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2019 Spring Flood Outlook Update
Issued on March 7, 2019
This spring flood outlook is for the rivers and streams in northeast
South Dakota, portions of central South Dakota, and portions of west
central Minnesota.

Due to the somewhat wet conditions across the area late last summer
into last fall, and the increasing snow pack over the last 8 weeks,
the chances for minor, moderate, or major flooding are above to much
above normal across much of the area.

The flood threat through this spring, both in location and severity,
will largely be determined by future rain or snowfall, and how fast
the melting of the snowpack occurs.

The outlook for the next 10 days is for higher chances for above
normal precipitation and below normal temperatures. The 30 day
outlook for the month of March shows equal chances for below, near or
above normal precipitation, and higher chances for below normal
temperatures. The 90 day outlook for March through May shows equal
chances for below, near or above normal temperatures and
precipitation.

The chances for river flooding are generally above to much above
normal across the entire area. The areas with the most increased
chances are along the James River, along the Grand River, and along
the Moreau River.
Current snow conditions

Modeled Snow Depth


Modeled Snow Water Equivalent



Snow depths generally range from 8 to 16 inches west of the James
River Valley, to 16 to 30 inches along and east of the James River
Valley. The water equivalent of the snow pack is generally 2 to 5
inches along and west of the James River Valley, and 4 to 7 inches
east of the James River Valley.

Current soil conditions

Frost depths remain fairly deep across the area, generally in the 1
to 3 foot range. With the wet conditions last fall heading into the
freeze up, the soils were fairly well saturated as they froze, which
will make them much more impervious to soaking up much of the snow
melt as it occurs. There is some uncertainty as to the current level
of the soil saturation as we head into spring, and this will play a
very big role in how severe the flooding will be over the next 2 to 3
months.
Current river conditions
River levels and flows are generally running near to above normal
across the region. All rivers are still ice covered. Ice jams are
possible as we head into spring, as the increased flows will raise
and break up the river ice before it melts.
Probabilistic 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:  03/10/2019  - 06/08/2019

                                       :    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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:Elm River
Westport            14.0   16.0   19.0 :  18   19   14    8    6    5
:James River
Columbia            13.0   16.0   18.0 : >98   37  >98   30   78   19
Stratford           14.0   17.0   18.5 : >98   43  >98   34   87   22
Ashton              13.0   14.0   16.0 : >98   39  >98   33  >98   29
:Turtle Creek
Redfield             7.0   10.0   15.0 :  80   33   57   25   23   17
:James River
Redfield            20.0   22.0   25.0 :  83   30   76   29   62   26
:Big Sioux River
Watertown           10.0   11.0   12.0 :  36   35   14   18   <5    6
Watertown            8.0   10.0   12.0 :  78   48   31   30   <5   10
Watertown - Broad   11.0   14.0   16.0 :  68   38    5    7   <5   <5
Castlewood           9.0   11.0   16.0 :  88   45   55   30   <5   <5
:Grand River
Little Eagle        15.0   17.0   21.0 : >98   12   75   10   43   <5
:Moreau River
Whitehorse          21.0   23.0   25.0 :  65    9   58    7   42    6
:Bad River
Fort Pierre         21.0   25.0   27.0 :  43   11   34   <5   31   <5
:Little Minnesota River
Peever              17.0   22.0   24.0 :  86   24    7   <5   <5   <5
:Minnesota River
Big Stone Lake     971.5  973.0  975.0 :  17    6    8   <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: 03/10/2019  - 06/08/2019
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Elm River
Westport              6.5    6.7    7.6   10.8   13.2   17.6   19.1
:James River
Columbia             17.7   17.8   18.0   18.7   19.7   20.6   20.8
Stratford            18.2   18.4   19.2   19.7   20.7   21.7   22.4
Ashton               17.2   17.8   20.8   23.3   25.4   30.8   35.1
:Turtle Creek
Redfield              5.7    6.2    8.3   10.6   14.0   16.8   17.6
:James River
Redfield             16.8   18.4   22.4   27.9   30.1   32.9   34.6
:Big Sioux River
Watertown             8.0    8.1    8.5    9.4   10.6   11.0   11.4
Watertown             7.0    7.2    8.1    9.4   10.5   11.3   11.6
Watertown - Broad     9.2    9.6   10.6   12.0   13.0   13.4   13.8
Castlewood            8.8    8.9    9.7   11.1   12.2   13.2   13.8
:Grand River
Little Eagle         15.7   15.8   17.0   19.3   27.0   32.6   35.6
:Moreau River
Whitehorse           15.6   16.4   19.6   24.2   27.2   30.0   32.2
:Bad River
Fort Pierre          10.9   12.2   15.3   19.6   27.8   29.2   29.6
:Little Minnesota River
Peever               16.0   16.4   17.5   18.8   19.8   21.1   23.2
:Minnesota River
Big Stone Lake      968.5  968.6  969.0  969.5  970.7  972.5  974.2

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: 03/10/2019  - 06/08/2019
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Elm River
Westport              4.1    4.1    4.0    4.0    4.0    4.0    4.0
:James River
Columbia              5.0    5.0    5.0    5.0    5.0    5.0    5.0
Stratford             6.3    6.3    6.3    6.3    6.3    6.3    6.3
Ashton                3.6    3.6    3.6    3.6    3.6    3.6    3.5
:Turtle Creek
Redfield              3.1    3.1    3.1    3.1    3.1    3.1    3.1
:James River
Redfield              3.3    3.3    3.3    3.3    3.3    3.3    3.3
:Big Sioux River
Watertown             3.6    3.6    3.6    3.6    3.6    3.6    3.6
Watertown             4.8    4.8    4.8    4.8    4.8    4.8    4.8
Watertown - Broad     6.0    6.0    6.0    6.0    6.0    6.0    6.0
Castlewood            4.5    4.5    4.5    4.5    4.5    4.5    4.5
:Grand River
Little Eagle          2.9    2.9    2.9    2.9    2.9    2.9    2.9
:Moreau River
Whitehorse            2.7    2.7    2.7    2.7    2.7    2.7    2.7
:Bad River
Fort Pierre           2.1    2.1    2.1    2.1    2.1    2.0    2.0
:Little Minnesota River
Peever               10.0   10.0   10.0   10.0    9.8    9.6    9.6
:Minnesota River
Big Stone Lake      967.3  967.3  967.3  967.3  967.3  967.3  967.3

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.

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

The next outlook will be issued later this month.