Preliminary Spring Flood considerations

HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE GRAND FORKS ND
700 PM CST FRI DEC 15 2006

...WATER RESOURCES STATEMENT AND OUTLOOK...

THIS OUTLOOK COVERS THE GRAND FORKS HYDROLOGIC SERVICE
AREA...HSA...WHICH ENCOMPASSES 35 COUNTIES ACROSS EASTERN NORTH
DAKOTA AND NORTHWESTERN MINNESOTA. THE PRIMARY RIVER BASINS ARE
THE RED RIVER OF THE NORTH...RED LAKE AND SHEYENNE RIVERS AND THEIR
TRIBUTARIES. MAJOR LAKE BASINS INCLUDE DEVILS LAKE...THE UPPER AND
LOWER RED LAKES AS WELL AS PORTIONS OF LAKE OF THE WOODS.

...SUMMER 2006 DROUGHT CONDITIONS COULD REDUCE SPRING 2007
FLOOD THREAT...

MODERATE TO EXTREME DROUGHT CONDITIONS DEVELOPED DURING THE SUMMER
OF 2006...WITH DRY CONDITIONS CONTINUING INTO THE EARLY WINTER
SEASON. THIS IS A SIGNIFICANT CHANGE FROM THE MOST RECENT 13
YEARS...WHEN PREDOMINANTLY WET SUMMER AND FALL SEASONS PREVAILED. AS
A RESULT SOME CONDITIONS WHICH NORMALLY CONTRIBUTE TO SPRING
FLOODING POTENTIAL ARE CURRENTLY REDUCED.

PREEXISTING CONDITIONS MUST BE CONSIDERED TO DETERMINING THE
MAGNITUDE OF A SPRING FLOOD. THE MAIN CONDITIONS INCLUDE...

1...THE FREEZE/THAW CYCLE
2...EARLY SPRING RAINS WHICH INCREASE MELTING OF THE SNOW PACK OR
LATE SPRING SNOW STORMS ADDING TO THE EXISTING SNOW PACK
3...THE SNOW PACK DEPTH AND ITS WATER EQUIVALENCE AT THE TIME OF THAW
4...FROST DEPTH
5...SOIL MOISTURE CONTENT
6...RIVER BASE FLOWS AND ICE CONDITIONS

SOME OF THESE CONDITIONS ARE DETERMINABLE IN ADVANCE OF THE TYPICAL
SPRING FLOOD SUCH AS SOIL MOISTURE CONTENT...RIVER BASE FLOWS...ICE
CONDITIONS AND FROST DEPTH. THE MOST CRITICAL CONDITIONS...THE FIRST
THREE MENTIONED ON THE ABOVE LIST...ARE NOT FULLY KNOWN UNTIL JUST
BEFORE OR DURING THE SPRING THAW. BY MAKING ASSESSMENTS OF FROST
DEPTH...SOIL MOISTURE AND RIVER BASE FLOWS THE NWS CAN MAKE A
PRELIMINARY SPRING FLOOD HAZARD ASSESSMENT. ANOTHER TOOL IS THE
PRECIPITATION AND TEMPERATURE PATTERNS AS THEY ARE FORECAST AND
EVOLVE DURING THE WINTER AND SPRING.

...SPRING THAW CYCLE...
A TYPICAL SPRING THAW OCCURS FROM THE MIDDLE OF MARCH ACROSS
SOUTHERN PORTIONS OF THE BASIN TO MID APRIL ACROSS THE NORTH.
NATURALLY...GREAT VARIABILITY IN CONDITIONS CAN EXISTS PRIOR TO THE
SPRING MELT AND RUNOFF PERIOD. FOR EXAMPLE...TEMPERATURE AND
PRECIPITATION AMOUNTS CAN VARY GREATLY FROM ONE LOCATION TO ANOTHER.

...FROST DEPTHS...
A NEWLY DEPLOYED FROST PROBE NETWORK WITHIN THE RED RIVER VALLEY
INDICATES FROST HAS INDEED DEVELOPED. AS OF EARLY DECEMBER FROST
DEPTHS RANGE FROM ONE TO TWO FEET. THE EARLY WINTER SEASON COLD
WEATHER WITH A LACK OF DEEP SNOWCOVER WILL ALLOW THE GROUND FROST TO
CONTINUE TO BUILD.

...SOIL MOISTURE...
LATE AUTUMN RAIN AND EARLY WINTER SNOWFALL IN MANY AREAS OF THE RED
RIVER VALLEY HAVE HELPED REPLENISH TOPSOIL MOISTURE. GENERALLY THE
CENTRAL AND NORTHERN RED RIVER VALLEY HAVE RECEIVED THE MOST
PRECIPITATION DURING THE PAST 30 DAYS.

BASED ON DATA FROM THE USGS GROUND WELLS...RECOVERY OF SOIL MOISTURE
HAS OCCURRED IN PORTIONS OF THE GRAND FORKS HSA. CONDITIONS HAVE
STABILIZED AS WATER HAS PERCOLATED DEEPER INTO THE SOIL. GENERALLY
SPEAKING...GROUND WATER LEVELS HAVE RECOVERED ABOUT ONE QUARTER OF A
FOOT SINCE EARLY NOVEMBER.

THE NWS ALSO PERFORMED SOME FIELD WORK TO DETERMINE SOIL MOISTURE
IN THE REGION. OVERALL THE SHEYENNE RIVER VALLEY IS NOMINALLY DRY.
ON THE MINNESOTA SIDE THE RED RIVER BASIN IS A BIT WETTER. IN
SOUTHERN WILKIN COUNTY NWS EMPLOYEES DETERMINED THAT THE FIRST 5
FEET OF SOIL IS FAIRLY WET. IN THE THIEF RIVER FALLS AREA THE TOP
THREE FEET ARE RELATIVELY DRY...BUT BELOW THE SAND LAYER SOIL
MOISTURE IS STILL QUITE HIGH. THESE OBSERVATIONS INDICATE THAT THE
TOP MOST 4 TO 6 INCHES ARE CONSIDERABLY DRIER THAN PREVIOUS
FALLS...INDICATIVE OF GREATER MOISTURE STORAGE POTENTIAL NEXT
SPRING. THIS IS A FAVORABLE INDICATOR FOR A REDUCED SPRING FLOOD
POTENTIAL.

...RIVER CONDITIONS...
STREAM FLOW VALUES HAVE FALLEN BELOW THE FIFTY PERCENTILE LEVEL IN
MANY LOCATIONS...ESPECIALLY THE TRIBUTARIES. OVERALL THE EARLY
WINTER FLOWS ON THE MAIN STEM RED RIVER HAVE BEEN NORMAL TO BELOW
NORMAL. IN RECENT WINTER SEASONS BASE FLOWS WERE CONSISTENTLY 200 TO
600 PERCENT OF NORMAL. DECREASES IN 2006 BASE FLOWS IS A FAVORABLE
INDICATOR FOR A REDUCED SPRING FLOOD POTENTIAL.

SOME SPECIFIC LOCATIONS ARE INCLUDED IN THE TABLE BELOW. NOTE THAT
CFS STANDS FOR CUBIC FEET PER SECOND. DATA BELOW WERE SUPPLIED BY
THE USGS.


LOCATION                             CURRENT        LONG TERM          PERCENT OF           LOWEST FLOW
                                             FLOW CFS      MEAN CFS            NORMAL                  CFS / YEAR
RED RIVER...
FARGO ND                                360                   488                          74                         0 / 1933
HALSTAD MN                          1058                  2360                          45                        52 / 1977
E GRAND FORKS MN              1080                  2229                          48                          8 / 1936
DRAYTON ND                           858                   2237                          38                       130 / 1977


...THE WINTER THROUGH SPRING 2007 WEATHER OUTLOOKS...
A MODERATE EL NINO IS OCCURRING IN THE EQUATORIAL PACIFIC. THE
CLIMATE PREDICTION CENTER INDICATES A FAIRLY HIGH LIKELIHOOD...60
PERCENT OR MORE...THAT THE BULK OF THE WINTER SEASON WILL BE WARMER
THAN NORMAL IN THE GRAND FORKS HSA. DURING MODERATE EL NINO
EVENTS...SNOWFALL IS TYPICALLY 85 TO 90 PERCENT OF THE CLIMATIC
NORMAL. THIS WOULD EQUATE TO 35 TO 40 INCHES OF SNOW DURING THE COLD
SEASON. LACK OF SIGNIFICANT SNOWFALL AND LOW MOISTURE CONTENT OF THE
SNOW PACK ARE ALSO FAVORABLE INDICATORS FOR A REDUCED SPRING FLOOD
POTENTIAL.

...SPRING 2007 FLOOD IMPLICATIONS...
BASED ON CURRENT CONDITIONS AND OUTLOOKS OF PRECIPITATION AND
TEMPERATURE THIS WINTER...INDICATIONS ARE THAT...AT THIS TIME...THE
FLOOD POTENTIAL FOR SPRING 2007 IS CONSIDERABLY LOWER THAN THE 2006
SEASON.

YOUR NOAAS NWS WILL CONTINUE TO MONITOR THE HYDROLOGIC AND
METEOROLOGICAL CONDITIONS THROUGH THE WINTER SEASON. THE NEXT
SCHEDULED UPDATE OF THE WATER RESOURCES STATEMENT AND OUTLOOK FOR
THE GRAND FORKS HSA WILL BE IN EARLY JANUARY 2007.

IF YOU HAVE ANY QUESTIONS...CONTACT THE NWS AT 701-772-0720.

$$

FGF HYDROLOGIC AND CLIMATE TEAMS


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