Flood Potential Outlook
Issued by NWS Denver/Boulder, CO

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COC001-005-013-014-019-031-035-039-047-049-057-059-069-073-075-087-
093-095-115-117-121-123-060000-

PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE DENVER CO
359 PM MST THU FEB 20 2014

...SPRING FLOOD AND WATER RESOURCES OUTLOOK...

THIS OUTLOOK IS FOR THE DENVER/BOULDER SERVICE AREA. IT INCLUDES THE
UPPER COLORADO AND NORTH PLATTE RIVER BASINS IN NORTH CENTRAL
COLORADO AND SOUTH PLATTE BASIN EXTENDING ACROSS NORTHEAST COLORADO.

.FLOOD OUTLOOK...THE 2014 SPRING SNWOMELT RUNOFF FLOOD POTENTIAL IS
MODERATE TO HIGH IN THE SOUTH PLATTE RIVER BASIN IN NORTHEAST
COLORADO AND MODERATE IN THE NORTH PLATTE AND UPPER COLORADO RIVER
BASINS IN NORTH CENTRAL COLORADO.

THE FLOOD POTENTIAL DUE TO SNOWMELT ALONE IS NEAR NORMAL. IT SHOULD
BE NOTED THAT IT IS STILL EARLY IN THE SNOW ACCUMULATION SEASON AND
CONDITIONS COULD CHANGE BEFORE THE RUNOFF BEGINS. ABOVE NORMAL
FUTURE SNOW ACCUMULATIONS COMBINED WITH HEAVY RAINS AND RAPID MELT
WILL INCREASE THE CURRENT FLOOD POTENTIAL WHILE BELOW NORMAL FUTURE
PRECIPITATION AND GRADUAL OR INTERMITTENT FREEZING AND THAWING WILL
DECREASE THE MAGNITUDE OF THE CURRENT ASSESSMENT. PARTICULARLY IN
JACKSON COUNTY IN EXTREME NORTH CENTRAL COLORADO...RIVERS ARE
SUBJECT TO ICE JAMS. WHEN FROZEN RIVERS THAW...ICE JAMS CAN OCCUR
CAUSING HIGHER RIVER LEVELS AND POSSIBLE FLOODING.

THERE ARE ADDITIONAL FLOOD CONCERNS THIS SPRING PRIMARILY ALONG THE
FRONT RANGE FOOTHILLS IN BOULDER...JEFFERSON AND LARIMER COUNTIES
DUE TO THE DESTRUCTIVE SEPTEMBER 2013 FLOODS. STREAM CHANNELS HAVE
MOVED OR SCOURED AND MANY HAVE HAD FEET OF SAND...ROCKS AND GRAVEL
ADDED. SIGNIFICANT DEBRIS AND A RESIDUAL HIGH WATER TABLE REMAIN IN
THE FOOTHILLS. THESE ISSUES COULD COMPOUND FLOODING FROM SPRING
SNOWMELT RUNOFF.

.SNOWPACK...HIGH COUNTRY SNOWPACK CLIMBED WELL ABOVE AVERAGE IN
FEBRUARY. THE MOUNTAIN SNOWPACK ON FEBRUARY 20TH WAS 142 PERCENT OF
AVERAGE IN THE SOUTH PLATTE RIVER BASIN WHICH IS JUST ABOVE THE
SNOWPACK ON THE SAME DATE IN 2011. THIS WAS THE FOURTH HIGHEST
FEBRUARY 20TH SNOWPACK IN THE PAST 35 YEARS IN THE SOUTH PLATTE
BASIN. THE ONLY YEARS WITH A HIGHER FEBRUARY 20TH SNOWPACK WERE
1986...1996 AND 1997. THE SNOWPACK IN THE NORTH PLATTE RIVER BASIN
WAS 134 PERCENT OF AVERAGE AND THE FIFTH HIGHEST FEBRUARY 20TH
SNOWPACK IN THAT BASIN IN THE PAST 35 YEARS. THE ONLY YEARS WITH A
HIGHER SNOWPACK WERE 1986...1996...1997 AND 2011. THE UPPER COLORADO
RIVER BASIN SNOWPACK WAS 132 PERCENT OF AVERAGE WHICH IS THE SIXTH
HIGHEST FEBRUARY 20TH SNOWPACK THERE SINCE 1980. LIQUID WATER IN THE
MOUNTAIN SNOWPACK GENERALLY RANGES FROM 1 TO 7 FEET. AT LOWER
ELEVATIONS EAST OF THE DIVIDE THERE WAS TYPICALLY LITTLE TO NO SNOW
ON THE GROUND EXCEPT 1 TO 3 INCHES OF SNOW FELL OVERNIGHT ON
FEBRUARY 19TH/20TH FROM DENVER AND DOUGLAS COUNTIES EASTWARD.

.RESERVOIRS...SINCE THE BEGINNING OF THE WATER YEAR THE COMBINED
RESERVOIR STORAGE IN THE SOUTH PLATTE BASIN HAS HELD FAIRLY STEADY
AT AROUND 105 PERCENT OF AVERAGE WHILE THE STORAGE IN THE UPPER
COLORADO RIVER BASIN HAS SLOWLY CLIMBED FROM 88 PERCENT OF AVERAGE
ON OCTOBER 1ST 2013 TO 99 PERCENT OF AVERAGE ON JANUARY 31ST 2014.
THE COMBINED RESERVOIR STORAGE RANGED FROM 68 PERCENT OF CAPACITY IN
THE UPPER COLORADO RIVER BASIN TO 75 PERCENT OF CAPACITY IN THE
SOUTH PLATTE BASIN AT THE END OF JANUARY.

.RIVER CONDITIONS AND WATER SUPPLY FORECASTS...THE MAJORITY OF THE
U.S. GEOLOGICAL SURVEY STREAM GAGES IN NORTH CENTRAL AND NORTHEAST
COLORADO HAD NORMAL TO MUCH ABOVE NORMAL FLOWS ON FEBRUARY 20TH. THE
APRIL THROUGH JULY STREAMFLOW FORECASTS FOR NORTH CENTRAL COLORADO
RANGE FROM 105 TO 116 PERCENT OF AVERAGE EAST OF THE DIVIDE AND 106
AND 130 PERCENT OF AVERAGE WEST OF THE DIVIDE.

.DROUGHT CONDITIONS AND OUTLOOK...CONDITIONS HAVE CHANGED LITTLE
SINCE THE BEGINNING OF THE 2014 WATER YEAR. EXTREME /D3/ AND SEVERE
DROUGHT /D2/ LINGERED IN EXTREME SOUTHERN LINCOLN COUNTY. MODERATE
/D1/ DROUGHT AND ABNORMALLY DRY CONDITIONS /D0/ PERSISTED ON THE FAR
NORTHEAST PLAINS. ABNORMALLY DRY CONDITIONS /D0/ CONTINUED IN
SOUTHERN PARK...SOUTHWEST DOUGLAS AND EXTREME SOUTHERN JEFFERSON
COUNTIES.

.CLIMATE SUMMARY...PRECIPITATION FOR THE PAST 3 MONTHS WAS 125 TO
250 PERCENT OF AVERAGE FROM SUMMIT COUNTY AND GRAND COUNTIES IN THE
UPPER COLORADO RIVER BASIN THROUGH WELD AND MORGAN COUNTIES IN THE
SOUTH PLATTE BASIN. IN CONTRAST...PRECIPITATION WAS ONLY 50 TO 75
PERCENT OF AVERAGE IN THE EXTREME NORTHEAST CORNER OF COLORADO...IN
EXTREME SOUTHERN LINCOLN COUNTY IN THE ARKANSAS RIVER BASIN AND IN
NORTHERN JACKSON COUNTY IN THE NORTH PLATTE BASIN. TEMPERATURES HAVE
GENERALLY BEEN NEAR AVERAGE IN NORTH CENTRAL COLORADO AND NEAR TO
BELOW AVERAGE ON THE EASTERN PLAINS.

.PRECIPITATION/TEMPERATURE OUTLOOK...ENSO-NEUTRAL CONDITIONS ARE
EXPECTED TO CONTINUE THROUGH THIS SUMMER. THE 30 AND 90 DAY CLIMATE
PREDICTION CENTER OUTLOOKS CALL FOR EQUAL CHANCES OF NEAR...ABOVE OR
BELOW AVERAGE PRECIPITATION AND TEMPERATURES IN NORTH CENTRAL AND
NORTHEAST COLORADO.

.LONG-RANGE PROBABILISTIC RIVER OUTLOOK...THE FOLLOWING TABLE GIVES
THE CHANCE OF REACHING FLOOD STAGE AT THE FORECAST POINTS DURING THE
VALID PERIOD.

CS VALUES INDICATE THE PROBABILITY OF REACHING A FLOOD CATEGORY
BASED ON CURRENT CONDITIONS.

HS VALUES INDICATE THE PROBABILITY OF REACHING A FLOOD CATEGORY
BASED ON HISTORICAL OR NORMAL CONDITIONS.

WHEN THE VALUE OF CS IS GREATER THAN HS...THE PROBABILITY OF
EXCEEDING THAT LEVEL IS HIGHER THAN NORMAL. WHEN THE VALUE OF CS IS
LESS THAN HS...THE PROBABILITY OF EXCEEDING THAT LEVEL IS LOWER THAN
NORMAL.

...TABLE 1--PROBABILITIES FOR MINOR...MODERATE AND MAJOR FLOODING...
                  VALID PERIOD:  2/22/2014 - 9/30/2014

                                       :    CURRENT AND HISTORICAL
                                       :     CHANCES OF EXCEEDING
                                       :       FLOOD CATERGORIES
                                       :      AS A PERCENTAGE (%)
                      CATEGORICAL      :
                   FLOOD STAGES (FT)   :   MINOR    MODERATE   MAJOR
LOCATION           MINOR   MOD   MAJOR :  CS   HS   CS   HS   CS   HS
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:SOUTH PLATTE RIVER
SOUTH PLATTE         7.0    9.0   11.0 :   9    9   <5   <5   <5   <5
DENVER              11.0   12.5   14.0 :  <5   <5   <5   <5   <5   <5
HENDERSON           10.0   11.0   15.0 :   8    5    5   <5   <5   <5
KERSEY              10.0   11.5   12.0 :  31   12   17    5   15   <5
WELDONA             10.0   11.0   13.0 :  18    7   12   <5    5   <5
BALZAC              10.0   11.0   13.0 :  26    8   19   <5    8   <5
JULESBURG           10.0   12.0   13.0 :  13    8   <5   <5   <5   <5
:PLUM CREEK
SEDALIA              8.0   10.0   12.0 :  <5   <5   <5   <5   <5   <5
:BEAR CREEK
MORRISON             9.0   10.0   11.0 :  <5   <5   <5   <5   <5   <5
SHERIDAN             8.0   10.0   11.0 :  <5   <5   <5   <5   <5   <5
:CLEAR CREEK
GOLDEN              10.0   13.0   14.0 :  <5   <5   <5   <5   <5   <5
DERBY                9.0   10.5   11.5 :  <5   <5   <5   <5   <5   <5
:N FK BIG THOMPSON RIVER
DRAKE                6.0    7.0    8.0 :  <5   <5   <5   <5   <5   <5
:CACHE LA POUDRE RIVER
FORT COLLINS 9NW     7.5    9.0   10.5 :  14   <5   <5   <5   <5   <5
FORT COLLINS        10.5   11.5   13.0 :  <5   <5   <5   <5   <5   <5
GREELEY              8.0    9.5   11.0 :  23    8    7   <5   <5   <5
:NORTH PLATTE RIVER
NORTHGATE            8.0    9.5   11.0 :   8    6   <5   <5   <5   <5

LEGEND
CS = CONDITIONAL SIMULATION (CURRENT OUTLOOK)
HS = HISTORICAL SIMULATION
FT = FEET

IN TABLE 2 BELOW...THE 95 THROUGH 5 PERCENT COLUMNS INDICATE THE
PROBABILITY OF EXCEEDING THE LISTED STAGE LEVELS (FT) FOR THE VALID
TIME PERIOD.

...TABLE 2--EXCEEDANCE PROBABILITIES...

                              CHANCE OF EXCEEDING STAGES
                                 AT SPECIFIC LOCATIONS

LOCATION              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:SOUTH PLATTE RIVER
SOUTH PLATTE          4.2    4.3    4.5    5.1    5.6    6.9    7.8
DENVER                6.2    6.2    6.2    6.2    6.7    7.5    8.2
HENDERSON             6.6    6.6    7.1    7.6    8.8    9.4   11.2
KERSEY                6.7    6.7    7.6    8.8   10.5   13.0   16.9
WELDONA               6.0    6.0    6.6    8.3    9.6   11.5   13.1
BALZAC                6.7    6.7    7.4    8.6   10.2   12.1   13.7
JULESBURG             7.3    7.3    7.3    8.2    9.0   10.3   11.4
:PLUM CREEK
SEDALIA               4.4    4.5    4.6    4.7    5.1    5.5    6.1
:BEAR CREEK
MORRISON              6.5    6.5    6.8    7.0    7.2    7.5    7.8
SHERIDAN              6.5    6.5    6.5    6.5    6.5    6.5    6.5
:CLEAR CREEK
GOLDEN                5.6    5.9    6.2    6.6    7.1    7.6    7.8
DERBY                 2.3    2.4    2.7    3.0    3.6    4.0    4.5
:N FK BIG THOMPSON RIVER
DRAKE                 4.4    4.4    4.5    4.6    4.7    4.9    5.1
:CACHE LA POUDRE RIVER
FORT COLLINS 9NW      4.6    4.8    5.3    5.6    6.2    8.5    8.6
FORT COLLINS          4.8    5.2    5.8    6.2    6.8    9.9   10.4
GREELEY               5.3    6.2    6.8    7.2    7.8    9.4    9.7
:NORTH PLATTE RIVER
NORTHGATE             5.0    5.2    5.6    6.3    7.2    7.6    8.7

THESE LONG-RANGE PROBABILISTIC OUTLOOKS CONTAIN FORECAST VALUES THAT
ARE CALCULATED USING MULTIPLE SEASON SCENARIOS FROM 30 OR MORE YEARS
OF CLIMATOLOGICAL DATA...INCLUDING CURRENT CONDITIONS OF THE
RIVER...SOIL MOISTURE...SNOW COVER...AND 30 TO 90 DAY LONG-RANGE
OUTLOOKS OF TEMPERATURE AND PRECIPITATION. BY PROVIDING A RANGE
OF PROBABILITIES...THE LEVEL OF RISK ASSOCIATED WITH LONG-RANGE
PLANNING DECISIONS CAN BE DETERMINED. THESE PROBABILISTIC
FORECASTS ARE PART OF THE NATIONAL WEATHER SERVICE`S ADVANCED
HYDROLOGIC PREDICTION SERVICE.

SPRING FLOOD OUTLOOKS ARE ROUTINELY ISSUED IN FEBRUARY AND MARCH TO
GIVE ADVANCED NOTICE OF POSSIBLE FLOODING. THE NEXT SCHEDULED SPRING
FLOOD OUTLOOK WILL BE ISSUED ON MARCH 6TH.

VISIT OUR WEB SITE AT WEATHER.GOV/DENVER FOR MORE HYDROLOGIC
INFORMATION INCLUDING GRAPHS OF PROBABILISTIC RIVER OUTLOOKS.

$$
TH



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