Flood Potential Outlook
Issued by NWS Rapid City, SD

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FGUS73 KUNR 161657
ESFUNR
SDC007-019-033-047-055-063-071-081-093-095-102-103-105-121-123-137-
WYC005-011-045-201800-

Probabilistic Hydrologic Outlook
National Weather Service Rapid City SD
1056 AM MST Thu Mar 2 2017

..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...Bad...White and Keyapaha River Basins.

.Flood Outlook Summary...
At this time, the probability of spring flooding from March through
June is below average. However, the flood potential is still very
dependent on weather conditions this spring. The amount of
additional snow and rain and the timing of peak flows will have a
significant effect on the flooding.

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.

.Precipitation...
Since October 1 2016 precipitation has varied from below average
across most of northeastern Wyoming and portions of far western
South Dakota to above average across central South Dakota.

Temperatures in February were above average across the entire area.
Precipitation amounts were slightly below average across the
northern sections and slightly above average south of a line from
Wright, WY to the central Black Hills, to Winner, SD. Overall, about
half of the days in February some form of precipitation fell, either
in the form of rain or snow. However, the precipitation amounts were
mostly light.

So far in March, temperatures have been above average and
precipitation has been below average. Average high temperatures for
March range from 40 degrees in northwestern South Dakota to around
50 degrees in southwestern South Dakota. Average lows are usually
around 20. Precipitation typically ranges from a half inch on the
plains to just over an inch in the Black Hills.

.Snow Cover and Liquid Water Content...
Little if any snowpack remains across the plains of northeastern
Wyoming and western South Dakota. The majority of the snowpack is
confined to the higher elevations of the Black Hills and Bear Lodge
Mountains. March and April are typically the two snowiest months,
when a third of the seasonal snowfall usually happens.

.Soil Conditions and Frost Depths...
Soil moisture is slightly below average due to the recent warm and
windy conditions. Most of the frost has left the ground across the
lower elevations of western South Dakota and northeastern Wyoming.

.Lake and River Conditions...
Ice has begun to diminish from most creeks, streams, and rivers.
Some ice cover remains on lakes in northwestern South Dakota and in
the higher elevations of the Black Hills and Bear Lodge Mountains.
According to the Bureau of Reclamation, reservoir levels are
slightly above average for this time of the year with the exception
of Shadehill Reservoir, which is slightly below average.

.Weather Outlooks...
Water temperatures in the tropical Pacific Ocean are around average,
indicating neutral conditions. The outlook for the spring and summer
is for neutral conditions to continue. Neutral conditions generally
bring a warmer and wetter pattern to the southern half of the United
States with a cold polar jet stream diving across Canada into the
northeastern United States. The northern plains will be in the
transition zone between the two air masses that would create varying
conditions for the northern plains.

The outlook for the rest of March indicates odds tilted toward
slightly above average temperatures with odds favoring near average
precipitation.

The three month outlook for March, April, and May calls for a
somewhat increased chance for normal to slightly above normal
temperatures with odds favoring above average precipitation.

.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:  03/04/2017  - 06/02/2017

                                       :    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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:Little Missouri River
Camp Crook          12.0   17.0   19.0 :  15   34   <5    7   <5    5
:Moreau River
Faith               16.0   18.0   21.0 :   6    6   <5   <5   <5   <5
:Belle Fourche River
WY-SD State Line    15.0   16.0   18.0 :   8   <5   <5   <5   <5   <5
Sturgis             15.0   17.0   19.0 :  10   13    6    6   <5   <5
Elm Springs         19.0   22.0   24.0 :   7    6   <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 :  25   26   20   21   13   13
:Bad River
Midland             21.0   24.0   25.0 :  13   18   <5   <5   <5   <5
:White River
Kadoka              13.0   15.0   19.0 :  31   21   14   13   <5   <5
White River         14.0   15.0   17.0 :  38   26   19   18   <5    5
Oacoma              15.0   20.0   25.0 :  60   48    9    8   <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: 03/04/2017  - 06/02/2017
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Little Missouri River
Camp Crook            4.1    4.2    5.3    6.7    8.3   14.1   16.0
:Moreau River
Faith                 4.4    4.5    6.6    9.3   14.5   15.7   16.2
:Belle Fourche River
WY-SD State Line      4.5    4.5    5.7    7.1    9.1   14.4   15.8
Sturgis               3.2    3.5    5.3    7.0    9.8   14.9   18.3
Elm Springs           4.6    4.8    6.2    8.5   10.2   17.0   20.8
:Cheyenne River
Wasta                 1.0    1.3    3.6    4.8    7.5    9.5   11.1
Plainview             9.5   10.2   12.0   13.2   15.9   19.5   20.5
:Bad River
Midland               3.2    3.2    4.6    7.1   14.4   21.9   22.4
:White River
Kadoka                7.0    7.0    8.2   11.4   13.6   15.4   17.1
White River           8.0    8.0    9.2   13.2   14.6   15.7   16.8
Oacoma               10.4   10.6   14.0   16.7   18.1   19.8   20.9

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: 03/04/2017  - 06/02/2017
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Little Missouri River
Camp Crook            1.9    1.9    1.9    1.9    1.8    1.6    1.4
:Moreau River
Faith                 0.8    0.8    0.7    0.5    0.5    0.5    0.5
:Belle Fourche River
WY-SD State Line      4.1    4.1    4.0    4.0    3.9    3.9    3.9
Sturgis               2.9    2.9    2.9    2.9    2.9    2.8    2.8
Elm Springs           4.1    4.1    4.1    4.1    4.1    4.1    4.0
:Cheyenne River
Wasta                 0.9    0.9    0.8    0.8    0.7    0.6    0.6
Plainview             9.2    9.2    9.2    9.1    9.1    9.0    8.9
:Bad River
Midland               3.2    3.2    3.1    3.1    3.1    3.1    3.1
:White River
Kadoka                3.9    3.8    3.5    3.4    3.1    2.8    2.7
White River           5.1    5.0    4.6    4.5    4.2    4.0    3.8
Oacoma                8.8    8.4    8.1    7.8    7.5    7.3    7.2

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 third spring flood and water resource outlook for 2017.
Long-range probabilistic outlooks are issued near the middle of the
month throughout the year. No more scheduled outlook will be issued
unless they are needed during the spring of 2017.

$$



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