Flood Potential Outlook
Issued by NWS Rapid City, SD

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000
FGUS73 KUNR 052014
ESFUNR
SDC055-063-085-093-103-105-123-137-151800-

PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE RAPID CITY SD
113 PM MST THU MAR 05 2015

Spring Flood and Water Resource Outlook

This spring flood and water resource outlook is for the Rapid City
Hydrologic Service Area /HSA/ which covers northeastern Wyoming and
western South Dakota. The main river basins include the Little
Missouri...Eastern Powder...Belle Fourche...Grand...Moreau...
Cheyenne...Upper Missouri...White and Keyapaha River Basins.

...Below Average to Average Flood Potential This Spring...

.Flood Outlook Summary...
At this time the potential for flooding due to snowmelt is low.
However...there is still more than enough of the winter season left
to provide significant snowpack before the onset of the spring melt.
The two snowiest months across the area are usually March and April.
Typically half of the snowfall received occurs after February 1.

The flood potential for ice jam related flooding is below average on
rivers and streams. Quite a bit of ice has already come off the
streams due to the warmer than average winter season so far...only
minimal amounts of ice remain.

For the Black Hills and higher elevations...flooding from snowmelt
typically begins in late April and May. Flooding on the plains due to
snowmelt and ice jams typically occurs between February and May.

The potential for rainfall-induced flash flooding is not quantifiable
because this type of flooding is usually caused by localized
thunderstorms during the spring and summer.

The flood potential is still very dependent on weather conditions
from now until the spring melt. The amount of additional snow and
rain...the timing and rate of the spring thaw and the timing of peak
flows will have a significant effect on the flooding.

.Snow Cover and Liquid Water Content...
Current snowpack is confined mostly to the higher elevations in the
Black Hills and Bear Lodge Mountains. Snow cover at lower elevations
is minimal at best.

.Soil Conditions and Frost Depths...
Soil moisture is average and frost depth values are a foot or less.

.Lake and River Conditions...
Most of the ice cover on the larger lakes on the plains has begun to
deteriorate with some open water reported near the shores. Quite a
bit of the ice on rivers and streams has come off...with only minimal
amounts of ice remaining. Most lakes in the Black Hills and Bear
Lodge remain ice covered with an ice thickness of 8 to 14 inches.

Reservoir levels are above average for this time of the year. This is
due to the wetter than average conditions since October of 2013 and
the above average inflows reported in January and February.

.Weather Outlooks...
Dry conditions and above average temperatures are expected through
the middle of March.

.Numerical River Outlooks...
In Table 1 below...the current (CS) and historical (HS) or normal
probabilities of exceeding minor...moderate...and major flood stages
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 more 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:  3/7/2015 - 6/5/2015

                                       :    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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:Little Missouri River
Camp Crook          12.0   17.0   19.0 :  32   28   10    7    8    6
:Moreau River
Faith               16.0   18.0   21.0 :  <5    8   <5   <5   <5   <5
:Belle Fourche River
WY-SD State Line    15.0   16.0   18.0 :  <5   <5   <5   <5   <5   <5
Sturgis             15.0   17.0   19.0 :  12   14    7    8   <5    6
Elm Springs         19.0   22.0   24.0 :   8   <5   <5   <5   <5   <5
:Cheyenne River
Wasta               14.0   16.0   17.0 :  <5   <5   <5   <5   <5   <5
Plainview           16.0   17.0   19.0 :  24   27   17   19   12   12
:Bad River
Midland             21.0   24.0   25.0 :  31   24   <5   <5   <5   <5
:White River
Kadoka              13.0   15.0   19.0 :  22   25   12   17   <5   <5
White River         14.0   15.0   17.0 :  35   44   25   17   19   <5
Oacoma              15.0   20.0   25.0 :  43   51   20   19   <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: 3/7/2015 - 6/5/2015
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Little Missouri River
Camp Crook            2.1    2.7    6.0   10.5   12.5   17.3   19.5
:Moreau River
Faith                 1.1    1.1    5.9    7.8   13.2   14.5   15.4
:Belle Fourche River
WY-SD State Line      3.3    3.3    3.4    5.1    6.8   10.9   13.2
Sturgis               3.5    3.8    5.1    6.7   10.6   15.5   18.5
Elm Springs           4.9    5.2    6.6    9.4   11.4   18.1   21.3
:Cheyenne River
Wasta                 2.1    2.1    3.7    5.0    7.3    9.2   10.5
Plainview             9.9   10.3   11.4   13.2   15.7   19.2   20.2
:Bad River
Midland               8.1    8.1    8.2   14.7   21.7   22.6   22.7
:White River
Kadoka                4.3    4.6    5.6    9.1   11.7   16.5   18.1
White River           5.6    5.6    7.7   13.1   15.1   20.1   20.6
Oacoma                9.4    9.5   10.8   14.6   17.4   21.5   24.3

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: 3/7/2015 - 6/5/2015
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Little Missouri River
Camp Crook            2.0    2.0    2.0    2.0    1.9    1.8    1.8
:Moreau River
Faith                 1.0    1.0    1.0    1.0    1.0    1.0    1.0
:Belle Fourche River
WY-SD State Line      3.3    3.3    3.3    3.3    3.3    3.2    3.2
Sturgis               3.1    3.1    3.1    3.1    3.1    3.1    3.0
Elm Springs           4.5    4.4    4.3    4.2    4.1    4.0    4.0
:Cheyenne River
Wasta                 1.1    1.1    1.1    1.0    1.0    0.9    0.9
Plainview             8.4    8.4    8.4    8.4    8.3    8.3    8.2
:Bad River
Midland               2.7    2.7    2.7    2.5    2.4    2.4    2.4
:White River
Kadoka                3.0    2.5    2.2    1.9    1.7    1.6    1.6
White River           4.2    4.1    3.8    3.5    3.1    3.0    2.9
Oacoma                7.6    7.5    7.3    7.1    6.9    6.8    6.8

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.

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

This is the second and final spring and water resouce outlook for
2015. Additional outlooks will only be issued if the flood potential
increases. Long-range probabilistic outlooks are issued near the
middle of the month throughout the year.

$$







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