Flood Potential Outlook
Issued by NWS Rapid City, SD

000
FGUS73 KUNR 281500
ESFUNR
SDC055-063-085-093-103-105-123-137-151800-

Probabilistic Hydrologic Outlook
National Weather Service Rapid City SD
859 AM MDT Wed Apr 28 2021

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:  04/24/2021  - 07/23/2021

                                       :    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 :  <5   27   <5   12   <5    6
:Moreau River
Faith               16.0   18.0   21.0 :  <5   <5   <5   <5   <5   <5
:Belle Fourche River
WY-SD State Line    15.0   16.0   18.0 :  <5   13   <5   <5   <5   <5
Sturgis             15.0   17.0   19.0 :  10   17    6   12   <5    5
Elm Springs         19.0   22.0   24.0 :   5    8   <5   <5   <5   <5
:Cheyenne River
Wasta               13.0   15.0   16.0 :  <5   <5   <5   <5   <5   <5
Plainview           17.0   19.0   20.0 :  15   26    9   20    5   11
:Bad River
Midland             21.0   24.0   25.0 :  11   21   <5   <5   <5   <5
:White River
Kadoka              15.0   16.0   19.0 :  28   31   13   26   <5   <5
White River         14.0   15.0   17.0 :  27   35   16   26   <5    8
Oacoma              15.0   20.0   25.0 :  36   50    5   14   <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: 04/24/2021  - 07/23/2021
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Little Missouri River
Camp Crook            1.6    1.6    1.7    2.0    3.9    8.6   10.4
:Moreau River
Faith                 1.2    1.4    2.3    3.4    6.3    8.1    9.0
:Belle Fourche River
WY-SD State Line      4.4    4.4    4.4    4.5    4.9    7.9   10.7
Sturgis               3.3    3.4    3.6    4.8    6.7   15.0   17.8
Elm Springs           4.5    4.6    4.8    6.5    8.7   16.0   18.7
:Cheyenne River
Wasta                 1.2    1.2    2.1    3.0    4.8    6.3    7.4
Plainview             9.2    9.6   10.4   11.5   14.6   18.6   20.1
:Bad River
Midland               3.2    3.3    4.3    8.2   14.6   21.5   22.5
:White River
Kadoka                6.3    6.3    7.6   11.0   15.3   16.4   17.1
White River           5.0    5.1    7.6   10.6   14.3   15.8   16.8
Oacoma                8.9    9.3   11.5   13.6   16.9   18.6   19.8

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: 04/24/2021  - 07/23/2021
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Little Missouri River
Camp Crook            1.5    1.5    1.4    1.4    1.4    1.4    1.4
:Moreau River
Faith                 0.9    0.9    0.8    0.8    0.7    0.7    0.7
:Belle Fourche River
WY-SD State Line      3.2    3.2    3.1    3.0    3.0    3.0    3.0
Sturgis               2.1    2.1    2.1    2.1    2.1    2.1    2.1
Elm Springs           3.8    3.8    3.8    3.8    3.8    3.8    3.8
:Cheyenne River
Wasta                 0.6    0.5    0.4    0.3    0.2    0.2    0.2
Plainview             8.7    8.7    8.6    8.5    8.5    8.5    8.5
:Bad River
Midland               3.2    3.2    3.2    3.2    3.1    3.1    3.1
:White River
Kadoka                4.8    4.5    4.4    4.3    4.3    4.3    4.3
White River           3.6    3.6    3.4    3.4    3.3    3.3    3.3
Oacoma                8.3    8.3    8.2    8.1    8.1    8.1    8.1

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.

The next outlook will be issued toward the end of next month.

$$