Flood Potential Outlook
Issued by NWS Denver/Boulder, CO

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FGUS75 KBOU 162325 CCA
ESFBOU
COC001-005-013-014-019-031-035-039-047-049-057-059-069-073-075-087-
093-095-115-117-121-123-031200-

Probabilistic Hydrologic Outlook
National Weather Service Denver/Boulder CO
400 PM MST Thu Feb 16 2017

...Spring Flood and Water Resources Outlook...

This outlook is for north central and northeast Colorado and
includes the Colorado...North Platte and South Platte Rivers.

...Flood Outlook Highlights...
* Near average risk of minor snowmelt flooding in the North and
  South Platte River basins.
* Above average risk of minor snowmelt flooding in the headwaters of
  the Colorado River in north central Colorado. Areas prone to
  flooding in the past may experience issues again this year.
* Significant flooding due to mountain snow runoff alone is not
  likely. However...it is still early in the snow accumulation
  season and conditions could change before the runoff begins.

Above normal temperatures have melted the snowpack in the lower
foothills and diminished frozen ground. Near normal subsurface soil
moisture was observed in north central Colorado with low soil
moisture in eastern Colorado. This has slightly decreased the risk
of significant spring snowmelt flooding in the North and South
Platte River basins. However...mountain snowpack is higher in the
Colorado River basin leading to a higher than usual spring flood
potential due to snowmelt west of the Continental Divide.

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. Near
average risk suggests that locations which typically experience
minor spring time flooding may flood again this year and those that
typically don`t will not.

...Current Hydrologic Conditions...
The Colorado River basin snowpack on February 16th was 144 percent
of normal and had nearly reached the peak normal snowpack (99
percent of the peak). In a typical year the snowpack is only 69
percent of the peak snowpack at this time with April 10th being the
normal peak date as reported by the Natural Resources Conservation
Service.

The mountain snowpack in the South Platte River basin was 138
percent of normal and 85 percent of the normal peak snowpack. In a
typical year the mid-February snowpack is only 61 percent of the
peak snowpack with the normal peak date being April 27th.
Therefore...there is still plenty of time remaining for the snowpack
to rise above the normal peak.

The Laramie and North Platte River basin snowpack on February 16th
was 130 percent of normal and 82 percent of the normal peak snowpack
which typically occurs around April 11th.

Liquid water in the mountain snowpack generally ranged form 8 to 40
inches. Basin reservoir storage continued to hold fairly steady at
105 percent of average and 73 percent of capacity at the end of
January. 85 percent of the U.S. Geological Survey stream gages had
normal to above normal flows in mid-February.

Widespread Moderate Drought /D1/ or Abnormally Dry Conditions /D2/
continued to be observed east of the Continental Divide. There were
no drought designations west of the divide on the February 14th U.S.
Drought Monitor.

...Climate Summary...
Precipitation since January 1st has been above normal in the
mountains and near to below normal at lower elevations. 2017
temperatures have been near to above normal with the exception of
the northeast Colorado corner.

...Weather and Drought Outlooks...
The 30 and 90 day precipitation outlooks and 30 day temperature
outlook have equal chances of being near...above or below normal.
The 90 day temperature outlook has a tilt toward above normal
temperatures. The U.S. Seasonal Drought Outlook valid February 16th
through May 31st indicates drought conditions persisting east of the
Continental Divide (D1 or greater on the U.S. Drought Monitor).

...Numerical River Outlooks...
In Table 1 below, the current (CS) and historical (HS) or normal
probabilities of exceeding minor...moderate...and major flood stage
are listed for the valid time 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: 2/18/2017 - 5/19/2017

                                       :    Current and Historical
                                       :     Chances of Exceeding
                                       :       Flood Categories
                                       :      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 :  <5   <5   <5   <5   <5   <5
Denver              11.0   12.5   14.0 :  <5   <5   <5   <5   <5   <5
Henderson           10.0   11.0   15.0 :   6    6   <5   <5   <5   <5
Kersey              10.0   11.5   13.0 :   8    9    5    6   <5   <5
Weldona             10.0   11.0   13.0 :   7    8    5    6   <5   <5
Balzac              10.0   11.0   13.0 :   8    8    5    6   <5   <5
Julesburg           10.0   11.0   12.0 :  <5    5   <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 :  <5   <5   <5   <5   <5   <5
Fort Collins        10.5   11.5   13.0 :  <5   <5   <5   <5   <5   <5
Greeley              8.0    9.5   10.5 :  <5   <5   <5   <5   <5   <5
:North Platte River
Northgate            8.0    9.5   11.0 :   5   <5   <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
                           Valid Period: 2/18/2017 - 5/19/2017
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:South Platte River
South Platte          3.7    3.8    3.8    3.9    4.0    4.7    5.2
Denver                4.0    4.0    4.2    4.7    5.3    6.4    7.1
Henderson             5.2    5.5    5.7    6.6    7.2    9.0   10.2
Kersey                4.3    4.3    4.7    6.0    7.7    8.9   11.3
Weldona               2.9    3.0    3.1    4.2    6.1    7.3   10.8
Balzac                2.6    2.8    3.0    4.2    5.6    7.6   10.9
Julesburg             4.6    4.7    5.0    6.0    6.9    7.9    9.6
:Plum Creek
Sedalia               4.0    4.1    4.2    4.4    4.6    5.3    6.9
:Bear Creek
Morrison              6.0    6.1    6.3    6.5    6.8    7.2    7.7
Sheridan              2.6    2.7    2.8    3.1    3.6    4.5    4.8
:Clear Creek
Golden                4.2    4.3    4.5    4.7    5.0    5.4    5.7
Derby                 2.2    2.3    2.5    2.8    3.3    3.9    4.9
:N Fk Big Thompson River
Drake                 3.9    4.0    4.0    4.1    4.2    4.4    4.6
:Cache la Poudre River
Fort Collins 9NW      3.3    3.4    3.5    3.8    4.1    4.8    5.7
Fort Collins          1.4    1.5    1.7    2.2    3.1    4.7    6.2
Greeley               2.2    2.2    2.5    3.2    4.8    6.8    7.8
:North Platte River
Northgate             4.8    5.1    5.3    5.5    6.0    6.9    7.8

In Table 3 below...the 95 through 5 percent columns indicate the
probability of falling below the listed stage levels (FT) for
the valid time period.

...Table 3--Nonexceedance Probabilities...

                            Chance of Falling Below Stages
                                 at Specific Locations
                           Valid Period: 2/18/2017 - 5/19/2017
LOCATION              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:South Platte River
South Platte          2.8    2.8    2.8    2.8    2.8    2.8    2.8
Denver                3.0    3.0    3.0    3.0    3.0    3.0    3.0
Henderson             3.9    3.8    3.3    3.1    3.0    3.0    3.0
Kersey                3.6    3.3    3.0    2.9    2.8    2.7    2.7
Weldona               1.9    1.4    0.2    0.1    0.1    0.1    0.1
Balzac                1.8    1.8    1.8    1.8    1.8    1.8    1.8
Julesburg             1.8    1.8    1.8    1.8    1.8    1.8    1.8
:Plum Creek
Sedalia               3.7    3.7    3.7    3.7    3.6    3.6    3.6
:Bear Creek
Morrison              5.6    5.5    5.5    5.5    5.5    5.5    5.5
Sheridan              2.2    2.2    2.1    2.1    2.1    2.1    2.1
:Clear Creek
Golden                3.5    3.5    3.5    3.5    3.5    3.5    3.4
Derby                 0.9    0.9    0.9    0.9    0.9    0.9    0.9
:N Fk Big Thompson River
Drake                 3.8    3.8    3.7    3.7    3.7    3.7    3.7
:Cache la Poudre River
Fort Collins 9NW      2.8    2.8    2.8    2.8    2.8    2.8    2.8
Fort Collins          1.1    1.0    0.5    0.4    0.4    0.4    0.4
Greeley               1.4    1.3    1.3    1.3    1.3    1.3    1.3
:North Platte River
Northgate             2.4    2.4    2.4    2.4    2.4    2.3    2.3

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 Thursday March 2nd.

Visit our web site weather.gov/bou for more weather and water
information.

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