Flood Potential Outlook
Issued by NWS Sioux Falls, SD

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000
FGUS73 KFSD 011427
ESFFSD
SDC005-011-027-035-061-067-079-083-087-099-101-111-125-127-135-
MNC033-063-081-083-101-105-117-133-NEC043-051-
IAC021-035-041-059-093-119-141-143-149-167-193-221800-

Probabilistic Hydrologic Outlook
National Weather Service Sioux Falls SD
825 AM CST Wed Feb 28 2018

...Spring Flood Outlook...

This spring flood outlook is for the rivers and streams in southeast
South Dakota, southwest Minnesota, northwest Iowa, and extreme
northeast Nebraska.

Due to the generally below normal snowfall for much of the region this
winter and the limited water content of the snow pack currently on the
ground, the flood threat through this spring will be determined by
future rain or snow fall. The outlook for the next 2 weeks shows that
near normal precipitation is expected through the middle of March.
The 30 day outlook for the month of March shows increased chances for
above normal precipitation, and the 90 day outlook for March through
May shows equal chances for above normal, normal, or below normal
precipitation.

For most of the rivers in the area, the chances for minor, moderate,
or major flooding are below normal. The exceptions are the Redwood
River in Minnesota where flood chances are slightly higher than
normal, and the upper and middle portions of the Little Sioux River
in northwest Iowa where minor flooding is likely and the
probabilities are near normal.

...Current Snow Conditions...

The current snow pack is widespread for all areas north of Highway
18, but depths are generally shallow with limited water content.
Areas in southwest Minnesota along Interstate 90 have snow depths
of 10 to 16 inches with 2 to 3 inches of water content. The rest of
the region has snow depths less than 8 inches with less than 2
inches of water content.

...Current Soil Conditions...

Soils in the area are generally frozen to 1 to 3 feet deep. 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 across the region. All
rivers are still ice covered. Ice jams are possible as we head
into the spring if there are increased flows to break up and move
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:  03/03/2018  - 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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:Floyd River
Sheldon             12.0   14.0   16.0 :  12   39    8   24   <5   <5
Alton               12.0   16.0   18.0 :  20   41   <5   15   <5   <5
Le Mars             20.0   21.0   24.0 :   5   16   <5   14   <5   <5
:West Branch Floyd River
Struble             14.0   15.0   16.0 :   5   17   <5    7   <5   <5
:Floyd River
Merrill             12.0   14.0   16.0 :  <5   12   <5    8   <5   <5
James               26.0   30.0   34.0 :  <5   <5   <5   <5   <5   <5
:Little Sioux River
Above Spencer       10.0   13.0   15.0 :  54   64   15   25   <5    9
At Spencer          10.0   14.0   16.0 :  67   72   10   25   <5    5
:Ocheyedan River
Spencer              8.0    9.5   10.5 :  36   44   11   37   <5   15
:Little Sioux River
Linn Grove          18.0   19.5   21.0 :  63   70   27   48    6   23
Cherokee            17.0   21.0   24.0 :  48   52    6   16   <5    5
Correctionville     19.0   21.0   23.0 :  10   17    8   16    7   15
:West Fork Ditch
Hornick             20.0   22.0   27.0 :  27   38   18   26   <5    5
:Perry Creek
Sioux City          24.0   26.0   28.0 :  <5   <5   <5   <5   <5   <5
:Big Sioux River
Brookings            9.0   10.5   12.0 :  56   55   24   44   13   31
Dell Rapids         12.0   14.0   15.0 :  37   47   19   39   12   31
Sioux Falls I-90    12.0   14.0   16.0 :  42   49   20   39   10   21
:Skunk Creek
Sioux Falls         11.5   15.0   17.0 :  <5   13   <5   <5   <5   <5
:Big Sioux River
Sioux Falls N Cliff 16.0   18.0   31.0 :  29   44   20   41   <5   <5
:Split Rock Creek
Corson               8.5   11.0   14.0 :  33   43   20   25   12   13
:Rock River
Luverne             10.0   12.0   14.0 :   9   24   <5   11   <5   <5
Rock Rapids         13.0   16.0   19.0 :  21   52   12   26   <5   18
Rock Valley         16.0   17.0   19.0 :   7   27   <5   24   <5   11
:Big Sioux River
Hawarden            19.0   24.0   27.0 :  49   65   23   40    9   20
Akron               16.0   18.0   20.0 :  43   59   32   47   23   40
Sioux City          32.0   38.0   41.0 :  <5   <5   <5   <5   <5   <5
:James River
Huron               11.0   13.0   15.0 :  14   43   10   31    8   27
Forestburg          12.0   14.0   16.0 :  14   37   10   31    5   21
Mitchell            17.0   20.0   22.0 :  16   50   11   32    7   21
:Firesteel Creek
Mount Vernon         8.0   13.0   15.0 :  16   39    5   15   <5   11
:James River
Scotland            13.0   14.0   16.0 :  16   44   13   36    9   31
Yankton             12.0   14.0   16.0 :  13   34   12   32    8   27
:West Fork Vermillion River
Parker               9.0   10.0   11.0 :  <5    9   <5    7   <5    6
:East Fork Vermillion River
Parker              12.0   14.0   16.0 :   7   35   <5   16   <5   <5
:Vermillion River
Davis               11.0   13.0   15.0 :  20   51   10   35   <5   11
Wakonda             14.0   15.5   17.0 :  23   42   19   40   12   37
Vermillion          21.0   22.0   30.0 :   9   31    9   26   <5   <5
:Redwood River
Marshall            14.0   15.0   16.5 :  42   19   36   13   22   10
:West Fork Des Moines River
Jackson             12.0   14.0   16.0 :   8    9   <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%
--------            ------ ------ ------ ------ ------ ------ ------
:Floyd River
Sheldon               6.2    6.2    6.8    7.5    9.4   13.0   14.2
Alton                 7.3    7.5    8.3    9.5   11.1   13.2   14.1
Le Mars              12.1   12.5   13.1   14.9   16.3   18.1   19.9
:West Branch Floyd River
Struble               5.2    5.9    6.6    7.8    9.6   11.1   14.1
:Floyd River
Merrill               1.8    2.2    3.0    4.4    6.1    8.1   10.7
James                10.5   10.7   11.5   12.8   14.7   16.4   21.8
:Little Sioux River
Above Spencer         7.1    7.3    8.0   10.7   12.3   13.5   14.0
At Spencer            8.1    8.2    9.6   12.2   13.2   14.0   14.7
:Ocheyedan River
Spencer               3.7    3.9    5.0    6.8    8.6    9.6   10.2
:Little Sioux River
Linn Grove           16.6   16.7   17.4   18.9   19.5   20.4   21.5
Cherokee             10.2   10.7   12.8   16.7   18.9   20.1   21.3
Correctionville       7.7    8.1   10.4   14.1   17.0   19.0   22.4
:West Fork Ditch
Hornick               7.2    8.7   10.9   15.2   20.9   24.0   25.4
:Perry Creek
Sioux City            7.5    7.7    8.1    8.6    9.1   10.4   16.1
:Big Sioux River
Brookings             4.7    5.5    7.1    9.2   10.4   12.4   12.5
Dell Rapids           6.6    7.1    9.0   11.1   13.6   15.5   16.9
Sioux Falls I-90      9.2    9.4   10.5   11.7   13.7   15.9   17.6
:Skunk Creek
Sioux Falls           4.8    5.2    5.8    6.3    7.7    9.3   10.3
:Big Sioux River
Sioux Falls N Cliff   7.6    8.1   10.1   12.1   16.7   22.6   25.4
:Split Rock Creek
Corson                4.6    4.9    5.7    7.1    9.6   14.9   16.9
:Rock River
Luverne               4.1    4.3    4.6    5.6    6.8    9.5   11.3
Rock Rapids           8.7    9.0    9.7   11.1   12.3   16.6   17.4
Rock Valley           6.0    6.6    8.1    8.8   11.9   15.5   16.5
:Big Sioux River
Hawarden             14.9   16.5   17.3   18.8   23.3   26.4   27.8
Akron                 9.0   11.7   13.0   15.1   19.0   22.1   22.8
Sioux City           12.4   14.6   15.5   17.3   21.4   27.4   29.7
:James River
Huron                 9.1    9.1    9.4    9.7   10.1   12.8   18.0
Forestburg            3.9    4.2    5.3    6.1    7.6   13.7   16.6
Mitchell             10.1   10.5   11.6   12.6   15.1   20.4   23.4
:Firesteel Creek
Mount Vernon          1.9    2.4    2.9    4.2    6.5    9.8   12.9
:James River
Scotland              4.5    4.6    5.2    5.7    9.3   15.9   18.5
Yankton               2.0    2.1    2.7    3.4    6.0   15.3   20.1
:West Fork Vermillion River
Parker                0.8    0.9    1.3    1.7    2.8    4.6    7.2
:East Fork Vermillion River
Parker                3.7    3.9    4.4    4.9    8.3   10.3   12.9
:Vermillion River
Davis                 3.0    3.4    4.5    5.8   10.4   13.1   14.3
Wakonda               4.3    4.9    5.7    7.6   11.7   17.2   17.5
Vermillion            2.9    3.7    4.7    6.9   12.2   19.3   24.4
:Redwood River
Marshall              9.2    9.9   11.0   12.8   16.0   22.1   26.4
:West Fork Des Moines River
Jackson               9.8   10.1   10.3   10.8   11.4   11.9   12.1

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/fsd for more weather and water
information.

The next outlook will be issued around March 22.

$$



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