Flood Potential Outlook
Issued by NWS Aberdeen, SD

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059-065-069-075-085-089-091-107-109-115-117-119-129-221200-

Probabilistic Hydrologic Outlook
National Weather Service Aberdeen SD
1040 AM CST Thu Mar 01 2018

...Spring Flood Outlook...

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.

Snow pack generally ranges from 3 to 12 inches across the area. The
outlook for the week of March 7th-13th calls for near to below normal
precipitation. The 30 day outlook for the month of March shows equal
chances for below, near or above normal precipitation, with below
normal temperatures. The 90 day outlook for March through May shows
increased chances for above normal precipitation, and near to below
normal temperatures.

For all the rivers in the area, the chances for minor, moderate or
major flooding are below normal.

...Current snow conditions...

Snow depths generally range from 3 to 8 inches across the area
between Interstate 29 and the Missouri River, and 9 to 12 inches west
of the Missouri River and over the far northeastern corner of South
Dakota into west central Minnesota. The water equivalent of the snow
pack is generally 2 inches or less.

...Current soil conditions...

Frost depths remain fairly deep across the area, in the 24 to 40 inch
range. However, given the dry Fall and early Winter, it is likely the
soil, while frozen, remains permeable to snow melt and Springtime
rains. Therefore, the frozen ground conditions currently existing
across the region are not expected to exacerbate runoff production.

...Current river conditions...

River levels and flows are near normal. All rivers are still ice
covered. Ice jams are possible as we head into the spring if there
are increased flows to break up the river ice before it melts.

...Probablistic 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:  03/03/2018  - 06/01/2018

                                       :    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 :  <5   18   <5    8   <5    5
:James River
Columbia            13.0   16.0   18.0 :   9   38    7   32    6   19
Stratford           14.0   17.0   18.5 :  11   44    7   34    6   22
Ashton              13.0   14.0   16.0 :   8   38    8   30    7   28
:Turtle Creek
Redfield             7.0   10.0   15.0 :  14   33   11   22    5   14
:James River
Redfield            20.0   22.0   25.0 :   8   27    7   26    6   25
:Big Sioux River
Watertown           10.0   11.0   12.0 :   6   34   <5   18   <5    6
Watertown            8.0   10.0   12.0 :  20   45   <5   29   <5    9
Watertown - Broad   11.0   14.0   16.0 :  13   36   <5    7   <5   <5
Castlewood           9.0   11.0   16.0 :  38   45   12   29   <5   <5
:Grand River
Little Eagle        15.0   17.0   21.0 :  <5    7   <5    6   <5   <5
:Moreau River
Whitehorse          21.0   23.0   25.0 :  <5    7   <5    6   <5   <5
:Bad River
Fort Pierre         21.0   25.0   27.0 :  12   18   <5   <5   <5   <5
:Little Minnesota River
Peever              17.0   22.0   24.0 :   7   24   <5   <5   <5   <5
:Minnesota River
Big Stone Lake     971.5  973.0  975.0 :  <5    6   <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: 03/03/2018  - 06/01/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Elm River
Westport              4.7    4.7    4.9    5.2    5.8    8.2   10.9
:James River
Columbia              4.0    4.0    4.4    5.6    8.1   12.5   18.4
Stratford             6.2    6.3    6.5    7.8   10.3   14.6   19.6
Ashton                3.3    3.4    3.8    4.8    5.9   11.9   23.1
:Turtle Creek
Redfield              3.1    3.1    3.1    4.2    5.7   10.2   14.6
:James River
Redfield              2.5    2.7    4.0    5.2    6.8   15.4   27.0
:Big Sioux River
Watertown             5.2    5.4    6.5    7.5    8.8    9.5   10.1
Watertown             4.7    4.8    5.3    6.2    7.7    9.4    9.8
Watertown - Broad     6.0    6.2    7.2    8.3    9.7   11.7   12.4
Castlewood            5.7    5.9    6.7    8.2    9.9   11.2   11.7
:Grand River
Little Eagle          4.8    5.4    6.5    7.9   11.4   13.2   14.6
:Moreau River
Whitehorse            7.7    7.7    9.1   12.5   17.0   18.8   20.2
:Bad River
Fort Pierre           5.4    6.2    8.2   11.9   15.9   22.1   23.4
:Little Minnesota River
Peever               12.1   12.4   12.6   13.4   14.3   16.5   18.0
:Minnesota River
Big Stone Lake      967.7  967.9  968.0  968.0  968.4  969.2  971.2

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: 03/03/2018  - 06/01/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Elm River
Westport              3.0    3.0    3.0    3.0    3.0    3.0    3.0
:James River
Columbia              4.0    4.0    4.0    4.0    4.0    4.0    4.0
Stratford             5.8    5.7    5.7    5.7    5.7    5.7    5.7
Ashton                3.2    3.2    3.2    3.2    3.2    3.2    3.1
:Turtle Creek
Redfield              3.1    3.1    3.1    3.1    3.1    3.1    3.1
:James River
Redfield              2.4    2.4    2.3    2.3    2.2    2.1    2.0
:Big Sioux River
Watertown             4.4    4.4    4.4    4.4    4.4    4.4    4.4
Watertown             4.1    4.1    4.1    4.1    4.1    4.1    4.0
Watertown - Broad     5.2    5.2    5.2    5.2    5.2    5.2    5.2
Castlewood            4.9    4.9    4.9    4.9    4.8    4.7    4.6
:Grand River
Little Eagle          2.7    2.7    2.7    2.7    2.7    2.7    2.7
:Moreau River
Whitehorse            2.6    2.6    2.6    2.6    2.6    2.6    2.6
:Bad River
Fort Pierre           1.7    1.7    1.7    1.7    1.7    1.7    1.7
:Little Minnesota River
Peever                9.9    9.8    9.6    9.6    9.6    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.

$$

Parkin





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