAVE SHOWN
SIGNIFICANT DECLINES IN THE PDSI OVER THE PAST TWO WEEKS WITH
THE NORTHERN MOUNTAINS OF NORTH CAROLINA SHOWING THE WORST
CONDITIONS. NEARLY 8 INCHES OF RAIN WOULD NEEDED IN THAT REGION TO
ELIMINATE THE DROUGHT.
STATE CLIMATE ZONE PDSI PRECIP NEEDED
TO BRING PDSI TO -0.5
NC N. MOUNTAINS -2.75 7.67
NC N. PIEDMONT -1.75 4.21
VA W. PIEDMONT -1.26 2.97
VA CENT. MTNS. -0.11
VA SW MOUNTAINS -1.13 2.26
WV SOUTHERN 1.07
FOR DETAILS ON THE PDSI SEE THE CLIMATE PREDICTION CENTER WEBSITE:
HTTP://WWW.CPC.NCEP.NOAA.GOV
SOIL MOISTURE...
THE NWS CLIMATE PREDICTION CENTER SOIL MOISTURE MODEL IS
USED TO ESTIMATE SOIL MOISTURE IN THE TOP 4 TO 5 FEET USING RECENT
OBSERVED DATA VERSUS LONG-TERM NORMALS. LITTLE OR NO DEFICIT EXISTS
OVER SOUTHEAST WEST VIRGINIA AND WESTERN VIRGINIA WHILE NORTHWEST
NORTH CAROLINA CONTINUES TO RUN DEFICITS OF 1 TO 3 INCHES.
SEE HTTP://WWW.CPC.NCEP.NOAA.GOV/SOLIMST/W.SHTML FOR THE LATEST
SOIL MOISTURE MAPS FOR THE UNITED STATES.
RIVERS AND STREAMFLOW...
STREAMFLOW VOLUMES ON MOST AREA RIVERS HAVE DECLINED SHARPLY OVER
THE PAST TWO WEEKS AND ARE NOW WELL BELOW MEDIAN FLOWS IN MOST
BASINS. THE EXCEPTIONS ARE IN THE UPPER JAMES IN VIRGINIA AND IN THE
KANAWHA BASIN OF WEST VIRGINIA WHERE FLOWS ARE CLOSER TO NORMAL.
THE UPPER YADKIN RIVER BASIN OF NORTH CAROLINA CONTINUES TO HAVE THE
LOWEST FLOWS IN THE HSA...RUNNING BELOW HALF OF THE MEDIAN FOR THIS
DATE. THE TABLE BELOW SHOWS CURRENT (APRIL 24)STREAMFLOWS IN CUBIC
FEET PER SECOND (CFS) VERSUS LONG-TERM MEDIAN FLOWS FOR THIS DATE AT
SELECTED LONG-TERM RIVER LOCATIONS IN THE BLACKSBURG HSA. THESE DATA
ARE PROVIDED COURTESY OF THE UNITED STATES GEOLOGICAL SURVEY (USGS).
RIVER/LOCATION FLOW MEDIAN PERCENT DRAINAGE YEARS OF
(CFS) FLOW OF MED. AREA(MI2) RECORD
JAMES R. AT BUCHANAN VA 2670 2420 110 2075 27
JAMES R. AT BENT CREEK VA 5520 4730 117 3683 27
ROANOKE R. AT ROANOKE VA 233 343 68 395 106
DAN R. AT PACES VA 2540 2240 113 2550 54
NEW RIVER AT ALLISONIA VA 3370 3370 100 2202 77
GREENBRIER R. ALDERSON WV 2040 1720 119 1364 111
YADKIN R. AT WILKESBORO NC 374 852 44 504 45
YADKIN R. AT ELKIN NC 660 1360 49 869 42
NF HOLSTON NR SALTVILLE VA 178 263 68 222 88
FOR ADDITIONAL INFORMATION ON CURRENT AND HISTORICAL STREAMFLOWS
SEE THE USGS WEBSITE AT HTTP://WATERDATA.USGS.GOV/NWIS/RT.
RESERVOIRS
MAJOR LAKE LEVELS HAVE CONTINUED TO IMPROVE OR REMAIN STEADY OVER
THE PAST TWO WEEKS.
RESERVOIR CURRENT POOL NORMAL POOL
SMITH MOUNTAIN LAKE VA 793.60 795
CLAYTOR LAKE VA 1842.98 1846
LAKE MOOMAW VA 1582.04 1582
PHILPOTT RESERVOIR 972.48 974
BLUESTONE LAKE WV 1410.60 1410
W. KERR SCOTT NC 1030.27 1030
IN ADDITION...THE CARVINS COVE RESERVOIR...A MAJOR SOURCE FOR ROANOKE
DRINKING WATER...IS NOW 11.1 FEET BELOW THE SPILLWAY AND HAS RISEN
ABOUT FOUR FEET IN RECENT WEEKS. SPRING HOLLOW RESERVOIR...WHICH
SERVES ROANOKE COUNTY...IS NOW 13.4 FEET BELOW ITS SPILLWAY...AN
IMPROVEMENT OF OVER EIGHT FEET IN THE PAST FOUR WEEKS.
IMPACTS...
FOR INFORMATION ON IMPACTS IN THE STATE OF NORTH CAROLINA PLEASE SEE THE
STATE DIVISION OF WATER RESOURCES WEBSITE:
HTTP://WWW.NCWATER.ORG/
FOR INFORMATION ON IMPACTS IN THE STATE OF VIRGINIA PLEASE SEE THE
STATE DEPARTMENT OF ENVIRONMENTAL QUALITY WEBSITE:
HTTP://WWW.DEQ.VIRGINIA.GOV/
OUTLOOK...
SEVERAL CHANCES FOR PRECIPITATION EXIST OVER THE NEXT FIVE DAYS
WHICH COULD LED TO SOME IMPROVEMENT IN THE DROUGHT. A COLD FRONT
APPROACHING THE REGION SATURDAY IS FORECAST TO BRING RAINFALL OF
0.25 TO 1.00 INCHES ENDING LATE SATURDAY. A STRONG UPPER LEVEL
SYSTEM MOVING OUT OF THE CENTRAL U.S. LATE IN THE WEEKEND AND EARLY
NEXT WEEK MAY PRODUCE MORE WIDESPREAD RAINFALL OF 1 TO 2 INCHES BY
TUESDAY.
ACCORDING TO THE NWS CLIMATE PREDICTION CENTER THE 6 TO 10
OUTLOOK PERIOD FROM APRIL 30 TO MAY 4 WILL BRING NEAR NORMAL
PRECIPITATION. IN THE 8 TO 14 DAY OUTLOOK PERIOD THROUGH MAY 8
THE HIGHEST PROBABILITY IS FOR BELOW NORMAL PRECIPITATION.
SEE THE NWS BLACKSBURG WEBSITE FOR LOCAL WEATHER FORECASTS OUT
TO SEVEN DAYS: HTTP://WWW.ERH.NOAA.GOV/RNK.
SEE THE CPC WEBSITE FOR ALL LONG-RANGE WEATHER AND CLIMATE FORECASTS
BEYOND SEVEN DAYS: HTTP://WWW.CPC.NCEP.NOAA.GOV.
SEE THE NOAA DROUGHT INFORMATION PAGE FOR A COMPREHENSIVE LISTING OF
DROUGHT RELATED INFORMATION: HTTP://WWW.DROUGHT.NOAA.GOV.
ANOTHER HYDROLOGIC OUTLOOK ON THIS SITUATION WILL BE ISSUED ON OR
ABOUT MAY 8 UNLESS CONDITIONS WARRANT AN EARLIER UPDATE.
$$
CORRIGAN